Red88Vert

I'm posting this thread in hopes of helping others track down and repair these codes in addition to the plethora of other guidance provided.
I am now a believer that much of the pain that we suffer related to these codes are related to using other than OEM parts. Many have suggested this, but I'm planting the flag.

My crazinest started with my 46k 88 Vert. Pre service manual, I changed TPS, IAC, TPS connector, MAF relays, and MAF trying to cure 34 and 33s with occaisional rough start. Post service manual, I ran the diagnostics but many hints pointed back to things I had already changed.

I then took the car to noted vette expert Ken Carrilo here in Phoenix. Ken used to own The Vette Shop, but now works from his home on referrals. Ken ended up changing the ECU, and having me install a PROM adapter in hopes of curing strange behavior in the stock prom. After running multiple SM trouble trees, rerunning MAF power and shared relay power circuits, he was able to get the car to only an occaisional 36. Ken said "take it and drive it a month or so, and see if the ECU sorts things out on its own". His scanner showed that everything was working the way it should (including the burnoff circuit) but the ECU was still throwing a code.

What about the ECU ground? Ran new ground inside the car. No change. So now, I have changed all the problem harness wires. Got to look someplace else.

I starting looking at the MAF and the relays as a source of issue. I was using Orielly Bosch rebuilds (7 to date) in hopes that I might get lucky. I tried a new Autozone Microtech. Now I had no 36, but I had a 33 again, and it was constant and ran like crap.

I located a new old stock MAF on fleabay and plunked down $238 for it. With the new GM Bosch MAF, my 36 came back after every 3 starts or so, but the car ran super. Getting close.

Now lets look at relays. Ken had pulled the aftermarket relays and put the original stock relays back in because they tested fine. I read where people had relays test fine, but not work. As my current code was a 36.....lets concentrate on that relay. I pulled the stock relay and put in one of the new Orielly relays. Now I get a 36 about every 5 starts. Getting close!

I noticed that the two Oreilly relays were the same part number but one was gray and the other was black. Hummm. I pulled the black burnoff and replaced it with the gray relay. Still have the stock relay for power. 2 starts....ok, 4 starts....ok, 6 starts....ok, 10 starts OK! It's fixed!

I'm now convinced that the ECU is really picky about total resistence of sensors. I know that the resistor pack side of the prom figures into the equation. My advice to anyone dealing with this headache, is to buy OEM parts first, or be prepared to swap out aftermarket until something (maybe) works! While it's painful to think that I could have saved myself some $800 in parts by concentrating on the MAF relays, I know that the ecu and the logic side of the prom was bad too. I also have the satisfaction of knowing all of my "future" trouble spots have been sorted with new parts (and MAF is OEM new!)

Sorry for the long post, but hope that it helps others! Now I can drive the dang thing!
-Jeff

84wuzmy1st

FletchUSMC

I agree that these cars are very picky when it comes to the MAF and the relays. For some reason not all replacement units work very well. I had similar problems and finally the third MAF worked for me!

http://forums.corvetteforum.com/c4-t...ng-thread.html

Ziggy91

WOLF ECHO

Ugh! This all sounds sooooo familiar!

Bought an '89 a few months ago with only 18K original miles. It has the same "cold start" issue as others here have complained about. Read many threads in C4 Tech that suggested some actions to take to address it. Here's where I stand:

- replaced the stock injectors with Delphi 22# injectors from "FIC" and had a local Chevy dealership install them. Injectors didn't help the "cold start" issue, but the engine runs much stronger now. Definitely an improvement in performance.

- replaced the stock MAF relays with a set purchased through Chevy (same part number for both, both are black, made in China ). The new relays did nothing.

- replaced the stock Bosch MAF sensor with a replacement Bosch MAF sensor purchased from AutoZone. Since the new MAF sensor was installed, the ECM is now spitting out a 36 trouble code, and the "cold start" issue still exists. Can't put the original back in because I exchanged it to save $50 on the core charge.



I'm intrigued by Red88Vert's observation of the different-colored relays (gray versus black). The pair I installed were both black. The replaced pair were both black. How do I tell the parts guy I want a gray one instead of a black one!?

Red88Vert

My rough running cold start was 100% ECU. Once I changed out the ECU and added a performance chip adapter, no more cold start. With the old ECU, you could tap on the case while plugged into a scanner, and it would throw a stream of giberish.

As for the relays.....I found that the OEM in the power slot and an aftermarket in the burnoff slot was the right mix. I actually had two OEM china GM relays in route when I stumbled on this combo. I'm convinced that resistence is the key to making everything work trouble free and thats hard to do when all the OEM parts are not available.

You might just try to change the burnoff relay with a number of other types. But before that, I would do the ECU ($130) and a Hypertech knock-off chip from Summit. Ken told me that EVERY ECU with that number went bad. Every one.

Also, is the Bosch MAF "new" or rebuild? If it was less than $300 it was a rebuild. They are all worthless (I had 8).

WOLF ECHO

Where did you get your new ECU and performance chip? And where did you buy your "aftermarket" MAF relays?

My MAF sensor is rebuilt.

This is great information, "Red88Vert". Thanks!

Red88Vert

I went through 8 rebuilt Bosches. Look up a company name Tomco. They have 16 new Bosch MAFs for under $400 each. The one I picked up was from an old parts house (ebay $238) so they do show up there too.

The relays I bought were O'reilly cheapies, but remember one didn't work well. People report mixed results with relays....cheap...expensive...aftermarke t....OEM. No real rhyme or reason.

I feel your pain. I was ready to find a new engine at one point I was so tired of it!

Wirelessrat

Guys I am having a terrible problem (somewhat similar) with my 89 F body. My maf power and burn-off are the same 14089936. I cannot find the correct part for the burn-off as I think the 14089936 is correct for power. What are the correct GM part numbers for these? Guy at autozone thought was crazy when I swapped out the ECM after one week, do I have this story to tell him next time he looks at me funny. lol Thanks in advance.

Red88Vert

14089936 is an ACDelco number. Prob fits a billion GMs. If Autozone workers used more of their own parts, they would understand. They shop at NAPA.

Here it is:

http://www.rockauto.com/catalog/more...027&cc=1041231

SPD KILS

I just had the same problem with my 86. I also used the gray relays from Orielly but I had to order two pigtails and redo the end of the wire harness's behind the battery to the MAF relays. I also had to move some wires around inside the new pigtails to match the old plugs. No more codes so far!

Wirelessrat

I think the 14103304 relay is for burn-off and the maf power is 14089936, BUT does anyone know for sure? Maybe, I will have to call the dealer....

Cliff Harris

On my car these are the part numbers:

10094701 AC Delco 212-305 Relay, MAF burnoff
10067925 AC Delco 212-300 Relay, MAF power

I recall reading somewhere that this is an '86 only configuration and the two relays have the same part number in later cars.

WOLF ECHO

When I purchased both relays from a local dealer for my '89, the part numbers were the same.