Chevy Car Questions & Answers - Performance Q&A

Kevin McClelland May 1, 2009 0 Comment(s)

The Benefits Of Moving
If you guys and gals are anything like me, you have way too much to do and many projects going at the same time. Well, faced with the move of my family and all my performance belongings, I embarked on trying to condense everything I could. This meant putting together everything to make the move as compact as possible.

0905chp_02_z Chevy_car_questions_and_answers Engine 1/2

To be more specific, I had three engines in various states of disarray. With heads, cranks, and other components lying all around the garage and on the shelves, putting them all back together was the smartest thing I ever did. First, I had a complete '88 L98 Corvette engine that had been fieldstripped for projects over the years, but the long-block was complete and had never been fired! I screwed this one back together and sold it with harness, sensors, computer, and calibration to a painter friend who needed an engine for his '85 Blazer. He is in the final stages of the conversion from carbureted to EFI on his daily driver.

Next came the engine from Daniel's '65 Malibu. It started life as standard '89 L98 from a GM development Corvette. I had taken it down to the short-block to install the GM Hot Cam Package, port the L98 aluminum heads, and add a Performer RPM manifold. This is a very nice 400hp, 400-lb-ft package that will run forever. It was meant for our Nova project, but I guess we'll take it to SoCal and look for a new engine bay.

Finally, I'm getting to the important engine: my 524 Dart big-block that has been apart almost five years. Back in early 2004 I lost a roller tappet in the engine with only 100 runs on it. This engine was built using a Dart Big M block, CNC-ported Dart 335 Pro 1s, a Dart 4500 inlet manifold, a Crane valvetrain, and Milodon oil components. It was built as a 9.75:1-squeeze 555ci and made 760 hp on pump gas, pushing my Super Gas Roadster to 9.90 at 152 mph. With the chance to change the combination, I shortened the stroke by a quarter-inch and brought it back to a 524. I increased the compression to 10:1 and went with CP pistons and matching Total Seal gapless low-tension rings and a vacuum pump. Everything else stayed pretty much the same, and with the reduced friction and vacuum pump I'm expecting very similar performances.

As I am sitting here finishing this column, the Smith Brothers pushrods just showed up at my door. This was the last thing I needed to finish off the engine and start packing the garage. At least getting three engines together will protect their components from the move-and make the whole process much easier. I'm off to lash some valves and dive into some boxes!

Tanks A Lot!
Q I have two Camaros. One is an '82 Z-28, and the other is an '85 Z-28 with a TPI 305 and a TH700R-4 that is a parts car because of a wreck I was in. (Watch out for little old ladies because they are not watching out for you!) I want to put the running gear in the '82 Z because it has a good body, and I want to keep the TPI. Can I pull a gas tank from a Camaro that has an EFI for a V-6 or from an RS that has a TBI? I don't want to buy anything new, and I can pick this up at a junkyard for $50. I am an aircraft electrician with the U.S. Air Force, so the wiring will be easy for me. Also, I have a disc-brake rearend that is a nine-bolt cover, which I pulled from a late-'80s GTA Firebird. What can you tell me about this rearend? A friend told me it's almost as good as a Ford 9-inch or a Chevy 12-bolt. Any info would be great. Thanks.
John Logsdon Via email

A Little old ladies, UPS Trucks, 18-wheelers-everything is out to get our cars. You have to drive under the assumption that you're invisible. Sorry to hear about the loss of your Camaro. Looks to me like you're going to have a very nice '82 Camaro very soon.

Do you want the good news or the good news? How about that the General used the same fuel tank in all Camaros and Firebirds from '82 though '92! The factory part number is 10269091. Your '85 tank, pump, and lines will all swap over to your '82. That was easy enough.

