Need advice - unexplained missfires

CWBenjamin

Member
Joined
Oct 10, 2019
Messages
76
Reaction score
12
Hello. So my jeep was doing okay and suddenly started missfiring a mile into my drive. Here are the details:
Recently replaced all of the timing chains and guides and gaskets throughout.
Replaced mass airflow sensor, replaced cam sensor, replaced throttle position sensor, replaced all spark plugs with ngk copper oem, replaced all coil packs.

I did have an intermittent 02 sensor code for delayed response, but there was some oil that had dripped onto that 02 sensor and burned off just before that code popped on so I thought maybe that was messing with it.
So nothing else was going on, and then randomly it started shaking and seemingly getting worse until I got home. If i could explain how it felt, it seemed like one cylinder was missfiring, then as i drove, went to 2, then 3... When i got home a couple miles later, it had codes for:
Multiple cylinder missfires.
cylinder 1 missfire
cylinder 2 missfire
cylinder 3 missfire

I tested the battery and alternator and they are both fine.
Starts up just fine every time (other than struggling with 3 cylinders)
I tried replacing the ASD relay, nothing changed.
It does sort of sound like a hissing or excess noise from throttle body area, so I pulled it off and cleaned it up with some carb cleaner and cleaned the idle air sensor off a bit, and replaced the throttle body gasket. Nothing changed, but (idk if coincidentally) it then showed Evap gross leak code.
All the hoses are on and no breaks I can see.
The only other thing I can think of is maybe the fuel filter? Or the fuel pump?

Any ideas greatly appreciated - TIA
 

Ksat

Full Access Member
Joined
Nov 11, 2018
Messages
170
Reaction score
70
Location
ny
The hissing could be a vacuum leak or a leak in the intake somewhere. Does your engine use a MAF sensor? I know the 3.7s only have a MAP.

Are you able to read fuel trim data?
 

CWBenjamin

Member
Joined
Oct 10, 2019
Messages
76
Reaction score
12
I tested the fuel pressure and it would get to 45 and then drop down pretty quickly so I replaced the fuel filter and fuel pump and neither of them fixed it. The check valve and pressure regulator are both part of the fuel pump assembly so that includes those 2. The only other thing I can think of is the fuel injectors but why would 3 of them, on both sides of the engine, go out all at once??
 

CWBenjamin

Member
Joined
Oct 10, 2019
Messages
76
Reaction score
12
The hissing could be a vacuum leak or a leak in the intake somewhere. Does your engine use a MAF sensor? I know the 3.7s only have a MAP.

Are you able to read fuel trim d
The hissing could be a vacuum leak or a leak in the intake somewhere. Does your engine use a MAF sensor? I know the 3.7s only have a MAP.

Are you able to read fuel trim data?
Sry i did mean MAP sensor, it is a 3.7.. When i ran the codes all of my fuel trim (short and long) said 0.0
 

Ksat

Full Access Member
Joined
Nov 11, 2018
Messages
170
Reaction score
70
Location
ny
Short term fuel trim (STFT) should (ideally) switch quickly between - and + 5% at idle. Long term fuel trim (LTFT) should (ideally) be close to 0% at idle. A 0 fuel trim, I would think, means the PCM isn't commanding the injectors on at all.

Did you take the reading while the engine was running?
 

DadOSix

Full Access Member
Joined
May 20, 2020
Messages
553
Reaction score
292
Location
Cumberland, MD.
Hello. So my jeep was doing okay and suddenly started missfiring a mile into my drive. Here are the details:
Recently replaced all of the timing chains and guides and gaskets throughout.
Replaced mass airflow sensor, replaced cam sensor, replaced throttle position sensor, replaced all spark plugs with ngk copper oem, replaced all coil packs.

I did have an intermittent 02 sensor code for delayed response, but there was some oil that had dripped onto that 02 sensor and burned off just before that code popped on so I thought maybe that was messing with it.
So nothing else was going on, and then randomly it started shaking and seemingly getting worse until I got home. If i could explain how it felt, it seemed like one cylinder was missfiring, then as i drove, went to 2, then 3... When i got home a couple miles later, it had codes for:
Multiple cylinder missfires.
cylinder 1 missfire
cylinder 2 missfire
cylinder 3 missfire

I tested the battery and alternator and they are both fine.
Starts up just fine every time (other than struggling with 3 cylinders)
I tried replacing the ASD relay, nothing changed.
It does sort of sound like a hissing or excess noise from throttle body area, so I pulled it off and cleaned it up with some carb cleaner and cleaned the idle air sensor off a bit, and replaced the throttle body gasket. Nothing changed, but (idk if coincidentally) it then showed Evap gross leak code.
All the hoses are on and no breaks I can see.
The only other thing I can think of is maybe the fuel filter? Or the fuel pump?

