Problem with supercharged 94GT, please read (long)

Killercanary · 03-27-2001, 11:26 PM

My cousin has a 94GT with a Kenne Bell blowzilla SC, 190lph fuel pump, FMU, stock injectors, stock MAF, off road X pipe and cat back. He jsut put the blower and FMU on it in december and all was fine until his fuel pump quit and he replaced it with a 190lph unit. At the same time he added a new clutch and bassani cat back. Now the car will buck under partial throttle, and when you get on it at WOT and shift gears it will fall flat on its face and throw a check engine light. We pulled the code and it was a 158, which is a too high MAF voltage. The only thing I could think of was that either the MAF was bad, or it was running too rich now. Well tonight I put on my MAF from my 95GT, reset the computer, and took it for a spin. It did the exact same thing. Now I'm really thinking its running rich. I figure under part throttle the fuel pressure is still pretty high with the FMU and 190lph pump, and since the vacuum is low under throttle, the fuel pressure is high too. I think that under this condition it is running way rich and drowning out the spark. The same goes for under full throttle. As soon as you leave off the gas, thr throttle body closes and the air is limited that's going into the cylinder, I imagine there is some unburnt fuel under this condition too. Well as soon as you change gears the throttle body blade opens, the vacuum goes down and the pressure goes way up again, I think that so much fuel is being dumped in so fast that the car is sort of "flooding" out till all the air gets in there and burns. Does this make sense or does anyone else have an idea? Things were fine until the addition of the pump, cat back, and clutch. Please help ASAP as we hope to make it to the track this weekend for the season opener!

dinomite · 03-28-2001, 08:06 AM

do you have a fuel pressure regulator? I would actually say that its running LEAN becuase you are running the stock injectors, and I don't think that they cna provide enough fuel under the squeeze.

Killercanary · 03-28-2001, 03:28 PM

What you said makes sense, but it was fine before the bigger pump went in. It also used to detonate until he changed his fuel filter, then it was fine. Now it just falls on its face when you shift gears, then it will go, but it then throws the check engine light and the code listed above. Does anyone know what too high of MAF voltage means? I imagine the answer lies there as the voltage being high or low tells the computer how much air is coming in, but I don't know which way it works.
He is not running a FPR either, just the FMU and 190lph fuel pump. I think the FMU jacks up the pressure to 72lbs, this is done by restricting the return line.

------------------
95 GT convt' 5 speed, 3.73's,FMS HD clutch, Pro 5.0 shifter, ASP alum. underdrive pulleys, Bassani offroad X pipe, 2 chmbr flowmasters, K&N w/o silencer, edelbrock performer intake, FRPP 65mm T-body, FRPP shorty headers, FRPP aluminum driveshaft.Hooker 4pt chrome car bar, Xenon/Wings West ground effects, custom interior
Best ET: 13.83
Best MPH: 98.55mph with Best 60': 1.91 on Nitto DR's
Homepage: <A HREF="http://www.angelfire.com/pa2/killercanary" TARGET=_blank>http://www.angelfire

Green92LX · 03-28-2001, 03:33 PM

I know my FMU spikes my pressure well beyond 85
I think the problem is that the computer is lost with the falty air reading and it is slamming fuel at the motor, and thats why it is falling on its face. If it was a lean condition, it would detonate, not die off. It sounds like both mass air meters are not calibrated to handle the blower...
You do realize that your buddy has a hell of a bottleneck going there, right?

------------------
1992 LX:V-1 S-Trim ,Edelbrock 6037 Heads,Cobra Intake,E-303,1.6 Rollers,65MM Holley TB, 75 MM Pro M Mass Air, 190 LPH FP,24 lb injectors,MSD 6A and BTM,BBK equal length shorties,offroad h-pipe,Mac Flowpath Mufflers,Pro 5.0, 3.73's,Motorsport "C" springs,welded subframe connectors,Ponies w/ 225/50 Nitto NT 450's on front,255/50 BFG Drags out back,93 Cobra Spoiler
Daily driver 89 Coupe:BBK shorties,offroad,flowturds with dumps,soon to be cyber green

