If a MAF car starts without the MAF being connected, but dies when it is connected, does that mean the ecm is bad or the MAF? I thought these things wouldn't run when the MAF was disconnected. I feel as if the ecm is giving out a false reading to allow the car to run, but not run well. Any help or insight would be terrific.

 

please help me.. Losing my mind here...

 

If the MAF is bad, you should be getting a code. With the MAF unplugged, I think the ECM goes into Limp Home mode, as though the Maf were bad. Check the connections at the MAF- loose connections there can cause poor running.

 

Thanks for the reply. Will check into them

 

Done some lookin around and discovered I am not gettin the required 12 volts to the end of my pigtail for the MAF sensor. The ecm is putting out the necessary 5volts to the green wire on the pigtail. So I am thinkn fuses.. does that sound right or should I be lookin for something different?

 

Check the fuses and MAF relay.

 

My 89 350 will not even start with MAF disconnected. I would say it's a bad MAF or MAF relay.

 

I agree with the above, check the MAF relay. Also check the main ground wires to the engine harness, which are bolted to studs on the back of both cylnder heads. If you have a loose or corroded ground wire, this could also cause the lack of any voltage at the MAF sensor. I'd definitely check the relay first though, since it's a PITA to get to the grounds on the back of the heads, especially on the passenger side!

 

ok here's what i got... I have backprobed the ground wire at the power relay (I tested the relay and it is fine, and bought another just in case). It is at a steady 0v. As i move further down the wire, like to the pass side firewall before it runs into its own loom and routes its way to the pigtail, it goes to 0.1v. At the pigtail, it is at 0.3v. I removed both bolts at the back of the heads, wiggled them really good.lol and then tightened them back up. I am lil skeptical about the drivers side, since I didnt use a studded bolt to ground these wires. I may go back and double check that.

Question... When the key is turned to run, the power relay is supposed to send the 12v to the MAF correct? Thats where I am stuck. Its not getting 12 volts. I have replaced the relay, the burnoff relay, triple checked the fuses for the ecm under the dash, all fuses for fuel pump and whatever else that I believe would be involved. Thanks for your help so far....

 

Well from what you've described so far, I'm beginning to wonder if you do, in fact, have a bad ECM. I do know that part of the circuitry on the ECM's board has to do with MAF control. I had to replace my '165 ECM about a year ago for a similar problem. I still had power to the MAF sensor, but my check engine light came on, and the code I retrieved said there was a problem with the MAF burnoff control. I went through the trouble code checklist in my factory shop manual for that particular code, and of course of the steps it said to take was replacing the MAF burnoff relay. Tried that and it made no difference, code still registered every time. The very last step on the code checklist said that if everything else checked out ok, then the ECM is bad. Luckily I had picked up a spare, remanned '165 from the boneyard for a paltry 25 bucks, so I swapped my prom into my spare ECM, reinstalled it, and lo and behold, problem fixed! Turns out there's a driver in the ECM for the MAF burnoff control, and I guess it must've gone bad. If all else fails on yours, maybe you could try buying a remanned ECM from the parts store, and try to get one from a parts store that allows you to return it. That way you can try replacing the ECM and see if it actually fixes the problem. If it doesn't take care of the problem, at least you can return it and get your money back. Or if you're luckly like I was, maybe you can buy an extra one cheap from a junkyard.

 

Thank you Pat. Yeah I am at a total loss here. I am going to pull the distributor so I have more access behind the engine and I am going to clean up some of the wiring a bit and continue to probe. I have a 165 ecm also. Those can be found in V6 cars also, right? I may go to the yard and ****** one or two for good measure. I don't like to throw parts at the car, so making sure that is the right move is important to me. Your input and advice is greatly appreciated. Do you think that if I made a jumper wire from the battery or an ignition turn on source, ran that to the pigtail and then hooked the MAF back up, and fired the car that that could show me that A) my MAF is in fact good, and that B) my ecm or wiring is the true culprit of my issues here?

