Help! MAF sensor has me stumped

[billd]

Hi guys,

I have been fighting with my MAF sensor. I have replaced it with many sensors they all fail the same way. The car starts and sounds great. Touch the throttle and instantly dies. I have changed everything in the circuit I can think of. When the sensor is disconnected car runs like a champ. Looking for ideas.

The code for a bad sensor goes on when it is disconnected then goes out when it is installed but that is when it dies.

Thanks

 

[65z01]

When you jumper ALDL pins A & B and turn ign to On what codes you get?
Code 33 = MAF hi voltage
Code 34 = MAF low voltage

 

[billd]

With the new sensor there are no codes. I thought maybe the TPS was acting up but when I check the voltage it looks pretty much dead on. Thought maybe the brain was scrambled so put a new ECM in and it still acts the same. Any suggestions?

 

[BRUTE86]

Hi Billd,
I presume that the replaced testing MFS were all for that year [there are 3 different operational but not looking, MFS for 1985 -1989, and they are not really interchangeable]. Also sometimes the the silent but violent culprit is the relays, and again not interchangeable.
What you did remove the MFS connection, that is one of the first test I would've done.
The fact that it 'ran like a charm' really puts other attempts/tests to find this problem aside for the time being.
Your test points to the MFS, relays, and/ or ECM, as when you disconnected the MFS and it ran fine. Now you tried other MFS [for your model only] and the problem still existed. This eliminates your MFS as the problem, as they can't be all bad, and point to the relays or ECM /wiring.
Check the relays, by inspecting the wiring [to and in]. Some relays do cause a problem because depending on its age, the factory grease with age is corrosive to the wire plastic coating, and it can expose the bare wires in the relay to make contact, this was very common problems with some of my clients, as relays were overlooked.. Check the wiring, remove relay cover,check inside, and trace wiring to MFS and ECM connections, there should be '0' resistance for good connections and condition.
After all that, including checking the wiring, and found no problem, I would remove the ECM and get it checked.
Good Luck,
BRUTE86

 

[65z01]

One indicator of a bad MAF/relays is when the engine runs better with MAF disconnected than when it's connected.

 

[billd]

Well leta see. Ive gone thru six MAF sensors they all have different failures modes. The one that i have in there now the ECM seems to like. When I pulled the connector off the MAF the car runs well. However there is a code interestingly I pulled the TPS and the car doesnt seem to care with the MAF disconnected. I verified that the TPS resistance is good through its travel. Again put a new ECM in and the car runs the same. Same falure modes.

 

[billd]

Quick update removed the TPS and just rotated it with out even moving the throttle . slight increase in RPM. Aside from that no effect. Could this be the relays you referred to?

 

[BRUTE86]

Quick update removed the TPS and just rotated it with out even moving the throttle . slight increase in RPM. Aside from that no effect. Could this be the relays you referred to?[/QUOT

There are 2 relays in the MAFS circuit. One is the power circuit relay which could help raise codes 33 and 34 [relay identified by "Power" painted on the top cover of the relay] , and the other is the burn off relay circuit, which switches on the "hot" wire in the middle of the air flow tunnel, any problem on that wire it will raise Code 36. This code will not affect the starting or the running of the engine. When code is raised you'll probably find that micro wire in the MAFS tunnel is broken.
The job of the red hot wire [when switched on] is to burn off all the micro impurities from the incoming air caught by the wire . When you switch off the engine the relay will activate the hot wire for 2 seconds to do its burning job. The relays are not interchangeable.
The relays are cheap to replace, but first you should try to identify the cause in order to eliminate the problem.
Check the condition of the wiring around the relay area, I have seen bare wiring [plastic wiring cover disappear through corrosion] up to 1/2" up from the relay.
Any contact between relay wiring will damage the relay and could damage the MAFS.
I personally would cut off off above the bare wire, and replace it with new wire, new brass connections, and use heat shrink for the job.
[Problems with the TPS circuits would set codes 21 or 22.]

Hope this helps, regards
Brute86

 

[billd]

Which twonwires should hit with my DMM to verify that tge burn off relay is working properly

 

[billd]

Figured it out. Turned out not to be the MAF at all. It was the knock sensor. Replaced that and bang everything worked great.

 

[billd]

Well this ornery sucker has managed to fool me again. The car ran great with the new knock sensor. Tried to start it again this morning and was distressed to find that it is back to its old tricks. Make me think that there is a short somewhere in one of the wiring harnesses that is sensitive to temperature.