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Discussion Starter · #1 ·
i have a 97 jeep wrangler 2.5L automatic that has been misfiring, ive replaced all spark plugs, spark plug wires and the distributor as well as o2 sensor, crank sensor and throttle position sensor. the misfire started in cylinder 4, after i replaced the fuel injector for 4 it still misfired but now 3 is misfiring too. i also checked compression and it turned out good. about a week ago i don't know how but i got it runnig just right for about 5 minutes before i hit the curb to my driveway and it misfired in 3 and 4 again, please help
 

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Check all of your ground wires for clean, tight connections. Double check your battery cables. Is the "Check Engine" light illuminated? If so, give us the codes. If not, it could be many, many things.

Make sure all of the connections to the ECM (on the firewall, passenger side) are on good and tight and that none of the cables are chafed or being compressed by the battery.

Sounds like a wire is not making good contact or has been abraded, just a little. Get a copy of the Factory Service Manual and take a look at all the wiring. Check for brittle/mising insulation on wiring and any place the wiring runs across the back of the engine.

Suspect Items (in the order of how I'd check them):

1) Grounds - all of them.
2) Battery terminals - clean/tight!
3) ECM connectors, installed tight and square to their mating connector.
4) Wiring harness near the battery - no rubbing, no chafing.
5) Wiring harness across the valve cover, make sure it's not chafed or rubbing there.
6) Coil - clean contacts for all points of contact, terminals and where it bolts to the side of the block.
7) Crank position sensor - back of bell housing on driver's side. Make sure it's in there good, screws aren't loose and that the connector to the wiring harness is tight.
8) Check all connectors to fuel injectors, Throttle Position Sensor, MAP Sensor, Idle Air Control motor

That's just what I'd do, for starters.
 

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Are your plugs gapped correctly? Distributor set with TDC in check?

So you swapped injector 4 with 3, and now 3 is misfiring and not 4? Or both 3 and 4 are misfiring?

What codes are you throwing? 97 can be read on the dash. Turn the key to the on position then off, three times. On/off/on/off/on and leave it on. The codes will be spit out on the odometer. If you did it right, you should at least get code 55 which means "done"
 

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Verify that injector wires three and four are not reversed

On the 2.5 something about the harness layout makes people tend to reverse injector connectors three and four

It still runs ok as fuel entering the cylinder is really timed by the intake valve but injection is supposed to be sequentially timed and reversing the harness plugs for three and four tends to make the 2.5 stumble starting around 1700-2200 rpm

Just a quirk of the 2.5

Check the wire colors on the injector harness plugs


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Discussion Starter · #5 ·
the check engine light is not on and has no codes on the dash except 55. i replaced fuel injector 4 and ifter i did, 4 was still misfiring but 3 started to as well,
 

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Discussion Starter · #7 ·
the fuel injector wires are correct but after looking at the wiring harness i found 4 wires that i have no idea where they go

Auto part Wire Cable Engine Fuel line


Auto part Fuel line Hand Engine Wire


let me know if you are having trouble seeing them
 

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Your 2.5L probably has the same problem common to '97-98 4.0L engines which also causes intermittent random misfires, the factory received and installed a bad/weak set of valve springs p/n 53020556. The 2.5 and 4.0 use the same valve springs.

There's a factory TSB (technical service bulletin which is not the same as a Safety Recall that is done for free) that addresses that issue, it basically just says to replace the valve springs. The same p/n is still used, they got all of the bad valve springs out of the system.

My '97 TJ had the same issue, replacing the valve springs fixed it. Though by now, weak valve springs might have caused the valves or valve seats to have burned where the better fix is probably a complete valve job.
 

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Discussion Starter · #9 ·
thanks, ill check the springs as soon as i have the time and ill get back to say if it works, in the meantime, does anybody know what those 4 wires are?
 

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Discussion Starter · #10 ·
i still haven'yt gotten those springs in yet because it has been raining a lot, however i did replace my battery and as soon as i did, i recieved a code 54 on the dash, it was a broken wire and now it starts again, i am also going to replace all my fuel injectors next sunday to see if that helps anything
 
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