View Full Version : 94 GT: Anyone have any suggestions for these codes thrown?

07-20-2014, 09:09 PM
OK, so Rick (the Prez) congratulated me at Mustang Mania this year on making it to the event without any issues. Well, he jinxed me. When I went to leave the event, as soon as I started the car it began sputtering backfiring through the plenum, stalling, generally refusing to rev when given throttle and generally giving me mega-cr@p.

I coaxed it home and read the codes: 511 twice and 157 twice. Also, the Anti-Lock light came on a couple of times. Here's what my manual says:

157: Mass Air Flow sensor fault, low voltage. Test Condition: Continuous memory.

511: Read Only Memory (ROM) test failure. Test Condition: Key On Engine Off (KOEO).

My ECM has a Moates chip on it.

OK, how bad is it? New MAF (just replaced in the spring)? New Moates chip (just reflashed in the Spring)? Just a loose chip? New ECM? Grounding issue? All ideas welcome.

07-20-2014, 10:03 PM
OK, apparently the 511 code can be ignored as it will occur and is normal when a chip is installed and it will not cause a CEL. This leaves the 157 code.

Sounds like nxt step is clean MAF connector and see if it goes away, if it doesn't check voltages on the MAF plug?

07-24-2014, 11:22 PM
Spent the last 2 nights cleaning the MAF sensor wires and cleaning the connectors. The current SCT Big Air MAF is actually the 4th MAF this car has had, counting the stock unit. About 17 years ago the stock one was replaced with a Pro-M unit and all of the after-market MAFs seem to have 6 pin connectors, though the original 94-95 MAFs were 4 pin. I think the other 2 pins are for an IAT built into the MAF on later models. Anyway, when the Pro-M went in, a small adapter harness from 4 to 6 pin went in with it.

When the 30# injectors went in the Pro-M got replaced by a (crappy) Summit MAF which came with a lot of headaches, so it eventually got replaced by the current SCT unit. Now, 17 years later I had pretty much forgotten about the short adapter harness.

Turns out where that adapter harness plugged into the main harness, the plug was not in all the way and the plastic clip to hold it in place was not latched. From what I could tell it was up about 3/16" from fully connected. Taking that apart I found some dirt in there - not a lot of dirt, but a small amount of fine dirt - and if dirt can get in moisture certainly can. Also one of the 4 pins looked a little corroded, but it was down inside the connector so it was hard to tell for sure.

Anyway, after burnishing all of the pins and receivers on all of the parts of the connectors and reinstalling the cleaned MAF over the past 2 nights, I took it for a ride tonight. It's not as hot as it was Sunday, but I drove for a solid hour without a single backfire, fart, buck, sputter, power loss or CEL. The A/F meter was registering pretty much as it always has. I'm very encouraged - it's not proven that the issue was what I found, but I'm hopeful and have my fingers crossed that I won't hear from this one again. For insurance I also put a zip-tie to hold the connector together between the main harness and the adapter harness.

07-25-2014, 06:35 AM
I'm pretty sure the 75mm in my car came from you and I don't remember any adapters??

07-25-2014, 08:24 AM
I'm pretty sure the 75mm in my car came from you and I don't remember any adapters??

Did you already have an after-market MAF in the car before the one I gave you? My original was definitely 4 pin, though I don't have it any more to prove it. It would also make sense because I have a separate IAT on the intake tube.