Intermittent misfire

John Middleton

John Middleton

TJ Enthusiast
Supporting Member
Joined
Dec 13, 2017
Messages
145
Location
Missouri, United States
03 Rubicon 185k miles: I’m stumped! Intermittent miss @ hiway speeds: almost like a stumble or hitting a big bump. No ours wheeling or @ slow rpm’s. Feels like a intermittent bad coil pack would.
I’ve replaced plugs, cam & crank sensors, cam sensor Driveshaft (OPDA on newer models), & coil rail.
Could it be throttle position sensor or what do I need to look at in fuel delivery system? Tired of being in the dark!

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How old are the fuel injectors ? Are they the originals ?
IF they are the originals; they may be really dirty and not flowing enough fuel at high speeds causing a leaning of the fuel mixture.
OR when the fuel injectors heat up the electrical resistance causes a short injector pulse duration.
You can test this with the newer style Scan Tools that do Live Data for engine operation, but you will need to be experienced to understand what you are seeing.
 
The injectors are not cleaned that quickly nor will it cure the electrical resistance problem if they exist.
A super concentrated mixture needs to be pressurized into the fuel rail for a 30 mins or so and it couldn’t hurt to clean the throttle body too.
 
What type of procedure & product can I use to effectively clean the injectors? Or do I need to remove them & clean?
If I’m running my engine & scan tool in live view, what should I be looking for?
 
John Middleton said:
I need to remove them & clean
If I’m running my engine & scan tool in live view, what should I be looking for ?
Click to expand...
Document the fuel enrichment trim adjustments before and after cleaning.
Realistically you should see the enrichment adjustments decrease slightly.
At 152K miles I replaced the original 1 hole fuel injectors with 12 hole fuel injectors; the trim dropped 3 on several of the injectors and 2 on others.
I attribute the slight bump in performance and gas mileage that I received to the clean injectors and better atomization of fuel spray.
 
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