Please forgive my great ignorance but
I have two questions concerning that MAF sensor:
- I was wondering if it is possible to replace the MAP sensor on a 87 Z28 350 TPI by a MAP sensor that would be powered on one of the 5V terminals of the ECM and by connecting the MAP signal in the MAF signal terminal on the ECM.
- Also, how can I make sure that my MAF sensor doesn't need to be replaced:
On a bench, I powered the sensor with 12V and monitored the output signal which was varying with airflow. The burnoff did not seem to work (I assume the wire should glow red for a second or so?). What I don't know, is if the output signal is properly calibrated.
The engine runs very rough when the MAF is connected in the car but runs good when I disconnect it.
I hope I don't need a new sensor...

 

First of all, you have MAF, not MAP. Don't get the two confused as they are very different. MAP didn't come out until 1990, so unless someone has switched out the motor, you have MAF. I have no idea what you are getting at with your first question, and as for your second question, there is no bench test that I or my mech know of to test for a bad MAF sensor. The only two ways I know of are: Tapping on the thing while the engine is running to see if there is any change in RPM or stumbling, or 2) replace it and see if your error codes go away. But if you don't have a service manual to walk you through testing of the MAF sensor then replace the cheap things first, the power and burnoff relays, adjust your TPS, check for vacuum leaks. Hope this helps.

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Kevin Irving
85 Trans Am WS-6, 305 TPI, custom burned '86 PROM with '87 "165"ECM, Accel Supercoil & 8.8 Wires, MSD 6AL, Aluminum Driveshaft, TB Coolant Bypass, Ported Plenum, Modified MAF, Syclone Fuel Pump, JET Airfoil

15.556 @ 86.65mph, Nov 10, 2000.... I know it sucks.. but it will get better!

http://www.geocities.com/transam85tpi/

 

*Usually* when you disconnect the MAF, and the car runs better, the MAF is at fault.

As mentioned before though, swap the relays to be sure.

You can't install a MAP in place of the MAF, signal outputs are different between the two, and the ECM won't understand what it's being told.

 

If you car is of the MAF setup and not Speed Density, disconnecting the Maf or a malfuntioning MAF sensor will let the car run like CRAP.

 

Steve is right.. in MOST cases (including mine). However, there are some cars for some reason where the car runs like a scalded dog when the MAF sensor is unplugged... go figure.

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Kevin Irving
85 Trans Am WS-6, 305 TPI, custom burned '86 PROM with '87 "165"ECM, Accel Supercoil & 8.8 Wires, MSD 6AL, Aluminum Driveshaft, TB Coolant Bypass, Ported Plenum, Modified MAF, Syclone Fuel Pump, JET Airfoil

15.556 @ 86.65mph, Nov 10, 2000.... I know it sucks.. but it will get better!

http://www.geocities.com/transam85tpi/

 

I would almost put money on it that your MAF is bad. When its plugged in it feeds bad signals when unplugged your prom goes into closed loop (or is it open?)or "limp home" mode, which is why your engine runs "better"
However, I had an 87 TA W/MAF the entire 9 months I owned the car it ran alright but was never quite the performer that I thought it should be. Well when I went to sell the car I took it to the local mechanic to have a exhaust manifold gasket replaced, well he noticed it didnt run quit right either, so he looks under the hood and found my wiring harness for me MAF to have been cut by the fan belt. He spliced all the wires back and tha thing ran like a bat outa hell. So you might think it runs better but your comparing apples to oranges.. might I add, I didnt know **** about cars then!

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1991 Z28 500hp383 TCI 700R4

 

Disconnecting the MAF should not allow the motor to run like crap, when you disconnect the maf prior to start up, the ECM defaults to "compromise' air flow condition, hugher than what is normally read by the ECM, which usually causes to motor to run a tad on the rich side.

If the MAF becomes disconnected while the engine is running, the ECM stores the last known parameters the MAf gave, and uses them for a default reading...now thiere is a possiblity that if this is done while the car is running, the motor would run bad, but once shut off, the start up default will be used.

Now ofcourse the car may not run optimally, fuel milage and performance will suffer, but it should still run, accelerate and idle smoothly...assuming you're still run stock, or close to stock EPROM parameters, I've no experience trying it with a customized or aftermarket chip.

 

I know what you are talking about trying to use a MAP as a MAF (because the voltage swing is about the same) but the signal on the wire is inverted by the pull down resistor built into the ecm. Basically the MAF is a low resistance at idle between the signal wire and the 5v reference and the MAP is a high resistance at idle in the same circumstance. If you get a good wiring shematic of the ecm difference you'll see the difference in the circuit limiting resistors on the signal line.

If there was an add on box to 'invert' the resistance of the MAP sensor with a trim on the voltage (to set it like a TPS) and get the proper range (.5v at idle 5v at WOT) it would work but I never saw one and never had time to design one myself.... although i'd like to see the results of ditching a maf and plugging in map in its place w/o changing ecms and being able to trim the 'curve' of signal to compensate for larger cams, mods, ect would be invaluable since the maf is a restiction in high hp apps and runs out of range on high flow systems (more cubes/supercharged). You're sparking my interest in this again... maybe i'll try to make this someday but work keeps me too busy to play.

 

yes, the car will start but driving it, well, a wheelbarrel would be more predictable and reliable.

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89 GTA G92
305 TPI WC 5spd w/3.45
Accel Cap & 8mm Taylor's
Custom 4" Cold Air Induction
Jet Airfoil
K&N Airfilter
160 deg stat/fan switch TB Bypass - Steel Rad
Cat back 3" Exhaust w/Terminator Muff.
HiGh FlOw Dynomax Cat
Spohn LCA's - KYB GR-2's
Autometer Vac+Oil Temp

 

yes there actually was and am assuming still is a way to convert maf to map, gm had a problem and in 89 some of there cars they conv. I am surprised no one on this board has an 89 like this. I tried to find this at work but, as many of you who work at gm dealerships know we don't keep that much info from back then. And I for one was not working on cars back then.

 

The ecms are different though. They probably did the correct conversion. I was thinking about using a MAF computer with a MAP sensor. When you scan it will measure 'grams of airflow' by using a MAP (tricking, but not really cheating or defeating the ecu)

 

I was kinda wonding if they switched the ecm too. I suppose it would be cheeper to in stall a ecm at there cost and map than have a new maf installed and have it go bad again.

 

You can ot use a MAP on a currently MAF controled car. You can change the system over. You need the following.

90-91 ECm, and chip
knock sensor 90-91
ECM pluges, and 165 ECM plug reciever This is to make the adapter so you can plug the new ecm into your current wiring harness in.
A MAP sensor from a 90-91
Plus some wiring

Tapping the MAF before you start the car is one thing to try. If the car seems to run better then it is the MAF. It will go back to running bad if is the MAF, which means you will have to tap it once an awhile. You can also tap it whilerunning and see how it does. If it makes tings worse it is bad, and if it makes thing better than it is bad. If it makes no difference than it is good. Also check your plug, and wires. While the car is running play with the wires, and plug. Playing meaning move then around a little, and see if the cars does better. Becareful since the engine is running. You can also unplug the MAF as mentioned above. Unplug it before starting the car and if the car runs beter with it unplugged then it is the MAF. I just went through all this myself for the second time. My car had a bad huntting idle, and with the MAF unplugged it idled fine. If unplugging the MAF works do not drive it like this. It burns really rich and will burn your cats up. Also replace your MAF relays at the sametime as the MAF. They cost like $8 for one. Insurance.



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88 Corvette
383 Waitting to dyno