Random Power Loss on my `93 W250

[matthewb]

Hi all,

I`ve been experiencing random power losses as of late on my 93 W250 with auto trans. I`ve done some searching here and found others having issues with air in the fuel lines and such, but from what I`ve been reading, my issue is different. While driving, it seems some times that my injection pump becomes randomly loud and results in a power loss. The pump / injection events become "raspy" and my power drops slightly. Then at random, it will fix itself and everything smooths out and my power returns. It seems that for the most part, this problem shows up when the truck is either cold, or has only been running for a short period of time. I noticed last night that, after about an hours worth of steady driving in moderate external temperature that the problem did not appear.

I have the following on my truck:

60HP Injectors (only a few thousand miles on them and this issue was present prior to these being installed)
M&H Fuel Pin
M&H Dynamic Timing Advance
AirDog 165 Fuel Pump (Fuel pressure is reading normal under all situations)
Minor Adjustments to the pump (pre-boost fuel and full-load screw, as I`ve done with my other W350 and had no issues)

My theory: I believe I have an issue with the KSB system. Either the ksb is intermittently problematic, or that the intake air temp. sensor is sending faulty signals. As I understand it, the KSB alters timing (advances timing). I remember hearing a truck run one time where the timing was advanced way far and its injection sounded very "raspy" or "clacky"

Any thoughts? I would appreciate any recommendations you can provide. THANKS!

 

[DVolk]

Did look close atvyour fuel lines ? Sounds like your sucking air some place ,could be the oil rings at the connection at the fuel pump and tank

 

[matthewb]

Volk,

Thanks for replying. I have checked the lines from tank to pump and all is well. I ruled them out primarily because this problem existed prior to me installing the airdog. I had originally thought that my factory lift pump was either weak or failing intermittently. The air dog did not fix that issue so I'm still searching for an answer.

Just drove the truck home from work today. It's about 65 degrees outside and the truck has been sitting since 7am. It sounded raspy for about 3/4 of the 15 min trip and about the time I got home the truck started to sound better. I know they run a little tougher in the cold, but this thing has acted up in warmer weather than this. It's puzzling. I'm still wondering about that KSB / intake temp sensor....

 

[NIsaacs]

On your next cold start I would unplug your KSB. What is the M&H timing thing? Does that add timing? If so, you might have too much when cold and the KSB is activated.

Nick

 

[DVolk]

You might run a jumper wire tonyour KSB and see if things change ,I HD to run another wire on minbe because the wire cracked cand broke justca though also I'd true a god fuel lubricant even a 6 Oz bottle of 2 stroke oil will work wonders

 

[matthewb]

Hello again all,

I appreciate all the comments. I`ve been busy between my two jobs lately so I haven't had a chance to do much tinkering under the hood. I have however, been reading up more based on the suggestions you made. Knowing that the KSB advances timing for easier starting, I logged on to my Cummins Quickserve account and pulled up some of the service manuals for it. From what I can tell, I believe my air intake manifold sensor may be bad. I think its sending errant signals to the KSB at random and causing it to advance the timing. As far as the M&H Timing Advance is concerned, I believe it is designed to increase the range of timing on the pump so that you get better use of the fuel at the top end, especially if you have larger injectors in the truck (which I do). This was installed by the previous owner, as were the injectors. The truck runs phenomenal when everything is working right. I`m still getting an intermittent power drop and that raspy sound comes back. I`m going to order a new intake temp. sensor first and see what that does. If it isn't that, then I`ll resort to pulling the KSB off and go through the diagnostics on it. The process seems fairly straight forward from what I read in the Cummins service manual. I`ll post back when I get more information. Thanks to all of you who posted, I truly appreciate it!

 

[DVolk]

Idbtry the jumper wire to the ksb , seen what that does renermber these engines are mechanical half of the exytras stuff could be unplugged and not affect how it runs

 

[matthewb]

I unplugged the KSB and drove the truck home from work tonight. Actually, I plugged and unplugged it a few times with the engine running after a cold start to see if any change was made in the sound. There was a distinct difference when the KSB was unplugged. The truck sounded smoother and it drove the way I feel it should. I definitely think this is the issue. I have about 1/8" of static timing on the pump currently, in addition to the M&H Dynamic Timing Advance Spacer. When the KSB was randomly triggering, it was advancing the timing even further, causing the truck to fight itself and adversely affecting performance. I`m going to leave the KSB unplugged for a few days and see if the random power loss returns. I still think my intake manifold air sensor may be going bad, but to be honest its not necessary with the way I run this truck. I only run this truck in good weather in the spring summer and fall. Since it has a grid heater delete, the air temp sensor is pretty much useless at this point. If it was intermittently sending pulses to the KSB, leaving the KSB unplugged will solve that issue. From what I understand, the only real reason the KSB was even there in the first place was to improve performance during cold starts in order to clean up tailpipe emissions on cold engines. (Not something I`m concerned with)

I`ll post an update after I log some miles in the next few days. If the intermittent problem does not reoccur, then I think I`ll have this figured out. I don't see any issue in leaving it unplugged permanently. If I`m wrong, please correct me!

Thanks to everyone who posted. I appreciate your time and input. As always, TDR to the rescue!

Have a good one!

 

[DVolk]

Some times with these extra goodies the trade off isn't worth the Hassel for the power you get