I have been messing with a constant misfire and have scoured the internet and asked pretty much everybody I could think of. I know most of the posts here relate to older cars but I have gotten some great advice here in the past so here goes.
97 Grand Cherokee, 4.0 liter straight 6 cylinder with fuel injection and non-adjustable timing. 284,000 miles. Stomped on it to pass on the expressway and it reved up pretty good. When I got to stop, it was missing and idling rough. It seems to be a misfire on #1 cylinder. Misses at idle, cruising and under load. If I disconnect #1 injector wiring connector, there is no change in engine while idling. Unplug any other injector connector and the engine stumbles more. Tried a new injector and no luck. I switched new injector with another from another spot and still misses at #1. Listened to them and #1 seems to be ticking so I think it is firing. Put test light on each injector connector and the light flashes with rpm equally at each connector. Ohm meter reads 12.5 ohms for all existing injectors and 16.4 for the new one. Switched #1 plug with one from another spot and no change. Switched #1 plug wire with another and no change. Coil wires are connected and look good. Checked cap and rotor, center contact going to coil has tip broken off a little (1/8") but there is spark going to #1 plug. Timing light showed 10 degrees on #1 wire. I pulled valve cover and all valves seem to be opening and closing properly. Did a compression check and #1 was 110, #2 132, #3 132, #4 140, #5 137, #6 112. Tried MOPAR Combustion chamber cleaner for the heck of it..........nothing changed.

I am running out of ideas here.............help me out guys.
Got any suggestions?

Thanks in advance,

ResQ911

You've got spark, compression, and fuel.

That's all you need.

I think you need to recheck some of your findings(no offense man, I have been there myself). Something must be overlooked.

I would concentrate your efforts in the spark area. Injectors to cause a dead miss are very seldom.

When you checked the injectors did you use a light that pluged into the connector, or just a normal test light? If it is plugged into both wires at once, then you are testing the power and ground, so can be more accurate than a regular test light.

Perhaps double check the stem tip height of the valves too. Sometimes a cam or valve problem is not easily seen in compression test. I once chased a miss in a SB chevy dead miss on number 8. Had spark and compression, and was a carb rig, so it had fuel too. found that exhaust lobe wqs wiped right off. Still had compression but had no where to send the exhaust after it fired, so it would spit it back into the intake.

I used a plain old test light. Tip of light on one spade connector and the clip on other spade connector. Is that what you meant by testing both wires at once?
What else could I do to check spark?
Thanks!!

97 is OBD2. you should at least pull the codes and make sure you are chasing the right cylinder

Have you leaked down the engine? Cranking comp doesn't give you an accurate view of the low comp issue in cyl's 1&6. Check the distr gear also, you may be in the edge of the timing window.

I get codes 27 and 43 when I check by turning igntition on/off three times. The check engine light is not on right now and I disconnected battery recently. I have gotten up to 5 27's in a row when I retrieved trouble codes. I guess I thought I had it nailed down to #1 because when I disconnected wiring to injector #1, there isn't any change in how the engine runs..........still rough.
Thanks!!

As stated, you need to do compression, and if possible, a leakdown test. At that mileage you are very likely to have weak or broken valvespring, or even a burned valve. Check your basics. Go buy a vacuum gage,and follow the diagnostic chart that it comes with, or look in a service manual.

Codes are:
12
27
27
27
27
27
43
55
The check engine light flashes the numbers as well. (One flash then two for 12, two flashes then seven for 27, etc.)
I pulled valve cover and the springs look ok, all the lifters are moving equally. I replaced the cap and rotor. Put in new plugs. Nothing changed.
I am taking it in to the dealership mechanic tomorrow.........ouch. I was hoping to figure this out on my own.

Well this is what I got from the Jeep mechanic. (Cost me $135.00 for the info)
He says there is an exhaust manifold leak. I had tried last year to weld it up, got most of it but couldn't quite get to the backside with MIG. He said the O2 sensor may adjust for leak and run rich causing rough idle. He said it is hard for him to diagnose root cause of misfire until I fix exhaust manifold leak. Problem is, it just now started idling rough. It has had this leak for awhile, maybe it's gotten a little worse but is it enough to make it run like crap?? With new plugs, cap and rotor my cruising misfire has gone away. Still idles real rough but when raised above idle, it smooths out some.
He did compression and leakdown tests and said they are all sealed up good for that many miles. Checked valvetrain and said all is well.
I drove away from the dealership disappointed and parked at a gas station. Still idles rough. When I drove away again the check engine light came back on with a code 43.

•43 Peak primary coil current not achieved with max dwell time
OR
•43 Cylinder misfire
OR
•43 Problem in power module to logic module interface

I disconnected the downstream O2 sensor just to see what happened and no change. Does not even trip a error code.

This is getting frustrating.
Help me out guys.......