Help me diagnose this...misfire?

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Adventure_Wagon88
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Help me diagnose this...misfire?

Post by Adventure_Wagon88 »

I've been chasing this issue forever and haven't gotten anywhere and it's really dragging me down making me not want to even work on anything on the Jeep. It starts and idles fine. It revs up OK (sometimes a little pop/misfire here and there but pretty strong. Put it in gear and under any acceleration it sputters and pops and has no power. Higher the RPM the worse it is. Warm it up it doesn't clear.

I replaced spark plugs, wires, cap and rotor with all OEM spec parts. Also rebuilt the carb. It was not doing this before that but it also did not start as easily or idle as nicely.

Here is a video hopefully you can hear what I am describing.

https://vimeo.com/211549038
Last edited by Adventure_Wagon88 on Tue Apr 04, 2017 12:45 pm, edited 1 time in total.
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Stuka
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Re: Help me diagnose this...misfire?

Post by Stuka »

Your URL is broken, so can't watch the video.

However, few things to check. What is your timing set to? Also, have you checked for vacuum leaks? And after rebuilding the carb, what procedure did you use to set it up?
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Re: Help me diagnose this...misfire?

Post by Adventure_Wagon88 »

Edited, is the video working now?

I don't have a timing light but I haven't messed with it. I can't find any vacuum leaks, but all the smog stuff was removed before I got the Jeep so some of the vacuum stuff is sort of a guess as to what is right. EGR is bypassed/capped currently also. I followed the instructions with the rebuild kit for setting up the carb but that doesn't mean it is right.
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Re: Help me diagnose this...misfire?

Post by Stuka »

Nope, maybe you have it set to private?

A timing light would be a good investment. As would a vacuum gauge to tune the carb.
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Re: Help me diagnose this...misfire?

Post by Adventure_Wagon88 »

I'm pretty sure you are on the right track that it has to do with the carb and or timing. I think my dad has a timing light bur I'll have to find out about a vac gauge. I was messing with it today and backed the idle mixture screws all the way out (alternating one screw at a time) and didn't notice a change in the idle at any point. I also can place my hand over the air opening on top of the carb which seals it pretty good and that doesn't seem to affect idle either - shouldn't that choke it a bit? When I rebuilt the carb I checked for play in the shafts and they were good and tight. I also did not notice any cracks or warping anywhere. Again it wasn't running like this before the rebuild and tune up but it also did have some idle issues as well as seems to have always run very rich since I've had it.

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Re: Help me diagnose this...misfire?

Post by Adventure_Wagon88 »

If the video still isn't working try going to Vimeo.com/deepfocus it should be the first video there
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Re: Help me diagnose this...misfire?

Post by Stuka »

If you backed the screws out all the way and it still ran you have a massive vacuum leak. Get some brake clean, and spray it around any vacuum hose, and around the base of the carb. If the idle climbs, you have a vacuum leak. Also, set the idle screws for 2 turns out, thats a good starting place. But when turning them in, just go until they stop, don't turn them tight, or it will ruin the needle and seat.
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Re: Help me diagnose this...misfire?

Post by Skerrvydog »

Video works for me - wow is all that popping and banging sound from the engine? Is it backfiring out the carb? Can you get another video from under the hood?


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Re: Help me diagnose this...misfire?

Post by Adventure_Wagon88 »

Well there's a knocking/tapping sound that is prevalent at the beginning, which is just a loose part (or parts) in the interior. That's probably the banging you're referring to. The motor does not knock or tap at all. When I shift into gear and raise the RPM it's like a little backfire pop. It is not regularly backfiring out the carb, though that has happened. I can get video under hood, sure but you probably won't hear the popping very well over the engine and fan noises.

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Re: Help me diagnose this...misfire?

Post by Adventure_Wagon88 »

I should add that all the abnormal ENGINE sounds in this video are coming out the tailpipe (have to specify, it makes a lot of abnormal sounds, it's a project haha)
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Re: Help me diagnose this...misfire?

Post by Stuka »

Ok, works for me now. Definitely check your timing! :)
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Re: Help me diagnose this...misfire?

