4.9L Flat Spot Near WOT and Integrator Shoots Above 150 (Page 2/2)
Ericthompson OCT 30, 04:01 AM
Why do think it's a lean condition that is causing your flat spot? Will it move past the flat spot if you stay a WOT or do you have to lift for it to catch back up? I just purchased my first Fiero 2 weeks ago. 4.9 TBI on the PFI intake....yep. I have no idea what has been done to it but after I got it home and got it running and took it for a test ride ,I really think if was to take the spare tire and jack out it would lift the front tires when I launch it hard! Its a BEAST!
La fiera OCT 30, 06:44 AM
Is there a way for you to pinch/restrict the return line? Also if the FPR is vacuum assisted, disconnect the vacuum source and plug it and test drive.
Warlordsix OCT 30, 07:25 AM

quote
Originally posted by Ericthompson:

Why do think it's a lean condition that is causing your flat spot? Will it move past the flat spot if you stay a WOT or do you have to lift for it to catch back up? I just purchased my first Fiero 2 weeks ago. 4.9 TBI on the PFI intake....yep. I have no idea what has been done to it but after I got it home and got it running and took it for a test ride ,I really think if was to take the spare tire and jack out it would lift the front tires when I launch it hard! Its a BEAST!



Because when the engine hits the flat spot the integrator shoots above 150 indicating the ECU is trying to add extra fuel to bring the AFR back into proper range.

Ernie

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'87 Fiero 4.9 5-speed

Warlordsix OCT 30, 07:38 AM

quote
Originally posted by La fiera:

Is there a way for you to pinch/restrict the return line? Also if the FPR is vacuum assisted, disconnect the vacuum source and plug it and test drive.



Yeah. FPR was replaced same time fuel pump and filter were replaced. I suppose the new FPR could still be bad. Thanks for the suggestion. I'll pull the vacuum line and see if pressure increases as it should with vacuum disconnected.

Ernie

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'87 Fiero 4.9 5-speed

fieroguru OCT 30, 07:36 PM
Fuel pressure could be low, but the other item to note is at WOT, the stock ecm should not be actively adjusting fueling based on O2 sensor feedback. If the INT is still moving around at WOT, it could be an issue with the TPS and the ecm not recognizing WOT, which could also mean that some of the power enrichment tables are not being enabled.
Warlordsix OCT 30, 08:42 PM

quote
Originally posted by fieroguru:

Fuel pressure could be low, but the other item to note is at WOT, the stock ecm should not be actively adjusting fueling based on O2 sensor feedback. If the INT is still moving around at WOT, it could be an issue with the TPS and the ecm not recognizing WOT, which could also mean that some of the power enrichment tables are not being enabled.



Agreed, Guru, thanks. However, the flat spot occurs near WOT.

Ernie

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'87 Fiero 4.9 5-speed

Dennis LaGrua OCT 31, 02:02 AM
If you change fuel pump I recommend the Bosch 69225. Better quality than the AC Delco and made in Bosch own factory. Not Chinese made. As for the question of what controls the pressure; it is the job of the regulator but a defective pump may not be putting out the right pressure. I might still replace the regulator first and see if the pressure comes back up.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Will NOV 01, 09:26 AM

quote
Originally posted by Warlordsix:

Agreed, Guru, thanks. However, the flat spot occurs near WOT.

Ernie




At low RPM, some calibrations enable power enrichment at a fairly low TPS%, as, at low RPM, the throttle doesn't have to be open very far to hit a high MAP.