Pulsation of the truck comming to stop or moving

[dersark]

My 04 truck has about 41000 miles on the clock with no problems. Recently I noticed if I put the transmission in drive without pressing on the accelator the truck moves forward with pulsation, also is the same situation when I come to stop. If I accelate or brake little faster, that does not happen. I took it to the dealer they said, the rear axccel seal is leaking and parking break pads are saturated. They changed it but still doing it. It becomes very apparent when I put the camper on. Any ideas, Thanks Sark

[Harley Bob]

Not sure if this helps, but my '02 does the same thing. Noticed it a couple of years ago. At first I thought it was brake drag, or a bad u-joint in the drive shaft. Hasn't gotten any worse in over 45 thousand miles, just annoying because it causes a little shudder.

Just returned from an 11K mile trip to the Atlantic Provinces and New England pulling a 13K lb toy hauler. The tranny was due for a flush, so I had the local chevy garage check the truck over. Regarding the pulsation you reference, and if it's the same issue as mine, the technician, after having driven the truck and experiencing the "pulsation", thought it was due to the Allison torque converter at the moment it engages or disengages. Is it a problem? He didn't think so! But who knows, and it hasn't gotten any worse. Maybe there's an Allison thread that has more detail.

[dersark]

Thank you for your reply, I am taking the truck back in, I will keep posted.

[dersark]

I took the car back to the dealer for pulsation problem. They hooked the car to the computer, but they have some sort of problems to read the OBD II. Recently I added I Pod conection to the radio that might possibly done that. Any body came up with OBD II reading problem after connecting IPod wireings. Thanks.

[dersark]

I am shocked, they told me it is fuel injectors. They replaced all, they have it all in the stock. They changed the oil and the filter. Also coolant ?. the pulsation went away. I Pod conection was causing interference for OBD diagnosis. I never had power problems. so where I am going from here. how long this set would last. do you think bad filteration is doing that. GM does not have the brain to improve filteration and prefer the cost of fuel injector replacement. I do not buy that. there has to be other problems. I always changed fuel filter every 5000 miles and always put clean deisel.

[epa1775]

My truck does the same thing except it only does it intermittenly when I first start it for the day. Doesn't affect anything the way it drives or runs. It would seem to make sense about the torque converter engaging. Keep us updated on what if anything improves. Unfortunately I don't think the dealer will cover any warranty work b/c of the mods I've made.

Pete

[dersark]

Mine was doing off and on until the day came which did it all the time. check your engine oil see if it is to dark. I had no problem with running or engine power, actually I had too much power, what ever that meanes.

[d-rails]

I took the car back to the dealer for pulsation problem. They hooked the car to the computer, but they have some sort of problems to read the OBD II. Recently I added I Pod conection to the radio that might possibly done that. Any body came up with OBD II reading problem after connecting IPod wireings. Thanks.

I found that if anything extra is connected to the radio, using the OBDII is a problem. I discovered this while trying to use a Bully Dog Power Pup while my Sirius module was connected. I had to disconnect the Sirius before I could do any programming.

[Steveesp52]

I will never understand why so many dealers go after injectors other than they pay big $$$ in warranty and tell paying customers they need injectors. These days, most customers who read these boards are prepared to pay for costly injectors. I can see one basic reason there are so many injectors replaced and that is they are easy and quick along with being a bandaid that covers up other problems for the short term.

The previous owner of my truck was chasing a problem since 80K where they threw the 2/7 injector harness repair at it, an entire engine harness at it, injectors at 100K (1st time), FICM module along with a bunch of other junk and NEVER EVER fixed the issue. I purchased the truck at an awsome price when the truck had 139K miles because of all these problems. While it was on the dealer lot I hooked up a TECH 2 Scan tool and found the cause of the surge you describe.

The description of the issue was a surge at idle with the truck creeping at a stop light. Not all the time but most of the time. Holding your foot on the brake, the torque converter would absorb the surge and make it not as noticeable. You could also watch the idle jump when the surge would occur. When watching fuel pressure and plotting the data, you could see the fuel pressure regulator was getting very slow to respond and fluctuating fuel pressure from 2000-6000 PSI. Off idle, the fuel pressure fluctuating was still there but not noticeable mainly because pressure was a lot higher.

The final and last repair was a $400 fuel pressure regulator that I replaced at 145000 miles and problem was fixed and has never come back. As you can imagine, the Dealer did tell me I needed new injectors. I was hoping they would find the fuel pressure regulator but very quickly overlooked that as there was no way that could be the cause. They had never replaced one so it could not be the problem. Due to the difference in cost, I chose the cheaper route to take as a first shot in the dark. I also could not see bad injectors after only 39000 miles and that did not fix the problem previously.

I am convinced that NONE of the other parts ever needed to be replaced but cost both Chevrolet and the customer a LOT of money.

At 191000 miles and counting I'll keep running it and cross my fingers that I don't have any other problems with it. I also will not just throw parts at it hoping they will fix it but will challenge the dealer and if they can't justify the parts, I'll take my truck somewhere else.

Hope the info above helps someone out there.
Steve

[branstew]

Steve. Your post helps a lot. I am having the exact same problem right now but in a 2005 LLY. I have requested service at the dealer, explained the problem, and told them to be on the lookout for a problem with the fuel pressure regulator. I have around 50K miles on my truck and given that injector problems are less common in this truck as compared to earlier Dmax engines, I would be willing to bet injectors are not the cause. We will see and I will make sure do a data plot for the FPR. This should be a warranty fix anyways, but I don't want a fix that's not going to fix.