Bad PCM? I'm at a loss...

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Jerseystyle

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I have intermittent driveability issues. She'll run fine sometimes and run like complete garbage other times.

When running bad the motor will buck and throttle response will be choppy and she'll stumble like it's a fuel issue.

This is a 2007 slt quad cab 4.7 4x4

What I've replaced:

Cats and the rest of the exhaust back.
coils
plugs
Cam sensor
crank sensor
map sensor
TPS
IAT
Coolant temp sensor
EGR
O2 sensors
fuel pump assembly

She seems to run fine after I reset the PCM and then turns to garbage after a while.

Yesterday she was running okay taking my daughter to the dentist but on the way home was acting up. I was using cruise control and when it starting acting up the cruise would turn completely off and I couldn't turn it back on. I pulled over, pulled the pcm fuse and turn the key to run. Waited for the second ding and replaced the fuse. Cruise worked again but only for a few minutes as it started to run bad again.

The last week I've been doing a lot of research on live data pulls from a scan tool. Specifically diagnosing problems by utilizing the stft and ltft readings. This would point to fuel issues including injectors and what not. But all the fuel trim readings are within normal tolerance even when she's at her worst.

I'm at a loss....

Yesterday I pulled the PCM and opened her up to check for any visual problems like something burned up but didn't see anything.

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chrisp2493

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I wish I could help you, but I don’t know much of anything regarding the 4.7’s. I never really had to troubleshoot too much on my truck either. My truck did similar things when I had some o2 sensor problems, it would run fine until the pcm started adjusting fuel trims and it would run like crap, I would reset the pcm and it would work for another 5 minutes then run like crap again.


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chrisp2493

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One other thing I can add is get oem quality o2 sensors. It’s been a known thing that dodge doesn’t like Bosch sensors for whatever reason. I only buy NGK o2 sensors, those are factory replacements. You can get them at orileys for around $30-40


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Jerseystyle

Jerseystyle

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Is anything else not working? I was thinking a bad ignition switch.
No but I had another issue about a year ago that went away. So sometimes on startup the check gauges light would be on and the oil pressure would be at 0. I'd turn off and restart and all was fine. I was going to replace the sensor but then it stopped.

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RonJon '06

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No but I had another issue about a year ago that went away. So sometimes on startup the check gauges light would be on and the oil pressure would be at 0. I'd turn off and restart and all was fine. I was going to replace the sensor but then it stopped.

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I believe the cruise control gets its 12V power supply from the ignition switch. If the cruise is acting up and the truck cuts out while driving I'd suspect something inside the steering column, either the switch or the wiring. Just my 2 cents.
 

jotin

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Pcm Codes?


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Jerseystyle

Jerseystyle

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Pcm Codes?


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At it's worst it threw a "multiple misfires" P0300. Never anything specific.

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jotin

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At it's worst it threw a "multiple misfires" P0300. Never anything specific.

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To me it sounds 02 sensor related. Like when it goes into closed loop , the fuel system goes crazy. Similar thing happened to my hemi ram when I called it. Once it went into closed loop, the thing would barely idle. It was a downstream 02 sensor. And to touch on the prior post. Aftermarket sensors are junk. I’m a firm believer in the Mopar sensors going back on the car. Can’t tell you how many times I’ve fixed a car or truck here at the shop by replacing a newly replaced auto zone/orielly part with a Mopar part.


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Jerseystyle

Jerseystyle

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To me it sounds 02 sensor related. Like when it goes into closed loop , the fuel system goes crazy. Similar thing happened to my hemi ram when I called it. Once it went into closed loop, the thing would barely idle. It was a downstream 02 sensor. And to touch on the prior post. Aftermarket sensors are junk. I’m a firm believer in the Mopar sensors going back on the car. Can’t tell you how many times I’ve fixed a car or truck here at the shop by replacing a newly replaced auto zone/orielly part with a Mopar part.


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Sometimes she runs fine in closed loop. Is there another way to test the O2 sensors?

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chrisp2493

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Do you happen to have a diablo tuner? Watching what the fuel trims do on their live gauge program could help


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Jerseystyle

Jerseystyle

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Do you happen to have a diablo tuner? Watching what the fuel trims do on their live gauge program could help


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I don't. But I have watched the fuel trims on my reader and they stay within spec.

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LoneWolf3574

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I had a similar issue but limited to the #1 cylinder but on a Hyundai Accent with a 1.6L 4 banger. It turned out that the injector was sticking, I just ran some Marvel Mystery Oil through a few tanks and it freed it right up. I'm not saying this is your issue, but given everything else you have tried up to this point, 10-14oz/tank of MMO for a few tanks can't hurt.
 
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Jerseystyle

Jerseystyle

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I had a similar issue but limited to the #1 cylinder but on a Hyundai Accent with a 1.6L 4 banger. It turned out that the injector was sticking, I just ran some Marvel Mystery Oil through a few tanks and it freed it right up. I'm not saying this is your issue, but given everything else you have tried up to this point, 10-14oz/tank of MMO for a few tanks can't hurt.
I pulled the fuel rail last week and cleaned/tested each injector.

You also think that it would show on the fuel trims when sticking. 38c536069a33441bbc5a50fc5abaa832.jpg

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SYKRAMMAN

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I’m a firm believer in the Mopar sensors going back on the car. Can’t tell you how many times I’ve fixed a car or truck here at the shop by replacing a newly replaced auto zone/orielly part with a Mopar part.

Amen to that brother!
 

JohnnyMac

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Did the problem start before or after you installed the exhaust? If after, how long after?
 

LoneWolf3574

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I pulled the fuel rail last week and cleaned/tested each injector.

You also think that it would show on the fuel trims when sticking.

It didn't see it on mine, all I had was a stuck injector that the PCM thought was firing normally on a cylinder that was misfiring.
 
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Jerseystyle

Jerseystyle

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Did the problem start before or after you installed the exhaust? If after, how long after?
Yes sir. The cats were clunking pretty bad which is why I suspected them so I went ahead and replaced the whole system.
It didn't see it on mine, all I had was a stuck injector that the PCM thought was firing normally on a cylinder that was misfiring.
I threw some BG 44k in it yesterday just to make sure.

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