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Thread: Started new build, loads of weird errors

  1. #1
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    Started new build, loads of weird errors

    1995 LT1, Caprice, tuned by Alex R (PCM Performance). Just installed engine today due to cam going belly up. Fired it up and it ran like it was missing, but eventually cleared up. Initially, left 02 wasn't swinging like it should and BLMs were pegged. Car idled ok in closed loop, but once open loop hit, RPM's climbed a bit and BLMs crept up to 160 and stayed there. Changed out left 02. Restared car.

    02's were not moving like they should, then it tossed out the following codes (eeHack)
    ERR84(1-4 CONTROL CIRCUIT)
    ERR83(REVERSE INHIBIT CIRCUIT)
    ERR26(CCP ELECTRICAL FAULT )
    ERR48(MASS AIR FLOW SYSTEM FAILURE)

    Changed MAF since that was easy, and the error persisted. Changed PCM's - no change, so it's definitely in the car. Checked all the wires thinking that something got pinched and everything is clear. Pulled off the covers off of half the harness and everything looks ok, but something is obviously not. Car will NOT go into closed loop.

    Looking at the codes, I am wondering if the harness that leads to the trans controls was somehow mangled in the install. I checked power on the pink lead at the MAF and it's very low. I checked resistance on that lead to ground and it shows 1.2k, so its definitely bleeding off voltage to ground somewhere.

    Anyway, anyone got any ideas other than what I have laid out above? About ready to toss a match into this thing...

    Thanks in-advance

  2. #2
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    Gonna have to go one wire at a time til you find it, bud. Grab your wiring diagrams, multimeter (NOT A TEST LIGHT!) and get comfy.

    Since you know the ground lead from your MAF is high-resistance, start un-looming at the MAF and work back along that ground wire until you either get to where it bolts to the engine block, or you find the bad connection. You should not have 1.2K resistance to ground, on a wire that bolts straight to the engine block.

    Once that has been taken care of, next on the list is the Charcoal Canister Purge fault. That's a solenoid valve that gets a ground signal from the PCM, so this one's easy to diagnose. Look up the pin number and connector on the ECM, set one of the probes on that pin in the harness, and then check your CCP valve connector. If that wire is good, next check your power to the CCP connector-there are only two pins. If you have +12v switched power there, and your ground back to the PCM is good, check the actual CCP valve for high/low resistance.

    Next up is the reverse inhibit switch, down on the transmission. Probably another ground fault, same as the MAF. Work it out the same way.

    1-4 control circuit, probably similar. One wire at a time.

    DO NOT USE A TEST LIGHT. Use a multi-meter that gives good resistance and voltage readings.

  3. #3
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    might try splicing into the pink wire with a known good ground and go from there.

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    Quote Originally Posted by Xnke View Post
    Gonna have to go one wire at a time til you find it, bud. Grab your wiring diagrams, multimeter (NOT A TEST LIGHT!) and get comfy.
    Since you know the ground lead from your MAF is high-resistance, start un-looming at the MAF and work back along that ground wire until you either get to where it bolts to the engine block, or you find the bad connection. You should not have 1.2K resistance to ground, on a wire that bolts straight to the engine block.
    I've got a Fluke 88v, so I'm good there. Thanks for your suggestions and I'll get cracking.

    The pink at the MAF is the positive lead, and is supposed to carry 12v key-on. Mine carries 12v key on, but also shows 1.2k resistance to ground - so there is something not right there. That pink lead also shows 440 ohms of resistance to the fuse block, which is no bueno, either. The purge valve has the same resistance to the fuse block.

    I pulled the harness and un-loomed it from the pass-head outward, including the trans harness. Nothing nicked or crushed, so I will start testing resistance on wires individually. Good times.

    I suspect the issue lies in the bundle of wires on the backside of the pass head. I have not gotten in there yet because they are so well buried. It would almost be easier to pull the engine out again to get to them.

  5. #5
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    from what i remember the maf and all the pink wire stuff is on a totally different power feed from the CCP solenoid and all the brown wire stuff, it's independent all the way back to the key switch, i don't even think they're on the same connector between the engine and body harness.

    having them both fail simultaneously may be a coincidence but is suspicious and that should be taken into account when tracing this failure. could be a ground thing?

