jtownc4

Ok, a buddy of mine has this 96 GMC Sonoma pickup. 4.3 V6. It has the W motor, 4x4... Ok here is what he told me and here is what we did so far...

He started having problems and a flashing check engine light all of a sudden. Read the code and it was a cylinder misfire and a MAP Manifold Atmospheric Pressure sensor, which he replaced. No difference. I guess the check engine light came right back on. So he took it to one garage that told him he needed a new ECM. So this garage recommended Lloyd to replace his ECM. When he took his truck over to Lloyd, Lloyd informed him that he in fact did not need a new computer, but that he needed a new fuel injection spider, an intake gasket, and that cylinder number 3 was dead. Three hundred bucks later, with the top of his motor torn off he had the pickup towed to his place. Lloyd did manage to put a new lower intake gasket set on the motor before he gave up...

Now my buddy and I live about two and a half hours away from each other. I am somewhat paranoid about mechanics in general, and I thought maybe Lloyd was bullsh*tting him about the dead cylinder because frankly it is a royal pain in the *** to get a spark plug into #3 let alone a compression tester with where the steering shaft is located in relation to the motor. So I went on a roadtrip (which was very pleasurable I might add, I had a chance to actually drive my car instead of putt around town) to at least get his truck put back together for him.

Ok, so we put a new fuel spider in the truck, buttoned it all up, and holy sh*t, Lloyd was right, #3 is dead. Totally. But why? How? Burnt valve? Bent valve? Cruddy valve? We have spark, we have oil pressure, no water in the oil, no overheating, just a dead cylinder... All of a sudden... We didn't pull the head off, I didn't have time to mess with it any more than I did... He can drive it to work, albeit it runs really, really bad....

My buddy does drive like an eighteen year old kid with a hard on, mashes the throttle to the floor every time he gets on the highway, likes to do burnouts in his pickup frequently etc etc... I'm not saying that to be rude or anything, but that is what he does. I have had around a dozen of these 4.3 motors, and I never spin them over 3500 RPM and they run longer than the bodies last. I have tried to tell him this but it is like telling an eighteen year old with a hard on something, so my message doesn't get too far.

Ok last thing... The truck only has 77k on the ticker. My buddy is desprately trying to get financing for a full size Chevy pickup and he realizes that he will get essentially nothing for his Sonoma... My old man has always liked this Sonoma, he is going to help my buddy out and take it off his hands. I happen to have an extra 4.3 that I bought several years ago for a different truck I no longer own, so I am going to give my dad the motor and hopefully we can live happily ever after.

Any thoughts on what went wrong with this motor? Any similar experiences?

MGorman

This is an outside possibility. The first thing to do is perform a compression check on cylinder #3. If there is little or no compression there is a possibility that an aluminum backing plate on the back of the throttle body came loose and became lodged under the intake valve.

This occurred on my friend’s S10 Blazer same year, same engine. While this is not a common occurrence, I have heard of this happening to other vehicles. This happened on his vehicle at approximately 70,000 miles. I removed the head, removed the obstruction and replaced the head with no machine work. Due to the fact the obstruction was aluminum there was no damage to the valve or seat. He drove the vehicle for an additional 100,000 miles with no repair related issues.

jtownc4

I am all for pulling the head... It isn't that much work, and if it is a problem in the head they are under $250 from the zone so I would rather do that if than change a motor...

Now my wife's 2002 is acting all funny also, same thing almost... Flashing check engine light, it has always had an evap canister code, P0300 misfire, but hers sounds like the exhaust is almost plugged up. Maybe the catalytic converter is clogged up? I had a 94 Blazer with the old Z motor and I removed the insides of the cat with a digging bar, the truck ran amazingly for 100k after I did that...

The more I wrench on these post 1996 vehicles the more I want to get rid of them.

MGorman

I would confirm low/no compression and pull the head and take a look. (Assuming you have checked rocker arms and valve springs) It’s not too difficult to remove the head.

Not sure what to tell you about the evap canister code. It could be the canister, the solenoid, the lines, or even the gas cap. These can be tough to track down. The P0300 could definitely be a clogged cat. As you probably know the P0300 is a random misfire code which means that multiple cylinders are randomly misfiring. Other possibilities are faulty plugs and or wires, a vacuum leak, or low fuel pressure.

If it turns out the cat is faulty, knocking out the substrate won’t work as well as it did on your 94 because the O2 sensor after the cat will set off the check engine light.

Good luck!

93Rubie

Your buddies dead #3. Best and easiest way to tell what is wrong. Is a leak test. Not a compression test, the leak down tester. Get #3 to TDC, install tester and add air pressure. Intake valve=air heard in Throttle body.
Exhuast valve=air heard in exhuast pipe, Air out the oil fill cap=rings/hole in piston. If its the rings add about a table spoon of oil and retest, see if readings come back up. A blown head gasket, might be bubbles in coolant.

The leak down test doesn't lie. I like them better than compression tests.

As far as your wifes vehicle goes. I'd focus on the P0300. The evap code should NOT in a long shot be causing a misfire on multiple cylinders.

I'd start with checking spark on all 6 at the plugs. Then fuel pressure.
If you suspect the exhuast is plugged, rip the pre-cat 02 out or loosen up exhuast pre-cat and see how it is. Loud but if its plugged will run better. That being said, I would not drive it much misfiring all the time, that can very well plug up a cat. They do not like that at all.

jtownc4

First guys, thanks. Little update on my wifes truck. I crawled under it yesterday and started investigating some things. It definately sounds clogged, and it needs a muffler... so I started by removing the muffler, and ran out of acetylene so I gave up for the day, and I was absolutely frozen laying on my garage floor. I was hoping it was a plugged muffler, but that just isn't my luck for it to be something simple or something I can fix for twenty five bucks, but, it ran the same without a muffler, so now it is all loud and obnoxious, and still running like feces... I checked all the plug wires, they all are fine, I didn't pull any plugs yet, but I plan on changing them anyway... could this be a bad fuel spider doing all of this? Something had to plg that cat up, this happened all of a sudden while my wife was driving it. My buddys truck sh*t the bed all of a sudden also, that is why I am so quick to blame this damn spider...