Post by tgreese »

Yes, re the vacuum leak. Normally you should be able to stall the engine by backing off the idle stop screw until the throttle flaps are completly closed. If these is a bypass (vacuum leak) the engine will keep running. A big vacuum leak will make the idle mixture very lean and could lead to a periodic misfire, typically from the cylinders that are furthest from the carburetor (leanest).

I would also check the compression. A burnt exhaust valve will make an irregular misfire on that cylinder. You can also feel that in the exhaust gas at the tailpipe, present as a puff in the exhaust stream at regular intervals.
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Re: Help me diagnose this...misfire?

Post by Adventure_Wagon88 »

Thanks tgreese, I am quite sure it has a vacuum leak. Also I did a compression check, the lowest on 2 cylinders was 90, the rest were all 110 or above. I did not know to do the oil trick at the time to distinguish between a ring and a valve causing the low numbers, unfortunately but my money is on valves causing it. Really not looking to rebuild this motor as my plans are for a Cummins swap in the next 12-18 months. Was just hoping to get some around town miles and local wheeling in while I stockpile the funds needed to complete the overhaul.

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Re: Help me diagnose this...misfire?

Post by Adventure_Wagon88 »

OK I did the brake cleaner thing and didn't notice any changes in idle no matter where I sprayed. I still think there's got to be one somewhere, thinking it's likely in the hoses that run to the fuel tank as they are the most aged looking hoses on the whole rig. I did however get the "misfire" to go away! I advanced the timing and got it running without any popping and accelerating pretty strong but the carb still needs some adjustment. I ran it around for about a half hour yesterday then parked it in the driveway. A few minutes later I went to start it back up to pull it into my barn and it did a really awkward fire/detonation thing when I cranked it. I'm not sure how to describe it really but it was like a pre-detiniation thing where it fired before a cylinder was at TDC and it seemed like the engine turned backwards or something maybe. I cranked it again and it seemed like a huge strain on the starter to get it to move and now any attempt to start, it won't crank, it just clicks like the solenoid is popping but the starter isn't or can't turn. I am going to try rotating the crank off the harmonic balancer today and if that doesn't work I'll check wiring and try a few other things. If anyone has insight into what might have happened based on what I attempted to describe I'd love to hear it. If I killed the 360 it just means I need to push it in the barn and heft that POS out of the way to make room for the Cummins a little earlier than anticipated :-)
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Re: Help me diagnose this...misfire?

Post by jpcrzy »

Did it run like that before you changed the plugs and wires? Sounds like maybe you got a plug wire out of sequence. Did you adjust the timing by ear? Sounds like when you tried to restart it, after your test drive it, may have jumped time, or the starter Bendix got stuck in the fly wheel......... Good times! If life was simple we would all be bored to death :banghead:
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Re: Help me diagnose this...misfire?

Post by Adventure_Wagon88 »

Yeah I think I need to pull the starter. It didn't run bad before I tuned it up but I never played with the timing at all. It definitely benefited from a little advancement and I think that issue is behind me. Plenty more ahead tho

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Re: Help me diagnose this...misfire?

Post by prospector »

Vacuum leak, make sure the vacuum hose from the distributor it attached to a nipple on the carb. above the throttle blades, this is called "ported vacuum", and it's where the vacuum advance cannister on the distributor needs to be attached via the hose. Check all vacuum hoses, also could be a vac. leak where the intake manifold runners align with the cylinder heads. If the intake is leaking at the intake gasket a small stream of propane gas will cause the engine RPM to increase. Easy way to diagnose, but use common sense and be careful.

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Re: Help me diagnose this...misfire?

Post by Adventure_Wagon88 »

Somehow I missed that helpful info Prospector! Is the propane trick the same idea as the brake cleaner trick? I was messing with this a little more today and discovered exactly what you were saying about the distributor vac line being hooked up wrong. It is currently connected to a multi-connector at the intake manifold directly in front of the carb. It actually runs better (at low speed anyway) WITHOUT the distributor connected to that vacuum port. I'm not sure exactly what this "discover" means, but I'll get a new hose and try ported vacuum.

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Re: Help me diagnose this...misfire?

Post by Adventure_Wagon88 »

Hooked distributor up to the carb, seems to work much better with ported vacuum!
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