maf........ongoing problem?
06-02-2012, 09:06 PM
#1
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maf........ongoing problem?
This MAF is still giving me fits! 1985 Vette with 350 starts and idles rough....but does not give me a MAF 33 code! When MAF disconnected the car runs better....ECM taking over......and idle much smoother. Disconnecting the MAF throws a 33 code but unless I disconnect the MAF I never get a code..........is this MAF bad? This is a $150 part and I am hesitant to switch it out. Is a vacuum leak possible? No other codes are showing.
cmj
cmj
06-02-2012, 09:51 PM
#2
Burning Brakes
MAF isn't the problem. Something else is causing the problem. Trust me, I went through this.
What is the condition of the distributor? Does the problem get worse when it is humid or if the car is wet? I forget the name but check the wires at the back of the distributor. Check especially the condition of the seal where they go into the distributor. Sounds crazy but that reports info to the ECM....so when the MAF is disconnected the ECM isn't paying attention to what is going on there so it runs better.
Keep me posted.
What is the condition of the distributor? Does the problem get worse when it is humid or if the car is wet? I forget the name but check the wires at the back of the distributor. Check especially the condition of the seal where they go into the distributor. Sounds crazy but that reports info to the ECM....so when the MAF is disconnected the ECM isn't paying attention to what is going on there so it runs better.
Keep me posted.
06-02-2012, 10:02 PM
#3
You have many other things to cause rough idle...
to begin there are MAF relay(s) or a MAF module (different yrs)
IAC issues.
Stuck EGR or bad EGR.
major vac leak.
crappy injectors (original?) guarenteed to be partially responsible.
Harness connection, grounds for the harness, power source contacts.
When you d/c the MAF you're simply forcing open loop mode and the ECM will operate off the cal-pak and run the car. Its not going to pass emissions but it runs. The signal is the ck eng lite.
When the thing has the MAF plugged in and runs like crap thats because its getting bad data or the signal is corrupted. Even a dirty plug-in can cause this. If there is no MAF code then its a fair assumption that its NOT necessarily the MAF at fault. Thats why I list a few other things.. You get a 33 when d/c the maf because that IS now an issue not being in contact with the system thats looking for maf input.
Better find a FSM to assist you in diagnosing this. Thats only $100 (or less used) and will take you directly to the problem instead of guess work. No amount of educated guessing will ever equal a fact, and facts is what the FSM uses to trouble shoot every system on the car. What can be said about a book thats 3/4" thick and is ONLY the electrical drawings and test proceedures? The other book is twice that thick for general mechanical and tuning issues.
Somebody has a link to new copies and used can be found on FleaBay.
besides, its the law to have a FSM if you own a Corvette thats out of warranty.
to begin there are MAF relay(s) or a MAF module (different yrs)
IAC issues.
Stuck EGR or bad EGR.
major vac leak.
crappy injectors (original?) guarenteed to be partially responsible.
Harness connection, grounds for the harness, power source contacts.
When you d/c the MAF you're simply forcing open loop mode and the ECM will operate off the cal-pak and run the car. Its not going to pass emissions but it runs. The signal is the ck eng lite.
When the thing has the MAF plugged in and runs like crap thats because its getting bad data or the signal is corrupted. Even a dirty plug-in can cause this. If there is no MAF code then its a fair assumption that its NOT necessarily the MAF at fault. Thats why I list a few other things.. You get a 33 when d/c the maf because that IS now an issue not being in contact with the system thats looking for maf input.
Better find a FSM to assist you in diagnosing this. Thats only $100 (or less used) and will take you directly to the problem instead of guess work. No amount of educated guessing will ever equal a fact, and facts is what the FSM uses to trouble shoot every system on the car. What can be said about a book thats 3/4" thick and is ONLY the electrical drawings and test proceedures? The other book is twice that thick for general mechanical and tuning issues.
Somebody has a link to new copies and used can be found on FleaBay.
besides, its the law to have a FSM if you own a Corvette thats out of warranty.
06-03-2012, 06:37 AM
#4
Le Mans Master
Hooking up to a scanner would let you know if its the maf.. My scanner shows if the maf is working and how much air is being metered through it... A scanner would also show if the IAC is working and if its working properly...Find someone that can hook you to a scanner or pay for someone to scan it for you...WW
06-04-2012, 01:46 PM
#6
Le Mans Master
$150 for a MAF? Must be a rebuild! 85 Vins F5100001 - F5101340 were recalled for this issue. If you've got one of those VINS a Dealer should fix it. '86, had a MAF Power Relay issue covered by a separate Bulletin. If you own an early C4, you might want to look at the numerous Service Bulletins and Campaigns on these cars.