1986 Code #34

[Ron Earl]

Two days ago after finally finishing the installation of a polyurethane suspension bushing kit I took my 1986 coupe to Derhams Frame and Axel (Newburgh NY) for a four wheel alignment. They did an excelent job, while I waited and watched. It took just over an hour and only cost $86.00 including tax I would highly recommend them. Thats the good news.

The bad news is that when I started the car that morning in my garage I went back inside the house for a minute while it warmed up, when I returned the car had stalled for no aparent reason. I chalked it up to condensation in the gas and proceded to the gas station to fill the tank like the service manual recommends prior to an alignment I also dumped a bottle of dri-gas in the tank just in case.

When I got to Derhams I parked the car in the lot and went inside. About ten minutes later the mechanic got in the car to pull it inside and it would not start. After five or six attempts it finally did start, a little rough at first and then it was fine. He performed the alignment and test drove it then returned it to me, which is when I noticed I had a "Service Engine Soon" light.

It ran fine for me the rest of the day. The next morning I performed the Diagnostic procedure IAW the service Manual. The code was 34 (MAF Sensor signal voltage low). I cleared the code disconnected the MAF Sensor and ran the engine until the light illuminated again this time it was a 33 (MAF Sensor voltage high) The fault isolation procedure says to change the MAF Sensor.

This morning while still trying to come to terms with spending $300.00 on a MAF sensor I decided to take a closer look. I probed the connector and observed that when the malfunction occured the signal at pin C of the MAF sensor would go to zero and the car would immediately stall. I then wondered what was hapening to the 12 VDC power on pin E of the sensor. To my surprise it too would go to zero and the car would immediately stall. What is interesting is that with the car still in this failed condition I simply unplugged the MAP sensor from the connector and the voltage returned to 13.5 volts.

If anyone can shed some light on this for me I would appreciate it. Do I actually have a bad MAF sensor?

Thank's
Ron

[Joe L.]

Re: 1986 Code #34

Ron-----

Unfortunately, I kind of expect that the MAF sensor is the problem, although it is curious that the problem began almost coincidently with the front end alignment. It may be that the sensor was "near death" and it somehow got "jostled" during the alignment which "finished it off". The sensor, GM #14094712, aka Delco #213-163, carries a GM list price of $720. So, if you can get one for about $300, that's got to be about "rock bottom".

One thing that you might try first, though, is to replace the MAF relay. This would be a good idea even if you were going to replace the sensor, anyway. It's GM #10094701, aka Delco #212-305. It has a GM list price of $21.71 so it's not an expensive piece.

[Joe L.]

Addendum

Ron-----

It is possible to save some money on the sensor if you're willing to go some way besides new GM/Delco. Delco offers a rebuilt sensor under GM #19112533, aka Delco #213-3418. These can be bought for about $175.

Also, sensors are available as manufactured by Standard Motor Products. I believe that this is a brand new sensor. SMP part number is MF 4712 and these sell for about $160.

I would normally go new GM/Delco, but I do recognize that the above parts might be just as good. They certainly do represent a big savings over new GM/Delco.

[Jim T.]

Re: 1986 Code #34

Have not consulted my 85's service manual on the MAF, however I believe that the sensor wire in the MAF can become contaminated and there is a cleaner that can be sprayed on it. Did you see anything in your 86's service manual on this procedure?

[Wayne W.]

Re: 1986 Code #34

I would wait and see if it does this again, and take measurements with the engine running. It will set that code some times for other causes. As Joe says, it is good to change to the newer relays. There were problems with the early design.

[Ron Earl]

Re: 1986 Code #34

A note of closure for anyone who may be interested. I had some time on Saturday and decided to do a bench check of the MAF relays prior to replacing the MAF sensor as instructed by the manual. As it turns out I had a high resistance (Approx. 45 ohms) across the normally open contacts and slightly less than that across the normally closed contacts. I opened the relay filed the contacts cleaned it with some contact cleaner reassembled and now it works fine. I will replace both relays this week for good measure. Thanks for all the good advice.

Ron