TRENDZ

I have an annoying issue thats been bothering me since I traded my 90ctd for this 91 I have.
First, I want to tell you that my 90 was a 90,000 mile truck when I got it, and a 200,000 mile truck when it went away. So I know how these things are supposed to run. Long story short... I traded it for this 91 because I wanted a dually, and there were extreme rust issues with the 90.
I knew when I got the 91 that there was an issue with the engine. It had a mis, and you could hear unusual noise from the intake. This didn't bother me because I knew I'd be going through the truck from bumper to bumper, and was going to be pulling the head off anyway. I pulled the valve covers after getting it home, and found a bent pushrod on #3 exhaust. I threw a new pushrod in to see how it would respond, expecting it to be smooth like I was used to. It ran better, but not smooth. Still, no big deal, I was going to be pulling the head, doing a valve job, and replacing the injectors. I figured that would clear things up. Anyway, I've been driving it for about a year now with this "not so smooth" idle, and an awful lot of black smoke from a stop.
I've tried cracking open injector lines to find the uneven idle. No one cylinder seems to be the culprit. 3 cylinders are stronger than the other three. I suspect one of the cam springs in the pump is broke, or problems wih a few delivery valves. Any suggestions or comments would be welcomed!!!

Exekiel69

No expert here but I do have a question, how do You get a push rod to bend? I would look in that direction.

93-12Smoke

I had a broken cam spring in my pump for who knows how long. I didn't know till I opened it for a reseal

G1625S

So the head has not been of yet? I would say the PO either over-tightened that valve or had the pushrod out for some reason and did not seat it fully in the lifter before adjustment. Either way, there could be a bent valve causing the miss. It is, after all, a tractor engine and they will run extremely well with a lot of things 'wrong'. I just put an old continental flathead six out of service. Worked it several times with no issues other than low oil pressure. Turns out the crank was snapped between two mains. Ran for hundreds of hours that way.

user name

It may be a slightly bent valve or weak spring. I broke and exhaust valve spring in my dakota (gas v8 not diesel I6) and at an idle it was only running on 3 of 8 you could pull the spark or fuel from 5 without much change and even pulled them all at once it was running on 3. Off idle it ran pretty good could hardly tell anything was wrong to drive down the road. Also it would pass a cranking compression test with the bad spring. That one took me a little while to figure out.

TRENDZ

Yeah, I guess I wasn't very clear. All new valves, springs, reworked guides, resurfaced head, and new (reman stock)injectors. Although I did not check cam duration, lift is the same on all cylinders. Checking with an infrared therm shows a little less than 200 degree temp difference between strong and weak cylinders.
What symptoms come up when a delivery valve fails? I've been working on heavy diesels for 16 years, and have never seen a failed d/v.

93-12Smoke

Not sure about the delivery valves but when I took my pump apart to replace a leaking seal on the head I picked up the seal kit at a local injectors shop. Told the guy it suddenly started leaking at the head. He handed me the spring kit and said you're gonna need this. Went on to say that the blown seal on the head usually has to do with the cam spring breaking. Tore it apart and he was correct. My only symptom was the sudden, heavy leak.

93-12Smoke

Are the weak cylinders on the same fuel rack? could something have damaged those three lines?

TRENDZ

All three weaker cylinders are from one half of the pump. When the engine was apart, I cleaned and painted the lines, so no visable damage, no leaks, and no... I didnt get paint in the lines.
The pump is coming out, because the tappet cover on the side of the block is leaking oil. I guess I'll be going through the pump then.