ok tpi swap from 86 iroc to 57 chevy ,idles fine free revs great! start driving surges lightly ,full throttle runs like a scalded dog then shifts to 2nd and shuts off...rolling punch runs a great for a second then shuts off.....have tried to remove vacuum from pressure reg..does the same thing..it has an accel fuel pump for this conversion and a painless harness...only code is 33... the car idles great freee revs great...soon as you start driving it surges a lightly over half throttle it stumbles after each shift then catches up and runs smooth..have replaced/set the throttle position sensor...this unit still carries the 305 injectors? is this what it acts like when you need bigger injectors? is the mass air meter bad? not enuff fuel? it seem to be running out of fuel but it surges under light throttle to? any ideas?


thanks max

 

MM57,

A couple of things may be involved in your installation.

First, a '33' is for a higher than expected intake air measurement than the ECM has calculated at a given engine RPM and throttle opening. This is almost always the result of a TPS base voltage setting that is too low., but has also resulted from the effects of removing the screens from a MAF and orienting it in the ductwork in such a way that the sampling tube in the center of the MAF is not getting an accurate representation of the total flow (what the screens are supposed to cure).

Second, if you are using the stock 1986 TPI CalPak for programming the ECM, there were many of these that were later determined to be faulty. The factory upgrade PROMs had a lot greater tolerance for MAF flow ranges, O² sensor readings, etc., as well as improved shift points, EGR function, and several other parameters.

Undersized injectors will generally result in poor WOT performance at or around 4,000 RPM long before setting an error code, and the code is normally a '44' (lean exhaust) instead of a '33' (high MAF flow).

 

hey vader nice to hear from ya!!
ok new tps was set to 0.5 screen is still in the maf i did have have to add ductwork between maf and tb..about 8 inches and then has the stck boot to that...when it runs it really runs!! all the peices here are stock 86 iroc stuff except the accel pump so you think it could be the ecm/prom?..i was thinking fuel but maybe not because of the response time for it to recover..it recovers real slow and with a eletric pump they usually recover faster

?
max

 

Is your VSS hooked up?

 

yes its hooked up
max

 

where would you suggest i set the tps?

 

If it is set to .5-.54 now, try setting it at .6 and see if that makes a difference, if not go to .45 (doubt that way will help and see if that makes a difference.

 

will try thanks

 

Max,

Increasing the TPS should help. It figures that I've just given away my last '86 EPROM, but I'm sure it's been at Byron recently. I can burn another as soon as I get some more erased, but if you're running the '86 TPI (305) tables on a 350, the engine is just naturally going to flow more than the 305 software expects (by about 15% based soley on displacement increase).

I don't know why I didn't catch that displacement change before.

You may need to get an EPROM from am '86-'88 TPI without VATS. Make sure you get one to match your setup - air conditioning or not, auto or manual trans, etc. And get one from a car with 'Z' rated tires, or you'll hit a fuel cutoff at 118 MPH on the VSS.

Maybe I can find a binary file that will work a little better for your setup if I had the details.

 

you dont by anychance have a aftermarket tb, do you?