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Quick vacuum question


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Hey all, chasing a gremlin that my truck developed recently. Quick question, should I hear an audible vacuum/air sucking sound from the area of the charcoal canister? then it dies off 3-4 seconds after motor is shut down. It happens during idle and revving no audible sound change. Trying to figure out if I have a vaccum leak somewhere in this area. Undoing the two hoses ontop of the canister seems to make no difference.

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Yea going to hunt around for it some more today, hopefully it is my issue. I am having a horrible misfire/stumble when any more than like 1/8th throttle is applied, but the truck will continue to accelarate while stumbling badly. It started doing this a week ago, put new plugs and wires and also a fuel filter the old one was very occluded. Fixed the issue for a bit, then a few days late it started acting the same. I checked the fuel filter again and it was VERY hot to the touch so I figured my exhaust leak had finally got to far out of hand and was heat soaking the fuel line.

 

I replaced the manifold and the truck is is great now quietest it has ever been, but the bad stumbling/missing issue is still present. A couple times it has completely stopped and ran fine for 5-10 minutes but comes back suddenly. Possibly the clogged filter or heat soaked fuel caused damage to the fuel pump? I will be on a wild goose chase for the issue this weekend.

 

Interesting thing, while tearing it down to replace exhaust manifold I noticed the end that screws the EGR pipe into the intake was just hanging down on the elbow so the end of the egr pipe was loose in the intake and obviously not sealed.... not sure if previous owner undid it or it somehow backed out. My exhaust manifold was cracked so badly that the entire furthest back pipes weld was completely broken all the way around only the thick flange was still holding it to the manifold assembly.

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Use carb cleaner sprayed at suspected areas for vacuum leaks. When the engine sucks that stuff in momentarily, you'll know there's a leak in that spot.

 

I'm very suspicious of your fuel pump being worn out.

 

A fuel pressure test should be done. 

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Alright update time, finally tracked down the vacuum leak, it was small hard plastic vacuum line that went to what I believe is the cruise control, had melted through on something. My idle seems to sound better but I still have the really bad miss/lurch. I did a fuel pressure test and I am showing 30 psi and 38 with the vacuum line removed so I think things are inspec on that front?

 

I am starting to feel like maybe I have a bad injector? A couple of them had alot of junk built up around them and inside their port on the intake. Going to do a compression test this morning and TPS to rule those things out.

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Ok 2nd update of the day and its a good one so far. Tested TPS. Reference voltage was 4.87, output was .33  not good.... So 4.87 x .17 was telling me I need .82 output. Adjusted it to the .82 started and idle was high but test drove and all was good, pulled over and turned it off, restarted high idle was gone but missing/lurching was back  :doh:

 

Drove back home tested output again and it had moved to .85, readjusted back to .82 and tightened down better, after 2 test drives now it has not high idled and the problem is cured as of this moment, Time will tell though  :laughin:    I really don't know what I would do without all the info you guys have compiled here it really is a life saver. thank you!

 

My idle does seem to wander just a tad, not a lot, honestly I probably won't even bother chasing that right now as long as its running well.

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My idle has wondered since day one coming off the lot. My uncle who bought it said he had jeep look at it from 1987 the year he bought it till 1990 area and he said the hell with it. Never had a problem just a idle that went from 650 to 750.

I have had it since 1997, replaced every sensor, and even put a 428 ECM in. It runs great but that wondering idle stay. The only time I ever had perfect idle was with a stand alone dizzy I dropped in. ran perfect and put old dizzy in and back to wondering. I even replaced the dizzy with a rebuild and same. So I just deal with it!

 

Yes done every mod and cruiser tip. Even added extra big ground all over.

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