# Engine seems to be stumbling when cruising at steady speed



## MP81 (Jul 20, 2015)

Can you tell if the vehicle is regenning when this is happening?


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## grs1961 (Oct 23, 2012)

Does it feel like the cruise-control is "hunting" to hold the speed you have set it at?

Mine - completely different engine and gearbox, but still diesel - does that sometimes when everything is juuuuust right. 

Clicking the speed up or down a notch or two usually clears it


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## MRO1791 (Sep 2, 2016)

I suspect you have crud in you intake, throtttle valve/EGR and intake generally. At that milage it likely has built up. This would explain the behaviour here and your excessive Regen. You can attempt a cleaning of this and it might help. Those with Gen 1s are familiar with this issue.


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## Barry Allen (Apr 18, 2018)

MP81 said:


> Can you tell if the vehicle is regenning when this is happening?


It is not in regen. Fuel economy hovers right around 60 mpg when the engine is fully warmed up so it's not doing anything to increase EGT.


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## Barry Allen (Apr 18, 2018)

grs1961 said:


> Does it feel like the cruise-control is "hunting" to hold the speed you have set it at?


Probably not. It holds the speed steady and there is a constant thrumming, bucking, whatever you want to call it from the engine. It's not violent - very gentle feeling. It's not present at higher speeds as far as I can tell.

I fueled up at a one-off stop that was still brand name, so I assumed it might just be one tank of fuel. A tank of fuel from a known source is in the car now and it's still doing it.


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## Barry Allen (Apr 18, 2018)

MRO1791 said:


> I suspect you have crud in you intake, throtttle valve/EGR and intake generally. At that milage it likely has built up. This would explain the behaviour here and your excessive Regen. You can attempt a cleaning of this and it might help. Those with Gen 1s are familiar with this issue.


Great, that sounds expensive.


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## JLL (Sep 12, 2017)

Barry Allen said:


> Great, that sounds expensive.


Properly maintaining a vehicle IS expensive. Why do you think there are so many POS's on the road.

But I don't think an induction system cleaning is to bad. Maybe $150?


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## Carminooch (Mar 23, 2018)

I have the same issue but it only exists under extremely specific and consistent conditions:

• It’s only happens during first 3 or so minutes of driving after a cold start.

• Between 1k-2k RPM only. The engine hesitates and stumbles severely right thru that power range and the second you hit 2k rpm, the problem disappears. 

I fought for over a year to have 4 dealerships clean my EGR valve and EGR cooler under warranty since I looked inside my intake and saw my EGR was all but plugged up. After they refused to clean my EGR cooler and agreed to take a brush to my EGR valve tip inside the intake, the issue persisted but less noticeable.

Now a year later the issue has returned with full vengeance. Enough vengeance to send a water bottle off the passenger seat when it “bucks”.


Question- what rpm range does this occur? Can you pinpoint it to only the 1k-2k RPM range?


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## Barry Allen (Apr 18, 2018)

Carminooch said:


> Question- what rpm range does this occur? Can you pinpoint it to only the 1k-2k RPM range?


It's happening between about 1,400 and 1,700 RPM. Those are the speeds that I use for 4th or 5th gear when idling at slow city speed driving. It's doing this while the engine is fully, completely warmed up, and it's nowhere near as violent as you describe with your car.


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## Barry Allen (Apr 18, 2018)

JLL said:


> But I don't think an induction system cleaning is to bad. Maybe $150?


With a diesel engine, it's a lot of parts to remove and clean. It's not the same as a gasoline engine where you can get a $10 can of Seafoam and spray it down the intake.


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## Carminooch (Mar 23, 2018)

Barry Allen said:


> It's happening between about 1,400 and 1,700 RPM. Those are the speeds that I use for 4th or 5th gear when idling at slow city speed driving. It's doing this while the engine is fully, completely warmed up, and it's nowhere near as violent as you describe with your car.


Sounds like two different issues but with all the problems the overaggressive EGR mapping our cars have for emissions, I wouldn’t be surprised if it was something related to the EGRs operation. I’m just spitballing here. Regardless I hope your issue gets sorted out and definitely keep us updated if you can


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## Barry Allen (Apr 18, 2018)

Carminooch said:


> Sounds like two different issues but with all the problems the overaggressive EGR mapping our cars have for emissions, I wouldn’t be surprised if it was something related to the EGRs operation. I’m just spitballing here. Regardless I hope your issue gets sorted out and definitely keep us updated if you can


I'm going to wait to see if it gets worse, or if it throws a CEL that might give me a clue what the problem is.


