Missing/Rough on both ULP and LPG

[Hamsteh]

Hey folks,

So I'm chasing a rough running/miss condition on my 1996 XJ dual fuel.

It is both under load and at idle, AND it is present on both LPG and ULP.

I checked spark plugs and ran a compression test yesterday with the following results:


So that's 68, 70, 70, 70, 75, 75 PSI (at 5 cranks each)

I did forget WOT during these tests, but given that I'm more interested in relative compression it looks okay.

Plugs looked alright, though I did manage to tear the #1 lead on removal so there's a chance it was already damaged - I've ordered a new set already.

I've also tried swapping out coil (which is fairly new) for the original, with no change. Distributor Cap and rotor look fine.

Perhaps the new leads will fix it up, but was just throwing this out there for any other ideas.

Cheers in advance,
Alex

[rainman]

umm that is low compression. like im suprised its running low,...140 150psi is unremarkable.
suggest u use a different compression tester. on the up side at east they are all similar.
possibly review yr technique/ method.
plenty on u tube
good luck with it.

[LuluBelle]

as rainman said .... one of 2 things your compression tester is stuffed or your engine is you should be getting at least 120 psi
_____ooooo
/__l_l_,\____\,___
l_---l_l__l---[ ]llllll[ ]
_.(o)_)__(o)_)--o-)_)

[awg]

Originally Posted by Hamsteh

So that's 68, 70, 70, 70, 75, 75 PSI (at 5 cranks each)

I did forget WOT during these tests, but given that I'm more interested in relative compression it looks okay.
Alex

not ok at all, something is very amiss there..should be much higher, even with no throttle and a "push in" tester.

confirm your tester is not defective, and redo the test with WOT

[Hamsteh]

Hey so I came across some conflicting information on how to run the test. Some said MAX pressure over ~10 cranks, some said just run 4/5 cranks consistently for relative pressure comparison. I know the first cylinder hit >120PSI after more than 5 cranks for instance.

Is max pressure per cylinder the preferred method? I was just looking for consistent results.

EDIT: I did notice that it climbed a lot slower than what I've seen in some of the YT tests.

[rainman]

i go till it stops climbing, i try to do it with a warm engine, all the spark plugs out, and WOT. go 1-6 if the last cylinder is down i redo it after charging the battery 6-1.

i realy struggled with the push in type tester and had to make a screw in one out of a old spark plug.

I also use a push-button switch on 2 leads that plug into pins 30 & 87 of the starter relay reciptical in the PDC. this allows you to be local to the pressure tester, and does not activate the injectors while cranking.

[Hamsteh]

Originally Posted by rainman

i go till it stops climbing, i try to do it with a warm engine, all the spark plugs out, and WOT. go 1-6 if the last cylinder is down i redo it after charging the battery 6-1.

i realy struggled with the push in type tester and had to make a screw in one out of a old spark plug.

I also use a push-button switch on 2 leads that plug into pins 30 & 87 of the starter relay reciptical in the PDC. this allows you to be local to the pressure tester, and does not activate the injectors while cranking.

Awesome thanks Rainman, I'll give that a shot tomorrow hopefully (though cold as I'm not going to rebuild it to strip it down again haha).

I have the screw-in type of tester, but its hard to get a decent amount of thread as there isn't room to tighten it down by anything other than the hose.