I am looking for a Corvette mechanic or specialist in the Kissimmee/Orlando area that can come to my home to diagnose the problems I am having with my 1991 Vette. I've had 3 jokers over and each one just makes it worse. It runs very rough, idles inconsistently, and now won't start. Of course I will pay for this service. I have 3 OBD1 scan tools here. Thank you for helping.

 

Using one of your scan tools, determine if any trouble codes have been set. If so, publish your findings, and maybe one of our forum members might be able to solve your problem(s) for free (?).

 

It might also not hurt to give a rundown of what the jokers have already done.

 

And what it does or does not do.

 

Check your fuel pressure. Idling and hose off it should be about 40+ psi. WOT it should hold steady. Do you have good spark?

 

We can help you in this forum if you do your own wrenching. If not you have Corvette clubs in your area. You can ask them for their recommendations on what mechanic would they recommend. Let us know and good luck. If you can trailer it about 1.5 hrs away from you I have an excellent C4 mechanic (only Corvettes) in the Port St Lucie area. I also know another in Jupiter.

 

Wow, Thank you everybody for your responses, you are great.
-The previous mechanics performed:
-in 2014
rebuilt engine before this all happened.
New ECM/ECU, mine got stolen
-in 2015:
rebuilt distributor
new fuel pump (44lbs fuel pressure)
hand cleaned gas tank, your fuel dissolved the rubber on the pump
new fuel filter,
repaired a few burned harness wires from a previous fire in the engine compartment.
changed spark plugs and wires
tried 4 different MAP sensors, one runs better than the rest
changed injectors to 42lb. which was wrong, so I had another mechanic put the 22lb injectors which made it run better, but still has an oscillating high to low idle when warms up and one cylinder still misses.

Anyway, no codes, spark plug wires are now in correct order. New mechanic had OBD1 Snap On and PC equipment to diagnose. The only thing he can think of is a vacuum leak, MAP, or a sensor wire may be bad.

My OBD1 tools are Snap On "Brick", Red Devil River ALDL PC software and connector, and OTC OBD1. All indicate all is well, but it definitely is not. Ive always suspected a vacuum leak? What do you think? And how do I look for a vacuum leak? Will the scan tools help diagnose that? Or do you have any smart ways to check for a leak?
Thx...

 

Do not see the ICM or coil being tested or new o2. For the vacuum leak get a cheap cigar and blow smoke in your lines to find the leak.

 

Way I do a fuel pressure test is to fire it up with the hose disconnected and see what it does. That simulates a WOT. Obviously you cap off the nipple on the intake to prevent an air leak. Take it for a WOT run and see what the pressure is when it is under load. Take it back, shut down and reconnect the air hose to the FPR. See what the fuel pressure is on shutdown and come back a couple hours later. For stock systems it should hold for a few hours.

Weird. MAP sensor should not have that much variance. What brands?

What a putz. 42 is for way modified cars not stock. Where did you get the injectors from?

Have you ever removed the TB, taken off the IAC, sprayed the pintle GENTLY with brake cleaner, wiped it clean, taken off the IAC housing, clean it and the passages, reassembled WITH NEW GASKETS and reset it? FORGET THE FSM. Use the scanner and set for 20 counts on IAC.

Don't much care for cigars in the engine bay of a gas car myself but those are more subjective than interrogating the ECM. Get the car hot to stable operating temp after you have cleaned the IAC as mentioned above. Everything but the motor off. Get the IAC reading. It should be about 20 counts. If it is higher, you turn the adjustment screw in. That would let more air in. Rev and read again when it stabilizes. Repeat till you get 20. If it is less, you turn the screw out. And here is the important part. If you get a 0 count, it means the ECM is saying it has all the air and possibly more than it needs. That could signify a leak

 

If you still have the original exhaust system on car check to see if you have a clogged or collapsed cat or muffler. Went thru ignition and fuel system on my 91 issue ended up being two bad cats. Runs great now with new single high flow convertor and all the new parts I installed.

 

A dead hole requires a compression test.

If fouled spark plugs clean them.

Engine bay fire? Check each injector plug with a noid light to insure a complete circuit for each injector.

Check fuel injector ohms.

When looking for a vacuum leak I spray WD40 with the supplied straw . The propane propellant will cause a change in rpm when the engine ingests it = vacuum leak.

Disconnect the EST connector & check/set base timing.

Good luck.

 

My car had rough idle when I bought it. There were 2 vacuum leaks that are very common. 1. was the vacuum check valve by the distributor. It's about $3 to replace. 2. The vacuum hose that goes into the cruise control. It makes a sharp 90 degree turn and tends to rot. The other spot to check is where the vacuum line goes into the brake booster. I bought 6' of vacuum hose and replace them all and my car went from a choppy idle to running smooth.

 

It's all about spark and fuel.

Crank no start? First check for spark, no spark? Find out why.

Got spark? Then check fuel pressure. It is that easy to find direction to the problem.