'94 LT1 Never-ending problem

I need help. I'll be as concise as I can be:

1. '94 LT1 police package. Opti-spark distributor. 5.7L v8.
2. Purchased 2/04 from BIL. Stock cop car w/exception of K&N intake and Flowmasters & no cats.
3. Late 3/04, very, very intermittent power cut-out to drivetrain while moving. Motor and all electrical still running. Needed to let off gas or put in neutral and rev, and it all came back, drop back into drive, and all is good
4.Above problem intermittent until 5/04. At that time, worsened, and also started stalling out completely (motor dead, needs restart). Also starting to backfire bigtime.
5. Late 5/04...to GM dealer. Scanner sez fuel pump. Had that and filter replaced. No go. Same problems.
6. Take back to GM dealer, tell em they messed up...same probs. Tell me need new distributor, or crank sens. I run away.
7. Take to independent shop in town (Columbus, OH), very reputable. Confirmed distributor with scanner. Waste close to a grand in parts and labor. Runs great for a few weeks.
8. Trip from OH to SC. 2 hours into trip, all the same old shit happens...no power, stalling, backfiring. Make it to SC, miraculously, and back to OH. Seems worse after a gas stop and it's hot.
9. Make it back to OH, barely, after about 1000 backfires and stalls. Whew. Backfiring causing flameouts through intake under hood, as well as from tailpipes.
10. Back to independent mechanic. Now it's a leaky sensor on manifold (?) that shed antifreeze down the wire into ECM. Tightens sensor and removes and cleans ECM and puts dielectric on all wires into ECM. Runs great! For about a month.
11. Is is MAF? Problems again. Swaps out one he had in stock, seemed fine, put old one back in. Runs fine again. Nothing really done. Keep in mind plugs/wires replaced in 8/01, so should still be ok. Platinum plugs and premium wires. No cooking going on from heat that we can tell. Heat shields in place and doing their job.
12. Starter fried & replaced. No wonder....all that restarting after stalls. Runs fine.
13. Dies at a light. New alternator installed. Still running fine...for a short while.
14. 2-3 weeks ago, same old shit starts up gradually. Occasional stall at a stop lite/sign. Occasional loss to powertrain as before, but motor still running. Lift off accelerator or put in neutral for a sec, and back to drive, and all is ok. Motor still running all the time.
15. Last week or two, again progressively worse. Backfiring all to hell again, stalling at stops, while driving, dying while driving, etc. AT NO TIME IS CHECK ENGINE LITE COMING ON.
16. Coil and coil wire seem ok. Not sure about coil amplifier though...
17. Swap MAF for another...same old shit. Put the old one back on.
18. Mechanic tells me he's stumped, and he's one of the best in Columbus. Maybe fuel injectors, he says? But says ohms test not definitive. If injectors, I said, wouldn't the damn thing still run if it were just one or two injectors?? Still stumped. Tells me he thinks it's a problem that is not connected to, or controlled by the ECM. Has no answer how to fix. Says it's a great, great motor (I agree, it's perfect when it is not having these problems!). Fast as hell.
19. Someone told me maybe tranny temp sensor. Doesn't make sense to me, cuz it will act up even after 2-3 minutes in 30-40 degree weather.
20. Could it be the fuel sending harness?
21. Could it be a bad MAF?
22. Could I have a bad opti sensor on the new distributor? That should show up on scanner though, right?
23. Just what the hell am I supposed to do with this peice of shit that is my most favorite car ever???? When it runs right, it runs perfect.

I am to the point of thinking: some electrical gremlin not recognized by the ECM, a vacuum hose/tube, a tranny problem (not likely). Fuel injectors? I don't want to go through that expense of replacing if not needed either. I am at my wits end folks! Any Ideas appreciated, and low cost diagnosis at that. I've already put $1800 into this so far and am still at square one! Thanks!
Sean

I spoke with my auto shop instructor who used to be a service tech. He's pretty sharp on car problems. He says this opti-spark distributor is a source of the type problems you've described.
Binderboy

