Hi Guys,
I normally just lurk around here, learning from others, but now I can't figure out the new problem. The vette is a 96 w/ LT4, 77800 miles. Friday it started to hesitate when the pedal was pushed down. It seemed to act like a bad accelerator pump in a carb from my old days, best description. My son drove it friday night and it ran ok as long as he was careful w/ the throttle. It ran fine as long as the RPMs were above about 2500 rpms. I tried to start it next morning and all it did was turn over and occaisionallytry to start like it was low on fuel. It does not throw a code (I disconnected the MAF and it showed a P0100 code for MAF, and I cleared it, making me believe the scanner and car are operating properly. I put a fuel pressure gage on it and get 41 psi steady w/ key on, and does not drop when shut off. I am stumped even with the troubleshooting i followed from the factory service manual, which was the best investment I have made, thanks to forum members.
I am totally stumped and would appreciate any advice and questions to check with.
I am 60 years old and still turn my own wrenches as I have done since i got my first car when I was 12.
HELP!!!

Thanks, Alan

 

Learning from us? You could probably out wrench most of us any day!
Be careful of some of our bad habits.

Ohm your injectors. This article is a pretty good way to go. This is kind of a long shot since I doubt all the injectors went bad at once. It's a good start though.

Are you smelling fuel out of the exhaust? It seems like it could be a no fuel or no spark issue. Then pull the plugs for the telltale sign of wet sparkers.

Another long shot, but it's happened to me before. Make sure the distributor hold-down fork is nice and tight. If that loosened up, it will pop every time the starter engages or you hammer the gas. It'll send the timing a little more retarded until it doesn't start.

 

If you can duplicate the no start condition, give it a shot of starting fluid. If it fires right up, you can limit your troubleshooting to the fuel system.

 

if it missed, shuddered, etc, I would suspect injectors. sounds like ignition, spark timing -if it was l98. you don't have a distributor so that won't be the problem.

no familiar with opti, but sounds like spark control

 

Thanks for the input. I'll go to the store after the race & football for spray cleaner.
Alan

 

Watching the Vikings game on NFL.com.....

If they screw it up in the 2nd half like they did last weekend, something is going to get broken...

 

poof!...says the opti. Before you go there however...

Make sure the coil wire is fully seated. Also check the wiring harness that runs from the passenger side of the intake to the opti to ensure it's fully seated. Not unusual for the connector on the opti end of the harness to break and that allows the harness to come loose. Typically it'll throw a code or codes, but not always.

 

Hi. GS96#007 I was afraid someone would mention that. I thought it would give some kind of a code. I'll go into the FSM to try to diagnose.
It has fire from the coil and the fuel pressure is ok. I just ran out of patience last night after the Dolphins made thier season perfect, 0 for 2!
Any other ideas or ways to check the opti will be appreciated. I have checked all connection I can get to and they are ok.
Where is the best place to buy an opti and water pump for an LT4?
I guess I deserve this as I have been talking about selling or trading for a C4 or C5 automatic trans as the clutch bothers my bad back.
Thanks for looking and commenting to all!
Alan

 

If you have spark coming from the coil, the next thing is to check for spark at the plugs. Pull a plug wire off one of the plugs and ground it while someone cranks the engine.

A bad opti will not necessarily set any codes.

It won't be an injector issue. Even if most of them failed at once, it'll at least start and run rough or try to start. The only way the injectors are involved is if they're not firing...and that would be because of a PCM issue, not the injectors themselves.

Just for completeness, pull the vacuum line off the Fuel Pressure Regulator (FPR) (driver's side near the rear of the intake manifold). If there's fuel in the line...any at all....the FPR is bad. In extreme cases, this can cause the issue your describing. Typically the only problem with a bad FPR is hard starting when hot.

 

Thanks GS96#007, I'll try it tonight if it doesn't rain. I didn't know the opte would not always throw codes. It sounds as if you had this experience before. If that is it, I guess that and new water pump are in my future.
Alan

 

96GS#007, in response to your sugestions, I have spark at the plugs, tried 2- plugs, 1 on each side. No fuel in the fpr vac line. In the FSM troubleshooting #6, 300- it says that if you pull the wire to the MAF it should run on the MAP circuit but doesn't. Throttle position sensor tested flakey so I replaced it. No change.
I'll be spending time this weekend trying to follow all diagnostic info from the forums and FSM.
Thanks for the input, you guys are the best.
Alan

 

At this point (as someone else said) I'd try a little starting fluid in the throttle body and see if it starts. If it does the next step IMO would be a noid light connected to one of the injector harness connectors to see if it blinks (pulses) while cranking.

 

Thanks to all of you that tried to help me. There were some very good ideas and I printed them and put into my folder for future use.
Now I must apoligize for my stupidity. I did not mention that I had a MSD 6A box and Blaster coil. When I disconnected the MSD stuff and went back to stock parts it started right up.
I had always used the old KISS method since the 60's but didn't this time. I assumed that it was going to be the opti. I am sure that if I told you guys that I had MSD that someone would've told me to remove it and then test things.
I think this is the best place to get help, sorry to waste your time with my stupid problems.
Now to hear the LT4 scream again on this beautiful day (Sunday) going thru the gears is Great.
Thanks again,
Alan

 

mine was acting like it was having a fuel issue. I noticed my intake and valve cover gaskets were shot and I had oil on my optispark. I changed the fuel filter, gaskets and all the shot hoses. I got 20 miles out of that repair and the car wouldn't start 2 days later. I put the car back in the shop and a day later went to check on it. The mechanic found that when he wiggles the wires that go into the computer above the battery the car will start. Maybe your problem lies there. I will keep ya posted.