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post #1 of 6 Old 04-17-2005, 07:54 AM Thread Starter
wdc
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vacuum problems

I have a jeep wrangler 1990 inline 6. I have lost vacuum pressure to almost everyting. Four wheel will not engage. Engine dies at a stop when engaging the clutch. When at idle after warm up rpm's go up and down. Will not idle smoothe unless I throttle slightly. I do have vacuum on vacuum fitting. I have also noticed a slight back pressure sound in exhaust when going down hill. I have checked all the hoses (very many of them) and can't find any leaking. If anyone has any suggestions or solutions to this you help is greatly appreciated. Thank you!!!!!!!

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post #2 of 6 Old 04-17-2005, 08:10 AM
drew2000
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wdc,
Hook up a vacuum gauge to a hose coming from the manifold and get a reading at idle. The two most important things are what the reading is, and how the needle fluctuates. A perfect reading is 18-20 with the needle perfectly still.

If your engine has no vacuum at all, that is a sign of a major problem.

If it fluctuates it can be an indicator of various types of engine problems.

Drew

1994 YJ - 2.5L, 2" BDS w/1" Shackles
2006 Dodge Charger R/T (5.7L Hemi)
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post #3 of 6 Old 04-17-2005, 09:59 PM Thread Starter
wdc
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Quote:
Originally Posted by drew2000
wdc,
Hook up a vacuum gauge to a hose coming from the manifold and get a reading at idle. The two most important things are what the reading is, and how the needle fluctuates. A perfect reading is 18-20 with the needle perfectly still.

If your engine has no vacuum at all, that is a sign of a major problem.

If it fluctuates it can be an indicator of various types of engine problems.

Drew
Thanks for the info. I checked the vacuum and it is holding steady at about 20. Never had this sort of problem before and it is frustrating me seriously.
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post #4 of 6 Old 04-18-2005, 10:00 AM
Wif
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Quote:
Originally Posted by wdc
Thanks for the info. I checked the vacuum and it is holding steady at about 20. Never had this sort of problem before and it is frustrating me seriously.
If you have vacuum at the manifold then you must have a leak on one of the lines .. check for cracked and broken vac lines .. these do get brittle.

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post #5 of 6 Old 04-18-2005, 10:10 AM
YJBlues
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I've found that a cheap can of starter fluid is your best friend when trying to track down a vacuum leak. Spray short bursts at the hoses in different locations, when you hear the engine rev when you spray, you've found the general area of the leak.
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post #6 of 6 Old 04-18-2005, 11:00 AM
amg61
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Quote:
Originally Posted by wdc
I have a jeep wrangler 1990 inline 6. I have lost vacuum pressure to almost everyting. Four wheel will not engage. Engine dies at a stop when engaging the clutch. When at idle after warm up rpm's go up and down. Will not idle smoothe unless I throttle slightly. I do have vacuum on vacuum fitting. I have also noticed a slight back pressure sound in exhaust when going down hill. I have checked all the hoses (very many of them) and can't find any leaking. If anyone has any suggestions or solutions to this you help is greatly appreciated. Thank you!!!!!!!
it's possible you have two unrelated problems. the fact that your 4-wheel drive will not engage is not that uncommon in these jeeps. search the forum for posi-lok solutions and that might help.

as for your idling issues, yes it may very well be a vacuum leak, but assuming you have that old carter carb, you may just have clogged idle tubes. there are a number of threads on this issue, but if you want to tackle your carb, without tossing it and swapping in a weber or mc2100, then try these fixes.

consider this carb fix:

http://www.jeeptech.com/engine/carter.html

with these pictures:

http://www.yellowjeep.org/Carb.html

and consider drilling out the venturi idle tubes to 0.040" with a #60 drill bit (by hand).

Also, a TFI ignition upgrade is great for that engine. search the forum for TFI upgrade info, or got to this site:

http://www.driveajeep.com/html/the__juicebox_.html

also, this site is awesome. http://home.sprynet.com/~dale02/list.htm

TFI/GM HEI Hybrid, MC2100, M.O.R.E. greasable shackles, TJ flares, AtoZ Fab Rocker panel, 31" BFG AT; Getting there.....
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