Ok my car jerks when im at a steddy speed between 35-45mph. It has been doing this since I had the motor rebuilt. While I had the motor being rebuilt i ported and polished the heads. Could this be normal with the aftermarket cam finally getting more air into the engine because of the port & polish?

 

I did check the tps and I checked the computer every thing looks normal. what could be the problem

 

That's just about the speed that the ECM will lock and unlock the tcc. IIRC, your model hits lockup at 41 MPH and unlock at 38 MPH.

 

IIRC?
So its a transmission problem?

 

anyone??

 

91,

No one said it's a tramsmission problem. I mere;y pointed out that the problem you are reporting coincides with the speed range at which the TCC locks and unlocks. If you suspect that could be the cause of the "jerk", you can disconnect the TCC electrical connector and take the car for a test drive.

 

I dont know anything about TCC. I dont know what it is or what it stands for or where it is located.. Vader could you please tell me a little more about it. Im lost in the dark here.

 

Try disconecting the vacuum line that goes to the EGR valve and plug it off. If the problem goes away, you have a bad EGR valve.

 

That's a good suggestion as well.

The TCC is the Torque Converter Clutch. It locks the torque converter into a direct-drive mode as opposed to the fluid clutch mode. The ECM controls the TCC based on vehicle speed, engine RPM, throttle position, and coolant temperature. If you have a manual transmission, you obviously won't have this device.

 

be more specific...how the hell are we supposed to diagnose your problem with your car without better exact description...

i had a similar problem. it was simply a fuel pump.

 

Apparently, Vader got the message.

And yes, I just put a high pressure fuel pump in 2 weeks ago:lala:

 

My guess is that the transmission is doing exactly as it is programmed to to.

However, since you've altered the intake tract and changed the cam profile, your ECM is reading MAP signals that are no longer within the normal range of operation for factory ECM programming. Your '91 should have a MAP sensor in lieu of a MAF sensor. The PROM has MAP value tables at a given RPM and TPS level (and some other factors) that are basically correct for a factory cam and heads. Since your cam and heads are likely flowing more, and the duration changes of the cam profile are likely producing less vacuum at all RPMs, the MAP signal is higher at a given RPM and TPS than the factory programming allows. Not high enough to set an error code, but high enough to alter the load (LV8) calculations that the ECM performs.

As a result, the ECM operates the TCC, the engine RPM drops producing a lower vacuum (higher MAP), causing the programming to interpret a higher load (based on the anticipated MAP range for a factory cam). If this calculated load is above a given value in a table, the ECM will unlock the TCC until the load conditions are "correct" for TCC lockup again.

Basically, you're probably teetering on the edge of the capabilities of the factory PROM for your setup.

The way to determine if this hypothesis is accurate is to disconnect the TCC so that it cannot lock, drive the car normally, and see if the condition persists. If it does, I'm wrong and there is a different problem.