Hey guys I have a 03 LB7 242, xxx I just bought it about 4 months ago and it's been running great since I got it but a couple days ago I started to notice it surging when I'm moving but let off the throttle. For example say I'm doing 50mph and traffic is slowing down in front of me so I just let off the throttle to slow down it starts surging almost sounds like it goes to a lope tune it's so bad but it doesn't change the rpms on the gauge and if I get in the brakes it will keep doing it on and off till I come to a stop but once I'm stopped it will idle just fine. It does this at all speeds only when I let off the throttle. Besides that it runs great still getting 20mpg in town in a cclb. No extra smoke that I can notice. I'm thinking the fpr or possibly the filter head but I'm ordering the filter head rebuild kit and Nicktane cat filter adapter tomorrow so it will eliminate that possibility.
Surging when off the throttle?
- Thread starter heavrolet98
- Start date
What is your rail psi @ idle? Good chance your fuel psi regulator is showing its age. What you can do if you have efi to try and get you by for awhile is go into the tuning and adjust the 1st 3 tables of the fuel psi current. I went like 1575, 1475, 1375 and it has fixed my regulater for now. Basically it takes a set amout of current to close the fpr. If it is not closing all the way @ idle you get a surge. Typically the fpr is worn out but this generally will get you by for awhile. Whoops I just read your whole thread and this is generally @ idle. I would log fuel rail psi to see what is going on with the surging while moving.
I'll have to see if I can get my hands on my buddies snap on scanner to monitor the rail pressure. My truck is totally stock besides 5" exhaust and a PPE boost valve. EFI is next on the list just have to wait till next month to get it.
My pickup started doing this when i switched from an '01 ecm os to an '02 ecm os. Does it sound like injector rattle seems to disappear and come back? Its not so much an rpm surge as injector rattle pulsing is what i would describe it. No idea why it does it though lol :spit:
I'd been running opti-lube but ran out a few weeks ago just ordered more Wednesday so hope that gets here soon. I can definitely tell a difference in the way the truck runs with that stuff I was highly impressed after my first tank with it and will definitely continue to run it. Just have to make sure I order enough that I don't run out.
It could possibly be a injector rattle I guess. It doesn't affect the rpms on the gauge cluster when it happens. Sounds like it switches to a lope tune on its own like it could stall out but as soon as I touch the throttle it sounds normal again.
So the surging just stopped yesterday on its own. I put a profab intake horn in on Saturday but I don't see how that could of affected it at all.
I know this is an old thread but did you issue ever return or did you figure out what caused it? I have the exact same issue you described going on. Mine is a 2004 LB7 with 186k. Completely stock except for a Superchips canned programmer.
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Monitor your commanded vs actual fuel pressure. I'd bet you'll see actual fuel pressure bouncing all over the place. Most likely caused from a sticking or failing fpr.
Try pouring a quart of good 2 stroke oil or a couple gallons of bio fuel in the tank on your next fuel up.
Try pouring a quart of good 2 stroke oil or a couple gallons of bio fuel in the tank on your next fuel up.