Did I Kill It?

"Justin Hughes" (justinhughes54)
12/19/2015 at 10:19 • Filed to: jeep comanche

I’m getting a little scared here. My Comanche (88 Renix 4.0) has run a little rough since I got it, but now it’s hit new levels of roughness. Despite an oil leak, the level hasn’t fallen to more than halfway between the “full” and “add” marks, and I recently topped it off to “full.” Soon after shooting this the oil light came on so I shut it down, and confirmed that the oil level is still full. Bad sensor, or a lack of oil elsewhere in the engine? Don’t know. I hope I haven’t killed this motor.

DISCUSSION (20)

crowmolly > Justin Hughes
12/19/2015 at 10:26

If you remove the oil fill cap does the noise change? What does the oil pressure look like?

Justin Hughes > crowmolly
12/19/2015 at 10:33

No change in noise with the oil cap on or off. Unfortunately this dashboard only has an idiot light, not an actual oil pressure gauge. (A spare cluster with gauges, not idiot lights, was included with the Jeep, but I only just got it and haven’t installed it yet.)

wafflesnfalafel > Justin Hughes
12/19/2015 at 10:41

how about temp? Is it getting hot? If it’s not getting hot I’ll bet its a bad/fouled plug and/or wire causing it to run crappy in addition to the marginally failing oil pump

Justin Hughes > wafflesnfalafel
12/19/2015 at 10:51

I haven’t run it since the oil light came on but before that I’ve had no temp problems. I just replaced the plugs, cap, and rotor (darn store sold me the wrong wires, still working that out), which made it a little better but that was before the knocking started. Doesn’t rule out one of the new plugs getting fouled.

JawzX2, Boost Addict. 1.6t, 2.7tt, 4.2t > Justin Hughes
12/19/2015 at 10:54

that noise is tough to pin down... It kinda sounds like it could be a leaky exhaust header or a loose spark plug, but if your oil light is coming on, I’d buy an oil pressure gauge and check that before I run it any more...

wafflesnfalafel > Justin Hughes
12/19/2015 at 11:09

got it - blows that theory...

crowmolly > Justin Hughes
12/19/2015 at 11:10

I’d get an oil pressure gauge on it as it sits. Not necessarily permanent, just something to check.

RacinBob > Justin Hughes
12/19/2015 at 11:16

Oil pressure just doesn’t go away.

- It’s is either prevented, oil screen is plugged
- Or it’s not possible - Pump broken
- Or something has opened up and all the oil is bypassing and there is not ough pressure
- Or the sensor has broken.

I don’t like the prevented, because screens don’t get plugged out of nowhere. I don’t think the pump broke, you would have heard it. Same with the bearing fail, that happens more at full load, not idle.

My guess is the sensor wen’t bad. PS, if the diaphram has failed that may be your oil leak. I had the similar story 40 years ago with a ‘66 stang. Going down the highway and guage went to zero. I pulled over and went to a farmer. He had me start it, it idled fine, no chattery lifters. He backed the oil sensor out had me start it, oil came flying out, diagnosis, bad sensor, put it back in and I was on my way, Suggest you try the same. Running it at idle will not hurt it cold.

Now if you put in the sensor and it still shows no oil at idle but goes off at running conditions, something is worn and it’s leaking by at low idle pressure. You will have to decide what to do with that. It could run a long time without idle pressure.

BTW, the best thing is google ‘88 Comanche 4.0 no oil pressure. From what I see not encouraging

interesting string

good luck

Birddog > Justin Hughes
12/19/2015 at 11:33

It’s hard to tell on mobile but it sounds like one of your spark plugs popped out.

Birddog > JawzX2, Boost Addict. 1.6t, 2.7tt, 4.2t
12/19/2015 at 13:06

I was thinking Spark Plug as well.

Denver Is Stuck In The 90s > RacinBob
12/19/2015 at 13:38

I was about to suggest the oil pump could be going.

RacinBob > Justin Hughes
12/19/2015 at 15:15

I did some searching and saw a lot of hits on oil pump. I suggest pulling the pressure switch and seeing if its pumping by turning over the starter.

Here is a link to a jeep forum with a lot of comments. http://abmforum.com/jeep-cherokee-…

RacinBob > Justin Hughes
12/19/2015 at 15:16

Ps - since you weren’t driving it under load, I think the motor is fine even if the pump failed. Motors will take a fair amount of abuse, even without oil pressure.

RacinBob > Justin Hughes
12/19/2015 at 15:53

Ooooh. I didn’t play the video till now. That doesn’t sound good.

Justin Hughes > RacinBob
12/19/2015 at 18:07

Yeah. Going to pull the valve cover and poke around. Gasket needs replacement anyway.

RacinBob > Justin Hughes
12/20/2015 at 13:17

Does the engine have a miss? I wonder if you have had a lifter come apart. It might explain the loss of oil pressure and the valvr train noise.....

Interesting comments on this one. read them

Justin Hughes > RacinBob
12/21/2015 at 09:17

I popped the valve cover, and I’ve lost both lifters in #2 cylinder. I need to assess the general condition of this motor, see what it needs, and determine whether to repair or replace it. I know the lifters themselves aren’t a showstopper, but the potential combination of issues may be. Still pondering.

You can tell a Finn but you can't tell him much > Justin Hughes
12/21/2015 at 13:56

The wires may not be wrong. I swapped wires on a 96 GC with the 4.0L and the firing order cast into the manifold did not make sense when I tried to hook up the plug wires. I put the old ones back on according to how they were set, then swapped them one at a time and everything ran fine. The oil pressure sending unit on 4.0’s is fragile. Like change the sending unit every time you change the oil amounts of fragile.

Justin Hughes > You can tell a Finn but you can't tell him much
12/21/2015 at 14:10

Further inspection revealed they’re not wrong, but a generic set for a V8. Sure, I could just use 6 of them on the Jeep, but I ordered a set made specifically for the Jeep 4.0 and will return the generic ones.

RacinBob > Justin Hughes
12/21/2015 at 14:20

Best string I saw on the topic. Have fun.

http://www.jeepz.com/forum/cj-yj-tj…

Still, unless the oil was just blowing out the destroyed lifter, maybe it was, you still have to figure out if you have a oil pressure problem too. If the oil pressure loss was coincident with the lifter noise, I’d figure out if the lifter failure can cause enough oil leakby to result in low pressure at idle. I am thinking it might because if it is pumping oil at all, it’s hard to believe you have both bad lifters and a bad pump or bearing........