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    Quote Originally Posted by steveo View Post
    from what i remember the maf and all the pink wire stuff is on a totally different power feed from the CCP solenoid and all the brown wire stuff, it's independent all the way back to the key switch, i don't even think they're on the same connector between the engine and body harness.

    having them both fail simultaneously may be a coincidence but is suspicious and that should be taken into account when tracing this failure. could be a ground thing?
    If the LT1s are similar to the Vortecs, on my Express vans Vortec 5.7 the MAF grounds to the engine block itself. If the block was painted it is likely not making a solig ground through the bolt itself.

  7. #7
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    Quote Originally Posted by steveo View Post
    from what i remember the maf and all the pink wire stuff is on a totally different power feed from the CCP solenoid and all the brown wire stuff, it's independent all the way back to the key switch, i don't even think they're on the same connector between the engine and body harness. having them both fail simultaneously may be a coincidence but is suspicious and that should be taken into account when tracing this failure. could be a ground thing?
    @Steveo According to the FSM, the 1995 Caprice/Impala has the MAF, both 02's, AIR, EGR, and CCP valve all running off fuse #4, which is the one that blew-out, giving me some of the codes. The trans codes are weird, and I am digging into those too.

    I replaced the fuse, codes went away. Started car. 02's initially showed "normal" voltage swings as the car warmed up. Once it entered closed loop, voltage swings slowed on both 02's, with one of the 02's stopping entirely. Car pegged BLM's, and the MAF started show an increase in flow, despite being at idle. Shut the car down before the fuse popped again because something is obviously screwed up.

    Tested pink leads at the CCP and MAF. Both over 400 ohms to the fuse block. Tested continuity on those same wires (positive leads) to ground - both show 12 ohms resistance to ground, so there's something to check into. (The positive leads carry 12v AND go to ground. Not good.) Interestingly enough, while I was confirming the readings from the MAF to ground, it showed the 12 ohms and then instantly went to infinity, like something switched off. The CCP also showed infinity. Could it be a sensor or switch failing internally that ground when hot?

    Quote Originally Posted by Fast355 View Post
    If the LT1s are similar to the Vortecs, on my Express vans Vortec 5.7 the MAF grounds to the engine block itself. If the block was painted it is likely not making a solig ground through the bolt itself.
    Good suggestion, but these grounds were 100% and nothing was painted there. The engine ground strap goes to the head - which is raw aluminum. The front grounding stud at the coil is the same I was using before - also to the bare head.

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    You *do* have all the sensors unplugged and the PCM unplugged during these tests, right?

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    Update: So I think I've found at least part of the problem. I took out as much of the harness as I could and removed the loom. The bit behind the passenger head is all that's left in there because the #(@)! trans dipstick tube makes getting the harness out damn near impossible. Anyway, the wires themselves all look great. No nicks or breaks that I could find; visually or with the meter. In looking at which errors popped, and then went away, (CCP, Opti low-res, 2 different transmission errors, 02's being lazy, MAF, and a blown #4 fuse) as well as digging into the FSM schematics, I noticed that the errors were not confined to one PCM plug as I suspected, but instead across 3 of the four.

    I took out the PCM and dug into the individual plugs and everything looked and tested OK. Checked the ground at the rear of the engine to the body and it was ok. Removed the 4 ring terminals at the driver's head, and that's where things went weird. On the stud, I was getting wildly sporadic ground readings holding the meter to the bare stud (going into the raw aluminum head). Holding the leads perfectly still, the meter would swing from infinity to .## ohms of resistance. Moving the lead to the other bolt holding the coil and ICM and the reading would be dead-steady at .02 ohms. Move it back to the stud and it would swing from 400 ohms to infinity, to .03. It swung around so much I had to turn off the audible alarm on my meter. Switched to alligator clamps on the leads and the issue persisted - so its something in that stud that is causing loads of inconsistency in the ground.

    It's the same damn stud that was in there before, so I've no idea what is going on, nor do I really care. I'll swap it out with a new bolt and see what happens.

    Question: would that have caused the #4 fuse to blow or should I keep digging?

  10. #10
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    Check the grounds from the battery to the body, and body to the engine, and battery to the engine. All three need to be good.

    Once you know those grounds are good, remove the stud and replace. You could have some corrosion down in the bolt hole.

    While that stud is out, start checking the wiring harness right there on the ring terminals. It's not uncommon on old harnesses to have wires broken inside the jacket, that appear normal.

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