Is there any way to check if the MAF isn't working properly? I have a scan tool, seems to go up and down with engine load. The only way I can drive my car is if I start it with the A&B ALDL connection grounded. If i start it w/o them grounded it won't run, idles @ 200-400 RPM then dies, and will barely accelerate the engine in neutral.

 

Don't you get any error codes?????

Try to disconnect the MAF and start the car, if it works fine check/replace MAF relays and connectors. Try again if its not working you may have a bad MAF....but the comp. should throw a code......

You should also do a TPS & min.air + IAC adjustment, the car should idle at 750 rpm.






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You didn't really give enough information to diagnose this problem. I'm not sure why grounding pins A and B let's your car run any better, but doing so is preventing the ECM from setting any codes.

If the MAF is faulty you should be setting either a code 33 or 34. A faulty burn-off circuit would set code 35, and an idle speed error code 36. I can list the proper troubleshooting sequence if you have any codes, but can't help out much without any codes.

A couple of things you could try are:

1. With the engine off, turn the ignition to the "ON" position, but do not start the engine. The "Service Engine Soon" light should stay on as long as the ignition is in the "ON" position. If this light does not come on, you have a problem with either the Mem-Cal(unlikely) or the ECM.

2. Disconnect the battery for ten minutes. If the Mem-Cal has corrupt data(admittedly a long shot), this will flush it. If this allows your engine to run acceptably, it will probably set some error code(s) to allow you to further diagnose the problem, assuming you have,...

3. ...removed the jumper from the ALDL to allow the ECM to report the error(s) it finds.

Also if you could list any recent work/mod's done to your engine, it might help to track down the gremlins.

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He who hesitates,... is lost!

 

My maf is bad too it won`t trhow any codes
but the car starts and stalls at once, if I
take the connexion off the maf it starts
fine, also when the car is warm the maf works
fine for some time and then it can stop the
engine.
Start the car ``without maf`` and see if the
problem goes away.
Benjamin

 

the car is all stock 305 tpi 5 spd, no codes, IAC seems fine 40's, TPS .52 idle, 4.29 full, to me it seems like the timing is stuck in full advance at idle. It sounds real bad when it trys to idle like the engine stops then fires around again. I'll try just starting it with the MAF disconnected though

 

Wow. Beast, DO NOT start the car with the ALDL A/B grounded, you could fry your ECU.
Also MAF problems are notorious for not throwing codes. Most likely one of your relays are fried.
Ben, after the car warms up it goes into open loop and does not rely heavily on the MAF input. You most likely have a toasted relay also.

 

No that is incorrect. After the car warms up it goes into closed loop mode and then uses the info from all the sensors to make adjustments.

While the car is cold it is in open loop and does not use sensors for adjustments, it uses pre-programmed info from the chip to manage spark and fuel.

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a quick check for the maf is to lightly, i repeat lightly tap the plastic housing with the end of a screwdriver, if the engine stumbles or stalls the maf is faulty and should be replaced.

 

a quick check for the maf is to lightly, i repeat lightly tap the plastic housing with the end of a screwdriver, if the engine stumbles or stalls the maf is faulty and should be replaced.

 

Yep, that was a mis-type. The rest is correct. Oops! I think I shall start to re-read my posts a tad closer. Thanks for the catch!

As an addendum, the best way I have found to test MAFs is to unplug it. Tapping it can cause misreadings in the MAF and lead you to falsly beleive it is bad.

 

Well, with the MAF disconnected, it starts and runs real bad for about 30 sec, then kicks a code(sorry didn't check which one,i'm sure it's one mentioned above), then it idles decent and drives alright except for bad throttle response and bad gas milage(makes sense in openloop), Any suggestions on whether I should buy a new one, that WELLS brand, or try one from a junkyard? thanks for the responses

 

I realize you guys are past this already...but actaully the ECM looks at the MAF on all starts..cold, hot, doesn't matter to assist in PW setting along with the CTS.

I don't know the exact relationship with startup, but it is used.

A couple other things too...a scan tool will only tell you if the MAF is not reporting data or is reporting obviusly wrong data (like 200gr/sec at idle)...if the MAF gets flaky, and does not give the proper data to the ECM, no code will set...assuming the data sent is within the range the ECM is looking for.

Also, if the car runs bad with the MAF disconnected..then chances are the MAF is not at fault.



[This message has been edited by 8Mike9 (edited October 30, 2000).]