Running ruff at startup

[tyates007]

Hey guys,

Installed my DPS pump and injectors last weekend. It wasn't quite as big a job as I was expecting thanks to all the help I found here. The truck runs really smooth and has tons of new found power. The problem is that after it sits overnight for example it runs rough on start up. I am sure that it is air in the system but I will be darned if I can find it. All the hard lines are dry and so are the return lines and injector caps. It only runs this way for maybe 30 or seconds or so and then smooths right out. I thought it might be my lift pump as it has 200,000 miles on it but it is not leaking. Any suggestions would be great. I am leaving for the week end so if I don't thank you for your help now it will be a few days. So thanks.

 

[rancherman84]

sounds like a air leak,even though you dont see a fuel leak,you still can air through a cracked return line or bad o-ring.
air leaks can be a real ****** to track down,good luck

 

[Exekiel69]

What can make it easer is if it did not run rough before the ip and Inj. then it may be a return line or o-ring from the installation.

 

[chris88]

Could it possibly be too thick of oil? I dont know where you live but maybe you have too thick of oil for the winter. Im just throwing ideas out there.

Chris

 

[rubberfish]

Sounds like a possible air leak to me too.
Sometimes the trouble is, just because air
is getting into the fuel system, doesn't mean
there will be a visible fuel leaking out.
Like rancherman84 said,

air leaks can be a real ****** to track down,good luck

 

[LUCKY_LARUE60]

This is normal for diesel motors at colder temps, now I am going to hear "my truck starts up smooth at -18*F right, I've got a bridge for sale in NYC" you have to remember that it takes HEAT for these motor to burn the fuel in the cyl's, to get the heat you have to compress the air and fuel for it to burn. IF anyone of the cyl's compression is below the other cyl then it will run rough for a little. I could go on at great lengths on the fundamentals of a diesel but this is not a course on diesels. DON"T EXPECT THESE MOTORS TO RUN LIKE A GAS MOTOR, THEY ARE DIESELS....... Jim

 

[tyates007]

Thanks,

I will double check everything again. I am sure it is air. I am not sure how a gas motor starts because I have never owned one in a truck. I have had this truck for 12 years now and the only time it stutters has been if I had a leak of some kind. I live in Idaho and it has been cold but the truck sits in the garage and it had only done this for the last couple of weeks since the install. My motor is kind of dirty on top since the install so maybe I will just wash it off and double check all my connections then watch to see if it leaks anywhere. I appreciate the replys.

 

[Agnem]

Jim's point is valid, but I'm sure this poster knows how it is supposed to run given the temps involved. Try a piece of clear fuel line in place of the one that goes from the filter head to the return lines. This will let you observe some bubble action that may help you figure it out.

 

[OkieGringo]

Go ahead and replace that lift pump with 200k miles on it(<$20), and tighten up the fuel filter with a filter wrench. My "elusive air leak was solved by filter wrench. OkieGringo

 

[Doggy Daddy]

I would try plugging it in and see if all is OK when the block heater gets it warmed up. If it runs OK then look to the GP system. If still rough then you will be proved correct on the air theory. I think that the little check valve (I'm assuming that you have a 7.3) on the filter housing can allow air into the supply fuel if it is bad. It is where the filter head connects to the return fuel system; might be a little plastic ball and a spring or a tiny reed valve inside the fitting (this style is more prone to failing). Remove it, dry it off and see if you can blow thru (first! so that the fuel will be blown out!) and you should be able to, and then see if you can draw thru and uou should not be able to.

I second the idea of replacing the lift pump when it has 200K and there is any fuel problem. You might also suspect the change-over valve connections (assuming that you have dual tanks) or cracked rubber hoses to the tank or pump. You didn't say if you replaced the return lines (sounds like you didn't); I've heard of the new return banjo fittings having a bit of a sharp edge where the seam is that cut the O-ring on installation, although that had a slight leak of fuel.

 

[troutwest66]

If the roughness only started since you did the IP and injectors then I'm thinking a T isn't seated just right. Where in Idaho are you? I'm in Post Falls and if you're close I could help. I've done my returns with no problems but sometimes the Ts need some persuasion to seat all the way.

 

[akoldnav]

I live in Anchorage Alaska and sometimes I need to start my trucks up at cold temps when they are not plugged in. When my glowplugs are working properly, the engine starts and runs smothly. I had one with bad glow plug wiring and it ran like $hit for the first minute after a cold start. After replacing the harness, it starts and runs loud, but smoth at cold startup.

Man the one with bad wires smoked and shook so much I thought I had a serious problem. I even posted about it here. It wouldn't start without starting fluid when it got below 15 deg F. Now all is better, but I still plug it in when I know I am going to be driving it the next morning.

Lucky, Where do you want that bridge delivered?

good luck in finding and fixing your problem.

akoldnav

 

[tyates007]

Thanks for all the replies. Thanks troutwest66 for the offer. I live in Pocatello which is quite a ways. I did replace the return lines and plastic caps. I will try plugging it in and see if that makes a difference. I may have hampered the GP wiring when I had everything off. It will be the weekend before I can take a look but I will keep y'all updated.

 

[troutwest66]

Keep us updated. There's not much that we can't talk someone through.

 

[tyates007]

Well, I plugged the truck in last night and this morning it fired right up, no miss. So, I guess it is probably GP related. This explains why I have been over every inch of the fuel system and could not find a leak. Will dig deeper this week end.