Hello folks. This is a long shot but Ive been trouble shooting the MAF. Ive been running on default for a while now and decided to replace the MAF due to a code being thrown and have to smog it. Well I replaced the MAF with no luck. Ops 1986 C4. Traced the wires to the relay. Changed out the relay and still throwing a code. The brown wire to one end of the relay has 12 volts continuous. The two wires on the other end lead to the MAF. I traced using a sound meter. Now this is the kicker. The center wire is a big fat red wire. It looks like a continuous 12 volt wire. I read 0 volts. Turn key on, 0 volts. Plugged it in and peeled a bit of wire housing off. Tested wire with key on and off0 volts. I am thinking this is the trigger wire that turns on the relay to supply voltage to the MAF or not???. Any help will be appreciated. Like i said its a long shot.

 

Mike that's the way the circuit works. 0 volts if the car is not running even with the key on - this it normal. What code are you getting from the ECM?

 

Ops, Ya im pulling a 33 code. Book sais to check for .5 volts at C connection to MAF. Ill jumper it and let see whats up. Should i check for .5 when vehicle is running? Thanks for the speedy response engle. Anything else I should look for ?

 

MAF test:

Good news it's easy to test it! All you need is a noid light, a dc volt meter and a long piece of wire. Noid light should be hooked up in series with RED lead of the voltage meter.

Test: (Test assumes that car battery is fully charged at 12v! Lower battery voltages may produce lower test results)

Hook one end of a long piece of wire from the a postive 12v source (battery) and now connect the other end of this jumper wire to term"G" on the ADL.

With the Noid light hooked up in series with RED lead of the voltage meter now ground the meter's other lead (black)to the engine or negative battery post). With the MAF sensor hooked up push into the MAF's middle wire - the voltage on this wire(the middle wire - dark green)should be 2.5v with the key in the "on" position and a postive 12v jumper wire to term"G" on the ADL. If less than 2v it's most likely a bad MAF sensor!

Push into the same wire with a test probe.With the MAF un-hooked the voltage should read 5 v with the key in the "on" position and a postive jumper wire to term"G" on the ADL. If less than 5v wire may be grounded/shorted out or you could have a bad ECM.

With the MAF still unplugged you can also test ensure that you have 12volts going to pin "E" (circuit 993).

 

wow friggin amazing. Thanks a bunch. Ill get on it first thing tomorrow

 

I have seen this happen when a larger TB was installed.The TPS seting and minimum air speed was incorrect and caused a code 33 to show up.
Car would run like crap when it happened.

What TB are you running? TPS set properly?Minim air speed?

 

helpful tip

TPS sensor should be between .54-.63ohms to be on the safe side.

That 5v runs through a lot of stuff.

 

ya all my components are stock. So shouldnt be the problem. Checked TPS a while back and was in the ball park of allotted voltage. Car actually runs great. There was no difference with the new MAF and the code didnt go away after clearing a few times. I did have the MAF unplugged all this time since it was screwing up on me. A while back I just unplugged it and ran default which isnt that bad. Trying to print out engles stuff. Love that schematic. It shows everything!!! Ill keep you updated.
Frivilous info... This engine has over 370,000 miles on it. I think the long life is due to regular mobile 1 oil changes. Little to no oil burnoff. I might add a half a quart every 3000 miles to top off. Friggin amazing

 

Hello again everyone. Update... I checked the appropriate voltage and found that I didnt have any voltage on pin "E" at the MAF. Changed out both relays and got the 12 volts back at pin E. I have 5 volts at terminal C MAF when disconnected from MAF. The kicker is I have 4.68 volts at terminal C when MAF is connected. Engle advised if the volts were 2.0 or less would indicate a bad MAF? Just to confirm. I have terminal G jumped to hot and fuel pump is heard operating. I also have Volt meter with noid light in series with positive test lead and negative lead alligator clipped to the neg of the battery. Does my 4.68 Volts indicate the same? Bad MAF? Thanks in advance again for all your help. Wish I could take yall out for beer and pizza haha.;...

 

That is close enough....your MAF is good....well done. A large % of post I read from people here on the forum with MAF problems find that by changing the relays out their problems are resolved. You were able to prove/identify that one of the MAF relays was bad/failing without just swappin' stuff out.

 

Dude....... That is awesome! Does the car have that many miles on it too, or just the engine?

 

4.68 volts sounds awfully high to me.

When read by the ecm this voltage level should represent approx. 248 gm/sec. which is very close to the top of the 0-255 gm/sec range.

I suspect your MAF isn't properly pulling down the current limited ecm supplied 5 volt signal on Pin C.

Note: I have read reports on tgo of strange voltage readings by those trying to monitor the MAF voltage with an otherwise normally functioning car, so this could be ok.

My set-up is a bit different, since I'm using a Ford MAF on another input circuit, but the voltage that I can monitor internally fits exactly with what I see on the raw MAF signal according to the MAF table.

I would expect the standard MAF and vmaf input circuit to behave in the same way, although I haven't specifically tested it with a working MAF. I have tested the vmaf circuit by grounding and applying various resistances to ground on the 5 volt signal line to observe different voltage and signal values at the ecm. This testing met my expectations at the time.

There may be more going on with the Vmaf input circuit than meets the eye. I would like to understand this behavior.

If anyone else has experience data logging the MAF voltage and resulting MAF signal, please share your results.

 

Ya, the whole car has over 370,000 miles. I think its because its manual. Ive heard autos dont last that long. that rear end I have never touched just oil changes. the 4x3 changed out the relay and plug once, and oil changes both overdrive and gearbox. Other than that. Changed out the calipers. They were gettng stuck. Lifetime brake pads. Lost track of how many I went through ahah. The drive train is a tank Ops this is my other account

 

Tequila boy, I agree. Im thinking of returning the MAF. Still under warranty. I actually lost my 5 volts at the C terminal I dont know what happened but I got it back. So plugged in should read about 2.5 as engle advised? Its still at 4.c8 plugged in. Im still pulling a 33.. I checked the C dark green wire for continuity and possible open circuit but its fully closed.
Thanks for all the help guys and gals!!!

 

Good news... Swapped out the new MAF from autozone and no more code. So thanks to all who contributed. This forum just saved me about 500 bucks!!! I love this place