Input on weird surging/lagging problem?

[gavio]

Hi Guys:

My van recently started a strange surging and lagging problem. It seems to be sort of random in terms of when it happens but it's like it'll be going along fine and then sort of takeoff like it's scared then kind of fall flat then be fine again, etc. When shifting gears, or at low RPMs it'll sort of buck a little then usually settle down. When it is just sitting in the driveway, the idle seems fine, then when I run the RPMs up a bit, sometimes it'll just run away for a few hundred extra RPM and other times it'll seem a little flat.

My inspection revealed nothing obvious - the fuel pump is working, no evidence of leaks, nothing disconnected, EXCEPT that I noticed the end of my throttle cable has lost its bushing where it connects to the IP lever and is WAY loose. As I write this, I'm thinking maybe that's the problem.

Is it possible for this to cause such symptoms? Or do I actually have TWO problems to fix (i.e. the throttle cable and some mystery problem?) The problem came on suddenly the other day, with no apparent warning.

Next, can anyone look up the part number for my throttle cable - it's for an '83 G20 with, of course, a 6.2 NA.

Thanks for any insight/help.

[dieselcrawler]

I don't know if I can be any help or not, but the problems you describe match my own a month or so ago. I ended up replaceing the engine driven fuel lift pump, and the fuel filter. At that time I noticed a drip from the back of the fuel filter houseing, long story short, I removed and pluged the hole for the dirty filter sensor/vacuum switch with JB Weld. I also replaced all the rubber fuel lines I could get to while I was there. What was the problem? I have no idea. It may have been a leak at the lift pump, it may have been the leak at the fuel filter, it may have just been a cloged filter itself. What ever I did, the truck now seems to run nice and smooth, and I have noticed no odd running behavior at all... from the truck that is. The driver on the other hand... no one can seem to be able to explane the new dents on the front fender. **grin**

Anyway, good luck with the ol' 6.2, maybe someone else will have some real answers for you...

Greg

[gavio]

Thanks, Greg:

I had uncovered your previous discussion thread when searching for "surging" and considered that, but a couple things lead me to think this may be different:

First is that the symptoms can be created while simply idling in the driveway under no load, but;

the symptoms created thus are inconsistent - i.e. in revving it up to 1000 RPM say 6 times in a row, it may run away 2 of those times and lag 1 of those times and be normal the other 3 times, and;

the problem came on suddenly - it wasn't there and then one night it was - just like that.

More comments, anyone?

Oh, BTW, I do have the throttle cable on order so Monday I should be able to rule that out.

[dieselcrawler]

Hey there,
When my problems showed up, at first I just thought it might be a tank of bad fuel. Maybe that WAS it, I don't know. But like you said, it was random. Might run good for a while, then act up for a while, or be ok. At any rate, good luck... hope you find your problem. As for me, I'm off to take my truck out to the parent's farm, and see my sister and soon-to-be brother-in-law, and see if I can scare him by takin' him for a trail ride in the ol' DieselCrawler! **grin**

Have a good evening...
Greg

[gavio]

From the pix you posted in the photo contest, I'd say you'll have no trouble scaring them! Have fun! I love that one picture with it just coming off that huge boulder!

Right now my van is scaring me and I still don't have any idea what's wrong. Under certain light load low speed situations it really gets to bucking like crazy.

[dieselbegreat]

I think erratic behavior you described can be caused by erratic timing which can be caused by erratic IP housing pressure which can be caused by varying fuel pressure, air in your fuel line or restricted return lines.

[gavio]

I think I'm going to follow up on that fuel pump some more - even though I hear it ticking (I have an electric lift pump - no mechanical), maybe it's getting erratic or weak. Of course it's just a month out of warranty :(

Thanks for the input - anything else?