98 Z28 Maf

**1badtk** · 05-06-2007, 02:44 PM

OK, guys I installed a new 255lph fuel pump and new water pump. Car starts but really bad hesitation, fall on face with hit or throttle, remover air box, and MAF................ cars runs normal?????? Do I need to do something with the fuel pressure regulator? Or am I missing something else?

**Sarge** · 05-06-2007, 02:59 PM

Is it throwing a code with the MAF on?

**1badtk** · 05-06-2007, 03:24 PM

There is a SES light on, but haven't read the DTC's yet. The fact that it runs normal with the maf off is very confusing to me. I am not vey familiar with the GM obd2 stuff, I am a blue oval tuner :-)

**Sarge** · 05-06-2007, 03:41 PM

Originally Posted by 1badtk

There is a SES light on, but haven't read the DTC's yet. The fact that it runs normal with the maf off is very confusing to me. I am not vey familiar with the GM obd2 stuff, I am a blue oval tuner :-)

I understand....I've built a few monster Fords in my day...OK.....
This thing is telling me something simple is fubar.....dont get pissed but I have to ask as I have done this myself more than once.....is the sum biatch on right? The correct position...I have seen them put on backwards alot of times and they do exactly what your describing.....the other thing that would cause this is the IAT sensor not being plugged back in.......and of course the dreaded I broke it while I had it off.....triple check you have the air flow going the right direction with the MAF...there should be a little arrow somewhere on it that shows the airflow.....triple check you got the IAT plugged in correctly.....

**Sarge** · 05-06-2007, 03:44 PM

After you have done the above ( hopefully you found the fubar

)....reset the ECM....pull the positive batt cable and leave it off....turn the key on to drain the capacitors.....let it set for ten minutes......put it all back together and fire it up...let it idle with the AC on full blast for a couple of minutes....it will be searching for idle.....so don't worry about it.....turn off the AC and let it idle for another two or three minutes......lets see where we are at....
I also have a Walbro 255...the FP Regulator will maintain about 62lbs of pressure...so it doesn't care what kind of pump is behind it...that shouldn't be an issue at all.....

**1badtk** · 05-06-2007, 03:52 PM

OK, good info, and no I won't feel stupid. I never removed the MAF from the oem air box, so ts still on right, and air flowing thru as the arrow shows. The IAT is plugged in, but right? i could only see one way to plug it in. I am going outside to look it all over again, just to be sure I am remembering this as I said, or before I look real stupid. Thanks Sarge, I'll be right back.

**Sarge** · 05-06-2007, 03:59 PM

It is something simple......Take your time...I'm drinking beer

**1badtk** · 05-06-2007, 04:13 PM

Thats what I keep telling myself, even took it all off and reinstalled it, but it still runs normal with the air box and MAF off. Battery diconnected, will try again shortly.

**Sarge** · 05-06-2007, 04:15 PM

HHHmmmmmm......Is that MAF De screened?
Fuse? Busted wire?
I mean taking the MAF off eliminates that circuit....putting it back on the MAF is sending some funky signals to the ECM and probably dumping fuel like a cow....so it has to be in the MAF circuit man......lets see what the reset brings us.....

**1badtk** · 05-06-2007, 04:39 PM

OK, redid it all, disconnected the battery, waited 20 minutes. Turned key on, waited all that time. Key OFF, reconnect battery, key on, start car, idles perfect, just don't touch the throttle, falls flat on its face. Hit throttle, let off, real fast several times car reaches about 4000 rpm, stop and it idles. I guess till I know what the ses light is, I am at a hault. Thanks for your help.

**1badtk** · 05-06-2007, 04:41 PM

Stock MAF, nothing has been done to this car, its all oem except for the fuel pump which died, and water pump which leaked really bad.

**1badtk** · 05-06-2007, 04:41 PM

MAF fuse? Where?

**1badtk** · 05-06-2007, 04:47 PM

all the electrodes are still in tack in the MAF, no broken wires.

**Sarge** · 05-06-2007, 05:45 PM

Hang on....

**Sarge** · 05-06-2007, 05:47 PM

Well...I hate to say this....but you think that fuel pump is good? Can you read fuel pressure at the rails? New fuel filter? Fuel restrictions? You say it starts right up and idles good....but then when revved it falls on its face.....sounds like fuel starvation doesn't it to you?

**1badtk** · 05-06-2007, 05:48 PM

On pins and needles

**1badtk** · 05-06-2007, 05:51 PM

Not tonight, tools at the shop. Like I said it will drive fine with the MAF and air box off, will pull DTC's and fuel pressure tomorrow. Thanks again Sarge.

**Sarge** · 05-06-2007, 05:51 PM

Did you drill holes in the bucket? That higher flow pump could be sucking all the fuel out of the bucket quicker than it can refill.....we had to drill holes in the bucket or that would happen every time...here are some pics of my fuel upgrade....
http://nelsonperformance.com/600hpGTO3.htm

**Sarge** · 05-06-2007, 06:03 PM

Originally Posted by 1badtk

Not tonight, tools at the shop. Like I said it will drive fine with the MAF and air box off, will pull DTC's and fuel pressure tomorrow. Thanks again Sarge.

Well shit...why do we do this to ourself?

So without the MAF and air box it runs/revs drives just fine? Man thats a bad MAF....check the voltage...it should go up and down as you throttle up and down...here go to page 3........
http://www.wellsmfgcorp.com/pdf/Counterpoint3_2.pdf