Thanks. Thing is I just had a whole new opti-distributor put in. It's not pulling any codes anymore like it did before with the old one. Any way to test the distributor by itself? Also, was talking to my mechanic today...he thinks it might be electrical problems with one or more fuel injectors. Again, hard to test those unless you do it while the problem is happening. Who knows, I'm about to give up on the thing. Thanks!

i had similar problems in my 94 camaro lt1. i spent about 2500 guessing trying to fix the problem. skipping missing inconsistently, did the whole electrical system including opti spark and dist., dist. cap, rotor button. the problem was definately the opti spark, i had it replaced twice, the second time it was installed with a new distributor and i think that was the trick. i think the new opti and the old dist just fouled each other out. the bad thing was the mechanics could not reproduce the problem when they had the car in their posession. they would slap some plugs in it and say its fixed, id be all excited, get 1/2 mile down and the road and the damn skipping is still there. definately has something to do with opti spark tho.

Here's a thought.....

Maybe you have a small small trickle of antifreeze going down your block. I have a '94 caprice....and just changed the water pump after realizing there was a tiny tiny trickle...shorting out the spark unit........runs good now. Had very similar behavior......but not as bad. Then again, it was a cop's car.

Another thought.....

'cuz your LT1 has the "reverse flow" cooling system, I read that another possibility to your problem could be simply a small intake manifold leak. The LT1's (from my reading) don't have coolant in the intake manifold like older small-block chevy's do. So you can have a small intake leak, which therefore would show no common signs like coolant in the smoke or oil. A small leak can cause erratic engine idle, and similar symptoms to yours......and 'cuz there's no coolant in the LT1 intakes........it's harder to determine. Because of your computer.....it'll keep trying to adjust the mixture to compensate for the small air leak......and your car will run goofy.

Get your car running warm (if possible) and run an UNLIGHTED propane torch around your manifold.....and see if the idle changes when the torche's nozzle is slowly run across the intakes peremeter, as in the "line" formed where the intake and cylinder head meet. Have the nozzle emit low amounts of gas/pressure so the leaking? intake can suck the gas in.

Just another thought from researching and trying to fix my own cooling system problems.

Also......mechanics have told me that a common problem with these cars is after years go by, a small cylinder head gasket leak can develop. And NO, a bad cylinder head gasket doesn't always show signs of it in your coolant or oil.

Please write back and let us know your progress.

PS My buddy's dad fixed a volvo's heating problem recently. His buddy's dealership sold a volvo to a customer who was angry/irrate cuz the volvo could not get heat. After $2000 later (new radiator, heater core, plugs, coolant, heater valves, water pump, etc.) and with a car still overheating and blowing cold vent air.......the dealership was stumped and dumbfounded. They gave the car to my buddy's dad. He purged the air out of the system.....and BAM! good as new!
Dealer machanics couldn't figure it out.....and spent $2000 only to realize it was simply trapped air.

Why do I ramble with that story? 'Cuz even ASE mechanics are humans and can make silly/stupid mistakes too.

OK, after almost a year and $2500 later, it turns out that apparently it was just a freaking loose coil wire at the distributor!!! ARRGGHH! And it wasn't a mechanic or any expert....the car died on me on the way to the doctor's in pouring rain and would not restart, a first. I popped the hood and started checking wires (again) and it turned out that the distributor end of the coil wire had wiggled it's way loose so that there was only an arc connection. Pushed that sucker back in tight and back to dream 9C1 city!! Only problem is it has had a habit since of working it's way back up. Thinking of rubber cementing the thing on the cap. Anyone heard of this problem? This is the second coil wire on the second distributor (opti) that this has happened with.

BTW...I'll never again by myself try to change out the plugs and wires on an LT1. Crap, 3 hours and a lot of scraped knuckles and bruises I gave up and took it in to Pepboys (ya, I know they suck), and cost me $450 for the plugs, wires and labor. Shit! Now the G-D ball joints are going out!! The wife wants me to bury this car, but now way. I told her...bury ME in the car, no matter how much it costs to keep it up. Guess I'm like that guy from Texas about 10 years ago who got buried in his Caddy. Peace...