The nine-bolt cover rearend you have was considered the Aussie rearend (they were built by BorgWarner of Australia). They debuted in the '88 Camaros and '85 Firebirds. The reason GM swapped these differentials into the Camaros was the weak 7.5-inch 10-bolts in the F-cars. The nine-bolt featured a 7.750-inch ring gear; 2.77:1, 3.08:1, 3.27:1, or 3.45:1 rear gears; bolt-in axles instead of the C-clip-style retention of the 10-bolt; and 28-spline axles. Another major strength increase was a reduced carrier bearing spacing. The 10-bolt diff had a spacing of 7 inches, and the nine-bolt came in at 6.125. This was a major reduction in carrier deflection. And finally, the differential uses a four-pinion spider gear arrangement verses the two-pinion in the 7.5-inch diffs. The rears were offered in both open and posi configurations, with the posi being a cone type.

The failure points of this diff were from excessive backlash from either excessive ring/pinion clearance or worn posi cones creating excessive clearance between the side gears and the four-pinion gears. Keeping the clearances correct keeps these rearends happy.

Finally, the General doesn't support these rearends any longer. Any parts and components needed for service will need to come from the aftermarket. Check with Differential Solutions for largest selection of hard-to-find parts for the nine-bolt: rebuild kits for both open and posi carriers, used ring-and-pinions, and mini spools. Check out the condition of your nine-bolt and get on the rebuild. Parts will only get tougher to get as time goes by. Enjoy your '82 Z28, and keep your eyes peeled for the other drivers.Source:9bolt.com

Stay Between The Lines
Q I'm trying to find someone who sells bent transmission cooling lines for a '90 Chevy Impala. The car only has 49,000 miles on it, but the Wisconsin winter caused them to rust through. I'm sure they're out there, but where? Thanks.
Mike Lefeber Via e-mail

A Now that is some tough winter! Rusting through galvanized plated steel tubing is hard to do. There must have been places where the galvanized plating had been compromised, which allowed the nasty, salty snow melt to reach the steel tubing. Nothing is offered by the General; however, the aftermarket has come to the rescue.

Fine Lines offers bent tubing for all your restoration needs, lines from fuel systems, brake systems, trans cooler lines-almost any bent hard lines. They're available for the most popular musclecars and some of the late muscle into the early '90s. Note "muscle." Fine Lines doesn't view the late B-body GM cars as muscle! However, it does have an extensive library of patterns of original lines from cars it doesn't offer as regular production items (or you can supply your car's original lines if there's no pattern), and they can be custom-made for you. Another really nice feature is that Fine Lines offers the original galvanized steel tubing or, as an upgrade, stainless steel tubing. This sounds like the perfect option for your nasty winters to prevent this problem again. Good luck and take care of that Imp!Source: finelinesinc.com

The Mystery 350
Q I bought a '74 El Camino to part out. The guy I bought it from told me the engine was a 350 that he bought from an engine remanufacturing company. The price was so good that I didn't even check the casting number on the block until after I bought the car. The casting number on the block is 3932373 with a late-'68 casting date. All my research shows it to be a '68-72 307. A little disappointed, I pressed on and tore the engine down. This is where it gets interesting. The first thing I noticed when I removed the heads is that all the pistons were stamped "40," indicating that they were 0.040-inch oversize. So I took my inside micrometer and measured the bores. To my surprise, they all measured 4.040 inches! Is it possible to take a 307 block with a stock bore of 3.875 inches and bore it 0.165-inch over? I'm not sure if this block can handle this much overbore.

Another interesting set of numbers is stamped on the right front deck of the block. First is the partial VIN, and the engine ID, which is T1111DC. The crankshaft is from a '77 casting date and is from a 350. The block is also a two-bolt main.

A couple bits of advice I've gotten so far is that since the block was cast in 1968, Chevy might have used the same forms for this block that it used to cast the 327s, so the cylinder walls would have the same thickness as a stock 327. The other advice I got was from the machinist who did the actual hot-tanking of the block for me. He told me the casting number on the block was used for both 307s and 327s. However, my research didn't show that anywhere.

So in all reality, the engine was a 350. It ran very well and did not run hot before I tore it down. My plans are to just do a stock rebuild to have an extra engine. I just wanted to get a few opinions about this engine to see if it's a safe gamble to use, or am I wasting my time and should find another block? Thanks for your advice.
Darrin Las Vegas, NV

A First, you must be careful getting advice and opinions-everyone has one, and only some will be correct. Some of the theories are quite plausible. Let's get down to facts.

