Black smoke limp mode with no codes when accelerating quickly.

[Jim Froelich]

Just completed a 1600 mile round trip.About 700 miles in I tried accelerating on to I 10 went into limp mode. No check engine lights. Learned if I baby the gas I can get to a shop. Shop checked no engine codes. Drove to my destination 60 miles away. Went in limp mode several times. If I baby the throttle I can get to and maintain 65mph. It maintains speed with cruise on. If i am going any speed and mash the gas black smoke and limp mode no warning lights.Had a Cummins rep check 400 miles after first mechanic.  Still no codes. I have changed fuel filters, air filter, crankcase filters. I am leaning towards accelerator. Has any one had this issue?

[Radar22]

Hi Jim,

Had the same issue but my coach would blow black smoke and come to a grinding halt. When cooled down I could proceed but not very far. Had repair tech telling me it was bad diesel and most likely algae in the tank. Finally after treating gas it was not the issue. Took to Cummins service center and they discovered a leak in the charge air cooler. Had to have the charge air cooler dropped, and re-cored. Had radiator re-cored at the same time figuring if both were dropped might as well do radiator. Fixed the problem but as you can imagine it was a very costly endeavor. 

[MyronTruex]

How is your boost pressure? If a mechanic did not check the hoses and connections in and around the turbo there could be a small leak. Hopefully anyway. 

[1nolaguy]

Check your Engine Brake. If it is on (switch near driver) turn it off. Let engine cool a bit and restart. You may need to blow out some soot but if this is the problem it should clear in a few minutes and then run fine.

I am not sure of the details but I had this issue several times about a year ago when going through Mobile Al at surface street speeds. Engine started belching sooty smoke and lost power. The more I tried to gun it the more soot it belched. I pulled to the side and a trucker pulled behind me. It took him a minute the find the issue. The exhaust bake switch was engaged. I had not use the exaust brake since and yesterday I switched it on to help me slow down coming off a steep bridge on I-10. Engine started belching soot and lost power. switched off the EB and with in 30 seconds I was at interstate speed with no issues. As always YMMV.

[Jim Froelich]

The Cummins Mobile tech  hooked up back at the engine. Did a turbo load  test, engine diagnostic test said performance of all cylinders was SAT, Injectors were SAT, no codes showed up. The 1st mechanic found a ASB sensor code  and I got that dash light but it went away. I did flip the exhaust brake switch back and forth it did not have an effect. 

Right now I am leaning towards the gas pedal but at 600 bucks I'm looking for a way to test it.

I forgot to say this is a 400 - ISL my boost is normal when I get up to speed. 27 or so 

[Jdw12345]

It’s a communication problem, accelerator pedal is likely bad, like was stated on FB, communication issues, if it worked correctly on the technicians Insite computer because it eliminated the accelerator pedal. 
 So take the coach for a ride, turn on the cruise control, at around 35ish if it’s displaying acceleration issues set the cruise and take your foot off the accelerator pedal and push the accelerate button on the steering wheel and see if it accelerates normally without blowing smoke, I had a similar issue on a truck of mine, didn’t blow any smoke though, I would try that. Jmo. 

[Bill R]

@Jim Froelich Did the turbo load test include the entire air intake system, hoses and CAC?  I had a very similar issue and it turned out to be a small leak in one of the orange air intake hoses.  Everything was fine until I accelerated causing the leak to be pronounced by the increased turbo pressure in the hoses, causing immediate turbo loss and black smoke (too much fuel with little intake air).  If I was just cruising, the leak was not pronounced because not a lot of pressure being created by the turbo.  I would check every inch of the air intake lines.

[Gerry f]

I experienced that same problem with a 2000 Diplomat with a PAC brake on a Cummins ISC engine.   The PAC brake would engage and when I tried to accelerate the valve would not open up to let the exhaust flow freely.  I usually had to stop the engine and occasionally would have to open the engine access in the closet and manually open the PAC brake valve.  If I lubricated the valve with a non oil base lube and seemed to help.  Anything with standard oil will just burn and jam the valve even worse.  

Just my 2 cents worth.

