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86’ 4000CS cranking but won’t start

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 Post subject: 86’ 4000CS cranking but won’t start
PostPosted: Thu Dec 24, 2020 5:20 pm 
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Joined: Sat Dec 19, 2020 4:58 pm
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Hey! I’m having a problem with my 4K - maybe someone can help me find a solution.

It was running great, until I decided to check the air filter. I took everything off, looked at the filter (it was fine) and put it all together - but now it won’t start unless I mess with the air plate.

I’m guessing it’s some kind of vacuum leak, but from what I’ve seen everything looks fine so I’m not sure what’s wrong. If I manually open the air plate then it will start, albeit not run well. If I leave it alone for a couple days, then I can get it to start once, but I’m guessing that’s just because there’s enough air that’s worked it’s way into the engine for it to kick start itself.

Any ideas?


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 Post subject: Re: 86’ 4000CS cranking but won’t start
PostPosted: Thu Dec 24, 2020 8:45 pm 
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Joined: Sat Jan 08, 2011 9:36 pm
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Location: Pennsylvania
sounds like you need carefully trace down all the vac & intake hoses near where you were working, also the wiring harnesses/ wires.. something had to come loose or crack by the sounds of it

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 Post subject: Re: 86’ 4000CS cranking but won’t start
PostPosted: Mon Jan 04, 2021 2:48 pm 
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A little bit of an update - today it started, but was running lumpy. Then, after about 5 min the negative battery cable caught fire and scared the crap out of me. Maybe a bad ground somewhere then? Still letting my garage air out, I disconnected the battery and’ll investigate what happened later.


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 Post subject: Re: 86’ 4000CS cranking but won’t start
PostPosted: Mon Jan 04, 2021 7:09 pm 
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I sprinkle rubber on my Cherios

Joined: Sun May 24, 2009 7:27 pm
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Location: Pleasant Grove, UT
That's crazy! Was it the ground wire to the battery, or the ground wire to the engine specifically? Did the copper burn out so now it's an open circuit? I can see two ways that would happen: Either the wire was badly frayed with just a few copper strands remaining and then a power surge came through and cooked them, or there was a nasty short from the positive lead of the battery (or likely the starter motor) and the engine/chassis, and the wire that caught on fire acted like a fuse.


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 Post subject: Re: 86’ 4000CS cranking but won’t start
PostPosted: Mon Jan 04, 2021 7:20 pm 
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Joined: Sat Dec 19, 2020 4:58 pm
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BlackBox wrote:
That's crazy! Was it the ground wire to the battery, or the ground wire to the engine specifically? Did the copper burn out so now it's an open circuit? I can see two ways that would happen: Either the wire was badly frayed with just a few copper strands remaining and then a power surge came through and cooked them, or there was a nasty short from the positive lead of the battery (or likely the starter motor) and the engine/chassis, and the wire that caught on fire acted like a fuse.


Might be something along those lines, the positive terminal now has a short to ground - but I think I know where. I was poking around and it looks like somehow one of the high amp cables (not sure if + or -) got too close to the exhaust manifold and melted. Still assessing the damage, so hopefully it didn’t take anything else with it.


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 Post subject: Re: 86’ 4000CS cranking but won’t start
PostPosted: Mon Jan 04, 2021 7:24 pm 
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I sprinkle rubber on my Cherios

Joined: Sun May 24, 2009 7:27 pm
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Location: Pleasant Grove, UT
That's good you know where it is. The exhaust manifold would be grounded along with the rest of the engine, so it would have to be a positive power cable that touched the EM to cause it to short like that. It's probably the high current positive power cable that runs from the battery directly to the starter motor that did it.


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 Post subject: Re: 86’ 4000CS cranking but won’t start
PostPosted: Fri Jan 08, 2021 6:35 pm 
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Ok. Starter cable has been fixed and zip-tied out of the way, so no more shorts (hopefully). I'm still running into the same issues as before, this time I caught on video what I'm experiencing. Low idle, pops and bangs, little to no throttle response, and the only way to get it started without help is to warm up the engine by forcing the air plate open.

(sorry for shakey video, but I guess it gives an idea how crappy it's running lol)
https://streamable.com/kxht4i
https://streamable.com/6kz572

Let me know if the streamable links go down


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 Post subject: Re: 86’ 4000CS cranking but won’t start
PostPosted: Fri Jan 08, 2021 6:50 pm 
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Oh yeah - forgot to mention, I found a way to start it (usually). If I open the air plate manually and let the engine warm up, then I can get it to start. That's the only real development.


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