Hoping I can get some answers about my T/A on here since everyone seems more knowledgeable here than some other sites. I have a 95 T/A w/ an LT1.

I was on my way home last night, doing about 60mph. I came to a bend in the road let go of the gas and the engine backfired like a machine gun about 5 times. Gave it a little gas through the bend and got about 10 feet from my drive way and check gauges light came on, started turning right into the drive way, and the engine just cut completely off. Noticed my gas gauge was leaning towards E and we all know how the gauges blow in these cars, so I called my g/f and had her bring some gas and jumper cables. Poured some gas in the car, hooked up the jumper cables and tried started it and it just cranked. As it was trying to crank the car seemed like the battery was dead, and all the lights would dim to almost off. Pulled the jumper cables off, tried started it a few times. Hooked my scanner to it and pulled code 16 low resolution pulse, gave up and pulled it the rest of the way home. This morning I got up hooked the battery charger to it and waited about 10 minutes and tried to start it, and it did the same thing it was doing last night. I pulled the PCM, let the battery charge for about 30 minutes than tried to start it up. It ended up starting, and stumbled horribly, backfired and fell on it's face again. I put a fuel pressure gauge on it, turned the key on and had ~40psi. Had my g/f try to start the car and had about ~50psi while cranking. I than put a spark tester on, cranked the key and the light lit up, with about a 1-2 second delay. I rescanned the car, and found no codes this time. For the hell off it, I ran through the diag chart I pulled from ALLDATA, and tested the PCM side of the opti harness and had 5 volts. Tested the opti harness it self, also 5 volts. The diag chart leads to faulty Opti connector or faulty distributor. The only problem I'm having with this is that the code is no longer being thrown so I suspect code 16 was thrown because the battery was pretty well drained the night before. I'm kind of leaning towards the timing chain jumping or breaking. When I go to start the car, it backfires really bad, which leaves me to believe the timiing is off, and the plugs are firing after TDC and when the exhaust valves are opened. Hoping I can catch some opinions on here so I know what to rip off my car tomorrow and get some parts ordered.

Sorry for such a long post, was trying to be as descriptive as possible

 

How many miles on the old girl. The butt link chains are very robust and usually don't cause much of a problem. However, what you're describing sounds exactly like the chain has slipped. A big clue is when you said you let off the gas and it popped about five times. That's when the chain will go from load to lag and that's when it will slip. The side of the chain that was tight when accelerating will become loose on deceleration. That's a good time to jump timing.

I'd probably want to remove the plugs and the serpentine belt. Try to turn the harmonic balancer back and forth and see how much play is in the chain. You should be able to feel that much slop in the chain. That would give you a place to start. Good luck.

 

It has about 114,000 on it. Thanks for the tip, I figured I would have to pull the timing cover off to be able to tell if it had jumped or broke. I will post back with an update on what I find tomorrow. Luckily this happened on my last day of work until Thursday so I have some time to straighten it out.

 

114000 sure isn't a lot on a factory chain but stranger things have happened.

 

If the timing chain broke, you would know it...you'd be picking pieces of valves out of the top of your pistons. A stretched timing chain won't result in a no start, not to mention they don't just suddenly stretch and kill the engine.

The low res code is the key. With no low resolution signal, the engine won't run.

Your opti is toast or the harness going to the opti has corrosion on the pins.

 

As I stated in my first post, code 16 was only thrown when the battery voltage was low. I'm pretty positive when the battery is putting out low voltage it sets a code 16. After clearing the code, charging the battery, and trying to start it or it starts and it runs like crap, backfires, stumbles and dies, no codes get thrown. And I've already tested, and inspected the opti harness wiring.

 

Will a 114k mile timing chain have a little stretch? Sure. Enough to cause what you're seeing No.

Based on symptoms, it's an ignition problem as you've surmised. What are the primary parts of the ignition system...The Opti itself, the plug wires, the plugs, the coil, and the ICM. Of all the parts, only a bad Opti or several plug wires that have popped off their terminals will cause what you are experiencing. Your own diagnostics point to the Opti. It acts like the Opti is bad. Seeing a trend?

How many miles on this Opti? Ever had it apart? Ever dab a little Loctite on the rotor screws? The screws like to back out over time, especially if the car has been run hard, and then the rotor moves, effectively throwing off the timing.

 

 

I only mentioned the chain because it's what fits most of his symptoms. It started all at once when coasting......code could have been low voltage or the PCM didn't see the low res pulse at the correct time. Based on his post he seems to have checked the Opti connector and associated electrics. He seems to know what he's doing.

The "popping-backfiring" through the exhaust is generally caused by the spark not occurring at correct time and Opti failures do not generally do that unless something is telling it to fire at the incorrect time. That would be the camshaft that is turned by a chain.

I agree that 100,000 miles is low for a chain failure but as I mentioned "stranger things have happened". Maybe the previous owner let it run out of oil/get hot or who knows what. It's just a guess but I think it's as good a guess as any. In any event, I believe the timing cover will eventually come off and the problem will rear it's ugly head.

 

I've been an active member on this forum and others for 10 years and don't remember seeing an LT1 timing chain failure.

 

Me either. Just sayin'........? A used car and the previous owner may have put a Pep Boys Chinese wonder chain in there. No one knows. Just guessin'.

 

In nearly 20 years of being around LT based C4s, I'm not aware of a chain stretching so much that what the OP is experiencing has ever occurred. Interestingly enough, I did have an L98 with a chain that was stretched enough to cause a bog on acceleration when cold. As soon as the ECM went closed loop, it would correct for it and the car would run fine.

When a chain outright fails on an LT1/4, the unlucky owner will absolutely be picking pieces of valves out of the piston tops. This is indisputable fact.

What often happens when an Opti fails is exactly what the OP is experiencing and so have many, many others, myself included. Have the rotor come loose inside the cap and the engine may barely run and pop through the intake (or backfire out the exhaust), or it may not run at all. Taught me and several others many years ago to loctite the rotor screws on opti's prior to installation. Grenade a rotor...pretty simple....no start, spark from the coil, none at the plugs, just the engine cranking. Been there and done that too.

114k miles. I'll bet the front of the intake is leaking oil on the opti. I'll bet the inside has oil fouling the optical sensor. In addition, with that kind of mileage, the cap and rotor are getting a bit long in the tooth and if it's been run hard, that doesn't help.

 

That was pretty much dead on. My intake is pissing oil out of the front. I pulled the opti out and things are rattling on the inside. Oil was pouring out of the opti somewhere because I set it down and walked away and there was a pretty good sized puddle when I came back. Went ahead and ordered a new opti. Is there any way to prevent oil from getting in there, it's gonna be another week until I can do the intake, and I'll need the car sooner than that.

And thanks everyone for your help, first lt1 vehicle I've owned so it's always nice to have other opinions when it's your first time with things

 

The intake r&r is really straight forward on an LT1. I know the engines are set back in the F-body, but assuming you can access everything relatively easily, the repair is a 2 hour job. A Corvette is a 90 minute job since the engine is more exposed. The LT1 intake is dry, so it really is just the matter of popping it off, cleaning the sealing surfaces up, and installing the new gaskets. There is no gasket for either end of the intake, you use RTV for that. The absolute best RTV to use is called "The Right Stuff". It's expensive...$15-$18 vs $5 for regular RTV..., but I've never had a leak on a car, even years down the road.

I'd spend the extra couple hours to fix the intake now.

 

I've changed intake gaskets on an F-body, a little more difficult than our Vettes, but nothing too bad.

Change the gaskets before you run the car with the new opti.