Your block is a '68-73 307-only block. The 373 casting number is specific to this model-year range. This casting number wasn't used for late, large-journal 327 blocks. Yes, if they would have used 327 water cores, the bore thickness would be the same as the 327. The "DC" engine code is specific to a '69 200hp, two-barrel 307, which could have been installed in any '69 Nova, Camaro, or Chevelle.

Should you give up on this block? The only way to be sure this block is sound is to have the cylinder walls sonic-tested, in which the thickness of the finished cylinder walls is measured. Most well-equipped machine shops will have this test equipment. What you will be looking for is an absolute minimum wall thickness of 0.200 inch on the thrust side of the cylinder wall. You can run about 0.020 inch less on the nonthrust side. Any less than this and you'll run into ring sealing issues from bore flex and will risk overheating and splitting (cracking) the cylinder wall. If the block comes in above these ranges, slap it back together. If not, get a new block. This test will take all opinion out of the decision.

Z Bar Baby
Q I need the years or casting numbers for a four-bolt-main Chevy small-block with the clutch-linkage boss cast into the block. The '65 Impala SS I found has no engine and needs this connection to operate the bell crank (Z-bar) clutch linkage. Could I be so lucky that even an '87 (or a little earlier) still has this, or was it eliminated in later castings?
Mike Weil Adel, IA

A It's your lucky day. GM did play with removing and reinstalling clutch cross-shaft bosses on the Gen V and Gen VI big-blocks but left the small-blocks alone. This goes for (real) small-blocks, Gen I and Gen II. This gives you a year range of '55-96 in passenger cars and up to '99 in some truck applications. Pick up an '87-and-later four-bolt and enjoy the one-piece rear seal and roller camshaft block for your early Imp. They are very cool cars.

I'm Causing Trouble
Q I have an '87 Corvette with an L98 engine bored 0.030 over, hypereutectic Mahle flat-top pistons, 128-casting aluminum heads, a ZZ4 cam, and LT4 valvesprings with 1.5:1 ZZ4 rockers. I'm looking to add torque (hard launch) and excellent low- to midrange power. I was told to add 1.5:1 roller rockers for the exhaust and 1.6:1 roller rockers for the intake.

Some Hotrodders.com members told me that in your Q&A years ago you said the ZZ4 camshaft does not work well with 1.6 rockers. Is this true? Why?

What's the best way to add more torque to my engine? I already have a 2400 B&M Holeshot converter, a B&M Shift kit, and Bosch III injectors, and I'm planning to add Hedman Elite Headers and the rockers. I'm currently stuck because of the rockers. Thanks a lot!
Sammy Calderone Via email

A Boy, we can even cause trouble on the Internet! At least people are listening-and remembering some important information. The reason I don't like 1.6 rockers on the ZZ4 camshaft profile is because when GM designed that camshaft, the acceleration rates and the opening and closing velocities were pushed to the max. With the additional acceleration of the 1.6 rockers, the valve actions become unstable. The valve will bounce on the seat on closing at high engine speed. There is also a lot of inherent noise with adding these rockers to the lobe, which was designed for a 1.5 ratio rocker. This camshaft was designed in the early '90s. Today I've seen the same things happen with some of the very high-velocity camshaft profiles. Any time you wish to add 1.6 rockers to a camshaft designed to run with 1.5 rockers, we recommend contacting the camshaft manufacturers for their recommendations. It will save you a ton of headaches and broken valvesprings.

To add slow-speed torque, you're on the right track with tubular headers. The factory tubular exhaust manifolds are quite restrictive. The Hedman Elite series headers are a shorty design. You'd be better served for your torque quest with long-tube, 15/8-inch headers. Hedman offers these headers both coated (PN 68446) and uncoated (PN 68440). Check with Hedman for more information.

Next, you'll need to build a very nice head-pipe system to connect the headers to the catalytic converter. A well-designed collector is the Flowmaster Y-collector, PN 250300, with D-port technology to improve scavenging.