03-27-2001, 11:26 PM	#1
Killercanary Registered Member Join Date: Nov 1999 Location: Altoona, PA Posts: 336	Problem with supercharged 94GT, please read (long) My cousin has a 94GT with a Kenne Bell blowzilla SC, 190lph fuel pump, FMU, stock injectors, stock MAF, off road X pipe and cat back. He jsut put the blower and FMU on it in december and all was fine until his fuel pump quit and he replaced it with a 190lph unit. At the same time he added a new clutch and bassani cat back. Now the car will buck under partial throttle, and when you get on it at WOT and shift gears it will fall flat on its face and throw a check engine light. We pulled the code and it was a 158, which is a too high MAF voltage. The only thing I could think of was that either the MAF was bad, or it was running too rich now. Well tonight I put on my MAF from my 95GT, reset the computer, and took it for a spin. It did the exact same thing. Now I'm really thinking its running rich. I figure under part throttle the fuel pressure is still pretty high with the FMU and 190lph pump, and since the vacuum is low under throttle, the fuel pressure is high too. I think that under this condition it is running way rich and drowning out the spark. The same goes for under full throttle. As soon as you leave off the gas, thr throttle body closes and the air is limited that's going into the cylinder, I imagine there is some unburnt fuel under this condition too. Well as soon as you change gears the throttle body blade opens, the vacuum goes down and the pressure goes way up again, I think that so much fuel is being dumped in so fast that the car is sort of "flooding" out till all the air gets in there and burns. Does this make sense or does anyone else have an idea? Things were fine until the addition of the pump, cat back, and clutch. Please help ASAP as we hope to make it to the track this weekend for the season opener!

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03-28-2001, 08:06 AM	#2
dinomite The Dude Join Date: Feb 2001 Location: Arlington, VA Posts: 1,262	do you have a fuel pressure regulator? I would actually say that its running LEAN becuase you are running the stock injectors, and I don't think that they cna provide enough fuel under the squeeze.

03-28-2001, 03:28 PM	#3
Killercanary Registered Member Join Date: Nov 1999 Location: Altoona, PA Posts: 336	What you said makes sense, but it was fine before the bigger pump went in. It also used to detonate until he changed his fuel filter, then it was fine. Now it just falls on its face when you shift gears, then it will go, but it then throws the check engine light and the code listed above. Does anyone know what too high of MAF voltage means? I imagine the answer lies there as the voltage being high or low tells the computer how much air is coming in, but I don't know which way it works. He is not running a FPR either, just the FMU and 190lph fuel pump. I think the FMU jacks up the pressure to 72lbs, this is done by restricting the return line. ------------------ 95 GT convt' 5 speed, 3.73's,FMS HD clutch, Pro 5.0 shifter, ASP alum. underdrive pulleys, Bassani offroad X pipe, 2 chmbr flowmasters, K&N w/o silencer, edelbrock performer intake, FRPP 65mm T-body, FRPP shorty headers, FRPP aluminum driveshaft.Hooker 4pt chrome car bar, Xenon/Wings West ground effects, custom interior Best ET: 13.83 Best MPH: 98.55mph with Best 60': 1.91 on Nitto DR's Homepage: <A HREF="http://www.angelfire.com/pa2/killercanary" TARGET=_blank>http://www.angelfire

03-28-2001, 03:33 PM	#4
Green92LX Registered Member Join Date: Jun 1999 Location: North Haven,CT Posts: 336	I know my FMU spikes my pressure well beyond 85 I think the problem is that the computer is lost with the falty air reading and it is slamming fuel at the motor, and thats why it is falling on its face. If it was a lean condition, it would detonate, not die off. It sounds like both mass air meters are not calibrated to handle the blower... You do realize that your buddy has a hell of a bottleneck going there, right? ------------------ 1992 LX:V-1 S-Trim ,Edelbrock 6037 Heads,Cobra Intake,E-303,1.6 Rollers,65MM Holley TB, 75 MM Pro M Mass Air, 190 LPH FP,24 lb injectors,MSD 6A and BTM,BBK equal length shorties,offroad h-pipe,Mac Flowpath Mufflers,Pro 5.0, 3.73's,Motorsport "C" springs,welded subframe connectors,Ponies w/ 225/50 Nitto NT 450's on front,255/50 BFG Drags out back,93 Cobra Spoiler Daily driver 89 Coupe:BBK shorties,offroad,flowturds with dumps,soon to be cyber green