Slight miss/stumble after new IP, FI, and Glow Plugs...

[z28cp]

92 C3500 Crew Cab, Dually, 2wd. Has had the IP hot start issue for a while, then developed a dead miss, so I figured it was time.

The miss was caused by a broken plastic rocker arm button allowing the rocker to slide off of the valve, thus not opening the valve. I had replaced the ones on the driver's side a year or so ago. This time was on the passenger/turbo side.

Replaced the IP, injectors, and glow plugs. Needed the IP, as evidenced by the hot start issue. Figured that the injectors and glow plugs were probably due, since the truck has 260k miles on it, and I don't know that they have ever been replaced. And, it seemed maybe a couple of glow plugs weren't doing much anyway.

So, got her all back together. Starts up quickly. Seems to idle ok. However, it seems to have a slight miss under light accelleration. Not a 'valve not opening' kind of miss, but just enough to feel and notice. Seems to not be there under fairly heavy accelleration.

Any ideas what I may have missed or screwed up? The mechanical injection engines are fairly simple, so not sure what's up. Gonna try changing the fuel filter tonight or tomorrow, see if that changes anything.

Thanks in advance!

DaveZ.

[john8662]

Is your fuel lift pump operating? Check that it is by getting under the truck while it's idling and feel of the pump in the frame rail. If it's pulsating chances are it's pumping.

While you're checking on the fuel filter up top ensure that it's fully bled of air.

J

[z28cp]

John8662: Yes, I have verified that the lift pump is working. Have dealt with an inoperative one in the past, so aware of that potential issue.

Update:

After taking the long way to work this morning (via McD's), I noticed that once the truck is warmed up, it runs pretty well. My normal to and from work trip only takes about 5 minutes, so it rarely gets to warm up on those trips. Seems to have a slightly rough idle, but otherwise seems to run pretty smooth once warmed up. Interestingly, before I did all of this, it idled pretty nicely.

Haven't changed the filter yet. Will get that done tonight or tomorrow morning.

It definitely seems to have more power now. :)

DaveZ.

[z28cp]

Also noticed it seems to smoke on startup a lot more and longer than it used to.

[z28cp]

Been driving the truck off and on. These seem to be the issues...

When starting it cold, it seems like for the first couple of seconds it runs smooth, then starts in with the missing. Doesn't matter if it is 80* or 20* outside. Of course, while it is dong this missing, it is smoking. If you let it sit and warm up, the missing at idle seems to mostly go away. Can still feel it miss once in a while at idle, even fully warmed up.

When you start driving first thing in the morning, it will missing pretty good in first gear when you first take off, again smoking, but once you put it in second and accelerate, it seems fine. I drive about a block from my driveway to the first stop sign. Always does it when I first take off. May or may not do it again a little bit when taking off from the stop sign. Then it doesn't seem to do it anymore once it has warmed up this much.

Also happened to have to move a trailer a few weeks ago. Trailer probably weighs around 8k#. Truck did not seem to have the power it used to before the IP, injector, and glow plug swap. I assume this is related to the missing issues I am having.

I have changed the fuel filter, no difference. Verified lift pump is working. Can feel it running, and seemed to pump plenty of fuel when I was bleeding the fuel filter.

It does seem to have a possible fuel leak somewhere, but I have been unable to locate it. Seems to leave a small puddle on the driveway after having been driven for a bit. Looks to be from the front of the engine. But I can see no wet areas on the engine. Filter drain is not leaking. Return lines all appear dry. Any idea where else it could be leaking from on the front side?:confused:

I read another post where it was suggested that the person maybe had leaking fuel lines, possibly sucking in air. Could that apply here?:confused:

Thanks for any and all help. I love my truck, but this is frustrating the heck out of me. Other than the hot start issue, it ran better before I changed this stuff... :(

[rameye]

When its doing the skipping thing why dont you start breaking the lines off the injectors one at a time...see if you can find a crappy injector.

It can be air also....no power and running like junk are classic signs. I would still do a rule out on a bad injector first.

If that doesnt pay dirt then start ruling out air infiltration..clear piece of tubing on return line will work.

The missing and smoking as you describe, might (as this happened to me one time) be a result of an air pocket forming as fuel leaks down overnight and is replaced by air. When you first fire it you are getting a good section of fuel..then comes the air section..and trouble hits.

Like putting air into an IV line..... murder mystery stuff

Maybe?

[JohnC]

Replace (temporarily) the injection pump return line with a clear plastic line. Watch for air bubbles. Also, you can plumb a fuel pressure gauge to the water drain on the filter. Anything negative is bad.

[phantom309]

think you have enough timing in it?? low power missing,. rough idle, smooths out as you step on it, sounds like it could be lack of timing, and you did jst change the IP,.
jm2c,..
Nick

[DmaxMaverick]

Advance the timing a little (~1/8" on the mark). If the previous pump was "worn out", and the timing chain wasn't replaced, the timing marks won't be accurate. You may need to advance significantly, in this case. Also, make sure the HPCA is working.

[z28cp]

Thanks for the replies! I will check these out when I'm off work between xmas and new years.

[BrIONwoshMunky]

The lift pump crapped out on my 6.2, and would stumble and bumble when the fuel was cold (like in the 20's), but when it was above freezing, everything was okay. Still did it after a fresh filter swap. I ended up getting it to run okay by spinning the gas cap almost all the way out so it didn't seal anymore, afterwards, I replaced the cap, thinking it wasn't venting properly and consequently realized that the lift pump had died, leaving all the work to the engine pump. This pump would do fine with warm thin fuel, but couldn't suck hard enough to break vacuum in the tank caused by the cap diaphragm on the cold stuff. The only thing I can figure is that the SLIGHTLY thicker cold fuel was harder to suck through the fuel lines.

New lift pump and all is jolly. YMMV

[arveetek]

I would definitely check the timing as well. As has been said, improper (retarded) timing can cause smoke, rough idle, and missing. When you step on the throttle, the timing is mechanically advanced, so it would make sense that it would smooth out at higher rpm.

Also, where did you purchase your injectors? I've had problems in the past with buying poor quality rebuilt injectors. The engine would run great under load, and smooth out at idle after a long, hard pull. However, normal starts and idling were rough. I even had one injector leak fuel and had to be replaced. I learned from that experience that you get what you pay for.

Casey

[z28cp]

IP, Injectors, and Glow Plugs all from Kennedy Diesel, so I doubt there is a problem there. I am assuming it is something I did. :o

I'm betting on the timing, since I set the new pump to where the old pump was, and have not changed the timing set. It didn't seem to be very loose, but I didn't check it that close. It IS on my list of spring projects though.

[z28cp]

Well, those who said IP timing were correct. Advanced it 1/8". Suddenly starts and runs like a new truck.

Big time Thanks to all who chimed in! :D