Need Leak down test help

[Kejtar]

The one and only Jeep Guru MJR has recommended that I do a leak down test on my XJ to see if I can figure out what is the culprit behind my misfire.... so on that note:
Who has the equipment to do it and can help me do it?

Preferably not too far from Westminster/OC as I'm not too keen on driving it too much with the misfire

 

[JohnX]

Too far?

 

[Kejtar]

Too far?

Not sure... let me see what I can get done in OC.... I might just tow it up there (don't want to put too many miles on the 5 banger ) I'll let you know

 

[JohnX]

MJR doesn't have a leak down?

 

[Kejtar]

MJR doesn't have a leak down?

Unfortunately no. He does have a nice fancy computer hookup for the PCM though

 

[BigSteve]

have you done a compression test already?

 

[Kejtar]

have you done a compression test already?

Yes.. compression is good.

 

[FordGuy]

So Remi, it runs fine when cold? So as soon as it goes into closed loop it misses?

 

[Kejtar]

So Remi, it runs fine when cold? So as soon as it goes into closed loop it misses?

I think that would be a fair assesment. I'm going to try and monitor the temperature better during my tests though (I haven't made the direct connection between the two till yesterday).

 

[FordGuy]

If it seems to miss as soon as the temp comes up, and its consistent with temp I am not sure what a leak down will tell you. When you did your compression test did you do a wet dry? I might check ad see if there are any HC in the cooling system. I have a test kit if you need it.

 

[JohnX]

Yes.. compression is good.

Maybe my brain isn't awake yet, but if compression is good, why run a leakdown? A leakdown is really only to tell you what is causing compression loss (valves, rings, etc.)

I would be much more inclined to start looking at sensors if it is a closed loop ony type problem.

 

[Kejtar]

Maybe my brain isn't awake yet, but if compression is good, why run a leakdown? A leakdown is really only to tell you what is causing compression loss (valves, rings, etc.)

Dunno: Mike said it's a good idea

I would be much more inclined to start looking at sensors if it is a closed loop ony type problem.

Yes but... here's what throws me for a loop (pun intended ) : if it's a sensor then why does it affect only cylinder 1?

 

[toyotawrench]

Was there any difference between cyc 1,2, and 3? what were the measurements?

 

[Kejtar]

Was there any difference between cyc 1,2, and 3? what were the measurements?

1 and 2 were in 140's IIRC and 3 was slightly lower... but not by much... I stopped on 3 and didn't measure rest as my issue is with 1.

 

[toyotawrench]

interesting, do you have a noid light? Use it to plug into the injector plug to make sure your getting a signal, I don't have one. I will ask the snap-on guy today about one. If i can get one for cheap enough I will come over tonight after work see if number one fuel injector is getting a signal.

I wonder if its a problem with the computer losing the injector signal once it goes closed.

Pm me ur number dude I will call you after i talk to the snapon guy at 1

peace
ted

 

[Russ Pottenger]

Maybe my brain isn't awake yet, but if compression is good, why run a leakdown? A leakdown is really only to tell you what is causing compression loss (valves, rings, etc.)

I would be much more inclined to start looking at sensors if it is a closed loop ony type problem.

I'm in agreement with John. A leak down just gives you a more definitive answer to a poor compression test.

For those not familiar with the process, a measured amount is air is put into the combustion chamber through the spark plug hole. A gauge on the tester reads the percentage of loss. depending on piston ring end gaps 5 to 12 percent are good numbers for a engine that is sealed up properly.

From that point, being able to detect the source of the leak make a leak down test a more accurate test than a cranking compression test.

Air passing through the intake = bad intake
Air passing through exhaust pipe = bad exhaust
Air passing through the valve cover breather hole = bad piston rings.

 

[toyotawrench]

russ what is the cranking psi suppose to be on a 4.0? Or rather what is the spec.

 

[Kejtar]

The injector is getting a signal. I tried different PCM's and I also bypassed the harness in case it's a harness issue with a cracked wire and heat causing a disconnect.

 

[FordGuy]

Did the plug on #1 look any different than the others?

 

[JohnX]

You could swap plugs and injectors (to different holes) and make note of what moved where. If the mis moves when a part moves...