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Discussion Starter #1
Hello, I have experienced a rough idle for about 3 years. I had managed to get by with it until recently when it became a hard failure. Since there were multiple misfires detected. I decided to replace the spark plugs, one coil cylinder 4, and one injector in that same cylinder because there was a code for cylinder 4 misfire. Replaced the intake gasket to ensure no vacuum leaks. Performed a pressure test on all cylinders - no issues found all cylinders are uniform.

Over the weekend, I met with a friend to perform further diagnosis. We reviewed long and short fuel trims, which looked to be normal. We also tested the coils using a pico scope and found normal coil functions. O2 sensors responded, but we observed a bizarre effect that brought me to this forum for feedback. With the engine warm, we observed the air temp sensor readings. My understanding is that if the air temperature sensor responds as air comes in, the temp sensor readings should decrease. In my case, when I maintained the RPMs at cruising speeds, the air temp reading started to increase and continued to increase as if hot air was coming in. I thought as cool air comes in at cruising speeds; the air temp sensor reading should decrease. We suspect there may be an issue with the EGR. A shop told me that the problem is in the catalytic converter is partially restricted. However, off of idle, the vehicle runs or appears to run optimal, with no problem or stumbling.

What are your thoughts? I plan to remove the EGR to inspect it, but I thought to seek insight from others before I do because of removal complexity.
 

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faulty air temp sensor ?,
 
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Khaki Nitro Nut
07Lifted,4X4,6sp-man,3.7L
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Welcome to the forum @sotor. When you have a chance, head over to the Newbie Section (<click this) and say "Hi".
Tell us a little about yourself and your ride.
That way we can welcome you all proper like.

Is the temp reading of outside air on the dash correct?
 
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Discussion Starter #4
Temp sensor reading appears to measure normal. As I mentioned in my post above, the bizarre behavior appears to be the air temp reading is supposed to drop as fresh air comes in. Where in my case, the air temp rise as I maintaining cruising speeds. This device's typical behavior is that as fresh cool air comes through the plenum, the temp sensor's job is to detect this noticeable change in temp. And report it back to the PCM. Consequently, my temp sensor reading increases as if hot air is being introduced into the chamber. The EGR's job is to recirculate exhaust gases to cool down the combustion chambers; however, it is supposed to regulate how much air is introduced at idle. I suspect that my EGR is partially stuck open (carboned up). Further, because multi-cylinder misfires are detected at 2-4-6, coincidently, the EGR metal hose connects directly above those cylinders.

I am not sure if it is all coincidental, which brings me to this forum where someone else may have experienced similar effects and found partially stuck open EGR to be the cause.
 

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Any fault codes or pending codes?
Possibly a intake manifold leak?
Spark plug gapped correctly?
MAP sensor reading correctly?
 

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I had a similar problem and replaced spark plugs, coil and intake gaskets. Still had the problem so I did a cleaning of the intake manifold and then another cleaning with CRC Intake Valve\Turbo cleaner in the manner instructed on the product. Followed up with a clean oil change. There was significant carbon buildup. That was six months ago and I haven't had a problem since.
 

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Discussion Starter #7
Any fault codes or pending codes?
Possibly a intake manifold leak?
Spark plug gapped correctly?
MAP sensor reading correctly?
The only codes are catalytic converter and multiple cylinder misfires - even cylinders. I replaced the intake gasket and performed a smoke test to ensure no vacuum leaks present. I replaced the spark plugs with the correct gap. The map sensor reading at idle and acceleration was normal. The issue I suspect is the EGR because of the commonalities between faults and performance at idle. If everything else is performing within ideal performance and drives like a champ with the exception of idle performance that almost leads me to believe it is something related to idle mixtures not at optimal performance levels.

Thoughts
 

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Discussion Starter #8
I had a similar problem and replaced spark plugs, coil, and intake gaskets. Still had the problem so I did a cleaning of the intake manifold and then another cleaning with CRC Intake Valve\Turbo cleaner in the manner instructed on the product. Followed up with a clean oil change. There was significant carbon buildup. That was six months ago and I haven't had a problem since.
Hello DasNitro, I replaced the spark plugs, suspected coil, injector, and intake gasket. I also cleaned the entire throttle bore to ensure smooth airflow into the chambers via an improved swirling effect. I continue to fall back on my speculation of a faulted or partially stuck open EGR. I just don't have all the facts to prove that is the issue it is more speculation from the data I gathered through analysis.
 

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Discussion Starter #9
faulty air temp sensor ?,
Temp sensor response through data analysis appears to be working at normal levels. However, there is a potential anomaly that points to the backpressure of hot air building at cruising speeds. Traditionally when air flows into the air intake where the air temp sensor is positioned the sensor should detect this fresh air coming in and temp should drop. In my case, the air temp sensor climbs hence my suspicion that it could be an EGR stuck open back-feeding hot air all the time into the plenum.
 

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The only codes are catalytic converter and multiple cylinder misfires - even cylinders. I replaced the intake gasket and performed a smoke test to ensure no vacuum leaks present. I replaced the spark plugs with the correct gap. The map sensor reading at idle and acceleration was normal. The issue I suspect is the EGR because of the commonalities between faults and performance at idle. If everything else is performing within ideal performance and drives like a champ with the exception of idle performance that almost leads me to believe it is something related to idle mixtures not at optimal performance levels.

Thoughts
Next thought would be clogged/bad fuel injector
 

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Discussion Starter #11
Next thought would be clogged/bad fuel injector
Already replaced the injector and tested the fuel pressure from the line up to the injector rail. No pressure or volume issues. Sometimes you can have pressure but the volume could be compromised. In my situation, the pressure and volume are at specs.
 

