I Might Be Bringing the 'Murlequin to Detroit Oppo-Meet

"Urambo Tauro" (urambotauro)
05/16/2018 at 22:30 • Filed to: wrenching, oppo-meet, oppomeet

...unless I can fix the Mustang within the next couple of days.

!!! UNKNOWN CONTENT TYPE !!!

The ’95 GT (stock 302) in my avatar has been pretty reliable, for the most part. I hardly ever see the check engine lamp, except for when I first turn the key forward (lamp check). Oh, and today when I went looking for stored codes and counted the flashes.

Why was I looking for codes? Well, on my way home today, my car developed a nasty tendency to stall when I would slow to stop. It’s got a T5 manual, but it didn’t matter whether I was coasting in neutral, or holding the clutch disengaged. Without constant pressure on the accelerator, it would try to stall. I had to restart the car nearly a dozen times (good thing I have a good battery & charging system). Once restarted, the engine would idle roughly, around the 400RPM range. It drove fine as long as there was pressure on the accelerator, but as soon as I’d lift my foot, the revs would rapidly start falling back down.

I had a hunch that there might be a problem with the IAC valve, so I thought I might try cleaning it once I got home. I stopped by the parts store for an IAC gasket, but they didn’t have one in stock. Before I got home, I figured I’d try disconnecting the IAC plug, but the problem persisted the rest of the way.

Once I got home and changed my clothes, I went back out to the car, started it, plugged the IAC back in and heard the engine speed increase. But before going any further, I decided to check for stored codes. This is what I found:

KOEO- 113, 157, 212
KOER- 116

113 - ACT Sensor Circuit Above Maximum Voltage of 4.6 volts (O), ACT circuit has intermittently failed above the maximum of 4.6 volts (CM)

116 - ECT out of self test range 0.3 to 3.7 volts

157 - MAF sensor went below 0.4 volts during the last 80 warm-up cycles

212 - Loss of IDM (Ignition Diagnostic Monitor) input to EEC or SPOUT circuit grounded

Now I could try chasing these down one-at-a-time, but I’m scratching my head over whether they might have something in common? I’ve got Ford’s regular Service Manual, and the EVTM, but unfortunately not the “Powertrain Control/Emissions Diagnosis” volume. As near as I can tell, the only thing that the IAT, ECT, MAF, SPOUT, and IDM all have in common seems to be the PCM. As you can imagine, that’s a conclusion that I’m hesitant to jump to...

All major ground points are clean and tight. I’m reading less than 1 ohm between the battery, engine, chassis, & PCM grounds. Battery passed a recent load test and its voltage is currently 12.5V. With the engine running, the charging system brings it up to 14.2V. And I put a trickle charger on the battery to help make up for all the extra cranking that the starter had to do today.

I tested the ECT sensor about a week ago (good), but I don’t have testing procedures for the other sensors. FWIW, all sensors appear to be intact, and the wiring looks good too (as far as I can see them before they disappear into the harness, that is).

Any ideas?

DISCUSSION (19)

shop-teacher > Urambo Tauro
05/16/2018 at 23:22

Honestly, I got nothin ... but good luck!

Is it weird that if I was able to get all the way out there (not happening), that I’d more excited to see the ‘Murlequin?

Urambo Tauro > shop-teacher
05/16/2018 at 23:44

Yeah, but I can see where you’re coming from on that though. I’ve definitely shared more wrenchventure posts here on getting that thing truck running good.

What I really wanted to bring though, was the Saab. Too much work still to do on it, though.

TheD0k_2many toys 2little time > Urambo Tauro
05/17/2018 at 01:20

Unplug battery for hour then reconnect?

atfsgeoff > Urambo Tauro
05/17/2018 at 01:45

No comment on the ‘Stang problems, but..

The ‘Murlequin is awesome.

