MAF issues - any ideas?
Thread Starter
Pro
Joined: Feb 2010
Posts: 677
Likes: 3
From: Metairie LA
MAF issues - any ideas?--UPDATE--FIXED--
86 4+3.
On my third MAF (reman Bosch from O'reilly). Getting code 33 after a short drive hot and cold. Busted out the FSM and did the diagnostic - points to bad MAF - again. I just replaced the MAF within 30 mins - both doing the same thing.
It says that it will throw a code 33 if the ECM sees 2.2 volts and the RPMs are under 2000. Back probed the ECM to monitor the voltage while driving. Key in run voltage goes to 5 volts (burn off signal?) then settles to 0.1 volt. Start car and idles at .40 volts. Start driving and it stays under 2.2 volts until after 2000 RPM (as it is supposed to) then suddenly it will spike and go over 2.2 volts (2.3 to 2.5) before it reaches 2000 RPM. Car starts running like crap and Check Engine Light comes on. Pull codes and it is 33 again.
Clear codes and repeat.
Is this just a case of getting bad parts?
Any other thoughts?
On my third MAF (reman Bosch from O'reilly). Getting code 33 after a short drive hot and cold. Busted out the FSM and did the diagnostic - points to bad MAF - again. I just replaced the MAF within 30 mins - both doing the same thing.
It says that it will throw a code 33 if the ECM sees 2.2 volts and the RPMs are under 2000. Back probed the ECM to monitor the voltage while driving. Key in run voltage goes to 5 volts (burn off signal?) then settles to 0.1 volt. Start car and idles at .40 volts. Start driving and it stays under 2.2 volts until after 2000 RPM (as it is supposed to) then suddenly it will spike and go over 2.2 volts (2.3 to 2.5) before it reaches 2000 RPM. Car starts running like crap and Check Engine Light comes on. Pull codes and it is 33 again.
Clear codes and repeat.
Is this just a case of getting bad parts?
Any other thoughts?
Last edited by cgantner5150; Jun 2, 2010 at 07:09 PM.
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
replace both relays, inspect the harness and clean the connections. The 5 volts you saw is the burn off function at work. Tap on the MAF sensor with a screwdriver handle while the car is running to see if it will replicate the voltage spike you were seeing.
The car should throw MAF voltage too high or too low if there is a significant voltage issue.
Team Owner
Joined: Sep 2001
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Replace the relays every time you change the MAF, as a rule.
But you might be gettin crap parts or there is a wiring issue somewhere, you'll have to trace all the MAF wiring.
But you might be gettin crap parts or there is a wiring issue somewhere, you'll have to trace all the MAF wiring.
Thread Starter
Pro
Joined: Feb 2010
Posts: 677
Likes: 3
From: Metairie LA
I replaced the relays the first time I replaced the MAF in March. Cleaned the connectors but didn't think about tapping on anything during my tests. Will try that when I get home. Strangely the spike seems to happen when exiting a left hand turn (has to be a wiring problem). Also need to check my ground again on drivers side bell housing.
Thanks everybody. Will let you know.
Thanks everybody. Will let you know.
Team Owner
Joined: Sep 2003
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From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
A known problem with the early C4's is the wiring insulation WILL shrink back at the connector end. This exposes the copper and makes for some interesting problems including fires!
Remember to inspect every connector in the engine compartment. Should you find and exposed copper, first disconnect the battery, then replace the insulation with tape or heat shrink tubing.
This is not something that can be accomplished when you have time. It should be done now!
Burning Brakes
Joined: Mar 2010
Posts: 1,151
Likes: 0
A known problem with the early C4's is the wiring insulation WILL shrink back at the connector end. This exposes the copper and makes for some interesting problems including fires!
Remember to inspect every connector in the engine compartment. Should you find and exposed copper, first disconnect the battery, then replace the insulation with tape or heat shrink tubing.
I was having the same issues last summer, found an exposed wire at the connector end, repaired with tape and haven't had a problem (with code 33
since.
Remember to inspect every connector in the engine compartment. Should you find and exposed copper, first disconnect the battery, then replace the insulation with tape or heat shrink tubing.
I was having the same issues last summer, found an exposed wire at the connector end, repaired with tape and haven't had a problem (with code 33
since.
Thread Starter
Pro
Joined: Feb 2010
Posts: 677
Likes: 3
From: Metairie LA
Thanks for the heads up on the wiring. The car is not on the street yet (just in the neighborhood). I have fixed numerous wiring probs so far (been a lot- even had part of the harness wrapped up in the steering shaft and all had to be spliced back together). The only shrunken insulation I have found so far are on the fuel pump and OD relays - already shrunk wrapped.
I work with low voltage as my profession - chasing wires su**s, but little nicks and voltage bleedover cause all sorts of interesting probs.
Thanks again for the suggestions.
I work with low voltage as my profession - chasing wires su**s, but little nicks and voltage bleedover cause all sorts of interesting probs.
Thanks again for the suggestions.
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Thread Starter
Pro
Joined: Feb 2010
Posts: 677
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From: Metairie LA
Alright - I followed all suggestions and ran through all the wiring (again and again) found one wire of the MAF power relay was not setting all the way in the connector, but that did not change anything.
I exchanged the MAF again - did not fix.
I broke out the FSM again and went through the tests again - no go.
Tried looking at this from a different angle and noticed that the FSM states that if the ECM sees 2.2 volts and it is not at 1/4 throttle it will give code 33. Checked TPS - at idle 0.54v, at full throttle 3.01v. That didn't seem correct. Checked the connections at the TPS - all good, but the resistance across the terminals did not seem right (resistance was not equal from top termial to middle and middle to lower and they did not add up to the reading from top to bottom). Getting 5v from the ECM with the connector disconnected.
Replaced TPS and drove around the neighborhood a bunch - no codes. And she seems to be a lot more responsive. Now reads 4.2v at WOT.
Thanks everybody - again.
I exchanged the MAF again - did not fix.
I broke out the FSM again and went through the tests again - no go.
Tried looking at this from a different angle and noticed that the FSM states that if the ECM sees 2.2 volts and it is not at 1/4 throttle it will give code 33. Checked TPS - at idle 0.54v, at full throttle 3.01v. That didn't seem correct. Checked the connections at the TPS - all good, but the resistance across the terminals did not seem right (resistance was not equal from top termial to middle and middle to lower and they did not add up to the reading from top to bottom). Getting 5v from the ECM with the connector disconnected.
Replaced TPS and drove around the neighborhood a bunch - no codes. And she seems to be a lot more responsive. Now reads 4.2v at WOT.
Thanks everybody - again.
