MAF Voltages

[jay69dogg]

99 Grand Prix GT 3.8L 85,000 miles
My SES light came on a while back. The RPM's were fluctuating while I was driving but the engine was idling (no gas). That went away but now the RPM's would intermittently fluctuate after I would start it. The RPM's fluctuate from 700 to 1500 then stabilize. I had the code read and it came up with a P0102, MAF current low. I pulled the MAF and cleaned it with electronic cleaner. I pulled the throttle body and cleaned it up with carb cleaner. After reinstalling everything, I noticed that I can see the orange o-ring gasket that seals the TB to the intake on the front part of the intake. It looks like it sealing but I don't think that I should be able to see the gasket. All the nuts are tight. The gasket is exposed between the upper nut and lower front nut. I'm curious if this I normal or if my intake may have warped. The car ran for about 5 days after this then the SES came back with the same code.

I installed a refurbed MAF sensor. It was refurbed by CarDone. Ran the car for about 20 miles with no issues. When I started the car again, the RPM's fluctuate from 700 to 1500 then stabilize, then the SES came back on. The RPM's start to fluctuate again after I rev it. The fluctuating RPM's has been intermittent.

I've been measuring voltages on the MAF connector.
Connector disconnected from the MAF, yellow wire: 5V
Connector connected to the MAF, yellow wire: Had 2.62V, now 11.5V w/ the engine running
Connector connected to the MAF, yellow wire: 10.3V, key ON, engine off

I’m wondering if 2.6V on the yellow wire is normal. With it at 11.5V, the RPM's are fluctuating.
Chilton's talks about reading the MAF frequency using a scan tool. I don't have one so I tried reading it with a DMM. My DMM has a frequency counter function but I'm not picking anything up on the yellow wire. I' don't know if I can read the frequency this way.

Anyways, I'm interested to see what the normal voltages are on the MAF when it's connected. I'm wondering if I have a bad MAF or a wiring issue.

I also seen in Chilton's that the TPS could cause a MAF issue. They say it should read ~4.8V at full throttle, I'm only getting 4.11V. Could this be a possibility as well? Also, my car only has ~ 13.9V while running. That’s a little low.

Any ideas? I'm really interested to see what the MAF voltages should be on the yellow wire. Also any input on the throttle body gap would be appreciated.

[BNaylor]

On the throttle body orange gasket, it is normal to see part of it around the area where you see the vacuum line feeding the purge valve and fuel pressure regulator but it should not stick out to where its so obvious its not sealing properly to the UIM. It should be recessed.

You could have an issue with the idle air control (IAC) valve. You can remove it and clean the passages with carb cleaner where it mates to the throttle body.

On the MAF sensor, you can rule it out by simply disconnecting it and save wasted time. The PCM will use fixed RPM values during the test. Take it out for a spin with the MAF disconnected. If the problem is still there, it is not the MAF sensor. If it cures it, then you could have a defective MAF sensor or wiring to it. BTW - the intial idle will be a little erratic with MAF disconnected but it will stabilize once engine warms up.
I've seen Cardone MAFs that are re-manufactured bad. Good luck!




Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials

[jay69dogg]

Would anyone be willing to measure the voltage on the yellow wire of the MAF sensor following the tests I listed above? Maybe we could find a general consensus of what the voltage should be.

[BNaylor]

Originally Posted by jay69dogg

Would anyone be willing to measure the voltage on the yellow wire of the MAF sensor following the tests I listed above? Maybe we could find a general consensus of what the voltage should be.

Sorry can't help you there. I have a Granatelli cold air tuneable GMAF and my readings with the engine running and connector hooked up will probably not be the same.

As for connector off at yellow wire with key on 5vdc is correct.

BTW - The MAF frequency range is 32 - 150 Hertz. Its a varying signal proportional to airflow. An oscilloscope would come in handy in your case.

I run the Autotap program and check the MAF for dynamic conditions which are the MAF signal should be relatively constant at cruising speeds, gradually changing with throttle angle and rapidly changing on sudden acceleration.

Other than that good luck.



Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials

[jay69dogg]

Thanks bnaylor3400 for the info. Does anyone else have any info or know where I could find what the voltages should be on the MAF wires?

[ChrisB-98GrandPrix]

Originally Posted by bnaylor3400

Sorry can't help you there. I have a Granatelli cold air tuneable GMAF and my readings with the engine running and connector hooked up will probably not be the same.

This is a little off-topic but... how do you like the Granatelli Cold Air Tuneable GMAF? I have a similarly modded GTP to yours and am curious if you see a noticeable improvement with it. Also... does it take a lot of tweaking to at first to dial it in? I do have Autotap now and am beginning to map the parameters.

Thanx again,

[BNaylor]

Originally Posted by ChrisB-98GrandPrix

This is a little off-topic but... how do you like the Granatelli Cold Air Tuneable GMAF? I have a similarly modded GTP to yours and am curious if you see a noticeable improvement with it. Also... does it take a lot of tweaking to at first to dial it in? I do have Autotap now and am beginning to map the parameters.

Thanx again,

It works great if you have a CAI, any brand. It has an adjustment to lean out or enrichen. You may get a SES light running a GMAF and it allows you to tune in. You can tune for different ambient temperatures throughout the year. Autotap comes in handy for this too. Once set its fairly stable. My 1/4 mile times improved by approximately .25 - .3 tenths of a second. Granatelli claims a 10 - 15 wheel hp gain. IMO it is a noticeable gain.



Thrasher CAI, DHP v1.0 PCM,
3.25 SC pulley, CAIT GMAF, Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 TB,
TB spacer, MSD 8.5mm wires, Autolite 104s,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials