Cummins ISC 8.3 300 Hp Warm engine rough Idle

[shadow7663]

Having a tough time with this issue so heres the skinny. Last week truck starts running extremely poor on the low rpm side. runs great on the High rpm end.

Took the truck in had all new injectors installed, new pass throughs, new exhaust manifold (old one was cracked) new turbo installed (old one was cracked). After all that still the rough idle. 2 of the injectors were confirmed bad before replacing. After this we found a bad transient surpressor, replaced that, replaced the fuel pressor sensor. Still no change. So we put a test ecm on the truck, Truck runs great no issues, put old ecm back on truck runs horrible again. Ok so it must be the ECM mechanic says. So purchase a ecm today had it calibrated yada yada put it on and the truck still runs horrible.

Engine only runs bad once its warmed up. Oil levels good no coolant in oil no fuel in oil. Not smoking. No engine codes.

2 months ago installed brand new from Cummins fuel injection pump and lift pump. All parts installed on this truck have been genuine Cummins parts installed by Cummins.

I am at a loss here and need some help. Anyone have any suggestions?

 

[greg334]

yea, but you may not like it.

Some time ago Cummins issued a service bulletin to change the wiring from the old connector and lead that goes to the fuel pressure sensor to a new connector and lead - an upgrade kit was issued for this which included a new connector, three crimp connectors and an instruction sheet.

A lot of time the connectors which are supposed to be sealed upon crimping, fail and the ecm sees the fuel pressure vary during idle hence rough idle and sometimes no starts.

The solution is two fold, one is to clean and inspect every connector (including the big one near the lift pump) and degrease/grease them with the right dielectric grease made for Packard connectors (which a lot of techs fail to get that part).

The second is if the upgrade was done, have the tech properly splice (read solder) the connection and use the correct method to seal the splice.

 

[shadow7663]

Greg,

Thanks for the info. This does have the updated connectors on it. However we just tried resplicing and soldering in new connectors anyways. Still the same problem.

I have a funny feeling that wonderful caps fuel system injection pump is failing again!

 

[greg334]

Just a thought, try moving the harness around at and near the pump.

 

[greg334]

Another dumb question, when you had the tech look at the ecm through the computer, did they check the ecm memory to see the reoccurring and inactive codes? If not maybe an ECM dump may be in order to dig those codes out.

 

[shadow7663]

Tried wiggling the harness and checked just about any wire that I could get my paws on! As for the ecm the old codes that were in there were from the original injection pump that failed. The old ecm is now in Grand Rapids as that's where I had to pick up the new one from Cummins.

It could be very possible this 2 month old injection pump is failing already but failing within spec and not enough to through a code out. It's going to Bridgeway Cummins in Dearborn on Monday as they are the one who installed the pump so I want them to check it out.

 

[greg334]

I wish you luck, and hope you get it fixed.

Those were all issues I had to deal with, either on my truck or a friends.

 

[shadow7663]

Thanks Greg, You gave some great advise! I just wished it worked this time....lol That's trucking for you! If there is money in the bank something is very wrong...lol

 

[shadow7663]

Well as it turns out one of the brand new injectors was bad. As the engine warmed up the o-ring on the injector expanded out of spec. and was failing.

To be sure that was the problem they moved the injector to different cylinders to see if the problem followed and it did.

 

[shadow7663]

So.......... The saga continues!
Cummins installs another brand new injector. That one was bad too! So 2 bad injectors both brand new right off the shelf. Had to wait to get the new one in stock. So they call me to day your truck ready, just test drove it and it's running perfect they say.

I get there let it warm up and the truck starts missing again before I even released the parking brakes!

Got a call from them again about an hour ago now they are going to listen to me and replace the new fuel injection pump that was installed July 5th of this year. They did not want to replace that pump I guess because its a $3600.00 pump at their expense. Of course they will be doing under warranty at their expense.

I am really beggining to dislike Cummins engines and their service!

 

[truckblue]

I'm just going to throw this out there. I drove an FL70 with this motor and started having similar rough running problem. I took it to a Frieghtliner shop. By my describing the symptoms, and hooking up computer, this seasoned mechanic says, " I think i know whats wrong", and proceeded to replace fuel tank vent tubes which were packed with mud from mud wasps. Problem solved.

 

[shadow7663]

Well the fuel pump was only part of the problem. It still ran rough at idle after all the above mentioned work. So we put it on the dyno. 9inches of blowby

Pulled the head. Cylinder #2 & #5 had bad valves with a lot of slop in them. Also pulled the piston out of #5 you could see where the compression and combustion were burning the sides of the piston thus the high blowby as it was getting past the rings.

Final result= Recon cylinder head from Cummins, and a engine overhaul. Finally runs great.

Old dyno test with a 300hp engine was putting out 210hp to the rear wheel.
New dyno test with the engine barley broke in was putting just over 230hp to the rear wheel.

I should notice a nice increase in fuel economy as well as now the engine is turning 1600 rpm less to achieve the same speeds I was running before.

 

[greg334]

Did you need an overhaul or just a cylinder kit?

 

[shadow7663]

2 cylinder liners and pistons was what I needed but I just couldnt see not doing all of them since we were already in there and the engine had 650,000 mile on it. More piece of mind for me I guess.

 

[Deville]

I'm just going to throw this out there. I drove an FL70 with this motor and started having similar rough running problem. I took it to a Frieghtliner shop. By my describing the symptoms, and hooking up computer, this seasoned mechanic says, " I think i know whats wrong", and proceeded to replace fuel tank vent tubes which were packed with mud from mud wasps. Problem solved.

Where are these vents u speak of located?