curtrod58

I think my '95 XJ with the 4.0 may have finally tapped out but I'm not exactly sure why... I've had it for around 5 yrs or so and have had no problems with it until now. It has 237K miles on it and just passed smog last December with flying colors. But since then I've had to replace the CPS in Jan. because one of the leads from the plug had shorted out on the manifold. Then in March I needed to replace the O2 sensor after it started running rough and the check engine light came on with an OBD code 21. While I was at it I also replaced the thermostat (195°) because it was due for coolant change and also replaced the housing and reverse flushed the cooling system. Now that I've done all that it has been running horribly (only on 4-5 cylinders) and I noticed a little bit of moisture and thin puffs of white smoke in the tailpipe so I've replaced the plugs and wires again but that didn't help. So Icve parked it for the last week or so. I was hoping it wasn't anything too major but got around to doing a compression check on it today and with the results I think (hope?) my head gasket is shot. Readings from cylinders 1 thru 6 are: 121, 112, 10, 12, 114 and 130. So obviously the problem is with cylinders 3 and 4. Dropping a little oil and retesting didn't help so I'm guessing it's the head gasket, right? What's kind of throwing me off is that the oil still looks clean as well as the water. Am I over thinking this and just need to pull the motor to inspect it or am I missing something? It's been a great ride and may just buy another 4.0 XJ to replace it if I can find another sweet deal like I did on this one.

doublechaz

Sounds like the head gasket has failed just between the two cylinders. No oil or coolant passages there, but the compression goes back and forth between the two.

XJ_XJ

Why not replace the head gasket? It would be the thin metal outline part that sits right above the top of the engine cover? Or the metal outline that sits under the block that holds all of those coils and rods?

curtrod58

I normally wouldn't hesitate to change the head gasket myself, especially on a straight 6 motor. However, since I've been on LTD after having my right hip replaced with a bionic one last year plus still needing the left one replaced, my back is in pain every day, plus I would hate to have some insurance guy come by from my work to see me working on my Jeep in the driveway. The other reason is because even with a new head gasket, motor or whichever way I go to fix it, with 240K miles on it, I think it's starting to move into the dreaded "nickel & dime" phase. And for a rig that might be worth $1500 at best, I just don't think it's worth the trouble to do it so I'll probably just try to sell it.

curtrod58

Update:
OK, I decided to take a "shortcut" and use some of the dreaded "head gasket in a bottle". I changed the oil & filter before using it and after running thru the procedure, I changed it again. I've put +/-200 miles on it just running errands around town, etc. since then but I'm not 100% sure if it has temporarily "cured" the problem as although the new oil has remained clean with no signs of water in the crankcase it still runs like it's not hitting on all cylinders. I do have spark to the plugs so I'm wondering if it could be something else. Someone told me to check the fuel injectors and clean or replace them if needed but I haven't done that yet because I haven't had a chance to do it but I'm also wondering if it could be something else I'm just not thinking of. There has been no OBD codes that are popping up since I cleared them after adding the sealant (#21 and #23 were coming up before I added the sealant) so I'm feeling a bit lost. I was thinking about at least doing another compression check to see if the head gasket between 3 and 4 is still the problem but I'm thinking my oil would look milky again...
Anyone have any more advice for me? I really can't afford to take it in to a shop to get a "professional opinion" but I'm running out of ideas...

RocketMouse

It may not be the cure all answer or end to the woes of what's going on with yours...but in all of your own diagnostic steps you've taken thus far... have you confirmed the strength and pattern of all of your injectors? Remember the 3 basic things required for fire...
Air, Ignition source (spark), AND a fuel source. You've got air and confirmed spark on all 6.
Just a thought and doesn't cost anything but a little time to test.
Could be other things too like valves not seating properly anymore... etc... but that's all just guesswork with the motor still assembled.

curtrod58

Being the old fart that I am, I've always tinkered with carbs and never had to troubleshoot a possible fuel injector issue. The fact that the problem was with 2 cylinders next to each other along with the very low compression in both of them led me to think it was a head gasket issue. I wouldn't think that the very low compression could be caused by the injectors, could it?

Idunno

Repeat the compression check of #2. From what I've read here another poster's suspicion of bleeding pressure between 2 & 3 makes the most sense to me. If anything that involves keeping pressure should suddenly fail the head gasket would be the first thing to rule out. Second would be valve related but easily accessed and inspected beneath the valve cover.