Quick question I have a 1990 iroc z 5.7 tpi that stumbles at wot and let me explain the wide open throttle stumble seems to happen when I floor it doing 80 mph the car would just buck and stumble as If fuel was not traveling fast enough I'm just lost and need some advice or answer as to what could cause this problem or have any one encountered a similar problem I'm thinking maybe a sensor but I'm low on cash right now someone please help

Things I check and did so far: spark plugs and wire, dis cap rotor ignition coil fuel filter belt tension

Haven't check: fuel pressure, timing,

 

Welcome aboard thirdgen.org.

Checking fuel pressure when it's actually stumbling would be a good thing.

 

It may be a coolant temp sensor. Ive had a sputtering issue on a few thirdgens that turned out to be the CTS.

If the CTS goes out, the ecm will go into cold start mode, starving the engine of air and enriching it with fuel. Simply stated it would be like engaging a choke valve.

You can find a replacement for about $15.

 

@ five7kid I'm new at this so excuse me know but stumbling during high speed is actually a good thing?? also added I checked the timing also and it's right on the money

 

@ five7kid/ parkertpiz I forgot to add that the block is from a 350 out of a 77 buick but the top half is from a 1990 iroc-z I have converted everything over from carb to fuel injection and the whole set up is in the 77 buick now with that said could you still give me a clear reason why it is stumbling during high speeds oh

 

Excuse me, my earlier post is irrelevant; I misread.

Did the tpi setup/ecm come off a 350 iroc or 305? What are you running for a pump?

I dont have values at this time but im pretty sure there is a pressure differential from the 305 to 350 tpi setups. If you have a tpi setup from a 305 then its not able to supply the req'd f.p. at those speeds.

If this is the case, then you would need to upgrade the injectors to 5.7 injectors, obtain a 350 ecm or have yours reflashed. You can also bypass it with an upgraded pump and adjustable high pressure fuel regulator.

I could be wrong, just thinking on the fly.

 

He means check the pressure when its running.

There are members on here that are knowledgable and know what the psi should be at different speeds.

Add a temporary gauge so you can take some readings.

Take some readings at idle, at 35mph, at 55mph and when the car stumbles.

Get a few readings for each so it can be cross referenced with what it should be.