Throttle Troubles

[1GTech]

New to DSMT, but was an AF when it was still "active". Anyway. Been working on the old laser for a few months now, new head, computer, 2 transistors(think it may be the culprit to my question), and other fixes, and finally got it driveable. However, when accelerating, the car does fine, unless you floor it. When throttle wide open, at around 4k it begins to lose power, almost like it may not be getting enough fuel. If you let off the accelerator, and slowly apply the gas, it will do fine-ish. The other day tried resetting the computer and took it for another drive, same thing, but then it even began to happen around 2-3k, then finally couldnt accelerate at all, then died. Restarted it and drove it home. Its a 91 Laser RS 2.0 NA.

Tried:
Changed TB
Changed IAC Sensor
Changed TPS
Changed CAS
Adjusted Throttle cables
Changed out the ign transistor twice
Removing gas cap
Fuel additives
Spark plug/wire replacement
New fuel filter
Fuel pump/screen about 6 months ago

The only "mod" that I did was the TB coolant bypass, and seriously doubt that would cause such an issue.

The computer is also out of a '94 I believe(had to replace it anyway)


Researched and tried a few other suggestions from other posts:
http://www.dsmtuners.com/forums/bolt-tech/422993-completely-random-stutters.html
http://www.dsmtuners.com/forums/articles-electrical-wiring/229419-how-test-power-transistors.html(Thats why I changed the transistor twice) Tested this time, seems to be fine.


Think that about covers it, Ive researched it and tried quite a bit, I keep getting pointed to the ecu and transistor. Thoughts? It only really seems reproducable at high rpms, the lower rpm issues are kind of hit or miss. Im stumped and have yet to find a scenario already discussed that covers it.

 

[Jeff90Z99GST2G]

I haven't run across this with my dsm, but with my del slow it was typicaly after it had warmed up and would just fall on its face and sometimes wouldn't even start back up. It turns out that the Idel air contorl valve was clogged. Cleaned it and put it back on and no problems after that. You may try that shouldn't cost you much but some carb cleaner and time.

 

[1GTech]

Tried that mate. Cleaned, no luck, replaced, no luck... thats why I replaced the TB, thought maybe the air ports(not positive of the technical term) were causing the havoc.

But for sake of checking, will give it a look over tomorrow.

 

[stars]

I would do some research and see if your 94 ecu is compatible with 91 wiring. If everyone has been pointing you to there, then sure they are correct. Sounds like your ecu cannot adjust the injectors to the proper fuel curve when you go full throttle, or something strange like that? Do you have access to a scan tool or dsmlink? That maybe helpful too trying to figure out the cause.

Would take a fuel pump pressure reading and see if maybe a "weak" output may be the cause. You have a few scenarios that it could be from where you are now.
It sounds like possibly ignition timing or fuel delivery may be the source of the problem.

I did come across an interesting article about setting base timing after installing a new timing belt. Since you put a new head on, I'd start there first. Sometimes the ecu has to relearn the base timing values to adjust the air and fuel accordingly. It makes since your pretty much helping it establish a point of reference so it knows where b4 and after TDC is. I would suggest you un-install back that TB coolant by-pass hose, it does serve a purpose. All the parts you have replaced are probably o.k. as obviously they have not solved your problem.

 

[Str8Tune]

I had a similar issue with my 99 GST, obviously dealing with boost... boost leaks are a major cause of this... hearing that you stated you were N/A I'm almost positive its a timing issue. I also broke a timing belt partially through and had the same issue as I was attempting to get it home..... I would check the timing on it or look for any damage on the belt.

 

[1GTech]

The car ran fine up until the first transistor went bad, replaced it, then the computer died(lost all ignition). Now, the issue I see with it being timing related, I know even new belts can be defective(might be a possibility), but gradual throttle with no load(in neutral) can take the rpms to 5k. no pinging, knocking, or odd noises. So now I know its only when under load.

Fuel pressure is good(not gauged yet though), gonna swap out the coil pack today, from everything Ive seen the computer should be compatible. Although Ive got a spare 1g turbo ecu, not too sure if running it on a non-turbo will work to test if its the computer being non-compatible, or even if it would run properly.

The car was a daily driver(my first car) for 2 years, and sat for almost 6 years after it bent valves(timing belt).
@stars It seems like that, but only when its under load. And sometimes it only does it at high rpm, and others it will even do it at low rpm. And Ive heard that bypassing the tb coolant can cause idling trouble when the car is cold, but will reattach to see if it helps any.

 

[Str8Tune]

I'm almost positive the Turbo ecu wouldn't function right and might damage your motor if you hook it up so I'd definitely tread lightly on that