 

Ttt

 

There's an ECM interchange chart somewhere on this site. Can't remember if it was in the general tech articles, or if it's in the DIY Prom forum, but it's on here somewhere. It tells you what other vehicles got the same ECM. I do know for a fact that the newer V6 3rd gens got the '730 ECM, but the last time I looked at that chart it seems like I remember seeing some of the mid-80's Sunbirds, S-10's, and other various V6 and 4 cylinder cars that used the '165. Running the jumper wire might not be a bad idea, as long as you're totally sure the MAF is supposed to receive a full 12 volts. I know a lot of the ECM inputs and whatnot only get something like 5 volts or less. I'd just hate to see you fry the ECM if too much voltage to the MAF could affect it. I know there's other members on here that are real gurus when it comes to the computer stuff on our cars. Unfortunately, I'm not one of them! But at a guess, I would think that the voltage supply running to the MAF should be 12 volts. I think the circuits that use less voltage are the wires that feed info back to the ECM from the MAF. In all honesty though, if it were me, I think the very first thing I would try is swapping in a different ECM with your PROM in it. If the MAF control portion of your current ECM is fubar, maybe that could be the reason your MAF relay isn't getting the signal to send voltage to the MAF. When I have some time I'll grab my factory shop manual and see what troubleshooting steps it lists for no power to the MAF. I followed the troubleshooting steps in my manual when I was getting the MAF burnoff trouble code, and it helped me figure out that my ECM was bad. I followed the chart step by step, and a bad ECM was the very last thing the chart suggested, and it cured my problem. I'll try to get back to you soon with the troubleshooting info for your problem.

 

you are a saint. I appreciate u takin the time to research this further for me. As a truck driver, I am only home on the wknds. So this would be huge for me. I will search the forum for that chart in the meantime. Thank you again!!!

 

I'll dig out my shop manual this weekend and see if I can find the troubleshooting chart you'll need.

 

Finally got a chance to look at my manual. Not sure if colors and terminals will be exactly the same as yours or not, since my manual is 1989, but I would think yours should be pretty similar, if not the same. The 1st thing you should check is this wire/terminal at the MAF power relay. Terminal A at MAF relay(orange wire)-This is the main 12 volt power source that comes from the inline fuse over by the battery. With the ignition key on, this terminal should light up when checked with a test light. If it doesn't, check the 20 amp inline fuse(it's the fuse that's over by the battery/passenger side fender). Has a red wire and an orange wire going to it, and there's a small plastic cover over the blade fuse. You could also try unplugging the MAF power relay and try jumping terminals A(orange) and E(red) with a paper clip. If you jump those with the key on, you should get power at terminal E(red) down at the MAF sensor plug. Here's a list of the 5 terminals at the MAF sensor plug, and which function they serve. Term.D (Dk Blue)-Comes from MAF power relay and powers burnoff function. Term.E (Red)-Comes from MAF power relay, this one is your 12 volt power for MAF. Term.C (Dk Green) MAF sensor output signal to ECM. Term.B (Black)-MAF sensor ground to ECM. Term.A (Black/White)-MAF sensor ground to main engine harness ground(back of cyl. head). My guess is that as long as you're getting power at the MAF power relay terminal (Term.A, orange wire), then you should be getting 12V down at terminal E(Red) down at the sensor plug. If you're not, you've either got a bad ground or your ECM's MAF control circuit is kaput.

 

Thank you Pat. Is there anyway u may be able to scan a troubleshooting page over to me to diag whether or not the MAF or ecm is the culprit? I found out in another thread that the maf doesnt get 12 volts until the fuel pump is in constant cycle (engine is started). So I am cleaning up a few wiring situations that arent up to my standards, then I need to do a step by stepper for this maf. If there is one online, u can just send me a link. Thank you.

 

I have traced my issue back to a couple of plug wires that were bad. I started to experience some backfire in the motor. Will update my results when the new wires show up.

 

Hey, that's good news! Funny how a lot of things end up being something simple. I always try to follow the "KISS" theory (Keep It Simple Stupid) when diagnosing a problem. Hopefully you'll get lucky and the new plug wires will get you straightened out!

 

The MAF gets its 12volts from the same source as the ECM, fuel pump, oil pressure switch for fuel pump, and Fuel pump relay; inline 30amp fuse by battery as was posted by Pat Hall.

 

Right on, thanks for that info rgarcia! I had no idea that fuse actually powers the MAF too. Good to know!