6.5 throttle problem

[metallicflame]

My 97 K3500 has started developing a weird issue going down the road. When you're driving and you let off the accelerator slightly to maintain your speed (like going down a slight grade), the engine drops to idle rpm immediately (like you've taken your foot off the pedal all together) but goes back to cruise rpm when you put more pressure on it. It not as noticeable during city driving due to the lower RPM's, but on the highway it's really predominant. I first thought it was the electronic accelerator, but it also does it if you have the cruise control on, just not as violently. I replaced the PMD which is located behind the bumper with a Heath heat sink but no change. I've also noticed that when this is about to happen the transmission shifts out of overdrive. Please any help would be greatly appreciated.

[More Power]

My 97 K3500 has started developing a weird issue going down the road. When you're driving and you let off the accelerator slightly to maintain your speed (like going down a slight grade), the engine drops to idle rpm immediately (like you've taken your foot off the pedal all together) but goes back to cruise rpm when you put more pressure on it. It not as noticeable during city driving due to the lower RPM's, but on the highway it's really predominant. I first thought it was the electronic accelerator, but it also does it if you have the cruise control on, just not as violently. I replaced the PMD which is located behind the bumper with a Heath heat sink but no change. I've also noticed that when this is about to happen the transmission shifts out of overdrive. Please any help would be greatly appreciated.

Welcome to the board!

At what vehicle speed does this occur?

Jim

[metallicflame]

I'm sure it's happening at all speeds, but is the most noticable above 45 mph due to the higher rpms. going down the road at 60 turning 2200 rpms, it's a sudden drop to 1500 when you start to let off the throttle. And there's nothing gradual about it 2200 to 1500 instantly and then back to 2200 when you apply the slightest pressure.

[Kennedy]

Typically erratic "fueling" with little to no change in APP is from sticky metering in the pump itself. A heavy does of lubricity may help, but typically this is irreversible.

Often times the truck will have a burst of acceleration as well.

[Robyn]

I agree with John on this one.

Try dumping a quart of ATF in the fuel tank. (Even 2 will not hurt)

The ATF will loosen up the fuel solenoid, if the issue improves, then you know its the IP giving trouble.

The ATF is high in detergents and if it's just crud, will possibly help

Does the IP have the miles shown in your signature ??? If so a new pump is probably in the near future

Once the fuel solenoid starts to scuff up and become erratic, it's only a matter of time until it's toast.

The ULSD is not a friend to these pumps, and truth be known is far worse than any reports published.

Have you or do you run Bio diesel ??

Depending on who is cooking it, it can be trouble.
I stopped using it in my big rig after having filter issues and injector troubles.




Keep us posted
Some folks are not real cozy using ATF in the fuel system, but it's been the choice of old truckers for eons.

It's a cheap and easy trick to see wasssssup.

[arveetek]

I've had this happen twice. The engine couldn't even maintain speed properly while driving with the cruise on and going down a slight grade.

The first time it was the IP failing. I was able to replace the Optical Sensor without replacing the whole pump. It was quite an ordeal to get the timing right after that, and I wouldn't recommend it if it can be avoided.

The second time it was a failing FSD. I installed a new FSD and it has been fine since.

Casey

[metallicflame]

Great. Just what I need, another IP pump going south. We had a 93 C3500 with the 6.5 that the pump failed. There was enough other things that needed fixed that we decided to cut our losses and by a newer truck. Now this one is possibly bad.
Kennedy: I have noticed the "burst of acceleration" from time to time when I'm taking off from a stop sign/light.
Robyn: I get my fuel from either the BP station by my house or a Pilot truckstop if I'm on the road. I've never messed with the BIO stuff before.
Arveetek: I replaced the FSD/PMD this last weekend hoping that was it.
Thanks for all the input from everyone, now I know where to start. Going to stop by the auto parts on the way home tonight a get a quart of ATF to see if I can be lucky for once and it cures it.

[Kennedy]

Kennedy: I have noticed the "burst of acceleration" from time to time when I'm taking off from a stop sign/light.


Pretty typical of sticking metering in the pump. Any diesel on today's fuel really should have a quality lubricity additive used consistently. The DS4 has a proven track record of electronic failures, BUT it also tends to hold up mechanically quite well.

A good Lubricity additive like FPPF Total Power will treat for pennies a gallon and help your IP live a long and healthy life. If you find yourself in need, we stock brand new DS4 pumps at a competitive price.

[metallicflame]

Ok, I've done some searching online and need some clarification. Are you guys talking about the fuel shutoff solenoid? I've seen that you can buy these separately and is it hard to replace without removing the whole pump?

[Dvldog8793]

Howdy
IMHO....if your injector pump has almost 300,000 miles on it then that is what I would save your pennies for....:(
All your symptoms seem to point in that direction and with those miles on it replacing some of the components or cleaning is not going to fix the overall problem. Sometimes a good healthy cleaning can actually make out of spec components seem worse as the gunk or varnish can be filling voids.

Good luck!

[Warren96]

I have always used "Stanadynes Performance Formula'' in mine. It's not only good for the fuel system,but I also get almost 10% better fuel mileage! With todays fuel prices it pays for itself.

[metallicflame]

Can not believe where the time goes. Here's an update on the problem. Finally found a reputable diesel mechanic here in Kansas City, took the truck in last month and had the injector pump replaced. WHAT A DIFFERENCE!! Drove it back and forth to work for a week with no problems and then hooked our 5th wheel to her and can not believe how much better it pulls. I've also noticed now that the weather is turning cooler in the mornings, it starts and runs so much smoother. the past 2 winters, it would run rough for a good 5 minutes before smoothing out, now it's down to maybe 30 seconds. Thanks to every one's help and input on the problem.