Any ideas greatly appreciated - TIA
i’m curious as to the timeline -

why all the stuff replaced at the top of the post?
were you having issues before replacing the chain & guides?
why the cam and tps change? Did you use Mopar parts here?

Did the misfires result in you changing all this out?

You mention hissing around the throttle body. Can you take your carb clean and spritz around on the top of the engine (lightly - don’t drown it) and see if the RPM / shaking is altered in any way? I am looking for a vacuum leak. In increase in RPM would indicate you are near the source of hte hissing - and less noise at that time.

Injectors are a thing. I had 1 stuck on my 06 that gave me the missing / loading up / poor running. If you suspect injectors 3 things can be at play - 1 - bad injector - 2 - bad wiring - 3 - bad ecm. As old as these jeeps are, I inspect thoroughly the wiring where ever i have a failure. Lots of engine heat, old and brittle insulation and rub thru come to mind.

Test an ecm with a noid light on the injector lead. Should flash and each should be about the same.

Test the injector by - 1 - unplug it while running - any change ? - 2 - remove rail and injector (have some spare o-rings on hand just in case you tear one, add a lenght of fuel line to the top of the injector and fill it with brake / carb cleaner. - 3 - i rig up a set of test leads to a 12v source and let the injector pulse thru the cleaner. should be able to see the spray pattern change if you watch closely.

my injector was plugged and i got it cleaned up this way. how or why it plugged, i dunno. btw - i went to the junk yard and scored 3 injectors for free on a newly wrecked kj. hard to find used injectors as the engines around here are sold asap.

None of the above advocate just changing all this to see what happens and HOPE we got it. I like to diagnose thoroughly first and replace when I know what is causing my problems.
 

CWBenjamin

Member
Joined
Oct 10, 2019
Messages
76
Reaction score
12
Short term fuel trim (STFT) should (ideally) switch quickly between - and + 5% at idle. Long term fuel trim (LTFT) should (ideally) be close to 0% at idle. A 0 fuel trim, I would think, means the PCM isn't commanding the injectors on at all.

Did you take the reading while the engine was running?
Yes it was at idle.
 

CWBenjamin

Member
Joined
Oct 10, 2019
Messages
76
Reaction score
12
i’m curious as to the timeline -

why all the stuff replaced at the top of the post?
were you having issues before replacing the chain & guides?
why the cam and tps change? Did you use Mopar parts here?

Did the misfires result in you changing all this out?

You mention hissing around the throttle body. Can you take your carb clean and spritz around on the top of the engine (lightly - don’t drown it) and see if the RPM / shaking is altered in any way? I am looking for a vacuum leak. In increase in RPM would indicate you are near the source of hte hissing - and less noise at that time.

Injectors are a thing. I had 1 stuck on my 06 that gave me the missing / loading up / poor running. If you suspect injectors 3 things can be at play - 1 - bad injector - 2 - bad wiring - 3 - bad ecm. As old as these jeeps are, I inspect thoroughly the wiring where ever i have a failure. Lots of engine heat, old and brittle insulation and rub thru come to mind.

Test an ecm with a noid light on the injector lead. Should flash and each should be about the same.

Test the injector by - 1 - unplug it while running - any change ? - 2 - remove rail and injector (have some spare o-rings on hand just in case you tear one, add a lenght of fuel line to the top of the injector and fill it with brake / carb cleaner. - 3 - i rig up a set of test leads to a 12v source and let the injector pulse thru the cleaner. should be able to see the spray pattern change if you watch closely.

my injector was plugged and i got it cleaned up this way. how or why it plugged, i dunno. btw - i went to the junk yard and scored 3 injectors for free on a newly wrecked kj. hard to find used injectors as the engines around here are sold asap.

