Dsandine

Did a compression test this morning, and everything seemed as it was supposed to be, butterfly was opened, spark was disconnected and there was no fuel going to cylinders. Compression built up very fast like 100 psi after 1st stroke and after like 4 complete rotations it was as high as it was going to get but I did seven rotations as book said to do just to be sure I had right readings. I have a 93 4 liter with 255k miles, and according to the book compession is supposed to be in between 120-150. Also all cylinders were well within 10% of each other, and I have read sometimes it is more important that cylinder's are within 10-20% of each other than the psi you get. But here is my dilemma

Cylinder 1:160 PSI
Cylinder 2:160 PSI
Cylinder 3:156PSI
Cylinder 4:160PSI
Cylinder 5:157PSI
Cylinder 6:160PSI

These number's are all higher than what manual suggests as the norm, and I know carbon build up on valves can cause higher compression, but to have almost an equal amount of carbon build up on every valve seems a bit unlikely. Any thoughts?

OverlandZJ

What book is starting seven revolutions? I thought it was three.

A_Jeepr

Its perfect....don't worry about it. as long all all cylinders are with in 10 PSI of each other.

Dsandine

It was pretty close or at full compression at like three or four compression strokes.

But, according to Haynes manual Chapter 2D-4.3.7

"Crank the engine over at least seven compression strokes and watch the gauge. The compression should build up quickly in a healthy engine. Low compression on the first stroke, followed by gradually increasing pressure on successive strokes, indicates worn piston rings. A low compression reading on the first stroke, which doesn't build up during succesive strokes, indicates leaking valves or a blown head gasket (a cracked head could also be the cause). Deposits on the undersides of the valve heads can also cause low compression. Record the highest gauge reading obtained"

That is the procedure I followed.

Desert Rat

If I pulled those numbers during a compression test I would feel no need to be concerned, appears pretty healthy. Question though, why the test, you having problems?

Hommersimpson

IMHO and ive done a lot of compression test... several hundred atleast... and yours would get a 98% ok IMHO... 100% if they all were 160 on the nose..

A_Jeepr

+1 bud I have checked some old Ford tractors and they were like 80-30-120-0 before....lo thats when you know its bad when you get readings like that!

My Cherokee is ~140 all cylinders. I wish I had this guys #s

Dsandine

No I wasn't having problem's just wanted to make sure engine was in good shape before I started throwing money into it like a better head and cam and stuff.

But now looks like I will be running a compression test again tomorrow. I was driving and getting on it (not to much, just a little bit but still giving it more gas than just casually driving as I like the sound of my new intake and stuff) and the jeep just died. Started running rough for like 2 seconds then just died and I cannot get it to start. The oil looks good (no antifreeze in it0 and also the coolant looks good, I disconnected fuel line going to rail and with key in run position no fuel came out but when I put key in run position fuel came flying out of fuel line. Not sure if it is getting past regulator. I am not used to regulator's on these vehicles but if it is that thing on a 93 on the fuel rail were fuel supply line hooks up to I am not sure how to remove it, I have an extra fuel rail with the regulator on it, and i took off the one bolt but regulator didn't want to budge, so I guess I will have to some reading. Hopefully all goes well on tomorrow's compression test and if that is fine it has to either be not getting fuel, air or spark, cause if it was getting all all those I would think it would start and run. I know this is way off topic but I am just doing a ittle venting because this is my only mode of transportation so I need to figure it out quick.

Hommersimpson

Id skip the compression test and find out why its not running.... its not compression..Trust me... its not compresion keeping you from running..heck this is motor i pulled out.. and it ran still..well on 4-5 cyl..and had good oil pressure to..moved it under its own power like this

A_Jeepr

LMAO that reminds me of the engine I tore down only to cylinder #3 cylinder broke in 2 and separated at the top of the piston....that piston makes a good paper weight now!

A_Jeepr

oh and homer....you dropped a valve, or ate a golf ball one of the too.....

cobb

Thats probably what my motor looks like lol!

Desert Rat

I have a buddy who likes to fix stuff that aint broke, until it is broke. The first thing I'd do if I were you is go back through everything you've recently done to the XJ. I'll bet you a glazed donut you'll find your problem. Not trying to dog on you, when having problems the first thing to check is the last thing you did to it.

96Cherokee113

Sounds like exactly what happened to me when my Crankshaft Position Sensor crapped out. Check the resistance of it with an multimeter set to ohms. Here's a picture of the location



Now what you do is pop off the connector and measure the resistance between prongs B and C. There should be absolutely zero resistance.



Also, when mine blew out is also blew out the Camshaft Positioning Sensor (AKA a stator or pick-up coil) which is under the distributor cap. Here's an article to read about that.

http://www.lunghd.com/Tech_Articles/...lse_Stator.htm

A quick test to see if your CPS is possibly the culprit is to test the spark. Pop the plug wire coming from the coil off the top of the distributor and ground it out on a bare metal surface. Have a buddy crank it over and see if there is a bright blue spark. If there's no spark, or a dim spark, CPS is probably your culprit. Good luck with your Jeep.

fishtaconc

That looks better than my first engine ever, 355 sbc dropped a valve a 6K