I continue to have performance issues with my 89 and have been unable to find the cause or a Mechanic in the area that can t/s and repair it. There are 2 problems and I believe they are related.

Some background might be in order, the car only has 18K miles, I bought it with 14k 3 years ago from the original owner it had sat for 10 plus years. I have flushed the fuel system, replaced the fuel pump assembly, filter, it has new FIC injectors, EGR, oxygen sensor, dist cap, relays, all of the soft vacum hoses have been replaced, new plugs, there is more but these are the important ones related to the issues I am trying to correct.

1st problem is it loses fuel pressure after sitting for 12-15 hours and it appears to leak gas into the cylinders. It is hard to start and until it completely warms up, it will back fire through the intake and have very little power, it is almost undriveable until it warms up. If you try to drive it cold it will throw lean engine and MAF error codes.

2nd problem is a lack of power at speed, if I am driving at say 65mph and step on the gas, the car hesitates and loses some power before kicking in and accelerating properly. If I have the car in a lower gear with the rpm up I don' t get the acceleration issue.

I really like. This car and enjoy working in it but it frustrates me that it doesn't run properly.
I should also say that one mechanic thought it was the FIC injectors, he insisted I buy stock replacements. I sent these back, FIC pressure tested a new set and replaced them. I don't think the injectors are the problem.

I have gotten some great advice from this forum and hope some one can point me in the right direction. I plan to get a data logger soon and am wondering if there is someone out there that I can send the files to for a analysis

Thanks Thom

 

FP leak down after 12-15hrs is not issue, so long as it holds steady for >10-15min.
Have you checked manifold pressure at idle?
What is base timing set at?

What codes does the ECM throw?

Once you have a data logger you will likely get some real clues as to what's the problem(s).

 

Once the car is started the FP will stay up for hours, I can drive the car all day and it will start as soon as the key is turned.

I am now sure how to test the manifold pressure, can you point me to a link on how to do this?
A coupe of interesting things though, I recently sea noticed an exhaust leak on the passenger side where it connects to the exhaust manifold. I tightened it but am not sure if the leak has been stopped completely. I trip to a muffler shop may be in order.
There is also some oil leaking at the front and back of the intake manifold, I plan to do a gasket replacement soon.

The timing is set at 6 degrees BTCD when I got the car it was set at 0 degrees I adjusted it per the repair manual recommendation.

The error codes are 33 - MAF and 44 Lean Exhaust - for the 44 I recently replaced the oxygen sensor.

Any recommendations on data loggers?

Thanks again

 

Did you Disconnect the timing connector by the firewall before adjusting the timing? The computer will change the timing back to where it was if you didn't.

Also, it sure sounds like a bad/weak Fuel Pump even though you just replaced it. You should connect a Fuel Pressure Gauge to the fuel rail and then tape the gauge to the windshield and go for a test ride so, you can see the fuel pressure as you drive. It sounds like the engine is starving for fuel when you punch it.

 

guys, wouldnt the code 33 MAF be pointing in the right direction. if he pushes on the accelerator which mechanically opens the butterfly in the throttle body allowing more air in, and the MAF does not sense this, then he would have a lean condition. Right??? what tells the injectors to increase the amount of fuel to be dispensed?? i am old school thinking (carb) on a newer technology engine. someone more advanced than me will need to chime in.

 

Yes, the MAF should be checked out!...But, I don't see how it could be bad with only 18k miles on it!?...

I guess age could've affected the electronics somehow?

 

Same problem here when it got cold out. Seems the ECM has a cold solder joint inside. Replaced the MAF cleaned cables, replaced relays, etc. Now its above 60 degrees it runs great and no more code 33. If i spray the ecm with cold spray it codes out.
When i get this rad cooling problem fix going to fix the ecm.

 

As noted above, test fuel pressure during starting, warm up, and driving, report back. What you are describing (backfiring) is indicative of an ignition issue. Take your ignition module to any part store and they will test it for free. Ensure that when you reinstall it, that it has a THIN coating of ignition module grease (the parts store will have it).

A lean condition on start up can also be caused by a faulty coolant temperature sensor. Test sensor per factory service manual. What is your TPS voltage when throttle body is closed?

Lean condition can also be caused by a vacuum leak. Yes, I know, you replaced all the lines....how many inches of vacuum at idle?

Assume nothing, test everything. Troubleshooting this will require testing everything methodically and using process of elimination.

 

You asked in a earlier post how to check vacuum pressure? You have to use a vacuum gauge that hooks to the plenum. Most chain auto stores will let you use one of theirs at no cost....GKK mentioned the Timing Cable, if you forgot to disconnect this cable your timing will be off which could cause your prpblem.. The cable is just left of the brake booster and is tan with black stripe...Picture below...WW

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Thanks everyone you have give quite a few things to check on I will make a list and check back in later this week.
I forgot mention that I did replace the ICM when I first got the car.
Thom

 

Did you make sure it had a thin coating of ignition module grease? Too much or too little can burn the module up and/or cause erratic performance.

 

It was actually done by a mechanic when I first got the car.
Originally, The car would start fine cold, but once it was hot it wouldn't start. You had to let it cool completely down before it would fire again. The mechanic said that was symptomatic of a bad ignition module. But now that you point it out these symptoms have been ongoing since then

 

Had to travel this week but got home yesterday and hooked up a fuel pressure gauge and took it for a drive. There was no pressure when I hooked up the gauge, but when I turned the key on I got 40.5 psi. that pressure held steady once the car was started and at idle. When I was driving the pressure fell and held steady at 30psi whether I was running at a constant speed or stopped. If I stepped on it the pressure would increase to ~38psi but it never got back up to 40.5. I also bought a GM Service manual and have been reading the trouble shooting section.
The manual indicates that a a low pressure could generate a lean engine code and make the car hard to start when cold. I have both of these symptoms although the lean code is intermittent. The car has a new fuel pump, screen, inline filter and injectors.
Am I on the right track here?
I have also ordered my Moates cable and am getting TTS Datamaster downloaded and configured.
I appreciate any opinions on this, thanks
Thom

 

As a first time Vette owner, and it had an intermittent problem. When I got it back from the shop, I got a "no problem found" note on the dash. But, before I got it home, the problem returned.

That is when I picked up a scanner (on sale). I hooked it up and went for a drive, and in 10 minutes I had the data I needed to determine an intermittend O2 sensor failure (shorting, actually).

My AutoXray has paid for itself several times over, AND has been used successfully on other cars as well. It only cost me $120, is handheld, and fits in the cubby behind the passenger seat; ready at a moment's notice. However, for serious datalogging and tuning, one of the software programs like TunerCat (and others) and a small laptop (a friend uses a dedicated "Net Pad" computer) comes in very handy.