None of the above advocate just changing all this to see what happens and HOPE we got it. I like to diagnose thoroughly first and replace when I know what is causing my problems.
Everything stated was at various times, for other issues related to the parts replaced.
The only things I have replaced since the misfires started is:
ASD Relay
Fuel Filter
Fuel pump cluster
Throttle body gasket.
The most recent repairs before the misfires was the head gaskets, timing chains, and guides etc. We replaced those because we were doing head gaskets, and everything in there was likely 100k or more miles on it... So since we had it opened up we figured we would do as much replacing as we could.
Since I replaced the fuel pump and filter, the pressure is now going up to about 40 and then dropping to 35, however all of the pressure testing i stated was with the car off and ignition on.
Tonight I rented the tool again and when the car is running at idle, the pressure goes up to about 52 (according to my rental gauges from oriellys) and stays there pretty steady...
The only positive thing about replacing all these parts is that none of them have been replaced for about 10 years. So they are all about due anyways. If there is a misfire caused by an issue other than injector, would it sound any different if I unplug the injector? Worth a shot there... I may just replace all the injectors since they are all likely over 100k miles anyways.
 

DadOSix

Full Access Member
Joined
May 20, 2020
Messages
553
Reaction score
292
Location
Cumberland, MD.
Everything stated was at various times, for other issues related to the parts replaced.
The only things I have replaced since the misfires started is:
ASD Relay
Fuel Filter
Fuel pump cluster
Throttle body gasket.
The most recent repairs before the misfires was the head gaskets, timing chains, and guides etc. We replaced those because we were doing head gaskets, and everything in there was likely 100k or more miles on it... So since we had it opened up we figured we would do as much replacing as we could.
Since I replaced the fuel pump and filter, the pressure is now going up to about 40 and then dropping to 35, however all of the pressure testing i stated was with the car off and ignition on.
Tonight I rented the tool again and when the car is running at idle, the pressure goes up to about 52 (according to my rental gauges from oriellys) and stays there pretty steady...
The only positive thing about replacing all these parts is that none of them have been replaced for about 10 years. So they are all about due anyways. If there is a misfire caused by an issue other than injector, would it sound any different if I unplug the injector? Worth a shot there... I may just replace all the injectors since they are all likely over 100k miles anyways.
so back up a bit - KSat mentioned that he thinks possibly ECU since fuel trims are zero. Good point.

Do you have access to the noid light? Basically an LED gizmo that plugs into your injector wiring to see if the ECU is indeed commanding the injector on? The noid is specific to your injection system due to the plug on the end. The noid should blink as the ECU asks it to pulse injector #x. Absence of a pulse does not necessarily mean the ECU is bad. Could still be a wire broken or affected with the ‘green crusties’ as Eric O of South Main Auto likes to say.

Also - when doing the sensors, did you use Mopar parts? These jeeps are very particular in running correctly on OEM stuff. I used an aftermarket sensor (once) because I could not get the mopar one quickly. Should have waited a few days for the real McCoy.

Testing injectors is like testing plugs. You know, unplug the plug wire and see if the miss / stumble improves, stays the same or gets worse.

It is a bit strange IMO that 1,2,3 are acting up and the jeep runs well on the other 3. I’m leaning towards KSat’s analysis, but I still would want to check the other stuff for sure before chucking down $ on a new ECU.
 

Billwill

Full Access Member
Joined
Nov 26, 2009
Messages
2,134
Reaction score
601
Location
White River, South Africa
If some injectors are acting up while the others are fine then it could be a wiring problem to the bad injectors!

You need to go through the Wiring Diagrams but I have read of a similar problem and it was the PCM...as it is known on the Gassers...ECM on the CRDs! :oops:
 

DadOSix

Full Access Member
Joined
May 20, 2020
Messages
553
Reaction score
292
Location
Cumberland, MD.
If some injectors are acting up while the others are fine then it could be a wiring problem to the bad injectors!

You need to go through the Wiring Diagrams but I have read of a similar problem and it was the PCM...as it is known on the Gassers...ECM on the CRDs! :oops:
I’ll get it right someday! lol. - I’ve always wanted the CRD, but wife would kill me. She isn’t a fan of diesel fumes unless it means clearing space for her garden or bee hives!
 

budget76

New Member
Joined
Sep 1, 2021
Messages
20
Reaction score
4
Did it run after assembly and then 1 week later problems, or are these problems after re-assembly?
I doubt it is the PCM because of coincidence. You did lots of stuff, then issues, with same PCM.