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Khaki Nitro Nut
07Lifted,4X4,6sp-man,3.7L
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Remind me if the "Heat" is a 3.7 or 4.0 Nitro.
 
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Discussion Starter #13
Hey Scar0, it's a 4L. I updated my signature with the rig details.
 

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The only codes are catalytic converter and multiple cylinder misfires - even cylinders. I replaced the intake gasket and performed a smoke test to ensure no vacuum leaks present. I replaced the spark plugs with the correct gap. The map sensor reading at idle and acceleration was normal. The issue I suspect is the EGR because of the commonalities between faults and performance at idle. If everything else is performing within ideal performance and drives like a champ with the exception of idle performance that almost leads me to believe it is something related to idle mixtures not at optimal performance levels.

Thoughts
I had issues with misfires on cylinder 1 & 2 as soon as I replaced the Ignition coil that serves both cylinder the misfire issue was resolved. I had tested my ignition coils prior to replacing them as they were working fine but i still went ahead and replaced it.
 

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Khaki Nitro Nut
07Lifted,4X4,6sp-man,3.7L
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Hey Scar0, it's a 4L. I updated my signature with the rig details.
Uh, oh.
Members here with the 4.0 have had some issues with misfire caused by the cam eating into the pedestals.
(Not saying that is it, but is a worse case scenario.)
Did they look OK when you were in there?

The air temp sensor is behind the grill. It reads outside air temp.
There there is the IAT (intake air temperature sensor) which is in the intake tube.
Which one were you observing?
Bad Cat readings can also mess with fuel mixture(pulse width). And will usually cause multi-misfire codes.
EGR, would not hurt to have a look. Oh, and I just remembered a very old thread where the tube leading to the EGR had busted loose, causing all kinds of havoc.
 

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check the wiring from the coil packs and injectors for rubbing agaist other objects, a couple of members have found wiring issues,
is the missfire only when the engine is at idle ?
 

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Discussion Starter #17
Uh, oh.
Members here with the 4.0 have had some issues with misfire caused by the cam eating into the pedestals.
(Not saying that is it, but is a worse case scenario.)
Did they look OK when you were in there?

The air temp sensor is behind the grill. It reads outside air temp.
There there is the IAT (intake air temperature sensor) which is in the intake tube.
Which one were you observing?
Bad Cat readings can also mess with fuel mixture(pulse width). And will usually cause multi-misfire codes.
EGR, would not hurt to have a look. Oh, and I just remembered a very old thread where the tube leading to the EGR had busted loose, causing all kinds of havoc.

Good afternoon Scar0, the compression per cylinder is within specs, so no problem with cam lob issues. The intake air temperature sensor is working with no issues. Interesting point you mentioned the cat readings because I have a cat code, and one of the technicians who ran a diagnosis said the issue I have is with the cat. I, however, have an issue with condemning components without having factual data to back it up. My days as an automotive diagnostician will not allow me to condemn a component without having hard facts to support it. I did not test the temperature of the cat pre & post to verify exhaust flow. If the cat is partially restricted, it could cause some backpressure into the engine, thus causing malfunctions with the computer reading varying engine temperature. I am not convinced of that theory just yet. I am having a difficult time understanding that rationale.

I suspect the EGR more than I do the cat, which brings me to another interesting point you shared regarding a busted loose EGR pipe. When I loosened the tube at the intake, the EGR pipe felt a bit lose, like it was not tight at the bottom where it connects to the ERG value. Maybe I am introducing fresh air through that pipe, although I do not hear any leaks. I suspect if the pipe is leaking exhaust, I would have heard it.

Thus far, Scar0 I say you have offered the most relevant possibilities that I need to investigate. I do appreciate everyone who has opined in this thread. It has been useful to hear things I have already instinctively done before posting in this forum.

Best,
 

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Discussion Starter #18
check the wiring from the coil packs and injectors for rubbing agaist other objects, a couple of members have found wiring issues,
is the missfire only when the engine is at idle ?

I will take another look at the wiring harness and perform a wiggle test. I remember back in the day (I'm aging myself here), Ford published a wiggle test on the wiring harness. Ford was notorious for wiring connectors breaking loose and or building resistance, causing a low current flow.

Thanks for sharing
 

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Uh, oh.
Members here with the 4.0 have had some issues with misfire caused by the cam eating into the pedestals.
(Not saying that is it, but is a worse case scenario.)
Did they look OK when you were in there?

The air temp sensor is behind the grill. It reads outside air temp.
There there is the IAT (intake air temperature sensor) which is in the intake tube.
Which one were you observing?
Bad Cat readings can also mess with fuel mixture(pulse width). And will usually cause multi-misfire codes.
EGR, would not hurt to have a look. Oh, and I just remembered a very old thread where the tube leading to the EGR had busted loose, causing all kinds of havoc.
I’ve heard of Catalytic converters doing that, replaced a few in the past on customers cars when I was working in a shop.
Also...not sure if it’s the same as the 4L, but my EGR tube has a rubber O-ring on the tube on the intake manifold side. If their’s a knick, cut, missing, or it’s brittle it can cause that as well
 

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Khaki Nitro Nut
07Lifted,4X4,6sp-man,3.7L
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A good compression test does not mean no possible Cam issues. The valves closing is not the problem.
The Cam wears into the pedestals and the Cam will shift rearward little by little. Eventually the Cam will not open the valves all the way causing the sign of something wrong, misfires. Past members have said they did not hear any obvious noise until ultimate failure.
Again. I'm not saying this is your Nitro's problem. I truly hope it is not. Just keeping things in mind.

Chase that EGR feeling, if nothing else to eliminate it.
 
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