Novak Conversions Jeep Wrangler JK engine mounts

2017 JK #3 Misfire

2017 JK Tony

2017 JK Tony

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Joined
Jan 7, 2024
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11
Location
Iowa
Hello,

It started one morning driving my wife to work, on the Highway to work the check engine light lit up, huh ok. I stopped to drop her off and noticed it running rough. So I drove to O'REILLY auto parts to use there scanner. It said #3 cylinder misfire ok fine. With 47,000 miles I will just give it a tune up and bought all new bosch injectors, plugs and NGK coils. The Jeep ran great but still had the check engine light on. Went back to O'REILLY auto parts and it said RICH fuel, so I called a local shop to reset the ecm or set the trim. They called me back and said it will not let them set the trim. They suggested install the original oem injectors and replace the one bad injector. I did exactly what they said.... the misfire came back just like before even with new plugs and coils.

So my question is.... why would it run great with the bosch injectors with too much fuel, then go back to the same issue with the old injectors???
I Inspected all wires and Connectors.
I bought a scanner to reset all codes, #3 Misfire will not go away with the oem injectors.

Bad ECM???

Thoughts...

Thanks
 
I would think RICH FUEL would mean a bad O2 sensor, the scanner should have given a CEL Code. Are you sure the guy at O'Reilly's knew what he was doing?

If the Jeep ran great with the new injectors then if it was mine i'd have left them in.
 
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2017 JK Tony said:
Wouldn't you be worried about too much fuel and washing out a cylinder or valves?
Click to expand...

But did he say which cylinder was rich, or were all of them? The ECM after it was reset should relearn any new Parts and adjust it's self, the O2 Sensors is what controls the fueling.
 
BLACKJKU said:
I would think RICH FUEL would mean a bad O2 sensor, the scanner should have given a CEL Code. Are you sure the guy at O'Reilly's knew what he was doing?

If the Jeep ran great with the new injectors then if it was mine i'd have left them in.
Click to expand...
The O'REILLY guy didn't hook it up, I did. Yes it gave me the code for Misfire #3 the first time.
2nd time with Bosch injectors it said P0172 - fuel systemRICH. 1/1 rich, P0513 - invalid SKIM key,
P0175 - fuel system 2/1 Rich.
 
Since you have a scanner I would put the new injectors back in and verify the code that comes up. It may be that the misfire code remains on #3 and the O'Reilly worker misread or misinterpreted it as @BLACKJKU stated. If the misfire is always on #3 I would look at the connector and wiring to the COP as you may be getting intermittent connectivity.
 
BLACKJKU said:
But did he say which cylinder was rich, or were all of them? The ECM after it was reset should relearn any new Parts and adjust it's self, the O2 Sensors is what controls the fueling.
Click to expand...
No it did not say what cylinders were rich just P0172, P0175, P0513 codes
 
2017 JK Tony said:
The O'REILLY guy didn't hook it up, I did. Yes it gave me the code for Misfire #3 the first time.
2nd time with Bosch injectors it said P0172 - fuel systemRICH. 1/1 rich, P0513 - invalid SKIM key,
P0175 - fuel system 2/1 Rich.
Click to expand...
I would drive it and let the system learn. No concern with fuel wash for a relatively short period of time imo
 
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tJKrider said:
Since you have a scanner I would put the new injectors back in and verify the code that comes up. It may be that the misfire code remains on #3 and the O'Reilly worker misread or misinterpreted it as @BLACKJKU stated. If the misfire is always on #3 I would look at the connector and wiring to the COP as you may be getting intermittent connectivity.
Click to expand...
I took each connector apart looked with a light for corrosion or anything that would make the connection bad. Everything looked good.
 
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2017 JK Tony said:
No it did not say what cylinders were rich just P0172, P0175, P0513 codes
Click to expand...
So global rich fuel. If the OEM injectors were getting aged the duty cycle may have been higher to achieve the proper air fuel ratio. It will take some time for the PCM to adjust back.

I like the PCM reset info @BLACKJKU provided above. Makes sense to me.
 
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tJKrider said:
So global rich fuel. If the OEM injectors were getting aged the duty cycle may have been higher to achieve the proper air fuel ratio. It will take some time for the PCM to adjust back.
Click to expand...
So your saying put the new Bosch Injectors back in, reset the ECM as per the forum and run it for a few days?
 
2017 JK Tony said:
So your saying put the new Bosch Injectors back in, reset the ECM as per the forum and run it for a few days?
Click to expand...
Yes. I would try exactly this. If you get an initial rich fuel code clear it. I'm also basing this off your observation that the vehicle was running well with those injectors when tried prior.
 
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tJKrider said:
Yes. I would try exactly this. If you get an initial rich fuel code clear it. I'm also basing this off your observation that the vehicle was running well with those injectors when tried prior.
Click to expand...
Yes it ran perfect with those 3 codes P0172, P0175, P0513. The misfire was gone
 
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tJKrider said:
Yes. I would try exactly this. If you get an initial rich fuel code clear it. I'm also basing this off your observation that the vehicle was running well with those injectors when tried prior.
Click to expand...
Ok I will do all this again one more time and I will let you all know what happens.
Thank you!!
 
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2017 JK Tony said:
why would it run great with the bosch injectors with too much fuel
Click to expand...
I also want to respond to this. Too much fuel can have different connotations. Lean and rich in the OEM world is relative, not absolute vs. stoichiometry (14.7:1). OEM calibrations try to run as lean as possible for any given speed/load operating point. There may be other metrics that force a richer mixture (temperature, emissions, etc) but in general, the cal is attempting to use as little fuel as possible. At idle, for instance, there is a critical lean threshold where the engine will not operate smoothly without enough fuel. So a little more fuel isn't necessarily grossly rich to where the engine would run poorly, just richer than the preset range the PCM is expecting for a given condition.

When you drive it try to run at different rpms, do some wot accels, etc.
 
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tJKrider said:
I also want to respond to this. Too much fuel can have different connotations. Lean and rich in the OEM world is relative, not absolute vs. stoichiometry (14.7:1). OEM calibrations try to run as lean as possible for any given speed/load operating point. There may be other metrics that force a richer mixture (temperature, emissions, etc) but in general, the cal is attempting to use as little fuel as possible. At idle, for instance, there is a critical lean threshold where the engine will not operate smoothly without enough fuel. So a little more fuel isn't necessarily grossly rich to where the engine would run poorly, just richer than the preset range the PCM is expecting for a given condition.

When you drive it try to run at different rpms, do some wot accels, etc.
Click to expand...
I did that with the new injectors when I had them installed. Didn't notice power loss except taking off from the stop, it hesitated for a brief second but ran great while driving, wot ran great, passing gear with down shifts ran smooth.
 
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2017 JK Tony said:
Yes it ran perfect with those 3 codes P0172, P0175, P0513. The misfire was gone
Click to expand...

If the was a misfire with the old injectors on #3 and then none on the new ones then the new ones were good. If you remember which old injector was #3 you could put it into a different cylinder and if it was bad you'd have a misfire on that cyl.

Somewhere I read how many miles you need to drive after resetting the ECM for it to relearn, but i'm sure it's going to be quite a few and also on the highway would probably be the best place to take it for a drive.
 
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Update on Misfire...
I installed the new injectors on the 1,3,5 cylinders, cleared codes took for a 20 mile drive codes stayed gone and no check engine light. Runs good.
I hope this works, so nerve racking when an issue pops up.
Thank you for all the help and ideas.
 
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