Help…Please! very frustrated

Well, the saga continues,
I got the bird together, now I have a stumble at 1500 rpm and when in fifth, if I floor it the car stumbles and stutters and the engine shakes. WHAT THE HELL?
I replaced DIS, fuel pressure regulator (fuel pressure is now where it belongs), new plugs (gap at .54) new cam sensor. New coil pack. Plug wires are in real good shape.
IC tubes are sealed very well and all fittings are tight…. No codes are being sent.
I can’t figure this out and I am getting real frustrated with throwing money and time at the car.
You guys have any ideas. I am guessing that one of the plugs is misfiring.
What do you guys think and I am asking what to test or change next???????
Any advise is appreciated.

Scmetalhead

By the way I should mention that the car ran fine last year. I parked it up for the winter and when I pulled it out this year the problems started. I used Stabil in the fuel.

The bird is a 90 5 speed.
I have the following mods;
S model charger with 90 pulley on it
70 mm throttle body and 70 mm MAS
Polished and ported intake and exhaust with header wrapped stock exhaust manifolds, gutted cats.
Intercooler fan.

Above 1500rpm the car runs great. But sitting and rev the engine to 1500 rpm and the whole car shakes somewhere around 1800 rpm the engine picks up and runs.

NEED HELP????

SCmetalhead

hmmn

SCmetalhead said:

By the way I should mention that the car ran fine last year. I parked it up for the winter and when I pulled it out this year the problems started. I used Stabil in the fuel.

The bird is a 90 5 speed.
I have the following mods;
S model charger with 90 pulley on it
70 mm throttle body and 70 mm MAS
Polished and ported intake and exhaust with header wrapped stock exhaust manifolds, gutted cats.
Intercooler fan.

Above 1500rpm the car runs great. But sitting and rev the engine to 1500 rpm and the whole car shakes somewhere around 1800 rpm the engine picks up and runs.

NEED HELP????

SCmetalhead

Click to expand...

start the engine and rev to 1200 rpm's for about 1 min. make sure it stumbles then shut it down, pull the plugs and look for wet plugs. replace the wet plugs and try again to run engine . if it still stumbles then replace wires . and try again you need to do this systematically or it will drive you crazy!!!

These parts you replaced, did you replace them after the issue, or prior to storage this winter?

Try unplugging the connector on the MAF sensor and then see how the engine behaves. If it clears up, pull the maf and inspect it. Make sure there is no damage.

Try unplugging the CAM sensor and then starting the engine. It may take a few tries to get the engine started without the cam sensor, but once it runs it'll throw default values in and should run normal.

If the Cam sensor unplugged doesn't change anything and the MAF sensor unplugged doesn't change anything someone will have to come up with some other ideas. Bad plugs or wires could very well be at play.

This sounds like a cracked spark plug or bad wire. Could be wrong but its a place to start as well.

The problems started right after I took it out of storage. I took her out for a run. Filled gas tank with premium. Then barely made it home, she was coughing. spitting & sputtering, blowing black smoke. I thought bad gas, but she was running in limp home mode. Well carboned up the plugs bad. Brought her home. Changed plugs. Put in some fuel water remover(thought maybe bad gas). No change. So I had a new DIS, cam sensor laying around that I had bought. So I installed them. I also put in a new fuel filter. She started, but then the whole 1500 rpm thing started. So I did a tear down(just to get to the fuel pressure regulator)as I was running 90 lbs @ idle) solved that problem. And yes the IC tubes are sealed. But the 1500 rpm thing is got me guessing and very upset with the car.
I am thinking of getting new wires and some iridium plugs to try in her, MAYBE JUST MAYBE one the wires and plugs are gone. Still no codes being thrown.
I want to thank you guys.!!!!!
But I still need some ideas!!!!
SCmetalhead

It's gotta be mechanical or intermittant electrical to not throw a code.

Have you investigated the crankshaft pully while it's running? I know it's a broken record thing, but if the balancer is failing, it may be hitting a harmonic at that RPM that causes it to move around a little. The vane is attached to the outer part of the ring, so if that starts moving it could create a intermittant Crank sensor signal. That sensor often will not throw a code.

Have you checked your fuel pressure at that RPM? You may also want to check your throttle position sensor output at that rpm. Try and think of things that can impact either fuel delivery or igntion.

If you feel it's ignition, you should try pulling one spark plug wire at a time and then bring it up to 1500. See which plug being disconnected doesn't have an impact on the stumble. You could even drive it with a wire off. But if you do that disconnect it at the plug, not the coil pack. you'll want some resistance on the coil pack.

If you find no plug makes a difference on the behavior it's likely a more system wide electrical issue or a purely mechanical issue.

The stumble at wot in 5th gear really sounds like a metered air leak. Is it only WOT in 5th gear, or can you do it at WOT in 3rd, 4th? Even a hint of it? At WOT the EEC goes into open loop and ignores basically most of the fuel mixture related sensors. To stumble there, you're either not getting enough fuel, or not enough air. (or no spark)

Maybe if you characterize the 5th gear issue a little further it could give some clues for others.

Well, I know it isn’t mechanical, as the engine was rebuild by a very reputable speed shop! The engine has less then 5000 miles on her. I am guess plugs and wires, but you did bring up a good point about the fuel. It may be a bad injector (hoping not) but I will start the long process of plugs and wires. Hopefully (fingers crossed) that it is the gremlin.
As far as doing in 2gear – 4 th, I really didn’t notice it, but the revs were above 2000 rpm. It seems to be in the engine is @ lower rpm(fifth and idle that it seems to be noticeable.

Thanks again
SCmetalhead

When you run codes, at the end trip the throttle and it will do a cyinder balance test. It will cut fuel and spark in each cylinder one at a time. It will give you a code at the end. If its a injector you need only to verify that you are getting a electrical pulse in that cylinder. Check all your plug wires with a ohm tester and coat the inside edges with dialetic grease. Its got to be something simple.