Between the headers and a properly designed head-pipe assembly, you should realize a nice torque gain of 20 lb-ft below peak and at least a 10hp gain upstairs. Enjoy the hard launch!Sources: flowmastermufflers.com, hedman.com

Happy Gap
Q I'm building my first engine for my '72 El Camino. I bought an Edelbrock Performer RPM cam, heads, and intake for it, along with a bunch of other performance goodies. I had the 350 bored 0.030 over and bought a set of Sealed Power hypereutectic pistons, PN H345NCP, for which I bought Hastings chrome-moly rings. I set the gaps like the piston ring instructions said to, a minimum of 0.004 inch per inch of bore, so my total was 0.016 inch of gap. I chose the minimum because I figured that tight gaps would provide better emissions and long-term compression for a street car. But recently I've read that with hypereutectic pistons you need big gaps because of the way they expand. I've never had the instruction sheet for my pistons to know what they called for. Sadly, I have my engine almost all the way back together-I just need to put the intake manifold back on. Do I need to take my engine back apart and change the gaps? If so, what do I set them to? Thanks for any help.
Jered Lobban Kent, WA

A Keith Black/Silvolite was the first to market and sell a high-performance hypereutectic piston. The term hypereutectic is derived from the amount of silicon added to the aluminum alloy. Keith Black hypereutectic pistons are cast with a 16-18 percent silicon content, which dramatically increases the strength and wear resistance. One of the challenges with this amount of silicon is that it also acts as a temperature barrier. This, in conjunction with the piston design, is the reason you must increase the top ring-end gap to the recommended 0.0065 inch per inch of bore size.

As for the pistons you've chosen, Sealed Power has built a hypereutectic piston using optimized metallurgy with 16.5 percent silicon to allow standard ring-end gaps and conventional ring-land locations. The pistons also feature Duroshield antifriction skirt coating, which not only reduces friction but is highly resistant to scuffing. This results in an enhanced ring seal, increased horsepower, and extended piston life. Specifications from Sealed Power state that you can run the standard 0.004-inch ring-end gap for an inch of bore size.

With all this information, go ahead and finish screwing your engine together. Give it a nice, long break-in time before full-throttle runs. This will give the piston rings and cylinder bores the chance to get happy and wear slightly. Also, with this wear, the rings will have a greater surface contact area to the cylinder walls to aid in cooling. You shouldn't have a problem. Enjoy your new engine.

Sources: federal-mogul.com,kb-silvolite.com

Rip Van Winkle
Q My '72 Chevelle has been in storage for the last two years. I was not expecting to store it that long, so I didn't perform proper maintenance before I put it away. I have been a Chevy High Performance subscriber for several years, and I know I saw an article at some point about how to go about starting a car that's been in storage for several years, but I cannot find it. Could you please point me in the right direction? Thanks!
Tim Francis Louisville, KY

A First, for the fuel system you'll want to pick up a bottle of Redline Water Remover & Antifreeze. This will allow any moisture built up in the fuel tank to be absorbed into the fuel and burned though the engine without a problem. It is also a great upper-end lubricant, which will help wake up your sleeping engine. You can either pick up a bottle at your local Advanced, AutoZone, CSK, NAPA, or Pep Boys, or order it directly online from Redline.

Next, change the engine oil and replace the filter. Since we don't want to start the engine until the new oil is installed, give the oil plenty of time to drain from the oil pan. Normally, you'd want to drain the engine oil when it's good and warm to promote drainage.

Finally, remove the spark plugs and shoot some oil directly into the cylinders. What we've had great luck with is Marvel Mystery Oil, developed in the 1920s to combat deposits on carburetors caused by poorly refined gasoline. It was used extensively in WWII on everything from airplanes to battleships to tanks. The best part about Marvel oil is that it burns with no deposits. The top piston ring of an engine is essentially a dry ring (not supposed to have oil on it). Standard engine oil will leave deposits on the ring lands that inhibit ring seal. You can pick up Marvel Mystery Oil at all the above-listed auto parts stores.

