gbody5

OK, so here's the story, I have been troubleshooting this problem for about a year now and I still have not figured it out. Many of you have helped (thanks!) and I thought I had it fixed two or three times but it just happened again.

I don't drive the car but about once or twice a month, and I get an intermittent error code for low voltage/high vacuum or high voltage/low vacuum on the MAF. Sometimes followed by a rich/lean condition O2 sensor error (this to be expected). I have replaced the MAF power and burn-off relays, and every other damn relay under the hood for that matter. Seemed to fix it for a few weeks, then as Emeril would say, "BAM"!

In May I replaced the MAF sensor with a remanufactured Bosch unit, car ran better than it had since I owned it, so I thought for sure that was it. Then last week, you guessed it, BAM! SES light, no throttle response, and the scenario starts all over again. It was during my lunch break so I parked the car and came out after work, started up fine, ran fine for about two miles, then BAM, SES light, etc, etc.

I get home, let it cool down (and myself), checked all my connections, made sure everything was tight, started the car, tapped on the MAF, no change in idle speed, go for a drive for about 45 minutes, everthing is fine, so now I'm just waiting for it to happen again.

One thing I find suspicious is that when I go to pull the error codes using the crude paperclip in the ALDL port approach, the ECM will not always go into diagnostic mode. I short the pins, turn on the key and it's just like I am going to start the car, no flashes, no fans running, nothing. I have to either remove and re-insert the clip or trun the key of an on several times before it will "catch" and begin the normal ECM cycle of 1-2, 1-2, 1-2, then display the appropriate codes.

I hate to think that I have a bad ECM, in that IT IS the intermittent problem, but at this point I would gladly replace it, if I knew for damn sure that it was the problem.

Any help is sincerely apprecitated.

The car has 51K miles, few mods listed below.

Thanks! :U

gbody5

Ok, forgot the mods in my signature.

K&N, TB bypass, 24 lb/hr injectors, open lid, low restriction mufflers, stock PROM.

Mark

Triple Black 88

I know how you feel. About 5 years ago I sold my 87 for this same problem. I never did find out what caused the "CODE 33"...still haunts me to this day. I replaced the whole circuit at the same time about 5 times, MAF, both relays, and ECM, but it eventually came back each time. I gave up.
The only thing that the one mechanic found is that the highest pully was rubbing the wire harness to the MAF. Although it didn't fix it, it's worth looking at, you never know. Good Luck!!!

Steve85

Check the MAF CONNECTOR.

The signal circuit should be 5 volts. (drk green wire into MAF). There is also a 12V feed to the MAF (blk/wht wire). If the connector is broken or corroded internally, the 12V feed could easily find its way over to the 5V signal circuit, hence "signal circuit out of range". Why intermittent, loose or corroded wires in a connector are subject to vibration and heat.

A connector is alot cheaper than an ECM, worth a shot.

Best of luck...

88-406

I feel your pain!

My 88 used to do this occasionally. My problem was traced back to the actual connector/pins of the harness were it plugs into the ECM. So in other words, when my ECM is stuffed under the dash, as it should be. A few of the pins will work/vibrate themselves loose enough to cause the intermittent connection.

You can test this scenario on your car by just dropping the ECM down from under the dash and then taking the car for a ride. If it screws up gently reposition the ECM and see if the problem ways away immediately

Best of Luck

KM

merrick

I agree it is probably the ECM. Check for voltage and ground at the MAF connector. Then disconnect the ECM and check the ohms on the wires to the MAF. If everything checks OK, then replace the ECM.

gbody5

Thanks for all your experiences and ideas, I will try to dig into the wiring today.

Let you know what I find.

Mark

gbody5

Well, I yanked and pulled on the wiring harness from everywhere I could reach without going under the car, all while I had the ECM in diagnostic mode, no luck. The ECM would go in and out of Diag mode whether I touched anything or not. I could just stand there and hear the relays click and the fan start and stop like a demon possesed, which at this point is not too far from the truth.

