96 Tahoe vortec 5.7 cranks / misfires

[NeilC]

I have a 96 tahoe with a vortec 350 that I purchased from auction not running. It cranks over but seems to be misfiring almost like it out of time. How would I check to see if its the timing chain that may have slipped a cog ? And could it possibly have a cracked distrubutor cap? Any input would be apprecated from anyone that has had this problem with a similar vortec 5.7. Thanks

[dougbfresh]

Timing light can help check timing, see if #1 fires at all . Does it even have a cap? I would check the crank sensor if you have no spark at all.

[m1k3sthemannn]

I'd put the "slipped tooth" idea out of your (and anyone elses) mind. If it slips, it's going to keep slipping. There are too many teeth on the sprockets in contact with the chain at all times. You'd have to be missing half the teeth on a sprocket, all in sequence, for this to happen.

I've only seen one GM vehicle that "slipped" time, but there was so little material left on the teeth that it slipped as soon as the engine rotated and would never start. They were all worn evenly, just so much of the nylon was gone that the chain rode over them, instead of them driving the chain.

[carsandcycles]

Agree, the chain isn't likely to slip a tooth. You might have a severely stretched timing chain causing timing issues but you see those on high mileage, not well maintained vehicles.

[NeilC]

Thank you everyone that posted ideas to solve my problem. I did put a timing light on and cranked the engine over and I am getting spark as well it always fires at the same position. There is spark at #1 but I can not find a timing reference pointer on the engine. This has the newer style distributor on it and is to be timed with a scan tool with the engine running apperently. The mark on the crankshaft dampener shows up in the timing light about 30 degrees before the top of crank rotation. Also I noticed that after loosening the dristributor hold down bolt slightly I could move the base of the distributor back and forth in the top of the intake manifold about 3/16 of an inch. I have never seen this much play so I am suspecting something is wrong with the distributor. I will push it into the garage on the weekend and get a little deeper into it. Its a warm day in canada @ 39 degrees but still to cool for this old guy to do much outside. Thanks again for the information.

[Saltmine]

I guess not...a '96 5.7 "R" code engine is a "crank learn" engine, completely devoid of timing marks. The distributor has no provision for "adjusting" the timing. The ECM does that. No, it probably doesn't have any "play" in it, that's the ECM changing the timing, and yes, it does actually idle with the timing aparently at 30 degrees....."crank learn"

As far as a misfire, check out the sparkplugs and wires...maybe even go so far as to check the compression. These engines do have a tendency to "shell" the distributor cap.

I agree with Doug on the timing chain thing...This is a roller tappet camshaft engine, with very little load on the timing chain...They seldom go bad.

The biggest problem we had with them was the CMFI fuel injection. They have the injectors in a central pod with the injector nozzles out at the intake ports. With plastic lines and prone-to-sticking poppet valves on the ends, they were quite a nightmare. The fuel pressure was also critical...62lbs minimum. Below 60lbs and the thing would be hard to start, and run bad. Below 45lbs and it wouldn't even start.
The plastic lines also were prone to cracking, and spraying fuel all over the place inside the plenium.

[justen]

Alot on 1996 or early vortecs will wear out the distributor gear. It's best to replace the complete distributor. Also while you are at it. Make sure you are getting gas. Make sure you have enough psi and volume for the demand the injectors require. If someone down the road changed injector sizes that could cause problems if not properly tuned for that air/fuel ratio value.

[NeilC]

Thanks to all of you who took the time to post tips and ideas as to my problem. Thankfully I took your advice and did not tear the front of the engine apart to check the timing chain. After getting the truck into a warm garage I checked the fuel pressure and got a 64 pound reading with the key on and a presure of 55 pounds holding after the key was off. I pulled the plugs to find they were all wet with fuel. The distributor cap was badly coroded so I changed the cap, plugs and wires. Installed a new battery as I found the old one was only sitting at 11.2 volts after sitting for a bit and with a turn of the key it fired back to life. Thanks again to everyone for the help and I hope sometime in the future this post will help another with a similar no start problem .

[danny]

congrats and thanks for posting the results.