Tampa 928s

Need to know the Maf voltage at idle!

AO

Use a DMM.

Tampa 928s

I have a Lm-1 and 3 it shows 2.35 Volts at idle I thought it should be around 1.5 Volts!

John Speake

2.7v is typical, 2.35v is much too low, if that reading is accurate. Your modified intake will give somewhat different values, and due to turbulance it is always difficult to predict what will happen to the MAF reading.

PorKen

I see 2.75 at cold idle. MAFs, even rebuilt ones, vary somewhat.


BTW, here's a trick (that I figured out by accident) to get the full range of the MAF signal, and also allow you to convert to an approx. grams/sec. It works with my SSI-4, so I'm assuming it will work with an LM-x.

Do not ground the MAF input into the SSI-4 (LM-1), IE. use the '+' input only, leave the '-' empty. Then use a custom table to multiply the voltage * 132 (may have to adjust #± to match your MAF).

EG:

gsec Volt
040 0.3
072 0.55
104 0.8
136 1.0
168 1.3
200 1.5
232 1.75
264 2.0
328 2.5
360 2.75
392 3.0
424 3.25
456 3.5
488 3.75
520 4.0
648 5.0

Tampa 928s

86 S/C

Well thats cool Porken:

I have a large idle fluctuation when first started up when cold 0-1300. This Maf is a puller and resides under the fender. The C.O pot was set for 194 Ohms I readjusted it to 380 and the A/F ratio seems closer to Stoic. But the Maf voltage does not change. I cannot get my idle under 850 I am checking for leaks now!

PorKen

The CO pot is just an input into the LH, it does not affect the MAF output directly.

The LH uses the CO voltage to add or subtract from the fueling calculation digitally. 'Zero' is ~372 ohms (B2h in the code*). The 84-86 EZF/LH2.2 service bulletin states the nominal setting should be 382 ohms, slighly richer than 'zero'.

Check that your idle switch closes with a cold and hot engine. The extra ignition advance at cruise will raise the idle speed, too.



*I'm working on code for my chips to hopefully add or subtract to the WOT fueling according to the CO adjustment to better deal with the range of individual MAF outputs. Just a tiny difference in voltage equates to a large change in fueling at high rpm.

BC

Would there be any reason to bench test the MAF and set it at the plug to 380 ohms? Is the ohms reading independent of the MAF's ability to properly read all air flows at all RPMS or complete dependent?

Meaning can you have a MAF that IS adjusted to 380 ohms and NOT be working properly?

hacker-pschorr

Tampa,

Are you still using that custom adjustable MAF Kevin made for you?

John Speake

The idle CO pot setting is entirely independant of the setting of the calibration of the MAF output volts versus air mass. A has been said, the idle pot is just an input into the LH ECU and that pot is not connected to any of the electronics on the MAF itself.

There are also typical ohms readings quoted for testing some MAF resistances, however these are only for idenifying total MAF failure. They vary from MAF to MAF and these variations are taken out during calibration, which has to be accurate to 1% or better.

Tampa 928s

Hacker, Yes I never adjusted the C.O, now that I did it starts and idles correctly. I have not ran a data log yet under boost, my concern is the adjustable pots show no change in my voltage or C.O. readings at idle. So this seems to be run, guess, adjust run and so on.