I have been having a long standing problem with a missfire. I have changed the coil, icm, checked the plug wires, and taken it to two mechanics without comming up with a solution.

Since the miss has come about, everyonce in a while when i start the car it will rev up to 1500-2000 rpms and stay there for about 4 or 5 seconds before slowly work its way down to idle. Could this be related to the missfire?

This afternoon when i started the car it cranked for about 3 seconds before firing up, which has never happened before. Once it did it seemed to run even poorer than ususal. But some thing that was especially odd was that the tach and speedo were not working. All of the other gauges worked though. I then put the car in reverse drove 15 feet, then drove it back into its original spot. Then the tach started working again (I did not notice if the speedo worked). There were no codes thrown and I'm at a loss. Any help would be appreciated.

 

It seems as though the car has a hard time firing up when it has been sitting over night. Also, this morning when i turned the car on i couldn't hear the fuel pump "whining" like usual. Could this be a bad fuel pump? The car gets about 11 mpg right now. Would a bad fuel pump cause bad gas milage?

Anybody have any idea?

 

Could be the fuel pump, I had a bad one last year. Pray it's not though man. They're pretty expensive to replace if you have a shop do it. Maybe you could replace your fuel filter to start and then run some of that fuel system cleaner through the car for a few bucks at any auto parts store. I do it to mine pretty regularly now.

 

Don't think that's a fuel pump, when a fuel pump quits, it just quits, not really signs of it. I had one go out on me when I got 4 new tires. It happens like that, went to start it and wouldn't start. I say you have an intake leak (vacuum leak) which would cause the excessive idle due to alot of air going into the car and it's not adding fuel for that extra air it's pulling in because it's not detected therfore it is a lean misfire you are having. That's my view. If your guages are doing that I would look into the alternator, i've also had misfires, stalling, etc due to bad alt because the car isn't getting the power it should be therefore not getting the spark it needs, but I don't think it would be that.

 

I would be looking for a bad ground with the speedo and stuff. Get some schematics and see how the VSS is grounded.

As for the high idle, maybe your blades are sticking a hair?

Clean the Idle Air Control Valve ... See what happens.

With the car running, spray some brake clean (Or equivilent) all around the intake, throttlebody, elbow, etc. If the RPM's fluctuate at all as you do this, you have a vacuum leak there.

Does it only missfire ones its warm? How are the O2 readings ? They should flicker between 100-900mV ...

MAF and MAP readings ?

Did you happen to try switching the fuel pump relay? you definatly SHOULD hear it. Mine is pretty loud.

 

In the past the car has thrown a code for the VSS, I'll check that one out.

What do yo mean by the "blades sticking?"

It missfires all of the time, but worse once it is warm. I have replaced the o2s recently and yes they seem to be reacting properly.

I recently replaced the MAP sensor after getting DTC 34 "map low," but it didn't fix the problem. I'm not sure about the MAF sensor though.

I haven't done anything with the fuel pump relay. I'll look into checking that out. When I turn the key to the on possition I always wait for the "humming" noise that pump makes, but today is the first time it didn't make the noise. Would you guys recomend checking fuel pressure? Thanks for the help.

 

Do this easy check first, get a hose and stick it around the intake up to your ear and look for hissing. LT1's have had alot of intake leaks in the past....trust I've had a few.