...or I guess, more specifically, can the chip cause the converter to act erratically? I have a new chip and a new torque converter in my '91 Formula with the 700R4. When I'm cruising at a sustained speed, the car jerks from time to time. I don't think it's engine related, it's more like the converter is going in and out of a locked mode of operation for a brief moment. Can the chip cause this, or do I possibly have a converter that's not operating properly?

TIA

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jimbo

Mosquito Coast F-Body Association (MCFBA)

1991 Formula SLP350
1999 Trans Am Firehawk

[This message has been edited by jimbo (edited April 25, 2001).]

 

Well, the ECM does tell the converter when to lock up. The prom chip program determines the speed at which the converter locks up, I believe.

Sometimes a car can have, say, an ignition miss, that you'll feel when the converter is locked up but not when the converter is unlocked. You could unplug the wiring harness from the trans (completely eliminating lockup) and then go for a drive and see if the symptoms persist. Just don't do this for an extended period of time.

Also remember that the converter should unlock whenever you touch the brake pedal. While the car is acting up, keep one foot on the gas and lightly depress the brake with your other foot.

If you are positive that your engine runs smoothly...do you still have your old chip? Can you swap it back? What converter are you using now? Is there a certain speed where this occurs the most?

[This message has been edited by Jed (edited April 25, 2001).]

 

Thanx for the ideas Jed...the new chip is a piggyback...the old chip (which is an SLP chip) is used in conjunction with the new one. The converter is an SLP with a 2600 rpm stall speed. The jerkiness just doesn't feel like an engine miss...it's almost like you are lightly applying the brakes then backing off right away. It occurs in the 45-55 mph range, although I haven't yet tanken out on the interstate and tried any sustained 75 mph cruising. That might be my next step before I try unplugging the harness.

 

I agree that the engine could be your problem here. A word to the wise, folklore says to eliminate L/U, usually with the brake but what you are doing is 1) taking some of the load off of the engine (possible eliminating a miss) and 2) dampening any miss through the torque converter where before you had a mechanical connection the sent it right through the car.

Do this, put vacuum gauge on the engine and go for a ride. When the problem occurs look at the needle. If it is smooth you have a tranny problem. If it bounces, you have an engine problem.

 

Jimbo, I wonder if it is your chip calibration.

My chip (custom fastchip) retained the stock lock up speed, so at 40 mph the converter locks up. If my speed then decreases a bit, the converter will unlock and lock, if I am below or right on the verge of lockup speed. This is the only time I feel such a condition.

I installed a switch so that I can manually enable and disable the torque converter in 3rd and 4th gear. If I am cruising right around 40 in 3rd gear, I leave the converter unlocked. Usually, 50mph or more in 3rd, and any time I use 4th gear, I lock the converter, a 2600 stall Vigilante.

The only other thing I could think of that would cause the condition you are describing, if you are sure it is not the engine, would be loose/bad connections in the tcc circuit, or perhaps a faulty lockup solenoid. But any of these possibilities would occur all the time, whenever the converter is told to lock up. And if you change two parts and then experience a problem immediately after, I guess I'd look at those two parts first. Why not call SLP and tel them about your problem?

You have to say though, nice launches with these converters, right jimbo?

 

...nice converters indeed Jed, and I intend to call SLP once I confirm it's indeed the TC that's giving me the problem. How did you install the switch to bypass the lockup feature? My new chip should have retained the stock lockup speed, because I didn't tell them to change that parameter, but you have a point, if I'm cruising right around that lockup speed, it could be causing the condition. I guess I need to cruise at specific speeds for a sustained period and see if I can narrow down the actual speed it occurs at. The local speed shop just hired an engine builder that used to work with Superchips, the company I bought the chip from. He's going to take a ride with me next week to see first hand what I'm feeling, and he feels he'll be able to help me narrow the problem down.

Thanx for the ideas...

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jimbo

Mosquito Coast F-Body Association (MCFBA)

1991 Formula SLP350
1999 Trans Am Firehawk

 

The switch was easy. I have a B&M megashifter, so I bought the shifter handle with the pushbutton wired in.

On my car I wired the switch into the tan/blk wire coming from terminal A7 of the ECM, the circuit that controls tcc lockup. That's it. You'd have to check the wiring diagram for your year though, it may be different.

Only problem is, well, I have to remember when it is locked and when it is unlocked. I don't have an indicator to tell me. Many vehicles that come from the factory with such a switch have a dash light that will say something like O/D OFF/ON. I have to figure out how to make an indicator like that. Wouldn't be too difficult, I just haven't gotten around to it.

Anyway, I hope you get everything straightened out.

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Jed
89 Formula 350