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2000 GTP Only Starts With MAP Unplugged


wrong3000
11-25-2008, 07:17 PM
hey, everyone

I have a 2000 Grand prix GTP supercharged 3.8. It will not start, but if i unplug the MAP sensor and pump the gas it starts right up and runs crappy. the gas gauge drops to empty or 0 on the display, and shifting is affected as well.
After a few minutes i plug the MAP sensor back in, and the car goes even more crazy, it rev's to 3000 rpm, and then drops to 900 rpm...then stalls. but other times the car will run perfect.

I have replaced the MAF sensor but that didnt help. I took it to GM but then could fix it..... help me please!!!!

Thanks so much.

tblake
11-25-2008, 08:44 PM
what brand maf sensor did you buy?

wrong3000
11-25-2008, 09:24 PM
I think it may be aftermarket, the # on it says AFH50M-05

wafrederick
11-25-2008, 10:56 PM
The new one might be defective and the GM factory one is the better one.

wrong3000
11-25-2008, 11:08 PM
I tryed unplugging the MAF but it won't start. But it starts right up if I unplug the MAP sensor, do you think it would be any help to try a new MAP sensor?

tblake
11-26-2008, 02:28 AM
Yes, I would try exchanging it for another one. Chances are the new one is bad.

Also make sure you have B+ and ground at the MAF connector.

CrazyHorst
11-27-2008, 07:15 PM
A couple other things to check.

Check your engine block ground...if disconnected/broken/incomplete you can be discharging spark energy elsewhere....undesirable.

Also I'd carefully look over the entire engine harness for any pinched or chafed places. A wire that's "leaking" 12v to ground but not enough drain to cause a short circuit and blow a fuse or melt a fusible link can cause all kinds of grief. Recall that the feedback signal for the O2 sensor is millivolts and so you see how little it takes to make that signal go wrong.

wrong3000
11-27-2008, 08:15 PM
Well...I tried a new MAP sensor and It still won't start with it pluged in. I think the TPS is failing too, and the fuel gauge doesn't work. The engine rev's to 2000 - 3000 rpm when the TPS is pluged in, but when its uplugged the engine runs perfect. When I plug the MAP and TPS back in and shut the car off, it won't start again. I have great spark, good engine ground....maybe the pcm is failing?????? or maybe its time for a match in the gas tank. XD

tblake
11-28-2008, 01:17 AM
Anyone know if the TPS and MAF share the same circuit? Could it be possible that the TPS is shorted internally, causing a bad MAF signal when plugged in?

wrong3000, try starting the car with the MAF plugged in and the TPS unplugged.

BNaylor
11-28-2008, 09:04 AM
Anyone know if the TPS and MAF share the same circuit? .

Technically separate circuits but they share the same PCM 5 volt reference signal so I would check that at the input of each sensor electrical connector.

For the TPS it can be tested with a multimeter (DMM) just to be sure or rule it out. .4 volts DC at idle and around 4.5 volts at WOT. Linear and progressive voltage change (no dips or erratic) as you slowly move the accelerator from closed to open.

Note: TPS can be tested with Ignition to ON only and engine not running.

wrong3000
11-29-2008, 08:42 PM
I tested the TPS and it seem's to be fine. (0.5V-idle and 4.12V WOT)
The MAF is getting 12-14V at termimal C, is this normal

tblake
11-30-2008, 10:19 AM
yes, 12-14 b+ is normal for the MAF.

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