Heavy hesitation problem/ power loss

I own a 91 gst eclipse. In warm weather it hesitates under moderate to heavy throttle and it feels very weak(not near as much pull). On the other hand, When there is cold weather(generally below 20 degrees) the hesitation is almost hard to notice at all and the engine pulls very well. Usually once the engine has been ridden hard a couple times after this, it begins the hesitation problem again. I did a boost leak test and fixed the leaks many months ago and did one recently and all is fine(beside the shaft seal leak but its not leaking enough boost to make a difference.) i have been told that it might be the FPR or timing or just about anything. Does anybody have any ideas of what it could be? Thanks 4 your time.

My guess would be fuel. Maybe its running fine when its cold because there would be more air condensed and the fuel is set perfect for that cold air. But once it heats up and its getting warmer air its running too rich... That would be my next guess if you have no boost leaks.

Hmm...Do you think that would be the fuel pressure regulator? It does seem like im getting crappy mpg.

What do you have your FPR set to now? Wrong tuning will cause really bad gas mileage.

Also, it helps us know a little more about your car if you put details about it in your signature. :wink:

Well I don't have an aftermarket FPR, just stock. I don't have any modifications other than some "fixes" here and there.

Hmmm... If its stock then I wouldn't see it as being changed unless the stock FPR is going bad. Do you plan on modifying the car or leaving it stock?

I definitely plan on doin some modifying to it..I haven' yet because ive been trying to figure this problem out. What do you recommend that I do?

Hmmm... Well, if your gonna modify it then I'd say start modifying things that will help the problem for sure... Maybe someone else here has an idea of something else it could be. Thats really the only thing I can think of right now. I'll post back if I think of something else it could be.

Any boost leak is bad, could be your O2 sensor

Any boost leak is bad, could be your O2 sensor
I agree, if it doesn't do it at full throttle. The computer goes into open loop at WOT, and doesn't use the O2 sensor. Also plugs, plug gap, and wires, and IAT sensor could be bad.

Edit: I am leaning toward the IAT, because the problem varies with temperature.

full boost doesn't always equal wot, I had the same problem but it was most prevalent at ~35% throttle going down the highway with the cruise set. Every time I went up a hill it would try and speed up but couldn't, but I had a combination of the 2.

full boost doesn't always equal wot, I had the same problem but it was most prevalent at ~35% throttle going down the highway with the cruise set. Every time I went up a hill it would try and speed up but couldn't, but I had a combination of the 2.
Agreed: WOT has nothing to do with boost. It is based on the position of the TPS.
Edit: I was saying that I agree to the o2 sen. being bad if the problem isn't present at WOT, and I also agree any boost leak is bad.

Gotcha :wink:

My guess would be fuel. Maybe its running fine when its cold because there would be more air condensed and the fuel is set perfect for that cold air. But once it heats up and its getting warmer air its running too rich... .
All that is controlled by the IAT based on temperature ;). Not the FPR, it only does what it is told to do. That is why some people relocate the IAT. It makes the comp. "see" colder air entering, and increases fuel to maintain air/fuel ratio. That is why I am convinced it is the IAT more than anything. The other things should be checked too. :2cents:

All that is controlled by the IAT based on temperature ;). Not the FPR, it only does what it is told to do. That is why some people relocate the IAT. It makes the comp. "see" colder air entering, and increases fuel to maintain air/fuel ratio. That is why I am convinced it is the IAT more than anything. The other things should be checked too. :2cents:
Ohhh... So I was on the right path but I didn't follow the problem back far enough?

IAT?... Intake Air Temperature? I am still learning all the abbreviations. lol :wink: Where is the IAT located exactly?

IAT should be on ur throttle body, or along the intake tube.

Hey Crow, here is some light reading for you :D. The rest is at vfaq comp primer (http://members.shaw.ca/costall/ECUprimer/ECU_ch3.html)

The ECU has several input sensors that help it determine the correct amount of fuel. The most widely recognized is the mass air flow sensor (MAS or MAF). The MAS consists of the air volume sensor, the intake air temperature sensor, and the barometric pressure sensor. These three sensors form a single component located directly behind the air filter, and it provides the ECU with the information required to calculate air mass.

[Why mass? Well, the ideal ratio of air to fuel depends on the number of molecules of each type of substance. Knowing the volume doesn't get you anywhere, since the number of air molecules in a given volume changes with temperature and pressure. If you know air volume, temperature and pressure, though, you can get air mass, which in turn can be used to determine the correct amount of fuel.]

So the input signals consist of the air volume, temperature and pressure from the MAS cluster. Feedback is provided by the oxygen sensor, located in the cars downpipe.

Update...My buddy and me hooked up the logger and everything was reading great. Then we looked at the TPS reading and instead of a smooth line, it was very "squiggley"...as if i was pumping the gas pedal very quickly over and over. Where do i go from here?

I checked the timing and instead of a steady pulse of light coming from the light, it was jumpy and would not flash in any specific pattern. Also the timing notch was jumping around in a 5 degree area so it wasnt exactly set to a specific setting. I'm so lost it's not even funny.

Hey Crow, here is some light reading for you :D. The rest is at vfaq comp primer (http://members.shaw.ca/costall/ECUprimer/ECU_ch3.html)
Ahhh... Thank you very much, I actually feel smarter after reading all that now. lol :wink:

I checked the timing and instead of a steady pulse of light coming from the light, it was jumpy and would not flash in any specific pattern. Also the timing notch was jumping around in a 5 degree area so it wasnt exactly set to a specific setting. I'm so lost it's not even funny.
Did you ground the timing adjustment plug?

Update...My buddy and me hooked up the logger and everything was reading great. Then we looked at the TPS reading and instead of a smooth line, it was very "squiggley"...as if i was pumping the gas pedal very quickly over and over. Where do i go from here?
Did you check the resistance on your TPS?

I did ground the timing adjustment plug and i also did check the resistance on the tps and i got weird readings

I did ground the timing adjustment plug and i also did check the resistance on the tps and i got weird readings
What were your weird numbers?

Update...replaced tps and problem still persists. Sigh...

Why replace tps? You never told me what your numbers were. This is going to get expensive for you if you just go changing out parts without knowing for sure if they are bad. Did you follow up on my other theory? Unplug your MAS and see if the symptoms change.

:iagree: not smart to randomly change things

Well the tps was bad so it needed to be replaced. I'm not randomly changing parts. it fixed my jumpy timing problem.

Problem fixed!! The whole time it was the capacitors in the ecu!! Thanks to everyone who helped.

:thumbsup: