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Went From Troubleshooting Intermittent PCM to Terrible Knocking Sound

Discussion in 'Stock 1991 - 1994 Explorers' started by Cedar, September 8, 2017.

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  1. Cedar

    Cedar New Member

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    I got busy and let the truck sit for a week with the battery disconnected after trying to track down an intermittent wire or relay. When I went to start it the first time this week the engine started awfully rough and sounded terrible. Only thing I did different was I forgot the crankcase breather tube. l got that reconnected and now what used to be a subtle tapping sound I thought I'd heard intermittently while driving sounds like an awful loud knock or rapping. I'm posting a video mainly for the audio.

    I'm really hoping someone's going to say check vacuum lines or some sensor or to let the PCM relearn, but I've never heard this sound before after working on the truck. Sounds kinda like a 25hp diesel tractor. Weird thing I thought I heard a fainter sound like this more since I got my truck back from the last oil change. No idea why but the shop used 10w30 instead of 5w30.

    I've got a suspect wire to the ignition coil, being the 12 v power. Seems unrelated at this stage.

    Any fixable causes for sounds like this or do I just need to get a professional diagnosis on the motor?

    Oil pressure test maybe?

    1994 Explorer 4x4 XLT OHV, 184,000 miles

    Oil is 3/4 up the hash marks cold

    First part of video is holding the phone above the valve covers, at ~1:00 I go under the engine.

     
    Last edited: September 8, 2017
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  3. Frank1669

    Frank1669 New Member

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    I can't tell anything from the recording, sorry. Get a mechanics stethoscope or in a pinch you can use a long screw driver to try and isolate the sound. could be anything bad Lifter , bearings. wrist pin etc. external accessories water pump alternator etc is usually a growling noise but check anyways. you can try adding a thick oil additive like Lucas or Engine Restore and see if it quiets down. That will narrow it to an internal problem.
     
  4. Frank1669

    Frank1669 New Member

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    OH oil additive is not meant as a cure. Just a diagnosis tool. if it does make it quitter, you still need to address the issue.
     
  5. Cedar

    Cedar New Member

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    I hear you. I need to be thinking it could be anything and trying to diagnose, kinda pessimistic about these kinds of noises given the age. Water pump was replaced last year this time.

    I'm tempted to try that and also do an oil change. I need some direction on notes and things to try as like with my electrical diagnosis, I changed the relays around without marking and notating it the first couple times which I should have done in the beginning so I'd know where I was now.
     
  6. 2stroke

    2stroke Elite Explorer

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    How long has this been sitting for? Looking at your past post this was rear ended, and you have been fighting electrical issues since. If it seems to have a miss on one cylinder, a stuck valve is a possibility, but it would have to have been sitting for quite some time.
     
  7. Cedar

    Cedar New Member

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    It was really just a week so not that long for basic lubrication to be an issue unless something was wrong with the oil pump etc right? All of a sudden this noise is worse, like I said it started terribly rough for some reason. It was rear ended years ago now, got the frame straightened and it's been running fine since. The electrical issues were all as of a month ago now. I've been pulling and poking at wiring though and let the PCM sit without power for a week.

    This looks pretty safe, I might give this a shot:
     
    Last edited: September 8, 2017
  8. natenkiki2004

    natenkiki2004 Blue Bomb!

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    Letting it sit a week definitely wouldn't be an oil issue. I've got a 94 as a farm truck that will sit for weeks at a time and even a couple months. However, my 1991 does something that might point you in the right direction. Maybe 1 in 40 drive cycles, I'll start it up and it will have a horrid tap/knock along with an engine vibration. It quits after a while but best I can figure is that it's one specific valve lifter that, when the engine stops in a certain part of it's rotation, will drain all the oil out and has a clogged passage. It takes maybe 10 seconds or so for it to knock (pun intended) it off. I'm wondering if you have a similar issue. Like 2Stroke said, maybe a stuck valve too. There's really nothing in these engines that would cause a sudden knock like that after sitting. You'd either have to run it hot, low on oil or hydrolock it to have something like that. My first thought would be to pop the valve covers and lightly tap the rocker arms back and forth with a plastic hammer. I don't know if that can cause lifter damage though, just a thought.
     
  9. cogs

    cogs Active Member

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    yes, probably the rocker arms, that's why it decreases with idle, and is a little quieter under the truck. change oil with the right weight, it'll probably quiet down a little.
     
  10. Cedar

    Cedar New Member

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    I unplugged one sparkplug wire from each coil and did not notice a significant change in sound. There are only three coils so the plugs fire in pairs right? I only need to unplug one from a pair in order to stop both if I'm reading right.

    Well, when I got done with that and plugged all the sparkplugs back in the sound is much harder to hear now. When I reach a long screwdriver and listen, the only interesting engine noise I hear is from placing the screwdriver next to the sparkplug boot for cylinder 4, driver's side farthest forward. There's a double-note rapping sound in there but I cannot tell yet whether it's actually in time with the noise that I'm hearing. Although, main problem is, I'm not sure where else I should be listening too. I didn't hear anything at the valve covers and not much access from down below so I went with near the spark plugs.
     
  11. 2stroke

    2stroke Elite Explorer

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    Unplugging one wire does not shut off other other. Being a sound that comes and goes, and in the location you describe is most likely a sticky/dirty valve lifter. They can bleed down, and that would cause a bad tapping if they don't pressurize with oil. I think Nate is spot on. I wouldn't worry too much about it, not much to do without spending a ton of money. It's not rod knock, it would sound twice as fast if it was.
     
  12. Cedar

    Cedar New Member

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    Thank you, especially for the corrections on the spark and rhythm of the sound! I need to go learn the basic firing cycle for this engine. At that rate I'll do some more testing and and unless anything else comes up I'll change the oil back to 5w30 and see.
     
  13. Cedar

    Cedar New Member

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    I drove it to collect some things for an oil change and the noise quiets right down even without driving too hard once it's warm. I changed the oil with some Pennzoil Platinum 5w30. Also grabbed another pile of nice looking Ford relays from the yard. Exploders are getting a little sparser. If it's lifter noise then really I don't need to be worried about driving it so much.

    Only major issue I can see now is wire worn bare an inch from the plug, the red-green wire going to the coil-pack. If it weren't next to the plug I'd solder in a splice but I'm not sure how problematic it is to remove the wire on these connectors? Otherwise I just need to go get a decent iron finally, maybe terminal kit?

    [​IMG]
     
  14. 2stroke

    2stroke Elite Explorer

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    You could separate those wires and wrap it good with electrical tape. No need to get fancy with the soldering gun. What was it rubbing on?
     
  15. Cedar

    Cedar New Member

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    I'll get some decent tape and do that then. Strangely the only thing it was backed up against is a length of that corrugated plastic conduit for another line going to the firewall. The wire comes straight back from the plug and rubs on that conduit.
     
  16. Cedar

    Cedar New Member

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    Okay, back to the original problem. Car drove fine to work since Wednesday. Immediately saw no check engine when I went to start it 7 hours later today. ECM relay was charred brown, started off as white. Worst discoloring is on the 87 terminal of the ECM relay. I popped in a replacement and got home. Fuel relay and ECM relay were hot as hell when opened the hood. Way hotter than the engine bay. My rig is straight up bbqing ECM relays. I've checked a lot of wires from the computer to the power box, not sure what else to look at here. I'm fixing to replace the fuel filter just for giggles.
     
    Last edited: October 1, 2017
  17. Cedar

    Cedar New Member

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    Everyone and everything I read says I must have a bad ground or some source of resistance somewhere. If it's the EEC relay burning up, the EEC relay feeds the injectors and the ICM and what else (also just realize I get ICM and coil pack confused)? It feeds the COIL side of the fuel pump relay, but that goes to the instrument cluster? I highly doubt it's burning out on that. I have no idea how injectors behave, but I do know that when the coil pack was on it's way out a decade ago it kept doing this crap... There's a test for that but I don't know how obvious this is going to be.

    All the discussions on burning out relays all point towards the fuel pump circuit. My notes show I get 9.3 V ignition on at the inertial switch. I need to see what that is when it starts. I also show I only had 11.8 V across the fuel pump fuse and 11.51 V across the PCM relay fuse. Is the latter due to the PCM load itself or ?
     
  18. Cedar

    Cedar New Member

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    Got some advice that the sockets/cavity in the power distribution box lose their tension somehow over time. If the sockets weren't holding/contacting the relay terminals well that would create a lot of resistance & heat right there. Would explain why my relays looked like burnt tater tots on the bottom where the plastic starts out a light cream color and meets the relay terminals.

    I took apart the power distribution box carefully removed and replaced each of the 30 relay socks using a dental pick to lift the tongue inside the socket and also very gently crimping some of them with a pair of needle nose pliers. They're super soft seems like tin coated copper. Truck's been running fine for a couple weeks no electrical issues, well, besides the instrument lights playing musical chairs on who's going to work at any given time.
     

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