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Old 11-14-2008, 11:58 PM   #1 (permalink)
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Intermittent misfire/rough running

Hi all,

I hope this isn't something I could have found by searching harder - I did do quite a bit and didn't find anything like this.

My new to me 1994 2500 is intermittently losing power and running rough on the highway. I'll be driving along, smooth as silk, then suddenly there is a loss of power, a rattling noise, and a rough vibration. Then it's gone, the power comes back, and she's smooth again. Then the misfire returns, and the cycle goes on. I can't determine any other factors that correlate - it happens sometimes as often as once a minute for 5-10 seconds, sometimes I go for more than an hour without it.

The only other indicator of anything strange is the temperature gauge - it cycles up and down. I'm assuming that's being caused by a thermostat that opens all the way instead of just a little - but maybe that's a symptom of some other - maybe electrical - problem?

Anyone seen anything like this?

I won't be able to check in regularly unfortunately since I'm on my way to pick up a boat with the truck (with my fingers crossed) and will only have sporadic access to a computer. But I'll check in when I can and pass on any other symptoms I can gather.

Thanks for any and all suggestions!

Cheers,

Chris

PS - I only noticed it tonight, so I haven't had it in to have the codes read - I'll do that as soon as I can.
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Old 11-14-2008, 11:59 PM   #2 (permalink)
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maybe fuel pump? fuel filter?
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Old 11-15-2008, 10:34 AM   #3 (permalink)
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Quote:
PS - I only noticed it tonight, so I haven't had it in to have the codes read - I'll do that as soon as I can.
To read codes> 94 Diesel Ram DTC's
doubt if you'll find any set codes though, your problem isn't electrical.

Your temp gauge is normal.

The rough running sounds like an injection pump problem, perhaps sticking delivery valves.
Try adding a qt of two cycle engine oil to a full tank of diesel and see if it changes.
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Old 11-16-2008, 12:40 AM   #4 (permalink)
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Rather than 2 stroke oil, add an injector cleaner, like PowerService, Howes, FPPF, or Lucas, even Amsoil makes one.
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Old 11-16-2008, 12:51 AM   #5 (permalink)
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its def something to do with fuel delievery and when is the last time you changed your fuel filter and even though its not common on a 94 your lift pump might be shot or worse you p7100 might be going
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Old 11-16-2008, 09:40 AM   #6 (permalink)
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I forgot to add, the temp gauge fluctuation is normal. If it really bothers you, there is an upgraded thermostat from Cummins.
Your problem is definately fuel related, it could be as simple as rotted fuel lines allowing air to be pulled into the system, which is common on older trucks, but usually causes a hard start condition.
The overflow valve could be going, or even something in the fuel tank blocking the pick-up tube.
Most importantly, fix the cheap stuff first. You don't want to spend the $$$ on a IP if thats not the problem.
Check out this write-up, hopefully it'll help you. http://www.cumminsforum.com/forum/94...m-writeup.html
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Trans; Dunrite VB/TC, Intelligent Engineering billet input shaft, Burt Brown rebuild/upgrade.
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Old 11-16-2008, 09:51 AM   #7 (permalink)
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Wow - you guys are good, and quick. Thanks!

Here's the latest. In a nutshell, we ended up concluding it was water in the fuel or dirty injectors, and put in some injection cleaner and some diesel 911 stuff that claimed to disperse water. I also used the thing on the bottom of the filter to let the water out - although it didn't seem to let very much out. We had seen the water in fuel light, but not until long after the problem first manifested. Now, after the introduction of the additives, we haven't seen the problem again in ~250 miles. More to go today, the fingers are crossed! But it seems like it's probably alright!

Here's some interesting other symptoms, or symptom: When the rough running starts (it starts and stops very abruptly, which is where my thoughts of electrical trouble came from) it seems to lock the throttle - taking foot off the throttle or pushing harder has no effect. In case I was misreading I tried taking my foot off the throttle and shifting into neutral - the engine revved right up and I put it back in drive. It seems that somehow the throttle was getting locked when the roughness was present. The engine also stalled a couple of times from idle.

Thanks again - it sounds like we probably have it resolved with the additives. What do people usually do about water in the fuel, by the way? Is there any way to get it out of the bottom of the tank? I didn't see any kind of spigot to drain the bottom off.

Thanks!

Chris
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Old 11-16-2008, 01:41 PM   #8 (permalink)
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About the only way is to drop the tank dump and flush it.
Even if you run your engine till it runs out of fuel there can still be as much as a couple gallons left.
And of course water sinks to the bottom...
Don't go to that station that gave you the watered fuel and warn others.
If you can prove where it came from they will likely pay for any repairs/flushing needed.
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Old 11-28-2008, 04:38 PM   #9 (permalink)
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Sorry for the delay in following up on this thread. I put in some additives that said they'd disperse water and the problem hasn't reoccurred since. The truck managed to pull my 10,000 lb. trailer from Eastport, ME, to Halifax, NS with no problems - although it was pretty slow up hills!

Speaking of slow up hills, should it be? Or should it's 400 ft.lbs of torque be able to pull that weight of trailer faster than 25 mph up a steep highway hill? I found that transport trucks were passing me up hills!

Thanks again for all the help and support.
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Old 11-28-2008, 08:20 PM   #10 (permalink)
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Stock '94s are dogs but 25 mph doesn't sound right.
If you had bad fuel the filters are likely plugging up pretty fast.
Clean the prefilter Fuel Pre-Filter Cleaning on Ram/Cummins
Keep on cleaning/changing filter or install a fuel pressure gauge to monitor whats going on.
Instructions> Checking 12 Valve Fuel Pressure

You might want to turn the power up, free and easy except you should add gauges first.
Instructions> Turning Up A P7100 Pump
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Last edited by illflem; 11-28-2008 at 08:23 PM.
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Old 11-29-2008, 01:19 AM   #11 (permalink)
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did you change the fuel filter or just drain the water. Its def a fuel delivery issue. Hense going 25mph up a hill. 10K is not heavy and your truck should have pulled better than that.

When its running rough, is it spewing unburt fuel out the pipe. Also, inspect and put some lithium grease on your throttle linkage. I dont like how the rig revs up when your foot isnt on the skinny pedal.
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Old 11-29-2008, 11:48 AM   #12 (permalink)
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I would say there is a fuel supply problem. The setting on the P-pump (plate, AFC, etc) or the fuel pump and filter. Possibly timing slipped too?

Quote:
Rather than 2 stroke oil, add an injector cleaner, like PowerService, Howes, FPPF, or Lucas, even Amsoil makes one.
As for fuel additives becareful even thought the P-pump in engine oil lube you got to remember these reduce the lubricity on the injectors too... Be sure to measure your additive properly and not just dump random amount in the tank...
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