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Old 06-20-2005, 06:39 PM   #1
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lets get technical-XJ vac leaks->

there seems to be enough people in here now with enough knowhow- think i`ll throw out the bone, see if anyones heard of this...

and yes, I have one just like it.

On the renix or earlier chrysler jeeps-usually pre 95, we all develop vac leaks. Almost all can be traced to either the hardline leaking at the battery, or the brake booster. We lose vacuum going uphill, or trying to meld the go pedal to the floorboard. Said action automaticly causes *0* vacuum, or a pressure build-where there should be none, causeing the MAP sensor to get all hissy and try to throw more fuel down the pipe. More fuel, more power, more vacuum...or so the story go`s......Been there , done that-it aint the case.

Why is it then, that the vacuum problem gets worse the warmer it gets?(not to be confused with the voltage dropping when tempetures rise- solved that)

think about this- several people have this same problem , and as far as I know, its never been solved on any of the forums for the years Ive been tracking it.

example- I have NO vacuum leak- its tested, it holds. Useing a vac guage in the driveway(HA!-) I have steady vacuum, no pips or dips-from idle to 6000rpm(no strain/all in nutreal),- In cold weather I do have a minor vac leak at the booster-when pressed-common.
Road test- at 70degrees ambient temp- I can get halfway up a hill (testhill)
before the defrost kicks in, which means no vacuum-starting pressure.
At 80+ degrees ambiant, I can get 1/4 up the hill.
Anything over 90 and the defrost kicks in at the bottom part, soon as the engine senses strain.....at 100, I have no vacuum as soon as the engine senses any strain-- the kicker?- downshifting causes an immediate vacuum return, followed by slow lose again.

One could therorize that the ambient temp would cause a vac line thats leaking to open more with higher temps. BUT, all the hoses are underhood at a constant temp-the engine bays stays around 130 to 150 reguadless.

ponderance: would a semi clogged cat convertor cause a buildup of exhaust that backflows into the intake where the vacuum begins? If so, why would heat be a factor?
solve it, and your "Da MAN"

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Old 06-21-2005, 10:17 AM   #2
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Aw, great! Now I have a headache after reading all that.

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Old 06-21-2005, 02:21 PM   #3
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Answer: I have no clue on the vacum thing.. but if you really want to solve it, can't you just go buy a posi-lock and be done with it? And yes it all has to due with air temps. Cars/Jeeps, what ever will run better with its cooler out, vs warm. engine does not have to work as hard, thus it will effect the vacum lines as well as other systems.. I think the answer is a combined effect not just one area.
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Old 06-21-2005, 06:14 PM   #4
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Quote:
Originally Posted by 4Jeepn
Answer: I have no clue on the vacum thing.. but if you really want to solve it, can't you just go buy a posi-lock and be done with it? And yes it all has to due with air temps. Cars/Jeeps, what ever will run better with its cooler out, vs warm. engine does not have to work as hard, thus it will effect the vacum lines as well as other systems.. I think the answer is a combined effect not just one area.
your probably right-- people have been trying to pin this down for years on a single fault. Everyone scampers around looking for the 1 thing wrong, and it probably isnt....

now, which group to check...one could start at the front bumper and work to the tailpipe.

mines a 2wd old desert prerace truck, converted back over to work truck years ago-- if I had a posi lock, it would make a dandy hood ornament. My chief deal is loss of vac, gas mileage, blowby...in that order.

when I have multiple vac lose`s over a weeks time, I get serious blowby- cause of no vacuum, pressure buildup-- it sucks it right out of the EEV and int the filter. Filters are cheap....but the problem, long term , remains.
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