Small Block & Big Block Chevy Specific - 96 Tahoe 5.7L 242k Miles Troubleshooting Help

Hey guys here is the story

96 Tahoe 4x4 has 242K+ miles still on the original engine and is not a daily driver nor is it driven hard.

I had some issues with tired starts, cylinder 2 misfire which cleared up after some Lucas Fuel system cleaner and then a week it completely died while driving and I could not get it started.

I took it to the shop where they found it had some bad fuel so they cleaned the tank and replaced fuel components. Then while still trying to get it started they finally tracked it down to the wiring harness after replacing the below mentioned parts.

So I get the truck back and its running like a champ, better than it had in years. A few days later I go to drive it and after around 15 minutes it starts misfiring horribly. I scan the code and its a cylinder 2 misfire again. It only happens after driving for around 10-15 minutes so I'm thinking once something reaches operating temp.

I take it back to the shop, they do some diagnostics and think its possibly a cracked head or maybe some valves not seating properly but can't tell without pulling the head. This is a good shop that I trust, they cut me some great deals on the above mentioned work since the problem ended up being the wiring harness so they are not just trying to take labor money since I bring them the parts.

However if it was something mechanical wouldn't it occur from startup each time instead of only after running for 10-15 minutes?

The recently replaced parts:
Fuel pump, fuel filter, injectors, distributor (less than 2 years ago), wires, plugs, battery, pcm and engine wiring harness.



I appreciate the time and help in advance but myself and my gearhead friends are stumped on this one and I don't want to take the time to pull the heads unless that's the only option. Thanks again.

Mark

Are they going to do a leakdown/compression check before they pull the head? That will give a good idea if the head needs to be pulled. What does the spark plug look like in that cylinder? Is 96 the year they have the spider thing inside the intake? It's been a while since I have worked on one.

Yeah 96 was the first year they went to that on the vortec 350's. 95 year still had the TBI but had the new model body.

I would definitely do a compression and leakdown test on cylinder 2 to see what's happening there. I suppose a cracked head or blown headgasket is possible, but I'd want another test to confirm before I pulled the head, such as combustion gases in the coolant or a clean/wet spark plug. When the "injectors" were replaced, was that just the poppets on the end of the spider or the entire spider itself? If the spider was replaced, was it with a reman unit or one of the updated SFI units with with actual injectors for every cylinder? The remans aren't usually the greatest quality out there, and I personally prefer the updated delphi units when possible.

A compression test was done by the first shop. I didn't get the exact readings but the cylinder was still good.


The entire spider injector assembly was replaced with a new BWD unit from O'Reillys. When they first pulled the plugs they were wet with that bad fuel, since then the plugs have been dry.


I tried a new ignition control module and coil just because a friend works at an auto parts store so I could return the parts if they were not needed.


I will pull that specific plug tonight and see what it looks like now

Have you drained and inspected the coolant? Any signs of oil is not a good thing. That will lead back to a cracked block. Had this problem with an engine owned by Uncle Sam a few months back. When the block heats up, the crack shows itself and plays hell on every system. Bear in mind, this is how a redneck troubleshoots this problem. Hope thats not it, good luck bud.

Intake Gaskets could be leaking if the leak-down comes back normal and it still does it

Man I love my 99 2 Door Tahoe...I think they are the best trucks ever. I'm sorry to hear about yours. But 242k is pretty damn good. I'll be happy as Shi* if I get that out of mine. They are still the sexiest truck on the road if done right.

I second the Intake gasket. I also know some of these headfs do crack after multiple heating/cooling cycles. If the fuel system is good id look at a intake or head hasket. while there have the head checked for cracks..