Need help diagnosing rough running issue

[pickupman]

I'm new to the forum and I figured it's time to start a thread about a problem that I have been having for awhile. I have a feeling it may be several issues and not just one problem.

Basically when I start the truck up in the morning, while the cold timing advance is on, it tends to run weird. The engine rpms will slightly speed up and slow down, in other words it doesn't hold a steady idle, but it is not very noticeable. Sometimes after the timing advance turns off the engine will start sputtering, but it will always clear up, either by me revving it a little or waiting 30 secs or so for it to clear up by itself. Once the engine is fully warmed up, the truck runs like normal, on very rare occasions it will sputter a little bit at idle when the engine is warm. One other thing is that sometimes when starting the truck up after the engine is warmed up it will sputter a little bit.

About 8 months ago, I was having the same issue as described above, but the engine was also surging a lot. At that point in time I figured it had to be an air intrusion, so I replaced the return lines, injector caps and o-rings. I also put in a new fuel filter and Racor filter for the water separator. That solved my surging problem, however, the sputtering problem has still lingered. I was unable to find any source of air intrusion using a clear line test for various parts of the fuel system, so now I am wondering if it could be a problem with the injectors or IP.

I understand that bad injectors could cause a sputtering problem, but I had assumed that it was most likely due to an air intrusion. I am not sure how to go about finding the problem, and I could sure use some advice.

 

[Wellused]

Before you start worrying about the expensive stuff(inj/pmp) make sure your basics are up to *****.I would get a gauge and look at lift pressure and then check volume.Get a small wire brush and clean up the terminal for the cold adv reall well.

 

[lindstromjd]

If any of your hard injection lines are extremely hot, that would tell you about a bad injector either stuck open or stuck shut.

 

[pickupman]

Thanks guys that gives me a good starting point.

 

[icanfixall]

Welcome to the forum. Can you tell us how many miles are on the injecters and the injection pump. Usually they last around 125,000 miles or so. If you decide to change them both please ask where to buy and where not to buy. There are plenty of ebay sellers pawning off painted shot to hell injection pumps as rebuilt pumps. Never buy a painted injection pump. Its most likely tested and cleaned off, then painted and sold as rebuilt. A famous shop in Florida is known for doing that. Several members here have had to get as many as 4 pumps from them till they got one that worked. I was suspect reading all the troubles that member was having till I ws privately informed what was going on with tha Florida shop. Its really enlightening when you know whats going on.

 

[pickupman]

Both the injectors and pump are original. The truck has 76k original miles on it, I know that because the PO was a relative. During the past 10 years, until I got the truck in 2010, it wasn't driven much, it was just garaged. I know it is low mileage for injectors/IP to go bad, but I am wondering if it could be a factor of age. I definitely don't plan to replace either until I am sure the problem isn't related to anything else, but on the other hand, I have been driving myself crazy trying to diagnose what may be a non-existent air intrusion.

 

[icanfixall]

Well with this new information what might be the problem is a gummed up injection pump. Try the simple easy fix by adding 2 quarts of auto trans fluid to a tank of fuel next fillup. Or remove the fuel filter and fill it with the auto tran fluid. Get the engine running and listen for the sound change. Then shut down the engine and let that atf sit in the pump and injecters overnite. then run it hard the next day to wash out any gummy crap that has probably fouled up the metering valve or other places in the injection pump. Adding to the tanks is a slow way to clean but it will work by the time you have mt that tank..