ROUGH starts on cold starts?

[Landrover1]

Been using 89 octane for awhile and no surging on morning startups. Engine running smoothly and am actually getting slightly better gas mileage. Reading about differences between octane levels. I had been filling up with 93 octane which is used for high compression ratio engines like my wife’s Mercedes gle 400 v6 turbo. The higher octane resists auto ignition. That engine is about 13:1 where the hemi is around 10:1. I think the higher compression engines create more pressure in the cylinder which, in turn, causes a much higher cylinder temp. That’s why it needs a fuel that resists premature combustion. The hemi doesn’t create as much pressure in cylinder head, therefore a lower temp that doesn’t ignite the high octane fuel completely. So in the morning when the engine is cold the engine surges from an incomplete fuel combustion until the engine warms up. Maybe. All I can say is that the surges have stopped.

 

[Dusty1948]

Been using 89 octane for awhile and no surging on morning startups. Engine running smoothly and am actually getting slightly better gas mileage. Reading about differences between octane levels. I had been filling up with 93 octane which is used for high compression ratio engines like my wife’s Mercedes gle 400 v6 turbo. The higher octane resists auto ignition. That engine is about 13:1 where the hemi is around 10:1. I think the higher compression engines create more pressure in the cylinder which, in turn, causes a much higher cylinder temp. That’s why it needs a fuel that resists premature combustion. The hemi doesn’t create as much pressure in cylinder head, therefore a lower temp that doesn’t ignite the high octane fuel completely. So in the morning when the engine is cold the engine surges from an incomplete fuel combustion until the engine warms up. Maybe. All I can say is that the surges have stopped.

Increasing the octane rating of gasoline, increases the temperature required to suppress pre-ignition of the fuel. Octane by itself will not be the determining factor that causes combustion temperatures to rise.

Heat generated in the combustion chamber of a reciprocating engine is the result of thermodynamic properties of the fuel, and the elements found in the air. Generally, the amount of heat generated is determined by the BTU output of the burn, which is a measure of the fuel’s energy. Fuels are made up of various combinations of oxygen, hydrogen, carbon, nitrogen, as well as deactivators, corrosion inhibitors, oxygenates and antioxidants. Each supplier will have a different recipe for any given fuel. To increase octane ratings there are a wide variety of compounds used, such as ethanol, toluene, benzene, methyl-tertiary-butyl-ether (MTBE), just to name a few, but generally have no effect on energy of the fuel.

Best regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Build date: 03 June 2018. Now at: 052303 miles.

 

[Landrover1]

Increasing the octane rating of gasoline, increases the temperature required to suppress pre-ignition of the fuel. Octane by itself will not be the determining factor that causes combustion temperatures to rise.

Heat generated in the combustion chamber of a reciprocating engine is the result of thermodynamic properties of the fuel, and the elements found in the air. Generally, the amount of heat generated is determined by the BTU output of the burn, which is a measure of the fuel’s energy. Fuels are made up of various combinations of oxygen, hydrogen, carbon, nitrogen, as well as deactivators, corrosion inhibitors, oxygenates and antioxidants. Each supplier will have a different recipe for any given fuel. To increase octane ratings there are a wide variety of compounds used, such as ethanol, toluene, benzene, methyl-tertiary-butyl-ether (MTBE), just to name a few, but generally have no effect on energy of the fuel.

Best regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Build date: 03 June 2018. Now at: 052303 miles.

Charles law

 

[Scram1500]

In the morning if I press the brake-start button right away, I get a rough start, sometimes stalling out. It will start normally by pressing the start button twice into the run position, then pressing the brake and start button. Seemed like a leaky injector(s) at first but now think some modules need time to wake up

 

[2wd]

Just started experiencing this issue. 20k miles. Been happening about 2 weeks.

Only on cold starts, I get a rough idle, goes away after about 10-20 seconds. Never again rest of day. Next morning, repeat. No CEL.

 

[2020Larrie]

Had the truck 9 months, now pushing 18,000 miles, we live at 6000 feet, and park on an incline of about 15 degrees. Rough start every time since new, dealer said not to worry. I didn't.

Until a recent service visit, now much worse after service at 15,000 miles where MAF/throttle body was cleaned. Now it has stalled and bucked a few times when placed in gear. I Will be taking it back in. Don't even get me going why a throttle body has to be cleaned every 15,000 miles, thats like 60's tune up distances... It seems worse on warmer mornings, when it was 25 degrees it didn't seem to have issues.

I have tried nothing but 87, nothing but 93, I tried nothing but Shell fuel. Mixtures of all. I tried adding fuel additive to remove any sign of water. No change. I use Circle K or Speedway because thats all we have around here.

I lived in Scottsdale and it didn't seem to do this rough start sitting flat on a driveway. Only happens first start then hauls like a beast.

 

[2020Larrie]

Update, after writing above I went to town and on start it backfired through intake and had about 4 seconds of wild rpm fluctuations and I smelled lots of gas, then all fine. I went straight to dealer with video of what just happened and they now have it

 

[2020Larrie]

Later same day, I talk with sertvice writer, said it repeated with their tech, but service manager said his does this so it's normal.

No way an advanced modern motor backfires and stall during start. No way. Service writer did say he would keep it and start something with mopar.

 

[Scram1500]

Sounds like the classic symptom of leaky injectors. It's definitely not normal, just because another POS does it is not an indication nothing is wrong. I'm sure the people burning up in a Pinto found little comfort that others caught fire as well

 

[2020Larrie]

I w

Sounds like the classic symptom of leaky injectors. It's definitely not normal, just because another POS does it is not an indication nothing is wrong. I'm sure the people burning up in a Pinto found little comfort that others caught fire as well

Sort of "OK" with it as long as it just did it's little shake and shimmy at start. Full on intake backfiring, stalling, not so much.

