ROUGH starts on cold starts?

[barrak]

I have an old Cherokee that has a failed check valve (notorious on them). I replaced it once and it lasted 6 months before it went out again. The symptoms are long crank times, and often stumbling for a few seconds once it does fire until pressure builds up completely. After 18 years, I'm used to cycling the ignition 2-3 times on it to get around the rough starts.

My 1985 Bronco II needed a permanent diet of STP fuel additive to prevent rough starting/stalling in the early nineties. Bought used with 80,000 miles, then. Good times... grad student on a tight budget.

 

[A-TEAM]

So a little update, I bought a new mopar IAT sensor to try but my rough starts cleared up again. My educated guess here is a bad tank and/or too “hot” of gas. I usually always run 89 octane gas with 10% ethanol but my station was out so I filled up with 90 octane rec fuel (marine/ethanol free) when this started happening. After I burned off that tank with a bunch of rough starts and started running regular 89 again it seems to start up fine again. Glad it worked itself out, will update again if it happens or if I do anything with the new IAT sensor.

 

[HSKR R/T]

So a little update, I bought a new mopar IAT sensor to try but my rough starts cleared up again. My educated guess here is a bad tank and/or too “hot” of gas. I usually always run 89 octane gas with 10% ethanol but my station was out so I filled up with 90 octane rec fuel (marine/ethanol free) when this started happening. After I burned off that tank with a bunch of rough starts and started running regular 89 again it seems to start up fine again. Glad it worked itself out, will update again if it happens or if I do anything with the new IAT sensor.

Probably something wrong with the fuel itself, as in water in fuel or something, and not the octane rating.

 

[barrak]

Interesting. Maybe if you give it a couple seconds before cranking, it gives the fuel pump some time to prime up the fuel rails. The fuel pressure may be bleeding back into the tank when the truck sits for an extended period of time, hence leaning mixture on cold start. Not sure what mechanism keep the pressure while the trunk is off tho. (check valve?)

Curious to see your findings with this.

I think you're on to something. I do get the occasional rough cold start after sitting overnight, even stalling at times after the first crank. Nothing to do with ambient temperature. Now I'm convinced it only happens when the tank is near empty. 33-gallon tank, short commutes, high-octane diet.

 

[cotonymopar]

mine 2019 ram 1500 is doing it, 60000 miles, when I back up, it almost dies, then when I get going, it is fine... never let it get under a 1/2 tank...

 

[cotonymopar]

well, took it to an exhaust/muffler place, and had them cut out the leaking flange that was messed up, and now have a welded connection, not the faulty bolt flange connector. too many issue with that.

 

[gy3772]

Hi All,

I’ve been looking through this thread and see that a lot of people have had similar issues to what I am experiencing.

Some back story:
2020 1500 limited
5.7 non mds
45k miles
Run 93 octane 99% of the time
All maintenance current

Issue started when it was under manufacture warranty and now under an extended warranty.

When starting my truck from cold on a hot day, with the ac set to automatic, placing the truck into reverse, slowly back out of garage, the idle fluctuates up to 2k rpm and more, down to under 500, sometimes stalling out, then surging back up and repeating the cycle. Put it in drive and slowly accelerate. The truck will sometimes surge and lurch forward as well. Sometimes the entire ac will shut down and after accelerating and getting to somewhat normal idle it will return.

The process still continues until I give it a decent amount of acceleration then it seems to normalize.

There are no check engine lights/codes to report. The techs have all been able to replicate the issue, but no resolution.

This has been going on several years for about 20k miles. It has been in the dealership countless times, currently going on a month. The techs have had a star case open and have been in contact conducting numerous tests and parts replacements.

So far they have checked/replaced the following with no change.

Checked vacuum pressure
Checked the brake booster.
Checked spark plugs
Replaced fuel filters.
Check fuel pressure.
Replaced the PCM and updated all modules.
Replaced the MAP sensor and the accelerator pedal.
Replaced the throttle body.
Updated all software
I am sure I am probably missing something.

Another point to mention as this seems to only happen with the ac on. So logically we looked at that first. One tech thought maybe it was a surge/short in the ac compressor.

They have provided many hours of data to Star and stars position now that they can no longer help as they are unsure what the issue is. The dealership will continue to try and find the issue but it would need to be at my expense now. I don’t fault them for that, they deserve to get paid for their services.

Does anyone have a similar experience or thoughts on what could be causing this issue?

Here’s a couple of examples

 

[theblet]

Hi All,

I’ve been looking through this thread and see that a lot of people have had similar issues to what I am experiencing.

Some back story:
2020 1500 limited
5.7 non mds
45k miles
Run 93 octane 99% of the time
All maintenance current

Issue started when it was under manufacture warranty and now under an extended warranty.

When starting my truck from cold on a hot day, with the ac set to automatic, placing the truck into reverse, slowly back out of garage, the idle fluctuates up to 2k rpm and more, down to under 500, sometimes stalling out, then surging back up and repeating the cycle. Put it in drive and slowly accelerate. The truck will sometimes surge and lurch forward as well. Sometimes the entire ac will shut down and after accelerating and getting to somewhat normal idle it will return.

The process still continues until I give it a decent amount of acceleration then it seems to normalize.

There are no check engine lights/codes to report. The techs have all been able to replicate the issue, but no resolution.

This has been going on several years for about 20k miles. It has been in the dealership countless times, currently going on a month. The techs have had a star case open and have been in contact conducting numerous tests and parts replacements.

So far they have checked/replaced the following with no change.

Checked vacuum pressure
Checked the brake booster.
Checked spark plugs
Replaced fuel filters.
Check fuel pressure.
Replaced the PCM and updated all modules.
Replaced the MAP sensor and the accelerator pedal.
Replaced the throttle body.
Updated all software
I am sure I am probably missing something.

Another point to mention as this seems to only happen with the ac on. So logically we looked at that first. One tech thought maybe it was a surge/short in the ac compressor.

They have provided many hours of data to Star and stars position now that they can no longer help as they are unsure what the issue is. The dealership will continue to try and find the issue but it would need to be at my expense now. I don’t fault them for that, they deserve to get paid for their services.

Does anyone have a similar experience or thoughts on what could be causing this issue?

Here’s a couple of examples

That is wild. First thoughts are fuel problem, vacuum leak, or sensor which seems to have been covered. The AC compressor puts some load into on the engine.

Would think live data would provide a clue.

What happens with the AC NOT in auto?

 

[gy3772]

That is wild. First thoughts are fuel problem, vacuum leak, or sensor which seems to have been covered. The AC compressor puts some load into on the engine.

Would think live data would provide a clue.

What happens with the AC NOT in auto?

Exactly the same thoughts. So we looked at the basics first. Fuel and air, then on to the sensor.

Nothing from the live data, star is stumped as well.

I am not sure about the a/c not being in auto. I haven’t tried that and not sure if the dealer has. I will mention it to them to see.

I confirmed that they did try it with no resolution.


Thanks for your input