Power drop off at full throttle

[Aspec]

I have a theory. Tell me what you think.

Symptom:

Under 75-80% throttle car pulls hard, runs great. If I go to wide open it flattens out, and doesn't pull nearly as hard or rev up as fast, almost like it's struggling to make power.

My theory:

At 9.5 psi of boost and what is probably the original fuel pump my guess is that I'm running the fuel rail dry because the fuel pump can't keep up and going lean at full throttle.

Conditions: No codes present, Timing dead on, all in all it runs great.

Thanks in advance for your input.

 

[jdub]

Is it a CT26 Turbo and is it upgraded?

 

[mkiiSupraMan18]

In my experiences with fuel pumps, it will stumble/miss out at full throttle, not just stop making power. Never had one go south in a turbo car though.

*edit*
Have you re-checked to verify timing is still set correctly? Do anything to the car to bring this about? (changed plugs, taken anything off the engine, anything of that nature?)

 

[gsxrwut]

you would think with a turbo car it would push more fuel because its needed.. but once u start upping boost wouldnt you want to increase the fuel pump flow so it can keep up with increasing amounts required to feed the engine.. just my opinion .. but if your going to upgrade soon to bigger injectors and the lex afm bizznaz.. then i would just upgrade the fuel pump now and if its giving you too mcuh just turn it down on the regulator.. that is if you dont already have your fuel regulator adjusted to max..

 

[Aspec]

Is it a CT26 Turbo and is it upgraded?

Stock CT26 - Fresh reman @ 6 months ago.

 

[jdub]

The stock CT26 runs out of "breath" at about 5800 rpm on a stock system...I seriously doubt you are running out of fuel (going lean) w/440 injectors.

 

[Aspec]

In my experiences with fuel pumps, it will stumble/miss out at full throttle, not just stop making power. Never had one go south in a turbo car though.

*edit*
Have you re-checked to verify timing is still set correctly? Do anything to the car to bring this about? (changed plugs, taken anything off the engine, anything of that nature?)

Timing still check okay. No changes made other than adding AFPR. I think the old o.e. FPR was prob toast. Car runs much better since install. Never really paid attention before upgrade (car was running lean most of the time never wanted to push it as hard as I have been)

 

[Aspec]

The stock CT26 runs out of "breath" at about 5800 rpm on a stock system...I seriously doubt you are running out of fuel (going lean) w/440 injectors.

Makes sense. But why would it pull so much harder at 80% throttle? Whether from a standing start running through the gears or going to pass, full throttle does not pull nearly as hard and it sounds labored. No boost leaks. Vac is at or over 20hg at idle and above that on decel so vac leak is unlikely. :icon_conf

 

[jdub]

What psi fuel pressure is your AFPR set at vac on?

 

[Aspec]

What psi fuel pressure is your AFPR set at vac on?

33 vac on. 40/41 vac off.

 

[jdub]

Drop it down a little bit...say to 30psi. Don't go less than 25 psi. I think you are actually getting rich above 80% throttle.

 

[Aspec]

Drop it down a little bit...say to 30psi. Don't go less than 25 psi. I think you are actually getting rich above 80% throttle.

Okay, I'll give it a try. Going on a test drive. Be back in a minute.

 

[johnathan1]

Yes, I also think you are running rich at WOT...I remember IJ saying something about how you actually get more power with the throttle at 75-80% than you do at WOT...I can't remember if he was referring to a stock system or not...Maybe a problem with the TPS? When you go WOT, does the TEMS system go full firm?

 

[Aspec]

Okay, I'm back. Weeeeee. Well I think you may have nailed it. Tried 30psi, better. 28psi, better. 25psi yehaw. I just checked the tsrm. Looks like I may have transposed some numbers last time I read it. Good catch JDUB.

Now, I have a Walbro 255 and a Bic dp coming next week. Any effect on required fuel pressure with those upgrades?

 

[Aspec]

Yes, I also think you are running rich at WOT...I remember IJ saying something about how you actually get more power with the throttle at 75-80% than you do at WOT...I can't remember if he was referring to a stock system or not...Maybe a problem with the TPS? When you go WOT, does the TEMS system go full firm?

Yup, TEMS working as intended. TPS tests good (pita to test btw. Throttle stop also properly adjusted).

 

[jdub]

Now, I have a Walbro 255 and a Bic dp coming next week. Any effect on required fuel pressure with those upgrades?

Yeah...you'll have to re-adjust. Just keep in mind, air flow and fuel are a balance. Don't just buy bigger injectors without a way to increase air flow....Lex AFM for example.

 

[Aspec]

Yeah...you'll have to re-adjust. Just keep in mind, air flow and fuel are a balance. Don't just buy bigger injectors without a way to increase air flow....Lex AFM for example.

Cool. Thanks for the help.

 

[gsxrwut]

hemm jdub is in phx eh ? damn i guess i juss needa get teh balls and buy that supra.. so i can be boostin with teh rest of ya ..

 

[Aspec]

hemm jdub is in phx eh ? damn i guess i juss needa get teh balls and buy that supra.. so i can be boostin with teh rest of ya ..

'bout time you came to your senses!:slap:

 

[gsxrwut]

'bout time you came to your senses!:slap:

lol dude.. he still has it for sale so i think imma barrow teh money to get it .. i just gotta talke to my dad..