With the plugs removed, Marvel in the cylinders, fresh oil in the pan, and Redline in the gas tank, crank the engine until you have good oil pressure or the oil pressure light has been off for 30 seconds. Reinstall the plugs, and you should be good to go. Of course, check all fluid levels, brake hoses, and tire pressure. We'd then service the car in about 1,000 miles-a complete service with all fluids. This will give the car a chance to wake up all its sleepy parts and get all the moisture out of its system.Sources: marvelmysteryoil.com, redlineoil.com

For Cryin' Out Loud!Q I was wondering if you ever might do a piece on building an 8.1 496 Voretc. I see tons of LS engine builds but have not seen one of these engines built in any magazine. Also, why does no one offer a carb intake for these engines? They have a place for the distributor in the block, although there might be a clearance problem with the intake runner. Everything else is either available or adaptable from Mark IV, Gen V, and Gen VI big-blocks. I have two of these engines and am installing one in a '47 Chevy sedan. Both of mine came from 4500 Chevy moving vans, where I think they are still available, although no longer in pickups. They have a strong, internally balanced 4.37-inch-stroke crank, a 4/7 swap roller cam, large cathedral-style ports, 2.19/1.72-inch valves, and thick cylinder walls that might go 0.125 inch over! The rods are 6.693 inch with light pistons. I know Raylar makes aluminum heads (expensive), so why does no one make a cast 4150/4500 flange intake for these things? It's a big-block rotting in a junkyard, for cryin' out loud! Like the early Chrysler Hemi was in the early '50s-no one wanted them at first.
Danny Marlow Mt. Vernon, IL

A Nice listing of all the great features of the 8.1 496 engine. We had a chance to get two from a Sheriff Patrol boat that required them to be replaced at a certain hour mark. Back when the 8.1L was being developed, we, with a friend named Mark McPhail, really looked hard at making a carbureted aluminum intake for this engine. You stated the major problem: The No. 7 intake runner is going straight at the distributor location, and since the inlet ports are symmetrical (all the same design), the No. 7 runner is pointed toward the flywheel of the engine, not toward where a carburetor would be mounted! They can get away with it in a fuel-injected, dry-flow design. But when you add fuel to the mix and try to make turns like that, you have real distribution problems that cannot be overcome.

Yes, Raylar Marine has released the BigPower aluminum cylinder heads, which also are accompanied by a new shorter-runner, large-plenum, fuel-injection manifold. The complete package for the 8.1L GM marine engine picks up right at 100 hp! It also kicks your credit card to the tune of $6,000. This puts the power up to 525 hp. Now that would be a nice-running dualie Crew Cab!

What you're doing with your engines is a perfect application. They will motivate your street rods with a ton of torque and burn the tires as long as you wish to keep your foot in the throttle. Sorry we don't have better news. And yes, it's a crying shame that we don't have a use for these engines.Source: raylarengine.com

Sparklers
Q I was wondering if you guys have heard about Pulstar spark plugs. I saw an ad for them claiming substantial gains in horsepower, torque, and mileage. I checked out the website, and they were $25 a pop. I have a '92 Camaro and a '93 K1500 (both with 350 TBIs) and was thinking about trying them out. It would be awesome if you could do an article with some dyno results in a few engines/cars. Thanks.
Ryan Telenga Oak Harbor, WA

A OK, guys and gals. This is how we usually get into trouble with our answers. What Pulstar is doing is basically putting a condenser into the spark plug to store the collapsing energy at the end of each firing cycle. This energy usually just travels back up the plug wire toward the open cap or coil in whichever arrangement your ignition is. This stored energy is added to the next firing cycle and increases the available energy.

Back at the end of the 1991 season, the NHRA Top Fuel cars were on the brink of running 300 mph. The problem they were having was lack of ignition energy. They could move enough fuel but could not burn it. We were working with Larry Meyer, the crew chief of Tom "The Mongoose" McEwen's Top Fuel car. Meyer had come to McFarland Inc. to pick our brains. One of our electrical engineers had the idea of making a condenser that would fit down onto the Hemi spark plug and be hidden by the valve covers. We built a set of 16 (twin plugs per cylinder) and showed up at the Winternationals in February 1992 with them on the car. McEwen proceeded to set the low e.t. for the race and the top speed of the meet at what we remember to be 299 and change! Unfortunately, the material that we used to make the condensers meant there was a specific amount of time before they would transfer the energy to ground and cause a misfire. We didn't know this until it happened. When Dale Armstrong, then crew chief of Kenny Bernstein's Top Fuel car, saw them, he promptly named them Sparklers. At Gainesville, Florida, that year, Bernstein broke the 300-mph barrier, and the rest is history. The concept has been out there for years and does work if you need the increased spark energy to light the fuel.

Let's get back to your TBI 350s. At McFarland we had test equipment that could record the cylinder pressure in a running engine down to 0.2 degree of crankshaft rotation. This is called engine cycle analysis. During these years, we did a ton of ignition and spark plug testing. We found that once the fire was lit in the combustion chamber, the burn speed and rate were controlled by the fuel mixture, fuel homogeneity, mixture motion, and combustion space design. Adding spark energy to a plug that fired the mixture effectively every time didn't pick up any power or economy. If you had an engine design that was prone to idle instability, lean misfire, or cylinder-to-cylinder distribution variations, you could see minor gains. Again, if you have adequate spark energy, you rarely have an issue.

Do the Pulstar plugs work? They could help an engine that has a borderline misfire condition. There have been many spark plug designs released over the years that have promised great things. We'll just have to wait and see. Maybe Pulstar would like to send us some plugs for testing.Source: pulstar.com

Didn't you mean Ls series?
Q What is the real, real story on the LT series of engines? Those engines seem to me to be the most advanced and best engines Chevy has ever produced. Thanks.
Kevin Hawkes Via email

A To compare the LT engines to the LS (Gen III) family is a night and day comparison. The LT1s and LT4s made very good power for their platforms; however, the LS (Gen III) small-block gives you many distinct advantages over the earlier engines. Outstanding stock cylinder head flow, all-aluminum package, aggressive camshaft profiles, stainless roller rockers, and low-friction pistons and rings are the reasons this engine shines. In my opinion, the Gen III engines will never be a small-block Chevy. However, the General has given it that tagline and it's here to stay.

The LT family of engines has basically been stepped right over. We jumped right from Gen I small-blocks to Gen III engines for swaps and performance upgrades. The Gen II engines are plentiful out in the junkyards, and almost all the Gen I engine components can be used in the Gen IIs. Pick one up and upgrade your early Chevy engine bay. The engine mounts and headers will bolt right up. Accessory drives are easily adapted from either Corvettes or Impalas.

Oil Spill
Q My '66 SS Chevelle with a 396 big-block is totally restored and beautiful. After I showed it off around town I noticed the clutch slipping. I looked under the car and saw an oil leak. It was coming from the back of the oil pan, where the main cap is. I figured I must have messed up the pan or gasket when I brought the engine home from my engine builder. I replaced the pan and gasket and it still leaked. I did a leakdown test and it seemed there was too much pressure in the crankcase. I had the engine gone through for the second time and installed Total Seal piston rings.

I put the engine back in and it still leaked. That is when I noticed the pan was touching the crossmember. My engine builder said the crossmember bends slightly on old cars and that I should put 1/4-inch plates under the motor mounts. After that, I could not close the hood, no matter what air cleaner setup I used. So I went with a low-profile oil pan from Milodon. Anyway, after all that, it still leaked, even though the pan was not touching the crossmember. I even used a one-piece gasket. I have heard from my engine builder that sometimes big-blocks just leak in that spot on the pan and there is nothing I can do.

I have spent six years and a ton of money with this so-called dream car of mine. What can I do to get the pan to stop leaking? Is there a special sealant or can it somehow be welded onto the engine? Please, any suggestions would help.
Don Way Collinsville, IL

A Wow, you have been through the ringer over the past six years! Chasing a pesky oil leak can be a real pain. You could be trying to fix what isn't the real leak. I'm slightly disturbed by your engine builder's statement that sometimes big-block Chevys just leak in that spot! I've been building big-blocks Chevys for 35 years and I've never had one I couldn't seal up. After all the parts you and your engine builder have thrown at this thing, let's look a little further.

