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96 xj misfire at idle

Joeygrimm93

NAXJA Forum User
Location
Arizona
So I’ve recently been having some issues with my 96 xj it all started after I accelerated quickly to pass someone. What happens is that it misfires on cylinder 1 at idle and runs just fine at any other rpm with no power loss. This occurs at any engine temp. Engine codes are p0300,p0301. The problem had went away for about a week and now it is back.

Current things checked or replaced:

Head was rebuilt 6k miles ago
Distributor-replaced
Cap,wires and rotor- replaced
Cyl 1 injector/wire-replaced(was not faulty)
Checked grounds
Checked for vacuum leaks
New plugs
 
Any other issues at all?

Have checked compression on #1

Fuel injector may be partly plugged.

I had a partly clogged Cat converter(s) from 10 years of head gasket coolant leaks cause a cyl 1 one miss fire that turned out to be the Cat converters being clogged up enough the throw a code (probably during heavy acceleration...) on a 96 Form V-6. But it idled it fine.

Why was head rebuilt???

Have you replaced the #1 plug since the problem started? Have you inspected the #1 plug???? What did it look like?
 
Fuel injector is brand new and is definitely functioning. I have switched injectors with others (no change)and had a spare and ended up leaving the new one in. Cyl 1 compression is good (135 psi). The cat was falling apart inside and was replaced.
Head was rebuilt just because of gasket leaks on the intake/exhaust so I figured I’m already halfway there and just had it rebuilt while I was in there. Spark plug looked a little fouled I cleaned it off and swapped it with another and it made no difference. The only thing so far that I found odd was that the spark on cyl 1 was orange.

The truck started driving normally again yesterday but I know the issue will come back.
 
Orange spark, may be the HV coil and or ICM going bad, or poor electrical contacts.

What plugs are you using?

Is the dist cap bad on cyl #1???? (tracking HV to ground,cracked or something?)

Did you properly index the Distributor when replaced?
 
I’m using the plugs everyone recommends I think it’s champion?

Dist cap is brand new and no problems that I can find I’ve checked just about every electrical connection I can find and yes the distributor is properly indexed.

all of the stuff that was replaced was in attempt to fix the problem, the previous distributor shaft had so much play the rotor would hit the cap but replacing it didn’t help fix the misfiring issue.

The orange spark is only on cyl #1 I have checked wires, swapped plugs ect.

The only thing I haven’t checked was the coil but I would think if the coil was bad/on its way out I would have no spark or weak spark on multiple cylinders.
I do plan on pulling the coil and checking it out this afternoon or tomorrow when I get a chance.
 
So I changed the coil to msd, and the fuel filter with no change I’m at a loos for what to do next nothing has made any difference that I can tell pulling the wire or injector on cyl makes little to no difference and it is definitely getting fuel and spark
 
Then you are not getting ignition all the time based on that test. Recheck the compression. You might try using a product like Gumout to see if cyl one has carbon crap on the valve seats, causing a temp compression problem.

Timing? Late or early spark? Perhaps the distributor is not properly indexed?

Factory indexing was not good enough on the older 4.0s. Not sure about the 96, but perhaps it is off by one gear tooth? Maybe you replaced one problem with another, off by one gear tooth? Cruiser54 has a great write up how sweeten the indexing process!!! 1/8" change in mine by cutting the tap and rotating it before locking in place made a huge difference on many of out rigs!!!
 
I’m going to re check compression and try to re index the distributor, at this point it has to be something timing related.
I’ve replaced everything and checked everything else that I can come up with. The miss went away (may have just gotten less noticeable) for a few days last week and came back after a little off-road trip two days ago.
I replaced the coil and fuel filter today and it got a little better not as noticeable but still misses(not shaking the steering wheel).
 
Follow this

http://cruiser54.com/?p=68

It should be the same on a 96 as the 87-90? Making the window cap, and cutting the tab so you can rotate the housing is the key trick.

I’m going to re check compression and try to re index the distributor, at this point it has to be something timing related.
I’ve replaced everything and checked everything else that I can come up with. The miss went away (may have just gotten less noticeable) for a few days last week and came back after a little off-road trip two days ago.
I replaced the coil and fuel filter today and it got a little better not as noticeable but still misses(not shaking the steering wheel).
 
