Surge and puff of smoke at idle

[1999gmc]

So, I was reading through my old MAXXTORQUE magazines and found a Q&A about this exact thing and it says it's probably an injection pump. is there anything else it can be? It started out by doing it once every 6 months or so. Then it went to every couple months, now it's usually every week or so. I did the test they say 3 times. It never dropped off going up or down in the rpm. But once it seemed like possibly a dead spot at about 1600 rpm. I was moving the pedal slowly and the rpm seemed to stay there for a little and then started to climb again. I checked and cleaned all the grounds when it first started last year, and it didn't seem to help. My injection pump was replaced at 86K for stalling. It has 150K on it now.

It is always at idle, and sometimes it feels almost like someone bumps the rear end of the truck, or a surge, and sometimes it feels like a misfire, or the truck shut off for a second, and a puff of smoke comes out the tailpipe. One time I was hooking up the trailer, truck was in park idling, and all of a sudden you heard what sounded like a miss, and then a puff of black smoke came out the exhaust.

 

[6.5L]

Not sure if it helps any but for the longest time at exactly 1600rpm, my truck would buck real bad. If I held it there it would just keep bucking, and it got increasingly bad when towing anything. Replaced injectors. Problem solved.

 

[JayTheCPA]

Mine did a quick <Grrrr> <WHUMP> <WHUMP> which seems similar to what you are describing and in similar / same conditions (in my case either at a stop or when returning the gear selector back to D after downshifting to slow down without the brakes (I really need a stick, but that is another discussion) and the TPS at idle); did not notice any additional plumage in the exhaust, but I did not look for it either. Did not get the 'miss' sensation, just the surge. Replaced the IP with a reman ~1,500 miles ago and the <Grrrr> <WHUMP> <WHUMP> has not come back since.

 

[WarWagon]

Called fishbite. Start by checking the lift pump system and then check for air in fuel. Restricted filters and screens are next. PMD is always suspect. But again check for air and the lift pump system first before it gets expensive.

 

[1999gmc]

Called fishbite. Start by checking the lift pump system and then check for air in fuel. Restricted filters and screens are next. PMD is always suspect. But again check for air and the lift pump system first before it gets expensive.

Did the feed the beast and ATT in April before I took a trip to Walker River towing the trailer and my lift pump died on that trip. So I have a new Walbro from Leroy, but I do want to get a fuel pressure gauge mounted permanently(on Xmas list). So is best way for checking for air to put in a clear fuel line to inj. pump? Did filters in April when I did the FTB. PMD was warrantied in 09 by Heath and it isn't a Stanadyne, So I'm thinking it is a flight systems. But from what I remember it was doing it before the PMD was replaced. That was back when it would do it once every 6 months or so. When I was pulling the trailer in April, I am pretty sure I sucked that thing down to a vacuum pulling the grades up the Sierra Nevada MTNS. It just lost power and would barely idle climbing a grade, so I pulled over and shut it off. Looked at a few things under the hood, had my wife turn the key on, and the lift pump made some funky gurgling noises and all of a sudden I had fuel again at the T valve. Picked up a lift pump in Reno and installed it, but when I got home I ordered the Walbro from Leroy and took the stock one back to Napa here. And it seems from then on it has been doing it more often.

 

[ak diesel driver]

sounds like a fuel pressure guage is in order, also put the clear tubing on the return coming out of the IP and just leave it there for quick checks