Unfortunately, I'm going to suggest you pull the engine out of the car. First of all, you will be able to put the engine on a stand and turn it upside down. This will allow you to really clean the pan rail and ensure that you get a good seal with the pan gasket.

Yes, the silicone one-piece oil pan gaskets are great. The Milodon oil pan is high-quality. Milodon features new pan rails on its fabricated pans to ensure leak-free operation. What I would like for you to try is to pull the engine and install it on an engine stand. Do not remove the pan just yet. Run the oil pump with a priming tool to create oil pressure, just like the engine is running. If you don't have a priming tool, check out Milodon PN 23000; it has the proper reproduction of the bottom of a distributor to feed the oil through all the oil galleys. Remove the flexplate and have a buddy run the pump primer so you can watch the rear of the engine. Rotate the crankshaft 90 degrees about every minute to change the way the oil is fed to the rear main.

Back in the day, when I was a line mechanic at a Chevy dealership, I found a small-block that leaked oil through the block casting at one of the main galleys. It only leaked while the engine was running, and it looked like the pan or the rear main. After replacing the pan gasket, and the rear main seal, I couldn't get it to stop leaking. I removed the transmission and the flexplate and drove the oil pump with a primer. The oil galley that fed the rear main bearing had porosity in the casting, and the oil sweated through the block under pressure. This took me several days of work to find it, and then I had to replace the block.Source: milodon.com

Chasing Your Tail
Q I read your column every month and like the way you provide detailed, down-to-earth answers to problems. I hope you can help me with mine. I have owned, since new, a '99 Chevy Tahoe 4x4 with the 5.7L Vortec engine. The engine starts skipping and losing power pulling up a hill when exceeding 2,000 rpm. It acts as if it is starving for fuel, just like in the old days when the mechanical fuel pump went bad. The truck gets great gas mileage (22-23 mpg on a trip), and the problem does not exist when the engine is cold.

Here's a list of what has been replaced without correcting the problem: fuel pump, fuel filter (many times), fuel pressure regulator (five times), distributor cap and rotor (three times), spark plugs and wires (three times), fuel pressure line from filter to engine, catalytic converters, intake manifold gaskets, and the No. 1 fuel injector!

A little background information: When the truck was 2 years old, the engine started to skip and shake on a long uphill pull and the "check engine" light came on. Because the computer trouble code said the No. 1 cylinder was skipping, the dealer replaced the spark plugs, wires, distributor cap, and rotor. But the problem continued.

Later a dealer technician plugged a laptop into the diagnostic port under the dash and drove the vehicle. When the truck started to skip, he noticed the fuel pressure dropped off. So the fuel pressure regulator was replaced for the first time. It continued doing the same thing and the computer trouble code was showing that the No. 5 cylinder was skipping. Then the fuel pump was replaced, along with the fuel regulator for the second time. This did not get rid of the problem.

Over a period of time, the items previously listed were replaced, and yet the problem persisted. I don't care if the truck gets worse mileage as long as it will run up a hill and pull my trailer. I hope you can help me get my truck fixed.
Herb Maheu Whiteford, MD

A First, you said the truck runs properly when the engine is cold. There is cold-start enrichment when the engine coolant sensor reads low temperature. Sometimes these coolant temp sensors will go bad and give the computer the improper signal based on the engine's temperature. The dealership should be able to check this on its Tech II diagnostic handheld, which gets its data through the diagnostic plug. Next, your troubles are a classic sign of a ground problem. There are about six grounds for the engine management system throughout the engine bay, not including those at the battery, the frame, and the engine block. If you have a ground issue, as the system heats up it creates resistance, which wreaks havoc on the entire ignition and fuel system. The engine management system runs mostly on resistance sensors. If there isn't a perfect ground loop back to the computer, all the data that the computer is receiving isn't accurate. Get your dealership to print out a wiring schematic and locate all the grounds. Track them down and clean and tighten them all to proper specs.

Sorry we don't have a silver bullet to give you. Sometimes you have to step back to basics. Sometimes throwing parts at something just doesn't work, and it can be very expensive. Good luck with your search.

Technical questions for Kevin McClelland can be sent to him at chevyhi@sourceinterlink.com

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