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Strange and horrible sounding '87 Renix 4.0 I6

M

matt0106

NAXJA Forum User
Location
Little Elm, TX
Hey all. Thanks for reading.

I'm having a really hard time figuring what my 4.0 is doing. It sounds really horrible when it's running. Almost as if it's not running on all cylinders/misfiring. 1987 Cherokee Laredo, Auto, 4.0 I6, lifted.
Recently changed spark plugs and oil. Also checked fuel injectors, all are working properly.
I made a YouTube video to give y'all an idea of the sound.
http://youtu.be/fnZMIlqwgVI



Also another thing that it started doing, IT WILL START, BUT WON'T RUN FOR MORE THAN A MINUTE.
 
Like Outlander said, check the ballast resistor/fuel pressure. Sounds like a fuel issue but could be any number of things.

If it is blowing clouds of smoke out the exhaust I'd check the MAP vacuum line. That vacuum line springs a leak or pops off, it may run really rich, almost so rich it barely runs at all.

I've also had them sound like that when a couple of cylinders aren't firing. It will run OK on five cylinders, pretty bad on four cylinders and hardly at all on three cylinders.

It may also run really ratty when the CPS is trying to fail.

It may also run really bad when coolant is leaking into a cylinder or two.

One trick I use trying to chase down misfires is using a timing light on each cylinder 1-6 and pointing the light at the relay cover (or something else flat and dark). If you have a misfire it will show up quick.
 
Double check the spark plug wiring. It can cause all of which you speak.
 
Remove the serpentine belt and run it briefly without (only very briefly of course, since it will disable the water pump). It's of course hard to tell from the video, except to confirm that it sounds nasty, but I'd want to eliminate various bad bearings such as AC pulley, water pump and alternator.
 
Thanks for the help guys.

But just recently, after I took the video, my jeep will start, run like complete crap, then just sputter out and die. I cleaned the coil contacts and the ICM connectors to see if that would help with the shoddy spark, no go. Got the battery checked and charged, just because I was reading that a low battery could start it, but not put out enough voltage for the ECM and various sensors, also no go. I have already checked the fuel injectors, they're squirting. Fuel pressure is always about 40psi +/-1 while running, and about 35psi+/-1 with the key in on position, not running.
 
Sounds like ignition doesnt want to advance
Has the distributor been pulled out lately?
barring that sounds also like maybe bad map sensor or bad vac line
 
I've never pulled out the distributor. Checked the MAP sensor by unplugging it, it ran better for like a second then died. I don't have a knock sensor right now because I broke the connector on the current one and I don't have money for a new one, but I read at the time that it happened, that running without one isn't a big deal.
 
87 will not have a ballast resistor unless someone too it in and complained about the pump noise to a dealer.

unplug the knock sensor.
a hard miss will freak the knock sensor, which freaks the ECU even more than just the miss.

unplug it, see if the timing/ignition advance works again, then go about diagnosing your miss without the ecu trying to compensate for it.
 
usually a new [plug wire get's hosed under the boot.

pull the boot back and make sure the crimps are good on your new wires.
 
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