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Old 06-30-2022, 04:33 AM   #1
Seminutin
 
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Default KA24E MAF Sensor Failed?

Hi all, never had much need to participate in forum activity until now but here we go!

I've been having much trouble with my '94 d21 ka24e in regard to the maf sensor. The behaviour is this - when I plug in the maf sensor the engine idle goes to crap, but with the maf disconnected the idle is near perfect aside from being stuck in limp-mode. Given this behaviour, I assumed the sensor had failed and I purchased another cheap one off eBay, which resulted in the same behaviour. I figured it fair the cheap one didn't work, so I found another OEM one off a wrecker (who tested the sensor was working prior to sending), and found the behaviour was the same again!

At which point I was curious if the source of the problem was in the wiring, so I took apart the plug and tested for power, ground and the 'reading' prong. Then having identified which wires were which, I stuck a paperclip I bent up in the back of the plug to see the voltage on the 'reading' prong while the engine was idling. As one would assume, when manually revving the engine, one should see the voltage fluctuate on the millimetre - but it doesn't. The voltage reads around really high at about 13V regardless of the engine revvs. The power supply is consistent at about 14V so I know the wires aren't mixed up. My thoughts are that this is caused by one of two things - either there is a problem with the wiring/electrical/computer OR it's something else that I'm entirely unaware of.

Does anyone have any ideas of what could be causing this? Thanks.
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Old 07-01-2022, 12:46 AM   #2
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Try running an extra ground wire. Sometimes this is an issue. Hope it helps. If not I would check the wiring all the way to the ecu.
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Old 07-01-2022, 10:35 AM   #3
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Agreed. Somewhere you seem to have a wiring issue.

As you guessed, the ECU is in closed-loop when the MAF is unplugged.

If you do not have the 1994 Service Manual, here are the pages from the EC section:

Here is how it works:



Here is where it describes failsafe mode when the ECU detects a malfunction:



And here is the main page on how to diagnose problems with the MAF sensor:

Attached Images
File Type: jpg 1994-ec-152.jpg (93.9 KB, 13 views)
File Type: jpg 1994-ec-165.jpg (79.9 KB, 12 views)
File Type: jpg 1994-ec-229.jpg (66.6 KB, 12 views)
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Old 07-01-2022, 01:45 PM   #4
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I think you may have a vacuum issue as well. The MAF (manifold air flow) sensor measures the air flow going to the engine. If you have a vacuum leak (which 90% of the vacuum lines are monitored by this MAF system) you will have an idle issue. I ran into this when I installed the 240 intake on my 96. I had 2 cracked vacuum hoses and the intake wasn't sealed correctly.
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Old 07-01-2022, 03:14 PM   #5
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Quote:
Originally Posted by dvdswan View Post
I think you may have a vacuum issue as well. The MAF (manifold air flow) sensor measures the air flow going to the engine. If you have a vacuum leak (which 90% of the vacuum lines are monitored by this MAF system) you will have an idle issue. I ran into this when I installed the 240 intake on my 96. I had 2 cracked vacuum hoses and the intake wasn't sealed correctly.
Good point.

Too many people want to throw a new sensor at the problem, and they are baffled when the new sensor doesn't solve the problem.

All the ECU is saying is that the value it received from the MAF was not within the acceptable values.
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