Code 33, MAF or burnoff relay problem?

[Peer81]

Hello everybody,

My friends '86 convertible gives a code 34.
Strange thing is, while cold it starts rev's up to around 1000 rpm then starts running rough drops rpm and dies. This all within 1 minute. But if you keep up the rpm with your feet the engine will warm up. Then the engine will run just fine. With the next cold start same problem...
So we looked into the code 34. When unplugging the MAF and cleared the codes the new code is a code 33. So the ECM should be fine and the MAF could be bad. The GM manual shows a diagram with the MAF wiring. While checking the dark green wire from the ECM it gives 5 volts while running, so that is oke. The purple wire from the power relay also gives the 14 volts like it should.

Now the question, how do I know or how can I check if the burn off relay is causing the problem or the MAF is really bad. A scanning tool is on the way so we can check if the MAF readings are in check. But can I also check the MAF for a broken wire by simply checking for resistance on the wire terminals?
In another topic I found there is a little mistake in the GM manual as the power and burnoff relays are switched, is this true? I know they're behind the battery against the firewall.

Ofcourse it's always better to first change the (cheaper) relays and after that the MAF if the problem is still there, or is everthing so dependent on each other that with a broken MAF the relays can also be damaged?

Last, if the MAF is defect. He is looking into new or modified ones, some pro's or con's? There are modified MAF's without the screens and cooling fin's are they worth the extra money or will removing the screen on a new one give the same effect? (as he already has a 52mm BBK throttle body and a KN airfilter?)

Greetings Peter

 

[muddywaters]

Hi Peter, I got the same code on my 88 after I put a K&N filter in it. I looked into the MAF and the burn off tang was coated with the oil from the filter and I didn't use much oil. I figured that caused the death of the relay which was $19 American to replace.

 

[jazfe]

code 33

Until you have a Factory Service Manual it's all guess work.
I have the manual and had a troublesome code 33. My MAF and burnoff relays checked ok and until I changed the throttle position switch the code would not go away. If you have a multimeter, check the resistance of the tps thru the full range of motion to be sure if it has no dead spots.

 

[Peer81]

Thanks for the replies.

The GM manual is a factory service manual for a '86 Corvette so that isn't the problem. But when you look at the code 34 page it simply says if you get a code 33 after disconnect the MAF sensor then you need to replace the MAF sensor and that is where I go ??? Of course I think more people had this problem so also more possibilities to get this right. We still need to take a look at the MAF sensors "inside" and see if something is damaged or covered in KN oil. We will also check the TPS sensor, if I recall we changed the thing about 5 years ago and also reset it to the right 0.56V or something like that but it's simple to recheck the full range so we will also do that

Greetings Peter

 

[boomdriver]

Thanks for the replies.

The GM manual is a factory service manual for a '86 Corvette so that isn't the problem. But when you look at the code 34 page it simply says if you get a code 33 after disconnect the MAF sensor then you need to replace the MAF sensor and that is where I go ??? Of course I think more people had this problem so also more possibilities to get this right. We still need to take a look at the MAF sensors "inside" and see if something is damaged or covered in KN oil. We will also check the TPS sensor, if I recall we changed the thing about 5 years ago and also reset it to the right 0.56V or something like that but it's simple to recheck the full range so we will also do that

Greetings Peter

With the MAF its really a process of elimination. This is the one area where the FSM gets vague....and a scanner is the ONLY way to really see whats going on.
Heres the deal...
you can spend $250 on a scanner that will show you exactly what the MAF is doing and tell you if its a relay or the sensor itself.
Chances are that it IS only a relay or plug/wire. The power/burn-off are the same relay. Power is 5 wire and burn-off is 4 wire plug. Clear the codes, swap relays and see if you get the same code....if you DO< then you may be looking at a dirty MAF burn-off wire/tang that can be cleaned with a Q-tip and some alcohol or buy MAF spray cleaner.

Oil from air filters screws up more MAFs than hammers...

IF cleaning fails to resolve the code problem, and the scanned is still indicating a real MAF malfunction, then its time to look at new sensors. They do NOT fail as often as people think they do. Most of the time its a bad relay, dirty plug, broken wire in the plug, or dirty MAF.

Performance MAFs are good for hi-performance tuning with an adjustable range....thats not nearly as beneficial as a good "tune" on a prom. A hi-per MAF will be $350 to $600 and won;t do a semi-stock engine that much good. After headers, intake work, injectors, THEN a big MAF would be a nice addition if you were running it on the track. Until then, its not good money spent...there are other things that will yeild better results.

If you do NOT buy a scanner and want to gamble a little, I'd trade the relays, see what that does, gently clean the MAF tang, and clean the plugs...If the relay swap does move from a 33 to a 36 or 34 code...buy relays and try again.

The plug to the MAF is good for breaking the wire off inside the insulation where it can;t be seen. I'm on my 3rd plug on this particular car...same MAF. Use a pick to separate the wires from each other at the plug. They sometimes get crushed against each other and can short. It only takes a single strand of wire to cause a weird short.

FYI....
if your display is showing the SES lite while the engine is running or driving the ECM has shifted to open loop operation and is NOT running as efficiently as it should. OL is basically cold operation, utilizing the CAL-PAK chip in the ECM to assign values to sensor inputs that are missing. In otherwords...the ECM is giving it a 'best guess' as to operating conditions because its shifted out of the normal running mode due to faulty sensor input. That is what happens when the engine burps, coughs and runs rough for a few seconds, then the SES lite comes on and the engine seems to smooth out...the problem still exist, the ECM just gave up and went to its program files to run the engine until good sensor inputs are restored.

The thing about buying a scanner is that this will NOT be the last time its used. As upgrades are made, the scanner can be used to document the engines health and behaviors to these upgrades and you then have a record that can be used to tune the engine and get ALL of whats there...everytime you change or upgrade the tune needs to change as well. So many upgrades get generic performance because other things were not adjusted to match...so the end result is somewhat less than it could be. A scanner lets you see what you;ve got and you can then compare that to what you should have......

If you have done other engine enhancements, you can de-screen and even cut out the heat sinks...but there is risk involved. You can break the filement wire and its toast. Vibrate the wire apart...junk. slip with the dremmel tool...yep. Flying debris while cutting the heat sinks is dangerous. Easy to get debris in the electronics or damage the wire.

Even then with a successful sink/screen delete you are only adding potential airflow thru the MAF that you won't need unless the engine has been enhanced in other ways and you;re running it WFO a lot. The delete is a judgement call. IMO not worth the risk for semi-stock. I know guys running stroked engines with the stock TB and MAF....and they do fine.