 

[2020Larrie]

Back from dealer. Odd, they wanted to know if I wanted them to keep it longer? At first they could duplicate it, then second day it started fine. Employee states now that I mention it his does this and never thought about it. I think things going bang in the intake is probably wrong.

It throws no codes nor has any memory of it doing what it does. Reminds me of college.

I'm tryin shell gas for a few weeks. Maybe some additives.

In my experience working on 2000 era BMW's and 80's efi mustangs, any knock, bang, stall, backfire threw a code. Why doesn't a 2020 record that?

 

[2020Larrie]

Day one after dealer, start was meh, stumbled a little sort of like it has for a year, BUT, it did not backfire nor stall.

No idea if techron or lucas oil stab made it better, or something else...

Tech made it sound like they found nothing did nothing.

Why did my MPG go from 20 to 16 then? I think they reflashed it. I hope it relearns back to 20mpg or thats not right.

EDIT:

Day three, googled and it appears techron can cause loss of 20% mpg for short term, mine is creeping back to 17.8 after 400 miles.

Todays start, no issue, started like an EFI should. I did try this start using the hit run without using brake, then recycled and started using brake.

So, don't know if it's fuel, techron, lucas oil add, or hitting run first without starting that makes it start correctly.

More later as I keep trying things, tomorrow I'll just hit start with brake on to get it going.


Edit, 2 July:

Day four and five post dealer, post techron post lucas oil and injector cleaner:

Last two days just started it regular way, brake pedal and button, starting even better now, no roughness, no backfire. Just vrooom.

Almost through 30 gallon tank with techron and lucas injector cleaner. Man you have to drive a lot to go 600 miles in a small town.

I'll start using top tier but only two places in town have that, 76 or shell, both pushing $4 a gallon.

Mileage is back to normal 19.6-21.1 So additives did not do the mpg drop, the throttle body cleaning did it when they reset the computer.

If I was anyone else out there reading this I would first start with Lucas full synthetic low viscosity oil modifier. This stuff:

Low Viscosity Stabilizer – Lucas Oil Products, Inc. – Keep That Engine Alive!

lucasoil.com

There is another version which looks like that but is more like seafoam. I did not use that.

About $9 a small bottle, don't buy the quart size. Sort of an STP but synthetic and does not hurt mileage. Just stops the lifter tick on start, and apparently in my case, a collapsed lifter or two, which is my first guess diagnoses of the issue.

I also used this stuff on my 2015 jeep 3.6 which is horribly noisy on the top end until oil flows, about 5 seconds, this stuff made it a silent start.

Thats all I have for now, I'll add more later if anything changes, but again, I think the fix was the lucas oil additive, the injector stuff was just insurance.

 

[2020Larrie]

read edits above, all for now, i think fix is lucas low viscosity oil stabalizer.

 

[2020Larrie]

read edits above, all for now, i think fix is lucas low viscosity oil stabilizer.

Also, I don't think altitude or incline has much to do with the rough start if any. Dealer rep said his did it level in a warm garage at same altitude and down in valley at 1,000 ft elevation.

I find it interesting the thing that probably fixed this, lucas low vis oil stabilizer, is name for exactly the reason most big engines have noise issue on starts, low viscosity oil runs off everything overnight.

One week on from lucas oil modifier, no knocks or stutters, just a normal efi grumble on start. I call this fix plausible.

 

[bigdaddymac]

Also, I don't think altitude or incline has much to do with the rough start if any. Dealer rep said his did it level in a warm garage at same altitude and down in valley at 1,000 ft elevation.

I find it interesting the thing that probably fixed this, lucas low vis oil stabilizer, is name for exactly the reason most big engines have noise issue on starts, low viscosity oil runs off everything overnight.

One week on from lucas oil modifier, no knocks or stutters, just a normal efi grumble on start. I call this fix plausible.

Also, I don't think altitude or incline has much to do with the rough start if any. Dealer rep said his did it level in a warm garage at same altitude and down in valley at 1,000 ft elevation.

I find it interesting the thing that probably fixed this, lucas low vis oil stabilizer, is name for exactly the reason most big engines have noise issue on starts, low viscosity oil runs off everything overnight.

One week on from lucas oil modifier, no knocks or stutters, just a normal efi grumble on start. I call this fix plausible.

Big thanks @2020Larrie - my morning stumble on a cold start is fixed!!

 

[2020Larrie]

Big thanks @2020Larrie - my morning stumble on a cold start is fixed!!

So lucas oil then did it, nice.

 

[MikeS54]

I think i may have to give the lucas oil a try. Mine has sputtered 4 times in the past 2 weeks. Just hit 18k on it. Never an issue before. Today, it actually stalled all the way out. Gave it a few seconds and it started on the second try. Really frustrating for such an expensive truck.

 

[2020Larrie]

Curious what your elevation and temperature is? "Most" here are well above sea level.

 

[HSKR R/T]

Mine has stopped doing it. Lasted through three tanks of fuel. Not sure what exactly the issue was, but also had an issue where my battery mysteriously died overnight and wouldn't take a change from battery charger. Jumped it and took it to dealer and battery tested fine, and hasn't had any issues since.

 

[MikeS54]

...and today it started just fine. Really drives me nuts. I ordered a 20oz bottle of Techron that I'll plan to dump in there at next fill up. I'm really hoping its just bad gas. This will be the 3rd fill up since the problem first started a few weeks back.

I'm in Maryland so I don't believe it would be elevation related.