[Guest Ray Davis]

The exhaust brake needs to be able to release quickly otherwise pressure can remain in the cylinder until it slowly escapes.  This is accomplished with a quick-release valve

My roadmaster brake in my tow car uses the same type device.   I bought my valve at a cleaning & laundry supply,  they seem to use them on their equipment.

It's a very simple and cheap valve.  I don't know if it is your problem but it could be and it's an easy replacement.

[dl_racing427]

21 hours ago, Ray Davis said:

The exhaust brake needs to be able to release quickly otherwise pressure can remain in the cylinder until it slowly escapes.  This is accomplished with a quick-release valve

My roadmaster brake in my tow car uses the same type device.   I bought my valve at a cleaning & laundry supply,  they seem to use them on their equipment.

It's a very simple and cheap valve.  I don't know if it is your problem but it could be and it's an easy replacement.

I had to replace that valve on my PacBrake when I bought my coach.  Mine was blown out and wouldn't activate the brake.
They're also used on air brake chambers, which is what you hear puffing when you release the brakes.
That well could be the OP's problem.

[Frank McElroy]

On 10/21/2023 at 4:05 PM, Jim Froelich said:

Just completed a 1600 mile round trip.About 700 miles in I tried accelerating on to I 10 went into limp mode. No check engine lights. Learned if I baby the gas I can get to a shop. Shop checked no engine codes. Drove to my destination 60 miles away. Went in limp mode several times. If I baby the throttle I can get to and maintain 65mph. It maintains speed with cruise on. If i am going any speed and mash the gas black smoke and limp mode no warning lights.Had a Cummins rep check 400 miles after first mechanic.  Still no codes. I have changed fuel filters, air filter, crankcase filters. I am leaning towards accelerator. Has any one had this issue?

On your engine, black smoke and no codes almost always means either a bad fuel injector or a leak in the turbo air boost.  You mentioned that the tech did a cylinder performance test.  So, it's unlikely a bad fuel injector.  I would focus on an air leak in the piping between the turbo and intake manifold including a leak in the intercooler.  This all assumes that your turbo actuator was verified as working properly.  Your engine is getting too much fuel and not enough air.

[Jim Froelich]

Not used to this site so I don't know if I replied but here is what my third mechanic found out by road testing with someone watching the engine from the bedroom. The COBRA elbow reducer collapsed when starting fast. this 5x4 reducer goes from the inlet air hose to the Turbocharger.  Donaldson P 600327 is the part number. They took the inlet hose to the air filter off and it did not collapse. The extra draw of 6 foot hose up to the outside intake screen area was enough to collapse it. I am changing this elbow this week.

Just to let everyone know. I appreciate all the knowledge. I did not know about oiling the exhaust break and now will do regularly with the correct oil.  Ray Davis if this doesn't do it your suggestion is next.

[dl_racing427]

52 minutes ago, Jim Froelich said:

Not used to this site so I don't know if I replied but here is what my third mechanic found out by road testing with someone watching the engine from the bedroom. The COBRA elbow reducer collapsed when starting fast. this 5x4 reducer goes from the inlet air hose to the Turbocharger.  Donaldson P 600327 is the part number. They took the inlet hose to the air filter off and it did not collapse. The extra draw of 6 foot hose up to the outside intake screen area was enough to collapse it. I am changing this elbow this week.

Just to let everyone know. I appreciate all the knowledge. I did not know about oiling the exhaust break and now will do regularly with the correct oil.  Ray Davis if this doesn't do it your suggestion is next.

That's some good troubleshooting there.  That possibility hadn't occurred to me.
Glad to hear it's fixed, and that it wasn't something expensive. 😎

[Bill R]

@Jim Froelich Jim - So glad you got this resolved.  I had the exact same issue happening, collapsed cobra head.  Turned out a collapsed air filter was restricting air to the turbo.    All this led me to find the factory installed filter size was not the spec for the coach.  The factory had installed 10" diameter with 6" inlet/outlet and it should have been 11" diameter with 7" inlet/outlet.  This was common on some 2006 models.  You might want to check you filter size.  Here is the post if you are interested.