Since the Crank Position Sensor locates the number 1 cylinder to start the firing sequence, it's a suspect. Try unplugging the CPS and squirting WD-40 on the pins and reconnect. Then see if there's any change.

If not the CPS, perhaps the ECM (as Ecomike mentioned). I believe the ECM grounds the coil to initiate spark, according to the CPS signal...and the sequence starts with cylinder 1.
 
Just dawned on me, he needs to test the fuel injector wiring harness connector for signal (Noid lights, tool, make that real easy) and check the injector resistance (or use stethoscope and listen for clicking sound).

That weak orange spark on #1 sounds like a clue, but I don't recall him testing the fuel injector signal.
 
So the weak spark seems to have been fixed by the new coil(cleaned spark plugs as well to check go fouling).
I have checked all injectors and they are in good working order I’ve even swapped them around ect.
I checked out the cps cleaned the connection and what not with no change it is a newer Mopar CPS with about 7k miles on it.
Did the timing with cruiser54’s guide with no change.
I reset the computer yesterday and haven’t had a CEL thrown yet but it still has a slight miss.
The only thing I can come up with now is that the ECM is failing in some way.
The miss isn’t as bad as it has been previously after everything I’ve done but it also could be going through a phase where It doesn’t miss as bad for a couple days.
 
I’m not sure if it helps any but I noticed it misses a lot worst at startup then when the idle settles down it’s not as bad but still noticeable.
 
Have you tried the NGK brand spark plugs Cruiser recommends? They made a huge difference on mine.

Have you tested the ECU to fuel injector connector on #1 with a noid light to see if it is firing all the time, like on start up cold idle....? I know that on the older ECUs they could loose a diode that fired (grounded) the injector to fire them.

Sounds like you could use an OBD-II blue tooth scanner/cell phone set up with the Torque program app. About 20 + 10 $ last time I checked, to see the fuel trim and some hard core data like spark rise time, etc. Or a scope.

You could be down to just some carbon fouling in the head/valves? Have you rechecked that #1 compression? Also the cylinders all need to be with 20 psi of the others that fire just before and after that one to make it run smooth.
 
Compression is still all the same 135-140(lower numbers may be due to rubber type of tester)I don’t think carbon would be the problem since all the engine internals only have about 7k on them and I’ve run some Seafoam in it but I’ll try another clean with the ol’ water trick.

I’m going to test out the ECU and try out NGK plugs over the weekend and see what I can come up with.
 
New internals? Hmm. ALL???

When did the problem start? Have you pulled the valve cover to see if the the valves/springs/rockers....all look and act the same?

New lifters? New Cam? details???

Compression is still all the same 135-140(lower numbers may be due to rubber type of tester)I don’t think carbon would be the problem since all the engine internals only have about 7k on them and I’ve run some Seafoam in it but I’ll try another clean with the ol’ water trick.

I’m going to test out the ECU and try out NGK plugs over the weekend and see what I can come up with.
 
Problem always starts after I get in the throttle aggressively to pass ect...

Yes I’ve pulled the valve cover and everything looks like they are functioning properly and all have the same range of movement that I can tell.

New internals were basically everything besides the cam and crankshaft
 
Does it do the same thing in park when you gun it?

If not it may be partly TPS/TCU transmission gear selection, or TC lock related. If yes, then the ECU is not get good data from the TPS, MAP and or O2 sensors sensors, or the spark is too weak at high rpms (load/heat), or the fuel pressure is off during acceleration. Is the gas tank fuel low?

Or the Distributor has a problem.

Is the air filter soaked in oil?

Problem always starts after I get in the throttle aggressively to pass ect...

Yes I’ve pulled the valve cover and everything looks like they are functioning properly and all have the same range of movement that I can tell.

New internals were basically everything besides the cam and crankshaft
 
I haven’t tried gunning it in park when it’s not missing as bad to see if that causes it(unfortunately it started missing bad again yesterday).

What I mean by it missing after driving agressivly is that it doesn’t miss when in the throttle it starts missing at idle speeds after driving aggressively.

Distributor is brand new and problem existed before new distributor.

Air filter is pretty new and clean.
 
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