is there any way to check the maf for proper function?

 

Rumple,

Welcome Aboard!

Yes, there is a way. You'll have to connect a digital voltmeter to the 'A' and 'C' terminals at the MAF, start the engine, and meter the output voltage:

 

Does -85 tpi maf have same output voltage as 86-89 maf's,and is there anything special about -85 maf's(exept burn off module).

Jari

 

Jari,

the '85 MAFs on TPI engines are a FM output (Frequency Modulated). The output voltage will be around 5VDC peak-peak, but will display on most meters as about 2.5VDC if it's a treu RMS meter. The output signal can be tested with an oscilloscope, frequency counter, Tach/Dwell meter. a DMM with a frequency/duty cycle display, or specialized sensor tester like the Actron CP-9085.

 

Vader

So if I measure maf's output at A and C terminals,will output voltage peak to peak and frequency raise when engine get's more rpm,or will voltage stay at 5v peak to peak and only frequency raise.
And second question,is there at 870 computer same 255g/sec limit as 165 computers?

Jari

 

Jari,

No. The P-P voltage should remain relatively steady.

Yes, the output frequency should increase with intake air flow. If you're using an old analog multimeter (like a Simpson 260 that doesn't indicate true RMS voltage) you may see a voltage change due to the frequency variation, but it won't be linear. A dwell meter or frequency counter will give a more accurate indication, but an oscilloscope would be ideal.

As far as I understand, the limits are the same for both the older and newer ECMs.

 

With my Fluke 77 multimeter connected to pin "C" and battery ground, I get 5.04 volts with eng idling. No change when I hit the accelerator. Is the MAF bad? I'm getting a code 33 just a few seconds after starting the eng.

Pins "A" and "B" both show very low resistance to ground (~.1 ohm)
I have batt voltage on red wire (pin "E")

BTW, it's a '87 L98 eng.

 

I just now replaced the MAF sensor and both the MAF power and burn-off relays. Same exact problem. WTF?!?
This time I measured from pin "A" to "C" instead of pin "C" to batt ground terminal. Voltage was still 5.04 volts.

 

ZZ,

A Fluke 77 is a great little item. It should give a correct reading regardless of duty cycling. The '87 L98 should use an analog (voltage) MAF. This is the circuit:



Pins 'A' and 'B' are both grounded, but to different places.

Check the voltage at pin 'E'. If there is not 12VDC, the electronics package in the MAF is not enabled, and the switching transistor will not pull down the 5VDC reference signal on pin 'C'. If you don't have 12VDC at 'E', check the wiring and contacts of the MAF power and burn-off relays. Power for the MAF electronics is routed through BOTH of them, and they must be intact for the MAF to function.

I'm guessing your original sensor may be O.K.

 

I have batt voltage at pin "E". After talking to a friend (who's a EE and has the 165 schematics), I installed a 270 ohm resistor from pin "C" to pin "B". The 5v ref signal got pulled down to ~1 volt. Started eng and the SES light stayed out. I'm pretty sure now the new MAF is bad.

One wierd thing I did notice, while monitoring the the MAF g/sec display on my ancient OTC Monitor 2000, is the g/sec with the ref voltage at 5 volts is ~25. I was expecting to see 255.
I double checked the MAF table #6 on my ABWT bin and according to that, with MAF ref line voltage above 4.66 volts, the g/sec should be 255.
(Now that I think abt it, maybe the ECM is seeing 255 and is going into limp mode before I have a chance to see the 255 on my scanner.)
The manual for the OTC says the MAF g/sec range is 0-150.


With the 270 resistor installed, the g/sec display is abt 12, but eng idles pretty good and doesn't send a code. O2 voltage is between .45 and .49 volts.

What would be considered a normal range for the MAF (in g/sec) on a 383 at idle?

 

If the grounds at 'A' and 'B' are intact, I'd suspect the replacement MAF as well. Is this a remanufactured unit or new? For about $165 you can get a thick film "indestructible" MAF from Wells.

 

Took the new (actually re manuf) MAF back to autozone and got another one. Same exact problem.
Where can I get the thick film Wells unit for $165?

 

In reference to the ground wires:
I measure 3 ohms from pin "A" to batt ground post and 3 ohms from pin "B" to batt ground post.
Measured 1.1 ohms from pin "B" of MAF conn to ecm connector pin# A11.
When I measured the resistance from the ECM metal case to the neg batt post, I got 44 ohms.
Is that bad?

Should I try a temp jumper from the ECM case to the batt -terminal?

 

Well, that isn't a good thing. Try the temporary jumper to the ECM case from a good ground. The case (and chassis) must be grounded.

 

Re-measured ECM case to batt ground and got 7 ohms. Must have had a bad connection last time. Added a ground jumped from ECM case to batt ground, no help.

 

Here is the source:
WELLS MAF P/N SU-145
WORLD DISCOUNT AUTO PARTS
1635 ELMWOOD AVE
BUFFALO, NY 14207
1-800-288-6728

$156.95 + S/H . Most of the time they have them in stock and can ship the same day if you call early. Hope this helps.