jeepdewd

I have a 97 grand cherokee straight 6 4x4

A couple of months ago I got a miss fire in cylinder 3. I replaced the spark plugs.

About a month later I had multiple miss fires.
This past weekend I pulled the cylinder head replacing the springs, pushrods, lifters and head gasket.
Today I got another check engine light for multiple miss fires

The plugs and wires are basically new and what I replaced this weekend is brand new.


Does anyone have any ideas whats going on?

Rock36

Heya! DId u figure this out? Some other threads are saying maybe it's the coil packs or the oxygen sensors. Do you have a number of the code that is thrown?

jeepdewd

Not really,


Im starting another thread with some pictures.


I developed a knock in the motor a couple of days after I got it all back together

dave1123

Check the distributor shaft bushing for sideways play. Looseness there can allow the shaft to wobble and even to strike the cam sensor ring.

97grand4.0

With the distributor system there is only one thing, to my knowledge, that will set a misfire cylinder code, that is an open circuit in one of the fuel injection circuits, most commonly being the injector itself first and then burnt wires or bad connectors. That being said, if you get odd random misfires on multiple cylinders I would suspect the pcm itself or connections.

jeepdewd

I will be replacing fuel injectors, the wire harnesses and fuel rail. 300k, I believe it's time and might as well make sure everything is new since I'm basically rebuilding the damn motor.

I can see that some wire sheaths are busy and can see copper wire however those particular cylinders were not giving miss fire codes

97grand4.0

you might try an ohm meter to check the resistance of the injectors, there is a spec on that. also they have noid lights to see if the injector is firing.

dave1123

I'm going to tell you right off that the original Siemens injectors are junk! The cases tend to crack and allow water to get into the coils. I replaced mine with Bosch 4-holers and got much better throttle response, idle, and better mpg.

97grand4.0

I once knew a girl they called Miss Fire.

dave1123

I'll bet she was smokin'.

97grand4.0

She ran hot.

97grand4.0

Here is a great video from ScannerDanner if the monitors will let me post it. Interestingly, unlike the Cherokee, the 96 and 97 grand cherokee does use this style of "adjustable" crank sensor also...I dont have a scope either, yet, but the first 4 minutes of the video tell a LOT of the story if you pay attention. First use propane to see if it eliminates the miss, if not, go to ignition, and use an inline spark tester...note the kind he uses, to observe for EVEN firing. This ends up being the crank sensor is gapped to widely. youtu.be/ws59zXvr1SM