Captain of the Enterprise > Urambo Tauro
05/17/2018 at 05:11

We had a similar problem with stalling and trouble starting on my Dads 95 F150 5.8L, we tried fixing a lot of smaller things but nothing fixed it. Eventually we took it to a shop and they couldn’t find anything wrong with it. We ended up selling it and the next owner said he had to replace the computer in it.

shop-teacher > Urambo Tauro
05/17/2018 at 07:09

Yep, it’s just got more of a story to it.

It would’ve been really cool to bring the Saab, but no surprise it’s not ready yet.

Urambo Tauro > TheD0k_2many toys 2little time
05/17/2018 at 08:40

Might try that later, but I’ve always hated turn-it-off-and-back-on-again “fixes”. They may be quick and easy, but they give me no confidence that it’s going to stay fixed.

Urambo Tauro > Captain of the Enterprise
05/17/2018 at 08:42

Interesting. Still a last resort, but if it comes to that, I will.

MasterMario - Keeper of the V8s > Urambo Tauro
05/17/2018 at 09:40

Not sure if Ford had an issue with the PCM on this generation of vehicles but I had my ‘93 F150 die on me, we had just replaced the plugs, wires, distributor, etc a few days before. It took me a couple hours to start questioning the PCM, I ordered a replacement swapped them out and it fired right up.

MontegoMan562 is a Capri RS Owner > Urambo Tauro
05/17/2018 at 12:00

Drive the reliable one. If you take the Mustang and have trouble you can come down to my place, which isn’t far from the venue and we can work on that and the Capri and have a broken down 5.0 party.

Urambo Tauro > MasterMario - Keeper of the V8s
05/17/2018 at 12:02

Every once in a while, I see Foxbody owners on the forums reporting having to change their PCM. I don’t see a lot of SN95 owners having to do that, but to be fair most SN95 owners have Modular engines and OBDII. 1994-1995 was a unique time for Mustangs...

TheD0k_2many toys 2little time > Urambo Tauro
05/17/2018 at 21:13

True haha. But im a person who drives a car around that always has a check engine light on so take my advice with a grain of salt

Urambo Tauro > TheD0k_2many toys 2little time
05/17/2018 at 21:25

Well I did end up disconnecting the battery anyway, just so that I could unplug the PCM and poke the harness pins with my multimeter. Haven’t put it back together yet though, as I’m in the middle of testing a few things.

TheD0k_2many toys 2little time > Urambo Tauro
05/17/2018 at 23:59

so if nothing works its time for this:

https://lmr.com/item/M9000PMCM/ford-performance-coyote-power-module-m-9000-pmcm

Tristan > Urambo Tauro
05/27/2018 at 00:36

I know I’m late to the advice party, but pull the PCM, take the lid off, and look for leaking/swollen capacitors. Ford EECIII/IV ECUs have problems with this as the years go by. The symptoms you describe are almost exactly what I went through with my ‘90 5.0 LX. The ECU was trashed. Also, my ‘93 Lightning had a terrible hard 1-2 shift I couldn’t figure out for the life of me. I could barely stand to drive it because it banged gears so hard. You guessed it- a capacitor in the ECU failed so hard it looked like a cigar burn in the middle of the board.

Urambo Tauro > Tristan
05/27/2018 at 11:17

Good call. You’re not late at all, unfortunately. I’m still working on it. In fact, I’m right in the middle of trying to hunt down a Ford Powertrain Control/Emissions Diagnosis manual for the car.

But before that, it just so happens that I did take a minute to pop that cover open and take a peek inside. Everything passes a visual inspection. Nothing’s visibly blown, it’s all clean with a nice coat of conformal coating. That’s hardly conclusive though...

Tristan > Urambo Tauro
05/27/2018 at 13:57

Do the SN-95 5.0 cars have the troublesome “salt and pepper shaker” engine harness connectors at the back of the upper plenum?

Urambo Tauro > Tristan
05/27/2018 at 14:09

Nope. That’s apparently one of those Fox-only things, like the 22k resistor and distributor-mounted ICM.

Tristan > Urambo Tauro
05/27/2018 at 16:43

I’ve had that stupid distributor-mounted TFI module fail on me in rush hour traffic... Moving it away from the engine’s heat was a good idea.