Sensor(s) Signal Return path problem???


ms88ranger

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Long time forum reader but haven't needed to post in years. Question is on a 88 Supercab, 2.9L, 5-speed manual and approaching 400K miles. Getting midrange bucking and loss of power. New sensors, cat replaced a year or so ago and exhaust new from cat back. ACT, ECT, TPS check OK with meter and behave as expected with temp or position change. Fuel pressure, vac and base timing good. I've pulled and cleaned all the connections and ground points I've found (several times).

If engine bucks/stumbles on the road at around 2,000-2,500 RPM and I open it up (WOT), we take off. More common and worse once engine has fully warmed. Stumble will repeat after backing rpm back down. If sitting in driveway and jacking idle RPM up to 2000-2500, I can create the same effect. It will some time correct on it's on and rpm's go back up. I'm thinking I'm losing spark advance due to an intermittent connection. Only code I get is 54 (KOEO, continuous, and/or KOER). I've yet to starting piercing wires for resistance/voltage tracing and testing and have a buddy bring me a breakout box and harness for the ECM hopefully this weekend to simplify things.

Reading the info on the 54 code and looking at wiring diagram is making me think there may be a problem at the one or more common joints for the signal return on the ACT, ECT and TPS. A intermittent due to temp and/or vibration there could well throw the EEC-VI out resulting in erratic timing. I've done lots of harness wiggling.

So in prep for further digging and troubleshooting, I'd like to know if someone knows about were in the harnesses some of the common signal return tie points might be? I don't mind opening the harness(es) up, just want to narrow it down if possible.

Thanks in advance - Bruce
 


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rusty ol ranger

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Good luck.

This is eerily similar to the issue ive been chasing for a year.

Id like to help ya out...but im lost to.
 

Paulos

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There is supposed to be a splice for the ECT, ACT, TPS, and MAP grounds in the wire loom near the ACT. I would do a continuity check between the ACT connector's ground (Black/W) and the negative battery terminal. While it's connected during the continuity check, wiggle test all the wire looms in that area. If it's an intermittent problem, it should happen during the wiggle test. Check the ACT connector also, as it may be the cause of the intermittent problem. Bad injectors will cause stumbling, but they would clearly not affect the ACT.

Cheap chinese replacement parts may not have the same tolerances on the pins/terminals of the new sensors, and a 30+ year old connector wouldn't help. Just a thought.
 

Uncle Gump

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Hard to say for sure where those points are exactly...

Component location views in a manufacturers publication may or may not have component location/harness routing views that indicate splice position. Even if you find that... probably still a crap shoot if you find a splice where they say it should be.

@PetroleumJunkie412 has probably been through a harness or two by now and may be of more help then myself.
 


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