So much for my coil wire theory. Driving in town everything's perfect. Get on the freeway and the same old crap happens. I'm almost convinced it's either a defective Opti distributor or I may have an intake leak. Beats me...I'm thinking of getting rid of it and going with a new '05 GTO, though I hate the thought of getting rid of my baby that still runs fast as hell, and the body, interior, etc. are in great shape. It's also got the Impala SS 17" rims, front grill, aftermarket sunroof, stereo/cd, K&N intake, dual Flowmaster '40's with no cats. New distributor, new fuel pump, new alternator, new starter. Any takers? I want at least 4 grand.

Thoose 94 opti-spark don't have drain holes[vents] so condensation builds up =shorts 95's have drain holes 96 have vac-vent one other thing is the o-ring seals on injectors[two,one black ,one brown] on each injector can leak cause the backfire and largely [even if they were replaced but not done right the reason for the colours]or throttle body gasket leaking or air cover gasket on t/b leaking these will cause a false maf code thought to be the MAF -----A homemade test for the o-rings and gaskets is to spray oil around them one at a time slowly seeing if it sucks in while running and the way the motor reacts/ if it stays seals good sucks in leak or not torqued right /motor starts to run better leak found

Thanks, dolluper. Actually when I had the Opti distributor replaced last summer, I got the vented cap, so that shouldn't be the problem. I'm convinced it's a defective cap, so we'll see what my mechanic says.

Thanks, dolluper. Actually when I had the Opti distributor replaced last summer, I got the vented cap, so that shouldn't be the problem. I'm convinced it's a defective cap or something to do with the electrical stuff with the injectors (I hope not), so we'll see what my mechanic says. I'll do the other suggestons you posed to see if that makes a difference. I really thank you for the "possibilities", I'm having a hard time with this awesome car!....Sean

I have a feeling that it is your optispark... I know you say it has been replaced, but shops often overlook small details...

specifically, if you switched to the vented style when you replaced the opti, it will now be driven by the cam dowel pin... the 94 setup has the timing gear with center splines and a "coupler" which connects to the opti... Since the new opti is driven with a dowel pin, the shop who did the vented opti conversion had to install a longer dowel pin...

A VERY VERY common problem people have when they install the vented optis is that they fail to check the exact dowel pin length... they assume that as long as it sticks out in the opti and spins it, then the install is done... WRONG... If the dowel pin is even a few throusanths too long, it will bottom out in the opti and cause damage too it... sometimes it takes a month for this to show up, sometimes it shows up within a couple of hours, all depends on how "too long" it was...

The GM spec for the dowel pin length is .620"... some have used .650" with no trouble, and others yet have claimed to use .685"... I would assume .685" is probably the max, but it needs to be checked on all optis... the goals it to make sure the dowel pin does not bottom out in the opti... I would set it to .620" to be safe... that will get it plenty far into the opti to drive it, and have no risk of bottoming out...

if you have a garage do the work, have them measure the length of the dowel pin from the face of the cam to the tip of the pin... if it is too long, that is your problem, and they can fix it by using a grinder to grind the dowel pin down to the correct length...

-Garrett

Thanks, that's the first I've heard of that, and it kinda makes sense! I'm going to show this thread to my mechanic. Hopefully he wasn't aware of this, and will do the work without charging me the labor. He might well agree, since I bring him a lot of money on my own car and through referrals.

Sean

I have a feeling that it is your optispark... I know you say it has been replaced, but shops often overlook small details...

specifically, if you switched to the vented style when you replaced the opti, it will now be driven by the cam dowel pin... the 94 setup has the timing gear with center splines and a "coupler" which connects to the opti... Since the new opti is driven with a dowel pin, the shop who did the vented opti conversion had to install a longer dowel pin...

A VERY VERY common problem people have when they install the vented optis is that they fail to check the exact dowel pin length... they assume that as long as it sticks out in the opti and spins it, then the install is done... WRONG... If the dowel pin is even a few throusanths too long, it will bottom out in the opti and cause damage too it... sometimes it takes a month for this to show up, sometimes it shows up within a couple of hours, all depends on how "too long" it was...

