Intermittent check engine light

tjg8675

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Sep 3, 2007
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Age
44
Hi all,

This is for my 95 bronco 5.8l 191,000mi

Starting a new thread for this...I have posted about this briefly in a previous unrelated thread and thought it was resolved but apparently that was not the problem...

My check engine light issue(s) have returned, I had forgotten to tighten my intake hose clamps at the throttle body and when I tightened them the problem seemed to go away for a few weeks until yesterday...

I started it up after work and let the warm up cycle run as per usual, a few seconds after the idle settled the check engine light came on and the idle stuck up around 1000-1200. I shut the engine off and waited a few seconds and restarted. The check engine light was still on and idle was still stuck 1000-1200. Previously when this happened it seemed to clear up after a short drive, so I reversed out of my parking spot put it in drive and attempted to leave but had NO power, it felt like it was in wrong gear so I shifted it down to "1" which was better, it still didn't feel like 1st gear but could slowly accelerate out of parking lot. When I got onto the road and gave it gas it wanted to bog/stall if I gave too much gas, so I went easy and got a little speed and shifted into 2nd then into drive. I approached a red light and the check engine light turned off and seemed normal for a moment until I stopped and the check engine light came on again (+ high idle) and turned off again, it turned on again so I shut it off and restarted and check engine was on and then turned off, light turned green and I proceeded cautiously and all seemed normal again. I drove a couple miles before the check engine light returned again so I pulled over and attempted to pull the codes but battery was dead in code reader, I shut it off and started it again the check engine light returned (+ high idle) and then turned off again, then on again and off again and stayed off. I was able to drive the rest of the way home with no further issue (seems to be OK once warmed to operating temp???)

When I got home I checked all vacuum lines (OK) and electrical connections (OK) pulled codes (all pass) then pulled PCM to inspect for capacitor leakage (at this point a bad PCM is all I can think of that could cause this strange behavior) and indeed the caps are leaking but all the legs are intact, a bit corroded, but still connected to the board.

I have new capacitors for the PCM but have not attempted to replace them, I want to have a replacement PCM available in case something bad happens during this process. So I went online and looked for a replacement but could not find one with the part #F5TF-12A48B75-BXA RoB0 (for an automatic transmission)

So now I'm stuck... its like something is shorting out, I thought maybe is caused by the rainy weather we've been having lately but am not sure.

Any input for diagnostic steps I can take or a lead to a reputable shop that has the PCM I need would be greatly appreciated!

Sorry for the long write up and thanks in advance for any help

 
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miesk5

96 Bronco 5.0
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Yo T,

Some info on the Intermittent CEL;
Wiggle Test Special Note:
The technician can attempt to re-create & detect an Intermittent fault using the Wiggle Test procedures.
Key On Engine Off Wiggle Test Procedure:
Hook up a VOM or Scan Tool.
Turn the ignition key to the ON position.
For VOM, activate, deactivate and reactivate Self-Test to enter Continuous Monitor Diagnostic Test Mode (DTM). For Scan Tool, enter DTM, then enter wiggle DTM.
*** BEWARE OF FAN, HOT ENGINE, HOSES, BELTS, PULLEYS ***
Tap, move, and wiggle the suspect sensor and/or harness to IAC FIRST, then coil, ICM, DISTRIBUTOR, EEC, PCM, FUEL INJECTORS, BATTERY + & GROUNDS ,
Malfunction Indicator Lamp (MIL) aka CEL: Lights
VOM: Needle Sweep
Transmission Control Indicator Lamp (TCIL) on E4OD
Scan Tool: Continuous Tone

Engine Running Wiggle Test Procedure
Special Note:
The Engine Running Wiggle Test may be activated any time the engine is running.
Hook up a VOM or Scan Tool as shown.
Key off.
Start the engine.
For VOM, activate Self-Test, deactivate and reactivate Self-Test to enter Engine Running Continuous Monitor DTM. DO NOT shut the engine off. For Scan Tool, enter DTM, then enter wiggle DTM.
Tap, move, and wiggle the suspect sensor and/or harness to coil, ICM, DISTRIBUTOR, EEC, PCM, FUEL INJECTORS, BATTERY + & GROUNDS , IAC, TPS, ECT, EVP, IAT, ETC.
When a fault is detected, a Continuous Memory DTC will be stored in memory and indicated as follows:
CEL Lights OF COURSE
VOM: Needle Sweep
Transmission Control Indicator Lamp (TCIL)
Scan Tool: Beeps
....

Intermittents are usually caused by one or more of the following: deteriorated electrical connections, terminal issues, etc. Start by carefully inspecting the suspected circuit for the following conditions:
Poor mating of the connector halves, especially if the locking tabs are broken, which occurs with our elderly Broncos.
Terminals backed out or not fully seated in the connector
Damaged terminals or poor terminal to wire connections
Corrision or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring causing the conductor to corrode inside the insulation. Look for swollen and stiff sections of wire in the suspect circuits.
Wires that are broken inside the insulation
Pinched, cut or chaffed wiring in the harness
Look for unravelled or missing harness wrapping and loose harnesses where PO pulled harness from its straps, and/or clips.
Wiring that is damaged as a result of being in contact with exhaust components, such as the O2 sensors, CANP solenoid where it's hose is known to melt on exhaust manifold

These bs pop up ads caused me to spend too much time trying to type

 

tjg8675

Member
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Messages
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Age
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Hi miesk5,
Thanks for that wiggle test info, I had forgotten about that test. I will try that on my way home tonight.
 

tjg8675

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Sep 3, 2007
Messages
87
Age
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The manual for my "Ford code reader" doesn't give instruction for a KOER wiggle test, only for KOEO. Should I just follow the KOEO instructions except with engine running?
Sorry for noob question, never done the wiggle test.
 
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tjg8675

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Sep 3, 2007
Messages
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So my "Ford code reader" probably won't do the KOER wiggle test, I think I need a real OBD1 scan tool, any recommendations?
 

miesk5

96 Bronco 5.0
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7,831
Location
Coronado, CA
The manual for my "Ford code reader" doesn't give instruction for a KOER wiggle test, only for KOEO. Should I just follow the KOEO instructions except with engine running?
Sorry for noob question, never done the wiggle test.
Yo T,
Sorry for the delay, I couldn't see foruns due to errormmessages.
Yes follow KOEO instructions.
Beware of fan blades, pulleys, belt, hot engine⚠
 

tjg8675

Member
Joined
Sep 3, 2007
Messages
87
Age
44
HI miesk5,
Thanks for info, I bought a new scan tool that can run KOER wiggle test.
Currently the truck is not throwing the check engine light, I will probably have to wait until it does to get any codes while running the test.
I will give it a try anyway, just to see what it says.

Thanks again
 

miesk5

96 Bronco 5.0
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Oct 18, 2005
Messages
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Location
Coronado, CA
Yo T,
YW!
There may be a code even though CEL is not lit while driving, for example, DTC 452 WILL NOT SET THE CEL.
 

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