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## MRO1791 (Sep 2, 2016)

Barry Allen said:


> It's happening between about 1,400 and 1,700 RPM. Those are the speeds that I use for 4th or 5th gear when idling at slow city speed driving. It's doing this while the engine is fully, completely warmed up, and it's nowhere near as violent as you describe with your car.


Ok, first thing to try, downshift. While lugging the torque heavy diesel is tempting, you might want to read up on Dual Mass Flywheels (DMFs) that are installed on these cars. You absolutely should avoid anything but coasting to a stop with RPM below about 1600. If you think cleaning the intake is complicated and expensive, I'm quite sure that you will hate the cost and complexity of replacing the dual mass flywheel. To put it simple, this DMF was put there to take up the lower end RPM rotational vibration (read fluctuating rotational speed), the lower the RPM the bigger the energy absorbed in the DMFs springs and buffers. I can speak from experience on the Cruze, mine failed at 12K miles (this following a few seconds of reverse engine rotation due something quite bizarre, I think letting up on the clutch pedal too early might have created the conditions for a reverse start, so NEVER DO THAT), and my truck was on its way out at 41K or so, I preemptively replaced it with a single mass flywheel and clutch. Next time the clutch DMF goes on the Cruze and out of warranty, it's not going to be a DMF if there is any way to avoid it. 

As to the intake, it's not all that horrible or complicated, yes it has a few more parts than the average gasoline car, but it's not beyond the ability of someone with basic skills, and it should not break the bank to have a dealership do that work. You do have over 50K miles on the car, many cars have major periodic maintenance items at 60K, others at 90K, like timing belt, water pump and antifreeze change intervals. The intake cleaning is not as expensive or as complex as those other typical maintenance items.. but as pointed out in another comment, there are tons of junk cars out there because people fail to properly maintain their vehicles, despite the modern car requiring much, much less maintenance than older cars, apparently any maintenance is too much for many people.


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## Barry Allen (Apr 18, 2018)

MRO1791 said:


> While lugging


I'm not lugging it. I live in flat land (Illinois)!

Lugging is when you add throttle and the engine cannot increase the vehicle speed, which is not what I'm doing. If I were to step on the throttle, the car would easily pull away without drama.


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## JLL (Sep 12, 2017)

Barry Allen said:


> I'm not lugging it. I live in flat land (Illinois)!
> 
> Lugging is when you add throttle and the engine cannot increase the vehicle speed, which is not what I'm doing. If I were to step on the throttle, the car would easily pull away without drama.


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## MRO1791 (Sep 2, 2016)

Barry Allen said:


> I'm not lugging it. I live in flat land (Illinois)!
> 
> Lugging is when you add throttle and the engine cannot increase the vehicle speed, which is not what I'm doing. If I were to step on the throttle, the car would easily pull away without drama.


Point remains. My Truck hits 600 Ft-lbs of torque at 1500 RPM, it will pull in high gear without issue even at low RPM, but that will DESTROY the DMF, and did, with a mere 41K miles or so. When the clutch started to slip, and it was not even worn down, I found out the hard way why it was a bad idea to use the low RPM torque with a DMF. Before that time I didn't even know what a DMF was, but I certainly do now. 

Do as you want, obviously your choice.. but if you are balking at cleaning the intake that gets clogged up with soot and oil from the EGR and turbo (BTW, I did first cleaning on my Gen 1 at about 48K miles, so your's is almost certainly due).. you are certainly going to hate it when the DMF lets go.. and it's not a matter of "if", it's a matter of when.


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## Barry Allen (Apr 18, 2018)

MRO1791 said:


> if you are balking at cleaning the intake that gets clogged up with soot and oil from the EGR


I'm looking into tuning to disable the EGR and then I'm wanting to thoroughly clean the intake. That way it can be clean and remain that way.


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## Carminooch (Mar 23, 2018)

Barry Allen said:


> I'm looking into tuning to disable the EGR and then I'm wanting to thoroughly clean the intake. That way it can be clean and remain that way.


I’ve been waiting and looking for the same, I can’t help but feel all of my issues are EGR related


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## MRO1791 (Sep 2, 2016)

Barry Allen said:


> I'm looking into tuning to disable the EGR and then I'm wanting to thoroughly clean the intake. That way it can be clean and remain that way.