The GM spec for the dowel pin length is .620"... some have used .650" with no trouble, and others yet have claimed to use .685"... I would assume .685" is probably the max, but it needs to be checked on all optis... the goals it to make sure the dowel pin does not bottom out in the opti... I would set it to .620" to be safe... that will get it plenty far into the opti to drive it, and have no risk of bottoming out...

if you have a garage do the work, have them measure the length of the dowel pin from the face of the cam to the tip of the opti... if it is too long, that is your problem, and they can fix it by using a grinder to grind the dowel pin down to the correct length...

-Garrett

Diffently right on info on that it will crush the rotor here's a link so you understand the Opti better
http://www.gmhightechperformance.com/tech/0310htp_optispark/

The unfortunate part is that if the problem is in fact a dowel pin that is too long, the opti that is currently installed will more than likely be permanently damaged...

If they find that the pin is too long, after grinding it to get the recommended spec, a new opti should be installed... at the very least, the current one should be rebuilt completely... I recommend a new one though...

any updates?

No updates....no money at the moment to investigate this further. Car's been running really well lately though. Go figure!!

I had same thing, try the temp switch in the water pump !!!!!!

any updates? I am having sim problems with a new 95 caprice 4.3 lt1 and I am leaning to the temp sensor in the water pump too...

any updates? I am having sim problems with a new 95 caprice 4.3 lt1 and I am leaning to the temp sensor in the water pump too...

This thread is over a decade old, it is very probable that everyone involved have moved on.

It would be best to start a new thread, so that others can find it and reply.

Also, the LT1 is not a 4.3, it is a 5.7.....

Temp sensor in the water pump?

As stated, start your own thread with it's own unique symptoms.....

Thanks keyboard king II, peeps in motor cycle forms are nicer, my v8 says on the radiator housing that its a 4.3l v8 and as I look at the motor I can see the water pump and the opti spark distributor behind it. So instead of telling me I don't know what I have do the nice thing and tell me what you think it is?

LT1 is 350/5.7. The engine you have is an L99. Sometimes called a 'baby LT1'.

It would be more helpful if you lost the attitude - nobody wants to waste time with someone who is a complete jerk.

Thanks keyboard king II, peeps in motor cycle forms are nicer, my v8 says on the radiator housing that its a 4.3l v8 and as I look at the motor I can see the water pump and the opti spark distributor behind it. So instead of telling me I don't know what I have do the nice thing and tell me what you think it is?

what you have is as silicon says is the L99... so you need to start working on what you have with this engine. I would subscribe to ALLDATA and find out whats going on, then post any questions you have. also a 1994 has some different parts on it than later models.

being this old parts finding will kill you, along with repair tech stupidity. soo even though you will not work this you best know much about this vehicle before you have some repair shop changing parts at your expense guessing why its screwed up..

Thanks j cat, I'm doing the work so I can only blame myself and I have 95, I may found problem the fuel pressure is jumping all over and finally dropped to 10 psi yesterday and she won't run but was giving the intermittent fault before got to the non start state. May be that hose in the tank but I have a new pump already just in case. No serv engine light at all.

Thanks j cat, I'm doing the work so I can only blame myself and I have 95, I may found problem the fuel pressure is jumping all over and finally dropped to 10 psi yesterday and she won't run but was giving the intermittent fault before got to the non start state. May be that hose in the tank but I have a new pump already just in case. No serv engine light at all.

good you have a 1995. the fuel pump on these is with a power switch on the oil pressure sender. these can cause problems on fuel pump power to pump....

fuel pressure is 41-47PSI key on engine off. engine on pressure drops down to 38PSI area. this is because at idle , high vacuum to the fuel regulator drops the fuel rail pressures.

what may be bad is the in tank wiring as well. the fuel tank must be at all times above the 1/3 mark. the in tank fuel level sender reports more fuel on dash than you really have . the pump motor and wiring connectors over heat then the pump gets a lower high resistance connection. when you open the tank and see burn't looking wires at the connectors this is very common at this age point.

check the wiring in the trunk. this is driver side, also the ground in trunk driver side as these wires supply power to tail lights and pump. open connectors look for bad pins. the heavy wire goes to the pump. then you have the under rear license plate pump connector to measure for voltage there. key on engine off voltage will be about 11 volts not 12 volts because the wire has some resistance that drops it down 1 volt or so to 11volts..

check out this video https://www.youtube.com/watch?v=MO6ofN8ZJBc