Timing issue

After a winter's worth of various engine/fuel troubles, I finally
resolved most of that a few weeks ago and got my rig running , heh, or so I thought
anyway......

10 miles into a test ride the cel comes on, I get the heep home, and it
is complaining about multiple misfires off all 6 cylinders, so I clear the code, go check all the usual sensors, etc everything checks out ok....o2,injectors,cam, and crank sensors all are doing exactly what they should be except that if I try to run it up past 1500rpms or higher and I get lots of misfires / back fires..(out the exhaust)..whether or not the engine is under a load or not.
so, on the recommendations of a friend who is pretty well versed in 4.0
engines, and has a scanner that gives more details, I clear the all the codes again add new wires, cap and rotor and replace the plugs. The cap and rotor were a year old but not abnormal wear wise, the plugs were fine all looked very normal. Still happens, this time with no
codes - engine warms up, rev to 1500 or higher, and there's misfires ....
next thing to try, add a new coil (had one in the parts box) starts
right up, idles nicely, but has the same problem, it seems something bad is happening to the timing, but not bad enough to throw codes......and only as the rpm's go up.......

There was a tsb for older renix Jeeps regarding the distributor getting
misaligned, causing these symptoms, so next I dig into seeing about how
bad the distributor is out of whack, it is way out of line, so, not
having much to lose, I try the recommended mod (removing the alignment
tab to be able to rotate the distributor shell inline with the alignment
holes in the shell and the shaft.) I get everything all back together,
start up the Jeep, the idle comes right down to 750rpm (it was a little
over 800 before) I let it come up to temp, the get on the gas, 1500 rpms
and it was rough but bearable, over 2k and I get the same thing....
My best guess at this point is something real bad is happening
mechanically with the timing. But, not quite far enough off to register
a code....

Any thoughts?

don't overlook fuel delivery as a possible culprit. Insufficient fuel volume will allow it to run at lower RPM, but starve for fuel at higher revs. Also, a TPS with a "dead spot" or a MAP that leaks vacuum can give symptoms under certain conditions, but still idle ok.

Thanks, I did check fuel pressure, and it was normal, but it might not hurt to look at it again, it has a new tank and fuel pump... old tank was a tad leaky and the pump stb....

was the disco ever removed from the jeep? if it has it may be one tooth off.

what year?

unless the distributor has been removed and reinstalled incorrectly, timing should be ok enough for it to be driveable unless the timing chain is really stretched or jump a tooth.

are you testing under load(driving in gear) or in park not under load?

as said, fuel starvation will allow a good idle but under load or high rpm the engine will fall on its face.

how about a plug wire(s) being on the wrong plug or cap terminal?

89xj said:

what year?

unless the distributor has been removed and reinstalled incorrectly, timing should be ok enough for it to be driveable unless the timing chain is really stretched or jump a tooth.

are you testing under load(driving in gear) or in park not under load?

as said, fuel starvation will allow a good idle but under load or high rpm the engine will fall on its face.

how about a plug wire(s) being on the wrong plug or cap terminal?

Click to expand...

96 (HO) is sort of drivable....(not)



New distributor indexed properly, (as much as it can be)

Been run Both under load and not

Plug wires are good, new cap & rotor,coil, ckp,cps

I am leaning towards fuel starvation or some type of problem with the timing chain (seems to be the two most popular thoughts about it....)

Art Triggs said:

96 (HO) is sort of drivable....(not)



New distributor indexed properly, (as much as it can be)

Been run Both under load and not

Plug wires are good, new cap & rotor,coil, ckp,cps

I am leaning towards fuel starvation or some type of problem with the timing chain (seems to be the two most popular thoughts about it....)

Click to expand...

how did it run before the new dizzy? why the new dizzy?

more history of problem

The old dist does not align with the alignment marks on it at tdc, like I mentioned earlier there is a "hacky" fix to line it up, which I did with the new dist, (old one had 150k on it
anyway..and showed some serious wear marks on the drive gear and oil pump drive) New one lined up exactly the same way, before I modified it, just tells me that something else isnt right about where tdc is and where it is marked.