PKRWUD or anyone with a DMM

[PrplMonster]

I am sorry to post about this again, but i really need some help.

This question pertains to the MAF sensor,

Now i know that Pin C & D are supposed to have between .6 - .9 vDC with the car idling.

Pins A & B are supposed to supply battery voltage.

When i test pins C & D with my DMM i get 5.8vDC with the KEY ON and the ENGINE OFF and the MAF disconnected. Is this right?

I just ordered a MAF new sensor and i would hate for it to let out the magic smoke that makes it work.

thanks for the help, I am only asking for less than 5 minutes of your time. again thanks..

.dave

[PrplMonster]

sorry, the car is an 89lx with an a9l computer.

[PKRWUD]

You couldn't have posted this at a worse time. I'm on my way to the track for the Sprint races tonight. Do this:

Set your DMM to ohms.
Key off.
Disconnect MAF harness.
Connect DMM between C & D at the harness connector, and then between B & D at the harness connector.
Must be 10,000 ohms or higher.

If the harness is disconnected, there is no reason C & D should have voltage. Run your Neg. DMM to the neg bat post, and touch C & then D with the pos DMM lead. Set to DCV. Which one registers voltage?

Do these and post the results. I'll be back around midnight.

Take care
~Chris

------------------
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MustangNet

My site: JimPorterRacing

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[PrplMonster]

Resistance:

C & D = 129.6K Ohms
A & B = 1.200K Ohms


Power with neg DMM at the battery:

I get 5.8vDC at terminal C

With the computer disconnected and the key on, no power, no ground.

any help chris?

.dave

[PKRWUD]

You've got a problem. If you attached your DMM negative lead to the batteries negative post, and then touched the DMM positive lead to the C pin, and got voltage, you've got trouble. The C pin is return signal (aka: ground).

WITH THE KEY OFF:

Set DMM to ohms on the 200k scale.
With the computer disconnected, the MAF disconnected, check the resistance between A & D

Set DMM to ohms on the 20k scale.
With the computer connected and the MAF disconnected, check the resistance between C & D and B & D (not A & B)

Why are we doing this, anyway? Did you get some codes? What brought this on? Give me all the details.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

[PrplMonster]

Well........ I changed TB's. I went from a BBK 70mm to a Motorsports 65mm. After all it was all said and done, i start up the car, and she barely runs. So i do a KOEO and get code 56. That made me call pro-flow for some idea's, considering the fact that ALL i did was swap TB's. When i talked with the guy at pro-flow, he said C & D wasn't supposed to have any voltage with the car NOT running but with the key on. So i started tracking burns/shorts.

I tested pins C & D while running(idling) and got anywhere from 9.2-11.4VDC
With the car on and the MAF disconnected with pin C & D i get 5.8vDC(with a known good computer)


As far as burns/shorts, honestly there are none, I have the entire harness out of the car.

To clear up how my meter works, the scale displays like this:
OUCH(auto)
OU.CHk - 20K
OUC.Hk - 200k

Resistance in 200k scale with PCM disconnected:

I got 0, nada, nothing... C & D or B & D

PCM connected in the 20k scale(OU.CH) i couldn't get a reading.

With the meter in the 200k(OUC.H)
B & D = 100.4k
C & D = 129.6k


thanx for the help chris!!!!!
.dave

[PKRWUD]

You don't have any shorts to ground, but this still doesn't make any sense. Now, this is where it get's confusing. Let me try to explain. The resistance tests I asked you to do have ruled out the wiring being shorted to ground as a problem, which leaves only the ECM and/or the MAF as the problem. You should not be receiving any voltage between the C & D pins when the MAF is disconnected because the voltage signal goes TO the ECM through the D pin (the C pin is nothing more than a ground that is controlled by the ECM rather than being constant like the B pin is). Since those wires come straight from the ECM, and the MAF is disconnected when you are getting voltage there, that pretty much leaves the ECM as the fault. HOWEVER, I also had you test for a short in the ECM at those wires, and there wasn't one. BUT, you said earlier that there was positive voltage present at the C pin even when the ECM was disconnected. Seeing as the ECM is what the C pin goes to, that doesn't make any sense. The C pin circuit must be shorted to positive voltage somewhere.

