Car bucking at high RPM

[ricksmol]

I have a 1989 SHO. The car runs great. No problems at idle ,starting, during normal driving. But when I accelerate hard and the car is already warm, at about 4500-5000 RPM the engine seems to cut off. If I let go of the gas engine slows amd problem disappears. If I keep accelerating engine bucks on and off until I let go of gas. Replaced the TPS and it seems to make no difference. Any ideas as to what the problem might be?

Rick

 

[AutoSHO]

ricksmol:
I have a 1989 SHO. The car runs great. No problems at idle ,starting, during normal driving. But when I accelerate hard and the car is already warm, at about 4500-5000 RPM the engine seems to cut off. If I let go of the gas engine slows amd problem disappears. If I keep accelerating engine bucks on and off until I let go of gas. Replaced the TPS and it seems to make no difference. Any ideas as to what the problem might be?

Rick

Is there any oil in your spark plug wells? When did you last do a 60K maintanence, or tune-up of any kind?

 

[DHMag]

id say plugs need replaced....same thing happened to me...took out one plug...had serious detonation...enough to make the gap about .070

 

[sdpatt]

Has the CHECK ENGINE light illuminated at all during these events? That would provide a BIG piece of information to diagnose your problem. The misfire due to old or incorrect plugs or damaged plug wires can occur at any rpm when even slight load is applied to the engine. This situation sounds more like an intermittent electrical connection to a component of the engine control system. It may be a bad connection in the crankshaft position sensor, but it could also be a broken conductor in a plug. You may want to try the "wiggle test" on your sensor's plugs and wiring harnesses. You can use the search feature at the top right of of the SHO Forum pages to look for a description of the "wiggle test." I remember a good explanation given not but a month or two ago in this topic section.

 

[ricksmol]

The spark plug wells are dry. Not long ago I did a thorough job on the car. Replaced valvecover gaskets and the spark plug well rubber gasket,replaced camshaft sensor,sparkplugs,sparkplug wires,cleaned the IAB valve, cleaned the injectors etc.etc.

When I do the KOEO test I get two codes 14 and 19. Iread the explanation for these codes but cannot make any sense out of it. Can somebody please explain to me what is PIP, TFI and CID?
Thanks Rick

 

[DougLee25]

That is your problem right there. Code 14 is the CPS (crank position sensor), and code 19 is the CID (cam position sensor). Both of these will contribute to the bucking condition you describe.

Doug

 

[sshewchuk]

Mine was the plugs with the exact same symptoms.

 

[sdpatt]

If you are getting codes 14 and 19, the crankshaft position sensor (profile ignition pickup - PIP sensor) mounted at the crankshaft behind the lower timing belt cover and the cylinder identification sensor (CID) mounted on the passenger end of the rear bank exhaust camshaft are in need of replacement...

OR

...you have a bad ground or connection to your distributorless ignition system (DIS) module on the intake manifold's crossover tube. Since it is a very low probability that both sensors would fail coincidently, I think this is your primary focus. The common denominator between the two sensors giving error codes is the DIS module.

First check the tightness of the two electrical connectors on the DIS module. Then check the connection of the metal ground strap to the top bolt on the passenger side, rear, intake manifold bracket. Then check the torque on the two 12mm bolts that attach the intake's crossover tube to the front and rear plenums. Last is the integrity of the four, 5.5mm bolts that attach the DIS to the crossover tube.

Which of these connections did you affect during your removal and installation of the intake when you replaced the valve cover gaskets? Trace your steps. I'll bet you'll find one of these electrical paths to be the cause of the misfire.

<small>[ November 25, 2002, 03:37 PM: Message edited by: sdpatt ]</small>

 

[ricksmol]

Scott:
I think you are in the right track. Today when I touched around the test connectors to get the codes I moved wires when the engine was idling and the idle became very erratic. I quickly wiggled some more wires and the idle went back to normal. After that I tried the car and no more bucking. I know something is erratic with the wires. I'll trace it down and correct. Thank you guys for all the answers.
Rick

<small>[ November 25, 2002, 08:23 PM: Message edited by: ricksmol ]</small>