97SPORTXJ

i have a 97 cherokee with 105000 miles, my check engine light came on about a 1000 miles ago. i read the code and it said cylinder 1 misfire. i pulled the plugs and the all looked okay except the cylinder one plug. also i did a tune up about 3000 miles ago with bosch platinum plugs along with wires, cap, and rotor. it runs terrible with a bad idle, so i did a compression test and these were my results after seven compression strokes according to the haynes manual...

cylinder 1- 135
cylinder 2- 170
cylinder 3- 170
cylinder 4- 170
cylinder 5- 135
cylinder 6- 170

not really sure what to do at this point any help would be much appreciated

MtnHermit

If it is the same issue as my 1997, then look VERY closely at the wiring harness between the engine and firewall.





In my case it was the sharp end of the fuel manifold. Others had one of the head bolts cut/ground the wires. Cheap fix.

I spent hundreds chasing my tail on idiot codes and "professional" jeep mechanics.

The Rooster

Change your plugs to the factory copper plug... I have brought a 4.0 with a bad misfire with play plugs and the plugs where new put factory copper ones in and the misfire went away.. What color was the plug when you took it out? Was it black with carbon build up??

The Rooster

Also has it been running hot at all?

CCKen

The Cherokee Factory Service Manual states that the compression reading should be recorded after three (3) compression strokes, not seven.

If done in accordance with the FSM those 170 psi readings may drop to 135 psi and the 135 psi readings drop to something less. The FSM states 120-150 psi is the normal compression pressure, with a maximum variation of 30 psi between cylinders.

If you redo your compression test and see reading(s) of less than 120 psi, add about a teaspoon full of engine oil to the cylinder, through the spark plug hole, crank the engine over, then recheck the compression. If it comes up, there's a likelyhood that the rings in that cylinder are worn/bypassing.

If the sparkplug from #1 cylinder was black/oily, the rings may be shot (?)

As advised, use Champion RC12ECC plugs (or NGK ZFR5N plugs). Bosch wires are good. In my book, distributor caps with Brass contacts are better is another myth.

It may be a good idea to do a compression loss check on cylinders #1 and #5. With 90 psi applied to the cylinder while it's at TDC compression, and you hear air escaping through the TB, the intake valve may be bad, or if you hear air escaping out the tailpipe, the exhaust valve may be bad, air heard escaping through the oil fill hole in the valve cover or oil dipstick tube would indicate bad rings. When I say the valves may be bad I mean there may be crap between the valve and the valve seat, or the valve is burnt or cracked.

Let us know what you find.

jebmccall

i second using only champion copper plugs on the 99 and older 4.0 and ngk on the 2000-06 4.0. i ran those expensive plugs in my 99 and it ran like crap.

97SPORTXJ

thanks for the replies, i changed the spark plugs with champion plugs and the rough idle went away. it runs pretty smooth now. but the check engine light is still on even after i cleared it. i got three codes back

p0201
p1398
p1491

also my crankshaft position sensor is brand new from the dealership just changed 800 miles ago

CCKen

The above fault descriptions are from a '99 FSM, but are OBD II like your '97.

1st, follow MtnHermit's suggestion about checking the wiring, as shown in his post.

These are possible causes for P1398:

DAMAGED TONE WHEEL/FLEX PLATE (CRANKSHAFT)
SENSOR CONNECTOR/WIRING
CKP SENSOR CONNECTOR/WIRING
CRANKSHAFT POSITION SENSOR
IMPROPERLY INSTALLED/LOOSE CRANKSHAFT POSITION SENSOR

TEST ACTION APPLICABILITY
These are possible causes for P0201:

WIRING HARNESS INSPECTION
ASD RELAY OUTPUT CIRCUIT
FUEL INJECTOR
FUEL INJECTOR DRIVER CIRCUIT OPEN
FUEL INJECTOR DRIVER CIRCUIT SHORTED TO GROUND
POWERTRAIN CONTROL MODULE

TEST ACTION
These are possible causes for P1491:

RADIATOR FAN RELAY OPERATION
GROUND CIRCUIT OPEN
FUSED B+ CIRCUIT
RADIATOR FAN RELAY OUTPUT CIRCUIT

RADIATOR FAN RELAY