PLEASE confirm this for me: KEY OFF, MAF disconnected, ECM connected, NEGATIVE DMM LEAD to NEGATIVE BATTERY POST. DMM set to DC Volts on the 20 scale. TURN KEY ON. POSITIVE DMM TEST LEAD to C PIN (while the neg. lead is still attached to the battery). Do you have ANY voltage at all? If so, TURN KEY OFF, AND DISCONNECT ECM, and check for voltage between the battery and the C pin again. If there is still voltage present, then there is voltage leaking into the C wire from somewhere. If their is no longer voltage, but there was before, then the ECM must be replaced.

I'm not done yet. You said: "I tested pins C & D while running(idling) and got anywhere from 9.2-11.4VDC". The voltage at idle shouldn't be more than 1 volt, and should never exceed 5 volts at WOT. This could be consistant with a voltage leak into the C wire circuit, but also could be a damaged ECM or even a bad MAF.

After you confirm whether or not the C pin has positive voltage going to it, and under what conditions (by following the instructions above), I want you to put everything back together again, except the harness to the MAF. Leave it disconnected. Start the car, and let it idle for exactly one minute. Turn the key off, and perform the KOEO self test again (pull codes). If a code 66 comes up, the MAF needs to be replaced.

That's enough for now. print a copy of this and take it with you. make sure you test everything EXACTLY the way I said to, and post the results.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

[This message has been edited by PKRWUD (edited 09-02-2001).]

[PrplMonster]

Chris, with the computer disconnected i get nothing, in ALL 4 wires key on or off

Key off computer connected: OvDC
Key on computer connected Pin C: 5.8vDC
Key on computer disconnected Pin C: OvDC

Chris again i have to say, I confirmed this 5.8vDC on pin C with a known good computer from a friends car. His car has no problems after hooking it upto my harness.

What does pin D do..? If A(+) B(-) C(signal return) D(?)

I have already sent my MAF meter to have a new sensor and to be recal.

The car will barely run without the MAF connected.

What confuses me is: ALL i did was change the Throttle Body, i did reuse my 70mm egr spacer. what gives..?

.dave

[PKRWUD]

I really don't know what to tell you then. The D pin is the wire that the MAF uses to send it's info to the ECM. The A pin is battery voltage that the ECM applies to the MAF when the ignition is turned on. This same wire is also spliced into the IAB Solenoid, the EGR Vacuum Regulator, the Canister purge Solenoid, both Air Management Solenoids, the WAC relay, the EEC relay, the Fuel Pump relay, and each of your injectors. This gives the ECM control over applying voltage to all of them only when the ignition is on. The B pin is goes directly to a junction between the negative battery post and the ground supply wire for the ECM. The C & D pins are used to send a specific signal to the ECM. basically, one is positive and one is negative, WHEN IN USE. The D pin sends the MAF signal, a positive voltage signal, to the ECM. The amount of volts sent are proportional to the amount of air entering the engine and the load the engine has on it. However, in order for any electrical signal to be sent, there has to be a complete circuit, which means there has to be a ground wire for the for the signal to return to the MAF on (a ground wire). While the MAF and ECM could function using the ground wire supplied with the MAF power wire, the engineers at Ford felt that that ground signal was too subject to fluctuation based on other possible loads (ie: turning your headlights on or playing the stereo. So they designed the ECM to regulate a ground wire that would always be at a constant, and used it to return the signal to the MAF (complete the circuit by grounding it). The C & D pins are not supposed to ever see much more than 5 volts at any time, while the A & B pins recieve battery voltage. That is why I am concerned that you read battery voltage at the C & D pins at idle.

When you reinstall the MAF, clear all codes and see what happens. If it sets any new codes, we can go from there. For future reference, next time you get a code 56, do what I said before: unplug the MAF, idle it for 1 minute, and then check for KOEO codes. If the MAF is bad, you'll get a code 66.

You should unplug the MAF connector on your friends car and see if he has voltage to the C pin.

Try this for me. Hook up everything but the MAF. attach the alligator clip end of a 12 volt test light to the C pin (use a paper clip if necessary). Turn the key on. Now touch the other end of the test lamp to the engine block. Does the lamp light up at all?

