1994 Silverado 6.5 Diesel - Let Off Pedal Jerky Decelration - What&#39

[msutiny]

Hello,

 

I'm new here and happen to run across the forum.

 

Great information!

 

I tried searching though for my issue and couldn't find a post offering help so here I am.

 

When going down the road at speeds 55mph or above and I let off the pedal to slow down the truck jerks down about 500rpm and then slowly decelerates (feels kinda like downshifting into a lower gear but it's not - as I mentioned the decerlation in the rpms). If I hit the gas it jerks up about 500rpm and then accelerates fine.

 

I tried reading up and it appears it may be a throttle position sensor but there are no codes stored and no check engine light.

 

Any ideas what the problem could be?

 

This is a 1994 Chevy Silverado with the 6.5 Diesel.

 

Thanks!!!

 

MSU (John)

[GMTRUCKTECH]

Hello,

 

I'm new here and happen to run across the forum.

 

Great information!

 

I tried searching though for my issue and couldn't find a post offering help so here I am.

 

When going down the road at speeds 55mph or above and I let off the pedal to slow down the truck jerks down about 500rpm and then slowly decelerates (feels kinda like downshifting into a lower gear but it's not - as I mentioned the decerlation in the rpms). If I hit the gas it jerks up about 500rpm and then accelerates fine.

 

I tried reading up and it appears it may be a throttle position sensor but there are no codes stored and no check engine light.

 

Any ideas what the problem could be?

 

This is a 1994 Chevy Silverado with the 6.5 Diesel.

 

Thanks!!!

 

MSU (John)

 

Trust me on this one. 94 and 95 6.5 engines have MANY possiblities of the concern you are having. It's sounds like you lift pump is weak and you are not getting enough fuel to the fuel seperator canister to meet the demand. This is more common at high way speeds. It is mounted on the inner frame rail under the drivers seat. It looks gold in color and is shaped like a gas fuel filter. TRY this first because it's the cheapest if this doesn't help you may be lookin at a injection pump issue. You may want to pull the fuel seperator out of the canister and shine a light into it and see if you see any metal flakes in the fuel because this is a sign of injection pump failure. Or put a magnet in and see what sticks. Hopefully you don't have this problem but it is pretty common on 94 and 95. Good Luck

[msutiny]

Thanks for the tip.

 

If you have a second help me to understand the not getting enough fuel comment. If I accelerate it doesn't have any issues at all, it's only when I let off the pedal. If it were having issues getting fuel wouldn't it have the issue when accelerating?

 

Also, I am new to Diesels - where is the fuel seperator located?

 

Thanks!

 

=========================================

 

Trust me on this one. 94 and 95 6.5 engines have MANY possiblities of the concern you are having. It's sounds like you lift pump is weak and you are not getting enough fuel to the fuel seperator canister to meet the demand. This is more common at high way speeds. It is mounted on the inner frame rail under the drivers seat. It looks gold in color and is shaped like a gas fuel filter. TRY this first because it's the cheapest if this doesn't help you may be lookin at a injection pump issue. You may want to pull the fuel seperator out of the canister and shine a light into it and see if you see any metal flakes in the fuel because this is a sign of injection pump failure. Or put a magnet in and see what sticks. Hopefully you don't have this problem but it is pretty common on 94 and 95. Good Luck

 

[nicholas.waldner]

My dad has a 94 silverado half ton with the 6.5 diesel. Could this fuel separator canister be the cause of trouble starting when its warm?

 

Nick

[msutiny]

Okay - replaced lift pump.

 

Took it down the road and doesn't surge nearly as bad but still is surging like i'm on and off the pedal.

 

Checked turbo actuator - no issues

checked a few glow plugs - no issues

 

Tried the magnet in the fuel bowl and got some brown sand textured metal to stick to the magnet.

 

Does this mean the IP is bad?

 

Help!

[Truckin2003]

my grandpa had a truck with the 6.5 and if i remember right he had to put an injector pump in it, and possibly some injectors too. its been 5-6 years since he had the truck so im not sure what kind of issues he was having that led up to replacing it. but i believe ive heard of others having injector pump failures on the 6.5