Topic: vacuum tests?

[pioneer4x4]

i have an 86 2.5 auto xj, and have been having an intermittent hesitation problem, some days it will do it and go for a while not doing it. i thought i fixed it when i noticed one of my egr bolts stripped out not sealing properly to intake, but now it returned yesterday. so i went out and bought a mityvac vacuum gauge and at idle i get a very rapid 19"-21", slow acceleration it decreases then slowly increases and steadies to about 22". when i rapidly open and close throttle its 0"-25", all this seems somewhat ok, except i would figure more than just 1" increase when i slowly rev up but manual says anything above idle indicates clear exhaust, was seeing what yall thought? kinda suspect clogged exhaust from not much noticeable increase in "hg. also manual states that lower than normal and rapid fluctuations in a range of 3" and as engine speed increases needle will steady indicates worn valve guides. but doesn't seem low to me, just very rapid and i just had a head job about a year ago. but I'm new to this vacuum testing scene. also Ive got some lifter clack going on, not real loud, but at idle its noticeable, and for jeeps this isn't anything too un-ordinary, would this have any effect on my rapid needle movements? any suggestions would be greatly appreciated. thanks in advance.

[pioneer4x4]

no imput on that question, well how about this one...when i got my 86 2.5 xj, there was not emissions vapor canister, so i pulled this one out of a Comanche and a buddy of mine hooked up all the vac lines. my question is does it matter to interchange them like this? will it work? and also my diagram says i should have a egr canister solenoid, but i dont, is it essential to have one? also i am questioning his ability to hook this thing up properly, can yall tell what lines should go where? i know the pics are kinda hard to tell, but from left to right i have one opening on far left, then in middle i have another which is capped off and the one under it has a perminant plastic cap, and directly up on top where the circle/cap is another (one yellow hose is going to), then further right is another opening. im pretty sure the circular cap is the purge and that should go to egr t'd into the solenoid i dont have. but not sure on the rest. just seeing if yall have a similar one to this one and could tell me how yalls is hooked up. thanks

[sharpxmen]

i have an 86 2.5 auto xj, and have been having an intermittent hesitation problem, some days it will do it and go for a while not doing it. i thought i fixed it when i noticed one of my egr bolts stripped out not sealing properly to intake, but now it returned yesterday. so i went out and bought a mityvac vacuum gauge and at idle i get a very rapid 19"-21", slow acceleration it decreases then slowly increases and steadies to about 22". when i rapidly open and close throttle its 0"-25", all this seems somewhat ok, except i would figure more than just 1" increase when i slowly rev up but manual says anything above idle indicates clear exhaust, was seeing what yall thought? kinda suspect clogged exhaust from not much noticeable increase in "hg. also manual states that lower than normal and rapid fluctuations in a range of 3" and as engine speed increases needle will steady indicates worn valve guides. but doesn't seem low to me, just very rapid and i just had a head job about a year ago. but I'm new to this vacuum testing scene. also Ive got some lifter clack going on, not real loud, but at idle its noticeable, and for jeeps this isn't anything too un-ordinary, would this have any effect on my rapid needle movements? any suggestions would be greatly appreciated. thanks in advance.

i read this about 3 times to understand what you're asking - if i get it correctly your question is this: "is it normal for the vac to fluctuate between 19 and 21?"

i am not sure if the egr comes in play here, my Jeep does not have one - all i can tell you is that my vac is steady at idle.

the other behavior is normal (0-25 when open closing the throttle). same with opening the throttle a little, the vac would go up and then once the rpm increases it will go back down.

[pioneer4x4]

yea thats pretty much the jist, i know most of the results are ok, but my main concern war the rapindness of the needle at idle.

[sharpxmen]

yea thats pretty much the jist, i know most of the results are ok, but my main concern war the rapindness of the needle at idle.

maybe you can block the egr for a test at idle and see if that changes the needle bouncing (i have no clue how the egr works). Or you can take a compression test to see if you have a bad intake valve.

[chardrc]

86 means that tis a tbi jeep so it has an egr.. the first page of this pdf has the entire vacuum diagram of the emissions stuff which should be helpful maybe.

http://jeepgarage.free.fr/OWN/2.5l%20cec%20system.pdf

the purge/egr solenoid can be seen in this pic to the right of that battery not the best picture but should give you an idea of what to look for.. although this is a yj so the placement will probably be different for your xj.

[chardrc]

maybe you can block the egr for a test at idle and see if that changes the needle bouncing (i have no clue how the egr works). Or you can take a compression test to see if you have a bad intake valve.

if the egr is activated at idle it will not idle / it would run very ruff. egr should only operate when jeep is warmed up and at partial throttle (assuming its functioning properly which would be doubtful if you don't have the vacuum solenoid but my guess is that egr is currently always off or your idle would be messed up).

[pioneer4x4]

thanks for the photo, i dont have that anywhere. i put vacuum on the egr and it does not hold any, so im thinking the diaphram is gone in it, but would that cause a leak into the system? kinda dont think so since the egr would always be closed if it rips. ill see if i can find a block off plate to see if any changes occur during vacuum test. thanks

[pioneer4x4]

ok so i went to the pick and pull and got a different canister and a solinoid. hooked up all vac lines properly. but as soon as i start it up the egr opens up all the way and idles like crap. if the solinoid goes out could it cause unrestricted vacume? is there a way to test it?

[chardrc]

the solenoid should block vacuum from getting to the egr when it is energized. so see if when your motor is cold / at idle see if it is getting power or not and go from there.

[pioneer4x4]

so check the connector when its unplugged or probe thru backside when plugged in?

[chardrc]

would probably be easyest to unplug it and either put test light between the 2 terminals or use a volt meter. with the motor on ideling. should have power at idle

[pioneer4x4]

well i just checked it and am getting 7.8 volts on the connector, but then when i kept the + prob on the connector and put the - probe on negative batt. terminal it showed 12 volts. why would that be different?

[chardrc]

computer must (edit might)be limiting voltage somewhere going to it.. or it has resistance somewhere that's not supposed to be there... im not shure what the voltage is suppose to be (ill have to try look it up tomorrow)

this may have an answer http://jeepgarage.free.fr/OWN/2.5l%20cec%20system.pdf

[sharpxmen]

just a thought but keep in mind that i am not familiar with the TBI so could be wrong: is the ECU giving ground or +12v on this? a bad ground can cause what he describes (less voltage)