wisconative

So, when I put it in Neutral and raise rpms, I notice a slight shudder that cycles about every one second at higher rpm. The shudder cycles faster or slower depending on rpms. At idle, I don't feel anything. I don't know what my idle is set to, b/c after I had trans mounts and motor mounts put in last year, I had to bump the idle so it wouldn't rattle apart.

It's just a subtle vibration that moves towards the back of the truck. I don't hear any engine stumbling. My guess is that is is a bad or clogged injector?Or maybe has to do with IP pump?

But I don't know too much, just enough to do the basics. What do the real gear heads think?

rrgrassi

Auto or Manual tranny?

wisconative

sorry, 727 auto
Also forgot
91 w250: looks stock to me
139k miles

rrgrassi

Have you changed the fuel filters and checked the lift pump?

wisconative

Changed fuel filter -- no apparent leaks
Haven't checked lift pump -- yet, I guess I will add it to the list.
I am guessing that's easy. I will search for it, any tips?

rrgrassi

After re-reading your post, I do not think the lift pump would cause it, unless air is getting into the fuel system some how.

If it's an injector of IP issue, it can vary with RPM. It can also sound like a misfire, running on 5 not 6.

Does it do this under load? Like idling in Drive?

wisconative

The shudder matches rpms, increases and decreases with how much gas I give it. I only notice it in nuetral when I give gas not at idle, In drive I never notice at any speed. Probably worth noting, and my apoligies for not including in begining, but I get haze @ idle after running engine for 30 minutes plus -- sometimes, the haze gets pretty thick. I think the shudder and haze might be related.
Start up isn't hard, and just a puff of blackish smoke. I found one post where I guy had a similar issue of haze @ idle when hot -- his post sounds like my situation. I have done some sea foam in the past and I run Lucas fuel treatment on most fill ups.
https://www.dieseltruckresource.com/...s-t289007.html
I am thinking crack injector lines to check, I will probably pull and clean injectors too.
Can I check lift pump by cracking open the tapped banjo bolt and hand cranking it? When I do fuel filter, I just fill filter with diesel and off she goes. The lift pump arm doesn't seem to have any friction when i pump it anyway.

rrgrassi

Is the haze blackish? Black smoke is unburned fuel. You may have an injector that is dribbling instead of spraying. The IP could also have an internal leak.

I do not think it's your lift pump. The lift pump feeds the IP. Can cause stumbling if the IP is being starved or fed air as well. A failing lift pump would cause stumbling because it cannot keep up with demand, especially when driving.

wisconative

haze is whitish/bluish and only at high temps, and not every time I drive. Around town, i don't notice it, but after goin down the freeway, whitish haze at idle.
I am hoping it's just gummed up injector/s.

wisconative

Checked lift pump again, seems to work fine.
I am guessing the beginings of clogged gummed up injector/s.

rrgrassi

That or an IP. Crack open the line to each injector, one at a time. When you get to the one where nothing changes in the running, then you found it. At that point then swap the injector with one of it's neighbors. IF the problem follows then you know it's the injector. If it does not, then it will either be the IP, or something with the cylinder.

Have you adjusted the valves lately>

wisconative

Valves is on the to do list, so is replacing trans pan, adding temp guage, etf guage, trans cooler, and some other crap too.

I have had the truck for 22,000 miles, so, it's probably overdue. Lady I bought it from said the original owner was the owner of a Dodge dealership. She had it from 90k -118K. I think she changed oil and ATF and the elec regulator box attached to the fire wall behind engine. Doubt she did anything else -- like greasing the zirc fittings.

For cracking the lines, I checked my 6 inch 17mm wrench to see how to do it b/4 jumping in, seems pretty tight in some spots with all those lines going about.
I was thinking a 17mm crows foot on a ratchet extension might make it easier to do. Any suggestions?
4" lift -- great for crawling under, not fun for top end stuff.

wisconative

cracked injector lines, only burned myself about 5 times on the manifold.
looks like 6 and maybe 3 are gummed up. So, add that to the list.