Erratic Idle After Fueling

[burnoil]

My '84 K30 with a Banks turbo'd 6.2L started idling very erratically immediately after a fuel stop today. I don't think it is all due to the fuel purchased as I drove away from the pump over to the cashier (about 50') and it wouldn't idle. Left fuel station and got on the freeway and it seems to run fine--normal power, normal ability to rev etc. Got off freeway about 16miles later and same idle issue. Got home and dinked around switching tanks (has three) and they made no difference. It will idle (a bit rougher than normal) with no loads, but as I add loads to it (auto trans in gear, turn a/c on etc), it runs rougher and rougher until ultimately it stalls. It will usually restart without touching the gas pedal, but sometimes it requires just a bit of fuel to get it to run. While in gear with foot on brake, add a little fuel to bring idle up and it will stay running.

Any ideas??

[Robyn]

Get a piece of clear plastic tube in the feed line from the filter to the IP and see if you are getting air.

This sounds like it could be an air in fuel issue.

Also try changing the filter/filters and possibly cutting the old one open to see if you have a nasty bunch of crud.
Also there is the possibility you have enough water in the lower part of the tank that it could be getting stirred up and then sucked up into the system.
Another thing is to make sure your lift pump is working properly. If the lift pump is having issues then the whole burden of getting fuel to the engine is saddled on the transfer pump in the IP. It was never meant to do this. Possibly with a refuel it is disturbing things just enough??????? The lift pump should be providing fuel to the IP at 2-6 PSI (Approx)
Have a look at these issues and lets see where it goes.

Robyn

[burnoil]

Well, I changed the filter last night and it made a nice difference. The motor will idle with all loads on now. It does not do it too smoothly, but it doesn't die. I was pressed for time when I did it so I couldn't check for contaminents from the drain tube. While bleeding the air out, the fuel came out of the air bleed port quite violently, so I'd venture a guess that the lift pump is ok.
This thing is odd. Once in awhile, it will idle smooth as glass (literally) and other times it acts like it has a cam the size of Lou Ferrigno's left arm in it. I did note that it was nice and smooth at startup this morning which deteriorated a bit as it warmed up. I'm hoping to get a little quality time with it tomorrow and check for air leaks.

[burnoil]

Well, I was stuck doing household type things today, so I didn't get to the store to get clear tubing, but I happened to have a fuel cap already set up for an airline to hook on to it. I took it and added an adjustable regulator to it and did the process that john8662 outlined in his tutorial on air leaks. I did not find any leaks anywhere. I even bumped the pressure up a bit higher than he stated and still nothing. Should I still do the clear tubing test or does the pressure test negate the clear tubing test?? Any other ideas??

[burnoil]

It seems like now the hot re-starts are the biggest problem. It still does its thing at idle occasionally, though not a bad as it was pre-fuel filter change, but the biggest problem is hot re-starts. On a hot/warm re-start it requires about 1/2 pedal and a fair bit of cranking to get it to run and the idle quality is terrible/non-existent. On cold starts, once the glow plug light goes out, bump the starter and it is running--smoothly. Hot re-starts are a whole different story.

[Robyn]

Im gonna say that there is a good chance that your IP is toast.

The pump is most likely just plain worn out.
The advance piston could be sticking along with a load of other issues.
Once the engine warms up the pumps internals expand a tad and the they can no longer provide the pressure needed to do the job.
Here is a little trick you can try. With a reasonable amount of fuel in the tank add about 3 quarts of tranny fluid to the tank of fuel. Mix the tranny fluid in a 2 gallon can with enough diesel to get it nice and mixed and dump it in the tank. Give it a go and see how it runs. It may smoke a little more than normal but this is ok and will go away as the mixed fuel burns off.
This test will "thicken up" the fuel some and make the pump work a tad better.
If things improve a bunch then you need to be getting your IP freshened up.

These pumps are good for a long time but they do wear out.

Good luck

Robyn