Unstable voltage could cause the pump to do odd things...... Failing voltage regulator/alternator?

 

Welp HeyYou, you were getting close. After some more testing, I determined it wasn't the fuel pump by isolating it and powering it off a jump pack. So I didn't have much time after that and figured let's pull the battery temp sensor. So I checked right before I disconnected it and it still had erratic pressure. Now it has stable fuel pressure and idle so going to be getting a new battery temp sensor.


I didn't record it but it still has a stumble and backfire when revved. So I am down to crank, cam, tps, or MAP sensor(s). I figured I had multiple issues. Leaning towards MAP since the cruise worked good when I tried it. Typically the cruise acts funny with a bad TPS.

 

Yeah, cruise will be strange, and TCC won't be able to make up its mind either.

Absolutely amazing the strange problems one little sensor can cause........ Wonder if Dodge has any clue about that.

 

So interesting development. Replaced the battery temp sensor and MAP. Started it up with a fuel pressure gauge on it. It was occasionally swinging 5psi. Left it run while I went back to get my phone to video. I by the time I got back out it was steady and idle the best it has since the initial start up. Blipped the throttle and no stumble/backfire. At this point I was excited to test drive. Shut the truck off to take off the gauge, truck is now about 180 degrees. Hit the key starts up, then dies. Hit the key again stumbles to a low rough idle and dies again. Next time I give it some throttle, it takes off and seems ok. I let off and it dies immediately. So I start it back up with a little throttle and painstakingly slowly let off the throttle until I was totally off the pedal it. At this point it idled a little rough for 2 seconds and just dies. So very carefully I decide to go for a quick drive using the throttle to keep it running. Drives good though, bog is only there if the throttle is jabbed a little at low speed. It just refused to idle after it was restarted and warm. At this point I was out of daylight. I plan on cold starting it and if idles I will drive it immediately to see if the bog is gone under open loop. I may just throw a TPS in to see if that helps. When I was using throttle to keep it running the rpm was going up a couple hundred up and down like it was hunting for something before it would steady. I am not quite ready to load the parts cannon, but getting close.

 

I think you only get two to three minutes of open loop, before the O2 sensors start working properly. (heated O2 sensors.....) Engine temp plays a role there as well... so, on a cold start, probably got a bit longer.

Does it run better with the O2 sensors unplugged?

 

It has in the past but still had the other issues, just a little improved. I will mess with it more today hopefully.

 

Ok so it has new O2 sensors, TPS (which didn't help much), IAC, battery temp sensor, and MAP. O2 sensors cured it not idling hot. It still idles low on prolonged braking and will sometimes stalls. First drive with the new O2 sensors. Keep in mind this it totally stock programming at this point.

 

What brand IAC did you put in? I had real issues using an aftermarket unit in my 96 with the 5.9, replaced with another mopar unit I had layin' about, and idle issues went away. Of course, my engine was still stock too...... so, the cam *might* be part of the problem...... Do you have a scanner that can log data?

 

I put an echlin from napa in it. The only thing I have that data logs is my x3 programmer. I can see if that will do it.

 

I did some data logging with my x3. I noticed as the speed approached zero the iac must be opening because the vacuum would go from -20in Hg just before stopping to -14.5in Hg without throttle input. However I finally got a code, no check engine light though. P0720 Low Output SPEED Sens RPM, Above 15 MPH. Cleared it and it came back immediately. So I am going to replace that and see what happens. Idle when not moving is fine, only just on take off and stopping at very low speeds. Fingers crossed this is it.