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Unread 09-04-2013, 02:13 PM   #1
ATjeep42
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1988 MJ Comanche 
 
Join Date: Sep 2013
Location: Sunnyvale, Ca
Posts: 2
Loss of power after overheat

I overheated to the point of engine stall after a bad coolant leak. After replacing lost fluid and field patching the leak engine ran OK and I've put a few thousand miles on it since. But I've noticed a significant loss of power (and it sounds like I have a mild misfire at full throttle as well), and 20% lower gas mileage. Noticed engine is running a little rich (blackish tailpipe as opposed to dark brown before), but plugs are clean. No indication of blow-by (oil clean, no visible smoke from tailpipe). No trouble codes. No fluid losses (beyond what deteriorating gaskets have been causing over the last ten years).

FYI 373,000 on original engine w/ no replacements other than typical maintenance (e.g. TPS, O2, crankshaft position sensors, plugs/wires/cap/rotor in the last two years).

Any idea what the problem might be?

1988 Jeep Comanche
4L, 4x4 5 speed manual

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Unread 09-05-2013, 02:46 PM   #2
TrucksBootsNGun
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1988 MJ Comanche 
 
Join Date: Aug 2013
Location: Flagstaff, ARIZONA
Posts: 46
Not to stray from the topic but you can scan your '88 MJ? I have the same truck ('88, 4L, manual etc) and I've had the dash apart a couple times messing with the dash lights and new radio and not once have I seen anything that I could use to scan the truck.
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Unread 09-08-2013, 06:37 PM   #3
wgirvine
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1992 XJ Cherokee 
 
Join Date: Oct 2007
Location: Rosamond, CA
Posts: 652
Start with the usual tuneup/sensors/fuel pressure items. Other than those... Hmmm.... I'm just thinking out loud here...

That's a lot of miles. Partially clogged fuel filter will show up as loss of power at heavy loads (high revs, or full throttle.) Or...
Camshaft is wearing out? (not as much lift at the valves.) Or...
The overheat softened the valve springs so now they float at high revs? (misfire)

Start with the easy stuff first...
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Unread 07-09-2015, 03:40 PM   #4
ATjeep42
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1988 MJ Comanche 
 
Join Date: Sep 2013
Location: Sunnyvale, Ca
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Update

It's been two years. Just an update in case anyone else sees this problem - per a suggestion, I added Seafoam injection cleaner to a nearly empty fuel tank and after doing this a couple of times the power was much improved - no longer needed to drop down a gear to get over the Santa Cruz Mtns , though gas mileage is still down about 2 mpg and occasional misfire still persists. Up to 398,000k on the engine now.Firest
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Unread 07-12-2015, 08:28 AM   #5
Luuca
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2005 LJ Wrangler 
 
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Quote:
Originally Posted by ATjeep42 View Post
It's been two years. Just an update in case anyone else sees this problem - per a suggestion, I added Seafoam injection cleaner to a nearly empty fuel tank and after doing this a couple of times the power was much improved - no longer needed to drop down a gear to get over the Santa Cruz Mtns , though gas mileage is still down about 2 mpg and occasional misfire still persists. Up to 398,000k on the engine now.Firest
Had a cherokee that did the same thing. After a bad overheat it ran, but seemed like it was sluggish. Changed all the fluids and cap rotor but it still ran rich. This was a 93 xj.

He coil on ours was bolted to the block and with the overheating, had gone bad enough to run, but was giving me issues. Changed the coil and it had better spark and ran a lot better. We had a similar miss in the engine occasionally too and that went away.
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