92 4.0 will not stay running with maf plugged in

[cvacc411]

Engine will start and then immediately shut off with maf plugged in. With the maf unplugged, the engine will run smoothly. I've tried cleaning and replaced maf with another one and got same results, both times disconnecting the battery to let computer reset. I then tried starting the truck with the maf plugged in , but out of housing. It will run and as soon as I put the maf in the housing , the engine stalls. Any ideas would be appreciated. I do get a check engine light when the truck is started, but it could be because the maf is unplugged.

 

[Moyer]

yes the check engine light will come on when the maf is unpluged. But the stalling when it is pluged in is weird whats your air filter like is it really bad?

 

[MrShorty]

I would be interested in seeing what trouble codes the computer put out.

 

[Billy177]

maby o2 sensors, or something like that that only infulence the car in open loop mode

 

[cvacc411]

Air filter was replaced a few months ago. Since no one has seen this problem, my next question is, can I run the truck with the maf unplugged. Since it does run smooth like that.

 

[MrShorty]

You can run with the MAF unplugged. Ultimately, though, the engine will run it's best if you find out what the problem is and get it fixed. Did you ever pull the codes? There are several possible MAF codes, and which one (or ones) come up could be diagnostic.

 

[cvacc411]

I ordered an Equus digital ford code reader. I will supply the code when I get the tool in.

 

[MrShorty]

I guess you didn't know, but you can pull codes with nothing more than a voltmeter and a paper clip. See "tests" at www.dalidesign.com/hbook/eectest.html

 

[Glacier991]

When you unplug the MAF, the computer uses derived numbers (from a lookup table)to substitute for it. The fact that it runs ok then is highly suggestive of bad inputs from the MAF. Like Mr. Shorty I'll be curious to see what you get. I'd go ahead and read the codes first and write them all down, but a lot of em will be because you unplugged the MAF. Then clear them, replug and fire it up and see if it will throw a code before it dies....

 

[ExplorerDMB]

tryin cleaning your MAF. This can sometimes cause problems with the readings. I've seen it before, not on an Explorer, but on other vehicles.

-Drew

 

[cvacc411]

With a KOEO test, I get a Pass code of 111. After the 10 is displayed, I get a 157 and 158 which is MAF fault low voltage and high voltage. I did this with the MAF plugged in. With a KOER test, I get a 998 code, which means "failure mode" followed by the same 157 and 158 code. Unfortunately, I had to do this test with the MAF unplugged, since the truck will not stay on with it plugged in. I do not get any other codes. Does this mean that the MAF is malfunctioned? Do the MAF's usually go like that? The only reason I ask is because this is the second MAF in the truck with the same result. Could it be the wiring itself? Any input appreciated.

 

[CDW6212R]

I had a low speed stumble a month ago. My Ford guru told me to unplug the MAF, after other normal checks. I don't know what the test was to discover, I found my problem before I got to the MAF. My problem was that the fuel pressure rubber connector had expanded, creating a vacuum leak, thus higher fuel pressure.

Call Ford, and ask about that testing of the MAF. Good luck,
DOn W

 

[MrShorty]

Any code could possible be bad wiring; the computer can't tell the difference between a wiring fault and a bad sensor, or an internal fault within the computer in some cases.
I find it interesting that you are getting both MAF low and high codes. I would suggest backprobing the MAF signal circuit to see what the MAF is outputting. Actron (www.actron.com) has an ignition module and sensor tester they sell. It seems to be little more than a glorified DVOM. I've found the users manual (available on their website) a useful reference for testing most sensors, adapting the instructions for a regular DVOM. Any good manual (Chiltons and Haynes sometimes satisfy this criteria, Many times libraries will carry better manuals. There's also the vehicle repair guides at www.autozone.com) will have test procedures for the MAF complete with wiring diagrams.