Coming out of boost stumble

[mcsvt]

My car has been doing this since I purchased it, but I got used to it and can drive in a way that it won't do it. I think it is time to figure out why it is doing it.

For example:
Driving down the highway, cruising in Vac. Go to pass another car and bring the boost up. After the pass if I only slightly get out of boost the engine will jerk and stumble, basically shakes the whole car. If I perform my pass then fully lift off the pedal and then get back on the pedal to continue cruising, no jerk or stumble. It will do this in any gear, just using this as an example.

Any ideas as to what to check? I have been attributing it to a cal issue, but I don't have any proof for that.

Mods to car: 2.5L T-II, A555, +40%, 17Psi on a 22Psi Cal(believe it was done by Paul V. years back), NGK plugs(but also did it with autolites that were in the car when I bought it), 1g BOV, stock intercooler/airbox(K&N).

Any help is appreciated :nod:

[GLHSKEN]

Check the TPS. Possibly could be a cal issue and a transition table issue.

[mcsvt]

What is the best way to check the TPS? Is there a procedure in my FSM? Sorry TPS isn't a good word to search the forums on and the FSM is at home :)

[Clay]

The TPS output is 0 -> 5 volts. Take a voltmeter and hook it up to the TPS output. Turn the car on (But do not start the car). You should have a reading somewhere close to 0 volts. Run the throttle by hand, and your voltage should go up gradually/evenly over the entire movement of the throttle. At full throttle you should have around 4.7 -> 5.0 volts output. Repeat going back to close throttle, with same result, except you will be back at 0 volts.

[mcsvt]

Thanks I will try that tonight, my volt meter might be dead though. I have never been good with what settings to use on that thing :o

[lametec]

Mine does the same thing, and I also have an (early) Paul V. cal.

It's something in the cal, I'd say. My car drove just fine with the stock cal.

[85glht]

You might be seeing overboost at part throttle. My car did this with the old cal I had while controlling the boost manually. The part throttle overboost cut out was set too low (for me). Might be something to check.

[mcsvt]

I have never experianced overboost before, but from what I have read that may be a possibility. I have been wanting to get into D-Cal anyway, maybe this will be my motivation to get the hardware setup.

Thanks for the tips guys :thumb:

[Sethyboy85]

it's with the cal, had the same issue with 2 revisions and then the last one I got it went away, another person had the same issue.

[mcsvt]

Yeah thats what I am thinking. Now I am trying to set myself up with D-Cal and see what I can do. Been a member on the message list for a couple months now.