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

[This message has been edited by PKRWUD (edited 09-02-2001).]

[PrplMonster]

Chris- sorry i have been out all weekend.. The MAF comes back from Pro-Flow tomorow.

Let me get this straight. Clear all codes, then start the car and let it run for 1 minute without the MAF plugged in..? I just don't see how it would give a MAF code with it never plugged in.. just trying to clarify before i go out and try to electrocute myself..

.dave

[Tony91LX]

I will be watching this one closely, I to am getting code 56, and have ordered a new MAF, but did not know how to test my existing MAF.

All I did was swap in a 351W

[PKRWUD]

Install everything and clear the codes. Drive it and see if it's any better. If not, try and retrieve any codes. If one of them is a code 56, you may have a bad D wire or a bad MAF. The way you find out is to unplug the MAF connector, and restart the engine. Let it idle for one minute, and shut off the key. Pull codes again. If another 56 comes up, the D wire is bad. If a code 66 comes up, the MAF is bad.

I have a hunch your old MAF was the problem, but I'm still susoicious of the ECM.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

[PrplMonster]

Ok here we go....

To start, With a DMM set on OHMS i connected one lead to the C Pin at the MAF plug, then checked EVERY pin on the computer plug. Only one wire showed resistance(0.0) Then i checked D, with the same procedure, only one wire showed resistance(0.0)

Again, i checked with a friends computer and still got 5.9vDC. NOW when i connect the MAF plug into the MAF, the voltage practically disappeared, it dropped to .021vDC. WITH the car running C & D read .860(high side) with a little variation.

So everything is connected, taped back up and ready to go, I start it up, she runs beautifully! I then let her run for 5 min idling, shut her off for about 7 min, Fired her back up went to pull out of the driveway, and about stalled it. Under LOAD it pops spits and sputters. When i try to rev it up from under the hood, it has very slow acceleration, and pops and spits.

After hearing this, i ran a KOEO - 85, 11, 11 KOER - 21(ECT) 42(RICH right) 92(RICH left)

Ok, so i replaced the ECT sensor and still get this code(21) I have the heater core tubes plugged right now, so there is no flow past the ECT sensor, but why would it be out of self test range even with a new sensor?

Just for kicks i tried his computer after replacing the ECT sensor and i still get a code 21, 42, 92.

Now this is where it gets weird, well even more than what i am dealing with now.. I left the jumper lead connected and tryed to rev her up, NO POP, NO SPUTTER. take the jumper lead out, pop and sputter come back!

any help...? ....please....

.dave

[PKRWUD]

This post is starting to resemble a jigsaw puzzle. If the code 21 keeps coming up, the ECM is going to switch into limp mode when the jumper is pulled. It's (the ECT) not getting hot enough. That would explain the 42 & 92 as well. The ECT needs to accurately reflect the engines temp. Did you thoroughly warm up the engine before running the KOER test?

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

[PrplMonster]

Thanx for the inspiration > Yes, the car was at 185 at when running the test. When you guys block off heater cores, do you use a 90* elbo and just re-route it back, instead of plugging it?

.dave

[PrplMonster]

I mean instead of capping the tubes that run along the intake. ALSO, i forgot to mention that the MAF sensor is brand new.

.dave

[PrplMonster]

The only way i can explain the problem i am having now is, it's like she's running out of gas. If i increase fuel press. it falls on it's face quicker. The less fuel pressure, the better it runs, but still falls on it's face. any idea's..?

.dave

[PrplMonster]

Ok after another day of cursing this is what i have come up with.

The ECT code is gone, both code 42 and 92 are gone. I replaced the sparkplugs thinking they were fouled, but still no luck. The new ones are BLACK. Adjusting fuel press really doesn't help, i had it all the way down to 20psi(vac off) and they are still black. Adjusting timing doesn't help, it's at 12* now, i have had it at 8,10,12,14,16. If i shut the car off, then start it again, it gets worse, then smooths out.

When i take this thing out on road it does good cruising around the neighborhood, when i get out on the main road and give her sum gas, she like shuts off(rich,lean) I think i am getting too much fuel because the plugs are BLACK. any idea's.. please..

.dave