Intermittent rough idle/surge 1998 / k2500 Suburban

[dllasota]

Hello All,

I have a 98 - K2500 Suburban that we have owned since 2001. It currently has 210k + plus miles on it. It has the PMD relocation upgrade and that's about it. Had the injection pump replaced at 120k. Recently had 2nd injection pump replaced due to idle hesitation and stalls (yes we replaced the PMD several times for troubleshooting). It did generate some codes pointing toward an injection pump so we had it replaced at a GMC dealership. It ran ok for the first week or so. Now we are back to intermittent rough idle and surges (at idle). It doesn't happen all the time, no real pattern or DTC's. Very frustrating. Any ideas?

[Robyn]

Welcome to TDP :)

My suspicion is AIR in the fuel system.

Get some clear plastic hose, run a loop from the main return line on the IP up past the wipers and then connect it to the regular return hose,

close the hood just to the safety latch and drive the thing.

If you see bubbles flowing through, therein lies the issue.

It will take a short to purge the new clear line, but once clear of air, you should see only clear fuel.

Give this a go.
Ahhh, when was the last fuel filter change ????

If you find air, it has to be coming from somewhere between the tank and the lift pump.
take note, if this issue happens only with a half tank of fuel or less, the the issue is likely the suction safety valve in the tank. This is a valve in the pickup tube designed to allow fuel to pass if the sock becomes plugged, and these valves fail on occasion.



Good luck

Missy