Tonight I pulled the ECM out from behind the dash, pulled both connectors off, checked for loose wires or corrosion, found nothing other than the ECM being a remanufactured unit from GM, everything looked like new. I did not take the cover off to check the EPROM, had to mow the yard before dark, anyway, I will do that tomorrow for the hell of it, but I'm guessing that the ECM is the problem.

So now I'm looking for the best price for a replacement unit and I assume thay are all remanufactured, also, anyone have the part number?

I show the original as 1227165, but when I searched for that part on gmpartsdirect.com. no such animal. I think they have re-numbered all the ECM's of that era, so any help with that and any suggestions on where to get one is appreciated.

Mark

:sleep:

88-406

Oh well at least you've narrowed it down some. MidAmerica and or Ecklers should have your ECM. I think they cost around $100 exchanged.

KM

Bob Mosaic

You can get an offshore reman for 80-90, but I am very weary of their uality. I would try Jeff Kopp for a AC-Delco ECM first. It shouldn't be too much more.

My old 88 had similar MAF issues. The last fix I did lasted until I sold the car (about 25k of no codes). I replaced the relay with a AC-Delco I had replaced numerous relays with offshore crap coming from Taiwan to India and they all would throw a code in due time.

Best of Luck,
Robert

Mike_88Z51

I had a very similar code 33 problem with my 88. As you noted, the original ECM is part #1227165. That ECM was prone to intermittant failure and was replaced by GM with part # 16198259. NAPA has the remanufactured GM originals for about $110. They are the same as what you get from the dealer except the NAPA ECMs come with a lifetime warranty as opposed to the 90 day warranty of GM. I replaced my ECM 4-1/2 years ago and have had no problems since. If I ever do, it's still under warranty.

gbody5

Hmm, Napa told me a 1 year warranty. CarQuest has the same part, same price, same warranty and they are just right down the street so I'll give them a shot.

Thanks to all for your help, we'll see what happens.

Mike_88Z51

NAPA probably changed their warranty since I bought mine. As I said it was 4 years ago. I still have the paperwork which says "lifetime warranty", but I bet that if I do have it replaced under warranty the next one will change to 1 year. GM only offers 90 days so it's still better than the dealer. If CarQuest has the same part for the same price, then I'd do like you are doing and get it there. As far as I know they are all GM remanufactured units. Let us know if it solves the problem.

gbody5

Success! Happy Independence Day to me! After replacing the ECM, everything is good again. No more intermittent MAF error codes. In addition, this also fixed my inconsistent idle speed, after which I had cleaned and re-set my original IAC, then replaced my IAC. These improved the situation, but did not do away with the idle problem altogether until replacing the ECM. Also, my INSTANT/AVERAGE MPG display would intermittently drop to zero, that affecting my RANGE display as well, now they work perfectly again. Finally, I set the ALDL to diagnostic mode, turned on the key and voila, instantly entered diag mode and began flashing 12’s just like it should.

Just goes to show that troubleshooting based upon what a computer is telling you is only as good as the data is spits out. When the processor you are relying on to help you has faults, you can chase your tail for a long time. Granted, a scan tool would have probably pointed me in the direction of the ECM long ago, but hey, since it was not my daily driver car I was really in no big hurry. My new Turbolink software version 3.0 that I use for my GN is coming out with ‘vehicle packs’, so I will be able to use it on all my cars soon.

Thanks again to all those who helped me figure this out, I really appreciate it and this forum is #1!

Mark
:cheers: :cheers: :cheers:

Triple Black 88

CONGRATULATIONS MARK!!! ;)
That Code 33 is a tough one to crack. It's a good feeling isn't it. I'll bet the Vett gets out more than twice this month!
:flag


[Modified by Triple Black 88, 8:02 PM 7/4/2002]

gbody5

>>I'll bet the Vett gets out more than twice this month!

Yes indeed! :seeya