EFIDynoTuning Forum

T4M0 95 Mustang GT

Is this normal J3 "goop" or am I looking at corrosion?

I'm reading 0v from the MAF even when putting 12v through a test light on the MAF return line. Confirmed continuity through the MAF return line to pin 9 on the EEC connector, lights up my test light nice and bright.

Since the wiring seems to be good, MAF seems to put out correct voltage, I'm strongly suspecting a bad PCM. No obviously blown caps, but one looks suspicious, large one closest to main connector opposite the j3.

Also, I am getting 0.9-1.1v on my TOT (73 degrees C), is that normal for a manual transmission? I.e. bias voltage? ECT and IAT are reading around 2 degrees C.

you probably burnt it up giving it 12 volts

the maf feeds 5 volts NEGATIVE not positive

tot doeant matter

did you enable datalogging in the tune before writing it?

That cap in the second picture looks like it is bulging at the bottom.

No quarterhorse installed, this is a vehicle meant to be a flip, but may play around with tuning it before selling it. Had what I thought was a wiring issue hence going this testing on MAF wiring. Fixed (almost) all of the mechanical issues first, now tackling this lack of MAF signal.

Feeding voltage through a test light is generally very safe as it innately limits current, seems unlikely I burnt anything up. MAF read 0v long before I screwed with anything. That being said, did not know that MAF would return a negative voltage.

I trust you, but I swear I read positive voltage on my DVOM from MAF return wire compared to negative battery terminal, but I wasn't looking for it. Will check again tomorrow.

Agree that cap looks like it's bulging at the bottom, will probably throw in another PCM ASAP and see how it behaves. Kind of expensive unless I can find one in a junkyard locally.

decipha wrote: ↑2023 Mar 08, 22:46the maf feeds 5 volts NEGATIVE not positive

This is going to be bothering me all day until I can look at the car. You're saying that pin 50, MAF 5V+ is actually -5v, so the PCM is expecting a range of approximately (-0.1v)-(-4.6v) on pin 9 as opposed to (+0.1v)-(+4.6v), but other sensors use a +5v ref (pin 26)?

Nevermind, I just read the MAF 101 page. http://efidynotuning.com/maf101.htm

Still going to have to try to wrap my head around that, but that's definitely making more sense now.

Regardless, sounds like I've got a bad cap that is causing bad readings. Will either order new caps or a used EEC, probably just the EEC for the sake of getting this car done and running properly as quickly as possible.