Doubt if you lost 3 injectors at same time, so I doubt 3 injectors are clogged up with dirt at same time. Need rule out things.

Sounds like vacuum leak, your words. Agree test for leak with starting fluid or similar.
Does jeep have vacuum idle valve? if so it could restrict or flow more air than called for.

FUEL PRESSURE: So do you have fuel pressure now? or is it bad? If bad, gotta fix that first before looking at other items.
 

Duster

Full Access Member
Joined
Dec 3, 2013
Messages
242
Reaction score
57
Location
NC
Sounds like the problem I had except mine ran OK just hissed. But it should have ran bad too I think.

What happened to me is that my PCV went bad and it sucked a hole in the PCV line running to the intake.

Crank it up, pull your dipstick and check for suction on the tube or air blowing out.

I replaced the line with the new Mopar part and the PCV valve, and I also replaced the breather filter in the side of the airbox with a fresh piece of foam. Ran fine after.

Check that PCV line. Mine had a hole in the bottom of the elbow where it turned to connect to the intake.
 

CWBenjamin

Member
Joined
Oct 10, 2019
Messages
76
Reaction score
12
Did it run after assembly and then 1 week later problems, or are these problems after re-assembly?
I doubt it is the PCM because of coincidence. You did lots of stuff, then issues, with same PCM.

Doubt if you lost 3 injectors at same time, so I doubt 3 injectors are clogged up with dirt at same time. Need rule out things.

Sounds like vacuum leak, your words. Agree test for leak with starting fluid or similar.
Does jeep have vacuum idle valve? if so it could restrict or flow more air than called for.

FUEL PRESSURE: So do you have fuel pressure now? or is it bad? If bad, gotta fix that first before looking at other items.
Thaanks for your reply.
It was months after we did the timing and all the work listed before. The only things I have done within the last 4 months or so is all of the things I have done trying to fix this issue.
It does have idle control valve. I think ill replace that because it did look kinda gunked up when I took it out when I replaced the throttle body gasket... I did clean it off best i could but who knows.
The fuel pressure now seems to hold... When the car is actually running it sticks at about 51 so i think that has been solved.
I took off the plug on one of the missfiring cylinders injector and tested with a light and it is getting power on one side, then switched to ground and tested again and both sides seem to work. Also tested it with a Injector tester and it sounds like it is pulsing just fine. Also used a stetheoscope on the fuel injector while jeep was running and it sounded like it was pulsing as it should...
 

CWBenjamin

Member
Joined
Oct 10, 2019
Messages
76
Reaction score
12
so back up a bit - KSat mentioned that he thinks possibly ECU since fuel trims are zero. Good point.

Do you have access to the noid light? Basically an LED gizmo that plugs into your injector wiring to see if the ECU is indeed commanding the injector on? The noid is specific to your injection system due to the plug on the end. The noid should blink as the ECU asks it to pulse injector #x. Absence of a pulse does not necessarily mean the ECU is bad. Could still be a wire broken or affected with the ‘green crusties’ as Eric O of South Main Auto likes to say.

Also - when doing the sensors, did you use Mopar parts? These jeeps are very particular in running correctly on OEM stuff. I used an aftermarket sensor (once) because I could not get the mopar one quickly. Should have waited a few days for the real McCoy.

Testing injectors is like testing plugs. You know, unplug the plug wire and see if the miss / stumble improves, stays the same or gets worse.

It is a bit strange IMO that 1,2,3 are acting up and the jeep runs well on the other 3. I’m leaning towards KSat’s analysis, but I still would want to check the other stuff for sure before chucking down $ on a new ECU.
The fuel pressure now seems to hold now... When the car is actually running it sticks at about 51 so i think that has been solved.

I took off the plug on one of the missfiring cylinders injector and tested with a light and it is getting power on one side, then switched to ground and tested again and both sides seem to work. Also tested it with a Injector tester and it sounds like it is pulsing just fine. Also used a stetheoscope on the fuel injector while jeep was running and it sounded like it was pulsing as it should... These are the only updates I have so far.
 

budget76

New Member
Joined
Sep 1, 2021
Messages
20
Reaction score
4
Normally you can clean and lubricate the air idle control valve and not, repeat not buy a new one. Hoping your vehicle is normal.
 
Top