If you figure that out, many will be interested for sure. On my 2009 Dodge Cummins, it is as simple as unplugging the EGR electrically and then just accepting the P0405 and CEL.. otherwise runs perfectly fine.. but in later years the EPA mandated the engine computers not let such a simple modification fly without a penalty, and hence the reduced power mode that exists for that reason. Know that any such modification is not going to be legal, of course.. but it's a bit hard to think the very few of these diesel cars can contribute any noticeable pollution compared to the many, many older cars on the road legally the emit far, far more pollution. The more they force these things, the longer people are going to keep those older cars on the road. I don't think the regulators understand that they could end up making things worse.


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## MRO1791 (Sep 2, 2016)

Carminooch said:


> I’ve been waiting and looking for the same, I can’t help but feel all of my issues are EGR related


I think you are correct, EGR does cause all kinds of issues and it's been a goal of the OEMs to find another way for some time for that reason. The new I6 Duramax uses POST DPF EGR (also known as low pressure EGR, many retrofit HD engines use this method too). By using soot free EGR it reduces the crud build-up and seems to be a far better way to get this done, if it really must be done.


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## Barry Allen (Apr 18, 2018)

MRO1791 said:


> The new I6 Duramax uses POST DPF EGR


I never could figure out why this wasn't done from the start on all modern diesel engines. It is far, far better to take the exhaust from after the DPF (where it is mostly free of soot) and then pipe that into the intake air.


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## MRO1791 (Sep 2, 2016)

Barry Allen said:


> I never could figure out why this wasn't done from the start on all modern diesel engines. It is far, far better to take the exhaust from after the DPF (where it is mostly free of soot) and then pipe that into the intake air.


It is about the cost and piping/space needed. It was cheaper to use the EGR before the DPF and it required no extra plumbing/or space.. the full size pick-up have more room to work with, and have you seen the sticker price! We agree, it is a far better system that we certainly all wish they would have used on our cars. I'm not against lower emissions, but I have a problem when the systems are problematic and cause reliability and drive-ability issues.


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## Barry Allen (Apr 18, 2018)

I've gone to the auto parts store and I'll be running a bottle of Stanadyne through the next two tanks of fuel. Will see if that helps anything, because it can't hurt much.


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## oregon_rider (Jul 21, 2017)

Barry Allen said:


> I've gone to the auto parts store and I'll be running a bottle of Stanadyne through the next two tanks of fuel. Will see if that helps anything, because it can't hurt much.


 My other diesel is a 1 ton duramax chev and in the truck diesel world - lopey idles and uneven running can be a sticky fuel pressure relief valve (fprv) - and using a cleaner/lubricity additive helps clear it up.

jeff


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## MRO1791 (Sep 2, 2016)

Barry Allen said:


> I've gone to the auto parts store and I'll be running a bottle of Stanadyne through the next two tanks of fuel. Will see if that helps anything, because it can't hurt much.


For the DPF there are some additives that claim to help, I used one on my 2015 at about 55K miles when it seemed to be doing excessive regens.. it appears to have been helpful, since using it the regens and random DPF pressure sensor error codes have cleared and have stayed clear. It was called Xado, I got it on Amazon:

https://smile.amazon.com/gp/product/B074DVP7G5/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I have also used Stanydyne which has a good reputation, but I don't think it will do much for EGR crude in the intake. Another good additive is Optilube, these are especially helpful for the health of the HPFP an fuel system, which might help the intake a bit if it makes for a cleaner less soot fuel burn, but that's not going to clear out the 50K miles of accumulated crud that is likely already there.


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## Barry Allen (Apr 18, 2018)

MRO1791 said:


> I have also used Stanydyne which has a good reputation, but I don't think it will do much for EGR crude in the intake.


I am no longer certain it is the EGR causing problems. I've run about 3/8 of a tank of different fuel through the car to purge the prior fuel, and in that I added some anti-gel (because it's dipping below 30ºF around here) and the Stanydyne additive. From driving around yesterday and today, the stumbling appears to be almost entirely gone.

This could just be one batch of bad fuel.


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## Barry Allen (Apr 18, 2018)

After running an entire tank of petroleum diesel from a steady supplier through my car, combined with 1/2 the bottle of Stanadyne fuel injector cleaner (treats up to 50 gallons, so I'm using it spread over two tanks of fuel) the stumble/flutter was already gone. I've filled up today with the other 1/2 the bottle and I expect it will be the same.

This was one tank of fuel from a Phillips 66 station. Weird that one tank of fuel seemed to cause this issue, but I guess anything can happen.


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