4.0 OHV Misfire at all rpms - Need help

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crazyracer

Tres Cuatro Tacos
Sep 27, 2006
2,616
75
48
31
Pacific Beach, CA
#13
I believe I have an ECM for a 94 4.0 5speed, if you wanna pay the shipping or pick it up you can try it out and see if it makes a difference.
I'm going to try Doug's First (see below) since we work together and he's close. Thanks for the offer, I might have to reach out still regardless.
I have a scanner and a 93 5 speed computer. pm me with your number if you need. im pretty sure I have the ignition module that is riveted to the drivers side core support if you want swap that too.
Can you bring both to work? I realize it's 10pm on a Sunday, but even if you can bring it Tuesday there's a slim change I can plug one of the two in and have it bring the truck to dirt-ready before Friday's trip.


Now that I have a scanner, the weirdest thing is happening.
It'll actually run fine, albeit at higher idle than it should, when the scanner is plugged in. It doesn't missfire or bog.

I was getting 211 and 212 codes initially, but after clearing codes, running the truck a while with the scanner plugged in and checking again, the fucker is saying it's passing all system test (Code 111 O and 111 C).
The tach isn't getting a constant signal I've noticed too. Internet reading says it could have something to do with the 211 or 212 error, but I don't know if it's causal or a symptom of my woes. Still investigating....
 
Jul 2, 2010
904
5
18
Bend, OR
#14
Have you tried a new coil? It's rare they go bad but worth a shot.

If I remember correctly, the codes will repeat twice. I have an old tool that plugs in to the four wire test port and that repeats. I don't know if the dashboard light method does
 

crazyracer

Tres Cuatro Tacos
Sep 27, 2006
2,616
75
48
31
Pacific Beach, CA
#15
Have you tried a new coil? It's rare they go bad but worth a shot.

If I remember correctly, the codes will repeat twice. I have an old tool that plugs in to the four wire test port and that repeats. I don't know if the dashboard light method does
Now that my code scanner is giving me digital readings, I'm quite sure it's not the coil. Plus, if it were the coil I don't believe the engine would have smoothed out when I plugged the scanner in. Mine repeats twice on the scanner, but I don't think they do via the dash bulb.

Whatever the root cause it, it's affecting the PIP signal or SPOUT signal. That could be a wire, pin, PCM, or ECU. I feel like I'm getting close, just need to find that smoking gun (or wire).
 

crazyracer

Tres Cuatro Tacos
Sep 27, 2006
2,616
75
48
31
Pacific Beach, CA
#17
Sorry for the lack of info last night/today, it's been nuts between this and travel for work.

TLDR: The truck seems to be fixed as of 9pm tonight

Discussion:
Last night the plan was to validate the PIP and SPOUT circuits check out for continuity. When I got home from work, I started the truck to ensure shit was still fubar'd (it was) then proceeded with tearing into the wiring to find the SPOUT wire and dongle (looks like a diode in the wire harness), checked that, then checked the SPOUT wire from the ICM to the ECU for continuity. The ICM plug was a bitch to get off the actual ICM. Finally apart, I was able to verify the SPOUT wire from the ICM to the ECU check out with no shorts. So onto the PIP...

I wasn't able to find continuity with the PIP wire from ICM to ECU, so I started tearing into the wire loom. I pulled apart the harness and traced what I thought was the PIP wire into the EEC test junction, and into the firewall plug. It's important to note that my 94 appears to have a couple Y's in the PIP wire that go to the EEC tester and a relay, whereas the wire diagram I have for a 93 only show the PIP going from ICM to ECU. Anyway, as I was trying to sort this wire out, the rain came. I didn't get a chance to test continuity since stuff was getting wet my ohm readings all went to shit.

Today I picked up an ICM and ECU out of a co-worker's 93 ranger and headed home. Before I plugged in the new equipment, I figured I'd get a baseline by re-plugging in the connections I tore apart and using the original ICM and ECU to replicate the problem.
With the plugs all reconnected with the factory stuff (Fully expecting it not to work), I started the truck and the sucker ran great. WTF!!!

Now the truck seems fine and I don't have a smoking gun. My thoughts are that the problem lies somewhere in the plug either at the ICM or the firewall. Since I believe the firewall would only receive outputs from the system to inform the dash, it must have been that tough-to-pull-apart ICM plug.

I started and ran the truck a few times for long enough to get warm and read codes. The entire system checks out, fault free. Engine revs clean, idles clean, has no issues other than a high idle (1000rpm)
After doing some reading, the high idle is symptomatic of a new IAC and the ECU needs to relearn it via a few warm ups and loads applied. I'll know more about that tomorrow night after I get it button up and driveable again.

So to recap:
New IAC
New Crank Position Sensor
New(er) Spark Plugs (I use em for testing)
New O2 sensor
New MAF sensor/unit
New Throttle Position Sensor
Pull apart ECU plug
Replace ICM & Fuel Pump relay
Verify Fuel Pressure
Check Plug wires for continuity
Inspect coil for crack/heat warnings
Spray carb cleaner looking for vaccum leaks
Run seafoam through intake
Curse obscenities
Pull hair
Loose sleep
Make GF think I'm avoiding her
Run engine scanner (211 & 212 codes)
Reset ECU
No fix.


Pull apart ICM plug
Continuity check PIP and SPOUT
Pull apart firewall plug
Cut apart wire harness loom
Reassemble
Fix


And for fun,
Here's my workshop for the evening.
Yes that's a tarp.
Yes it's raining.
Yes I fucking need this to work for epic tacos.
IMG_20190115_212401.jpg
 
Likes: ucd baja

Jester9

The Jester's Workshop
Apr 1, 2014
179
2
18
Riverside, CA
#18
Just wondering whether your new TPS is from vatozone or a motorcraft sensor...on my bronco, I threw in a vatozone TPS and it was off a hair causing a high idle issue. There is a YouTube video out there showing how to modify it in order to allow the butterfly to fully close at idle and it fixed my high idle problem. Just a thought! Good luck!
 

crazyracer

Tres Cuatro Tacos
Sep 27, 2006
2,616
75
48
31
Pacific Beach, CA
#19
Just wondering whether your new TPS is from vatozone or a motorcraft sensor...on my bronco, I threw in a vatozone TPS and it was off a hair causing a high idle issue. There is a YouTube video out there showing how to modify it in order to allow the butterfly to fully close at idle and it fixed my high idle problem. Just a thought! Good luck!
I bought a motorcraft one. What i'll do is get this thing back on the road and let it go through a couple warm up cycles. If after a few drives it still idles at 1000rpm, I'll take a stab at lowering the idle by adjusting the throttle set screw and subsequent TPS position. Thanks for the feedback!

Also, started the truck this morning - Seems to run great still. So BAJA BOUND Friday! WHooooooot.


Thanks for all the feedback and help DR.
Double-D (Doug) really helped a lot with diagrams and spitballing troubleshooting via text. Granted, he' a coworker as well, but we met via DR and this is where he saw my cry for help. Thanks again!
 
Jun 28, 2006
6,517
135
63
42
San Diego
#20
I just saw this.... I have a 94 4.0 OBD1 manual computer for future reference. ;-)

What scanner did you get?? Been wanting one for my OBD1 pile too .... I remember playing games counting beeps before. so retarded
 

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