Cuzne

New owner of 93 40th with 188,800 miles. It’s really hard to get started, sounds like the timing is off but once running , it idles great. If I give gas it falls on its face though. Coughs and sputters. Only had it a week and afraid to drive it. I’ve changed the plugs but no difference. The opti was changed 4 years ago with the wires. Injectors seem fine. I’m not sure what to try next. The check engine light doesn’t come on while it’s running( when I can get it started) any ideas? Thanks

billschroeder5842

Check your fuel pressure at the rails. My guess is that you don't have enough.

If it is low, you need to check your pump, filter then regulator in that order.

Cuzne

[QUOTE=billschroeder5842;1595991687]Check your fuel pressure at the rails. My guess is that you don't have enough.

If it is low, you need to check your pump, filter then regulator in that order

Cuzne

I did test the injectors and make sure fuel was coming out the bleeder valve.

belairbrian

Was it doing this when you bought it, or did it happen after you brought it home?

You get a substantial amount of fuel out of the schrader valve even at 20 psi. So fuel coming out doesn't mean you have good fuel pressure. You need to put a fuel gauge pressure gauge on it. If you don't have one, your local parts store can loan you one under their loaner tool program.

when you say test the injectors does that mean with a noid light?

billschroeder5842

Cuzne

The car started ting like it was missing on the way home for purchasing it. I’ll dig out my fuel pressure gage and see what I’m getting. Also I tested the injectors with a ohm meter,and they all was about the same resistance. Can’t remember exactly what it was though.

Cuzne

I just checked fuel pressure. It’s at 40 when the pump primes up and stays at 36 while the car is running. Today it cranked right up, somtimes I’m not so lucky. Still cuts out on me while accelerating though. Kind of nervous to drive it to far but I’ve been taking it around the block to see how it does.

Cuzne

fuel pressure is running at 36 and the ohm meter reads 13 - 13.5 on the injectors does that sound right ?

Cuzne

I just took it for a spin and it seems like it’s running good until I push the gas peddle. When I do the valves start to clatter and it starts popping. Sounds like the timing is off. Maybe the computer is bad ? I have a new opti and water pump to put on it but I don’t think that’s the problem. Uhggg 😣

PLRX

IME, a 93 with the non-vented opti-spark and all the symptoms are the ones from a faulty opti-spark.

I always tell 92-94 owners to upgrade to a vented optispark.

Your posts are exactly what my 92 had when I bought her. The dealer installed a new optispark and it lasted for 100K miles.

belairbrian

Fuel pressure looks good.
So what is causing the misfire?
Did the car sit for an extended period of time before you bought, maybe bad gas.
Could be a knock sensor causing timing to reteard.
Could be a failing Opti, since it provides spark and injector fire input.
The plug wires aren't original right? Only factory wires have plug numbers on them. The replacements don't.
Another check is to run the car in the dark and look for wire arching, spraying with a mist of water (use a spray bottle). If the wires are failing you'll see arching.

The physical timing can't be off as the keys on the opti drive shaft are keyed. So if timing is off the ECM would ahve to be commanding it.

ICM or coil could be at fault as well.

Cuzne

the opti was replaced 4 years ago along with the wires and the car has been sitting for about a year. The tank was about empty when I got the car so I put 10 gal of freash 93 octane in it and let it idle for about 15 min. Just checked the map sensor. It seems fine. Could old vacuum lines be causing this ? There not looking good. I’ve replaced one and trimmed some off of the others.

Cuzne

I changed the plug wires on the passenger side( found one that was burnt) looks like I have to get under the car to do the drivers side. Seems just as bad , if not worse now. I’m starting to think that the problem is in whatever advances or retards the timing. Knock sensor maybe ? Or the computer is messed up. Been on it for 4 days straight, going to have to give the old back a break for a few days then I may change out the opti and the other 4 plug wires, maybe the coil. Uhhgg ��

belairbrian

This is how I did the drivers side. Remove the serpentine belt, remove the belt tensioner assy (one bolt). You can then route the drivers side wires.

It's easier if the drivers front tire is off so you can stand in the wheel well rather than lean over but not necessary.

JimLentz

Is the firing order correct?

81c3

You say the fuel pressure checks out.. Good. Now you need to do all the plugs and wires...all basic maintenance items... I would even do the fuel filter... Once you get that done, I would start thinking Optispark. I had a 93 Z28 that sounded just like what you're experiencing. It was indeed the Optispark.

Cuzne

Thank you all for the help with my 93. She’s running good. I patched a exhaust leak , new plugs/wires, opti and water pump and changed the original coil for good measure. I got it all back together this morning , bumped the key and all is good again. Thank you , thank you thank you . Happy corvette owner