Bogging Problem With More Than 50% throttle

Kraest · Jun 30, 2012

Hey, guys.

I have a 98 GT and have replaced almost everything on the car... There are no codes present, but the car runs fine at part throttle, but bogs like it's starving for fuel at 50% throttle when cold and down to 25% throttle when warm... .I'm at my wits end... Any ideas?

I've replaced:

Fuel Pump
Fuel Filter
Fuel Injectors
Spark Plugs
O2 sensors

Tested the MAF and it appears to be ok with a couple little voltage differences (1.3v idle, goes dead during the bogging situation)

Also tested the TPS and it works fine.

The only thing I can think of is maybe a MAF problem or Fuel Pressure Regulator problem.

slo4.6 · Jun 30, 2012

What spark did you use? I hade about the sme problem. I slaped a set of NGK's in and it fixed it.

Kraest · Jun 30, 2012

slo4.6 said:
What spark did you use? I hade about the sme problem. I slaped a set of NGK's in and it fixed it.

NGK TR5 Platinum

ttocs · Jun 30, 2012

I had that problem but replacing the TPS fixed it for me.

Kraest · Jun 30, 2012

ttocs said:
I had that problem but replacing the TPS fixed it for me.

I wish it was that.. shows 1v at idle and a smooth change to 4.5V at WOT, so it's ok AFAIK.

ttocs · Jun 30, 2012

did you test it both while warmed up and cold? Mine was not nearly as bad cold but once it got warmed up it seemed to make a difference.

Kraest · Jun 30, 2012

ttocs said:
did you test it both while warmed up and cold? Mine was not nearly as bad cold but once it got warmed up it seemed to make a difference.

Yep.. Tested after the motor was warmed up.

Kraest · Jun 30, 2012

Kraest said:
Yep.. Tested after the motor was warmed up.

Guess I'm going to give up on it for a while until I drop in the carbed 306. :shrug:

ttocs · Jun 30, 2012

I was also suprised to recently discover a couple of bad spark plug wires that made a big difference in driveability.

FrankenStang · Jul 1, 2012

if ur mafs is is showing in opt codes...replace it....i had the ecact same problem with no codes but i cleaned the mafs and fixed it...but did it again 2 months later so i ditched the k&n wetoil filter for a dry and new mafs...no problems yet!

slo4.6 · Jul 1, 2012

Kraest said:
NGK TR5 Platinum

I thank thats them.

Kraest · Jul 1, 2012

FrankenStang said:
if ur mafs is is showing in opt codes...replace it....i had the ecact same problem with no codes but i cleaned the mafs and fixed it...but did it again 2 months later so i ditched the k&n wetoil filter for a dry and new mafs...no problems yet!

no MAF codes ever.

Tested it with a multimeter and it goes smoothly from idle to 5000 rpm the entire time.

FrankenStang · Jul 1, 2012

you said your using NGK platinums...if its anything to you,my car ran a little rough on those NGK, had a sputtery idle and it would feel like my engine had a Vtech becuause it would take a sec for all the power to comeon...JUST LIKE A Vtech...i had those plugs in for 2 weeks and yanked them out in favor or bosche tripple platinums with the quad tip so i didnt have to worry about gappage...

FrankenStang · Jul 1, 2012

" Tested the MAF and it appears to be ok with a couple little voltage differences (1.3v idle, goes dead during the bogging situation) "

id still replace the mafs...even if one from a junkyard just to see if it helps...and if it still shows the same voltage diffrences its another issue..a mafs in a junkyard will only be like 20 bucks and they are abundant for out cars...F150 MarkV's crown vics , plenty of them in the yards... if it will help you out for 130 plus shipping ille sell you my VERY low mileage stock coilpacks, 19lb injectors(have under 2000miles on them) and brand new iac and a almsot new pcv and an 80mm 2002 gt mafs thats was also used under 2000 miles..if the housing units too big for ur car the sensor can b taken out and put inot ur mafs housing body...

Kraest · Jul 2, 2012

Looks like the fuel tank is rusted to shit -- Pulled the fuel filter this time and it spewed out rust-colored gas.

Sounds like detonation from the low octane and the CPU retarding timing is the culprit.

I guess it's only a matter of time before it destroys the new fuel pump.

FrankenStang · Jul 2, 2012

that sounds like it could be causing an issue....

Ninety8stang · Jul 3, 2012

Kraest said:
Looks like the fuel tank is rusted to shit -- Pulled the fuel filter this time and it spewed out rust-colored gas.

Sounds like detonation from the low octane and the CPU retarding timing is the culprit.

I guess it's only a matter of time before it destroys the new fuel pump.

get that shit outta there! haha at least its not too bad of a fix if thats your problem. tanks are pretty easy to come by.