# 12v Cummins advice



## rebelplow (Jan 30, 2008)

I've got a 94 3/4ton, 2wd that has 349,000 miles on the clock. My dad bought it brand new, so we've put all the miles on it. He was never very good with preventative maintenance. For the last who knows how many miles, it's been very smoky, stumbly, and doggy for the first 10 miles of so after you cold start it. It doesn't matter if it's 85 degrees or 15 below. I was planning on doing the injectors, and having the timing set to fix it....until I started reading about the P7100 overflow return pressure regulator valve on the injection pump. This part is only 25 bucks, super easy to install and pretty much fixed the problems. Well it's at least 90% better in my case. I bought it from Larry B's Foster Truck. Here's the writeup from their website.

New P7100 overflow return pressure regulator valve.
Part # 1 417 413 047
Fits Dodge Ram with Cummins, 94-98 12 valve
This overflow valve regulates the primary pressure inside the injection pump. If this pressure is not within standards it can effect your timing, injector function and a number of other factors. This can cause your engine to run poorly in many ways. Low RPM stumble, low power, excess smoke, hard starting, poor fuel mileage. Check your fuel pressure. 


Just thought I'd pass on this little tidbit. For 25 bucks you can really bring your 12v back to life!


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## DAFFMOBILEWASH (Dec 9, 2006)

My 95 has about the same milage. I have not had it very long but it seems to me running on the rich side of the spectrum. Very stinky too!!! Needs to be parked a certain way in the drive so the fumes will not smoke us out on cold morning start ups. Everyone raves about the milage of the 12 valves, this one get less than my 06 with plow and salter fully loaded plowing. (14mpg on the lie o meter)....

I have been working on the 95 sorting out a life time of neglect. The good news is the trans is new and the steering isnt too bad...... Planning on turning up the P pump and changing the fuel plate early in the spring. Also looking for a blade for the truck for back up.

Perhaps an overflow valve will help clear up some of the runability problems as of late.


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## rebelplow (Jan 30, 2008)

I know exactly what you mean about parking a certain way to keep from getting smoked out. I had the truck hooked up to our 16 ft enclosed bumper pull one morning a few weeks back, and started the truck up. The smoke cloud was so huge that you couldn't tell there was a truck OR a trailer inside the cloud. When you'd push on the throttle, it would buck and jerk, and smoke even more. So far with the new overflow valve it is much much less smoky. I'd say its worth a try!


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## Y-town IceMan (Jan 10, 2011)

could possibly be a failin lift pump as well. just be thankful you don't have a 24v lol


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## rebelplow (Jan 30, 2008)

That's funny you mention the 24v. I've got one of those as well. A '99 one ton, extended cab, long box, dually. That truck has 219,000 miles. I've replaced the injection pump, and 3 lift pumps and just about every sensor on that engine. I've got gauges now so I can watch as the lift pumps fail. haha.


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## justme- (Dec 28, 2004)

Are you guys starting these without having them plugged in? Plugging mine in and no smoke cloud- ever.
Fuel pressure is very important to ensure- but it has a wide range of acceptable pressure for them. 

They do stink, even without making a cloud when idling. Fuel mileage depends on a lot of things- gearing (4:10 average 15mpg, 3.52 can get up to 22mpg at highway), timing (which can slip), air leaks (common in a lot of places on these trucks), etc. 
Check the strainer in the fuel heater (should be cleaned/replaced) and it's common for the heater element to create an air leak.
Odds are it's not an injector only problem- not saying new injectors would not make a difference with that mileage, but odds are they are not causing the issues.
Several cummins/dodge web forums with good info on them - pm me if you want them.


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