99 K3500 7.4 454 Rough Idle

[jjdward]

Recently got a 99 k2500 flatbed, DRW,5 speed, with 245k. When I first got it, I did a tune up which helped a lot and then fixed a hot start issue. Its still got a rough idle and seems kinda weak while driving. I tested the fuel pressure yesterday and it was 48psi at idle down to about 42 when driving down the road. It doesn't cut out or bog down when driving just seems a little weak, but I've never had a 454 before. It starts right up no issues. No check engine light(bulb is good as it lights up with key on, not running) , but when I use scan tool it shows "P0327 Knock Sensor 1 Circuit Low Input (Bank 1).  Any suggestions?

 

Here at the things I've replaced:

Plugs

Wires

Distributor

ICM

Coil

MAF

Fuel Pressure Regulator

Both O2 sensors

Both Knock sensors

 

[CamGTP]

A knock sensor code can make the computer pull a lot of timing, so you may want to look into that further. A new sensor could be out of spec or faulty. And you could have a harness issue.

 

Watch your fuel trims on the scanner, see what they read. If they are very positive, it's a possible vacuum leak and negative means it would be running rich.

[jjdward]

The fuel trims have been around +/- 5. I'll try and track down the knock sensor issue. 

[Tom_1991]

On 6/26/2020 at 9:19 AM, jjdward said:

Recently got a 99 k2500 flatbed, DRW,5 speed, with 245k. When I first got it, I did a tune up which helped a lot and then fixed a hot start issue. Its still got a rough idle and seems kinda weak while driving. I tested the fuel pressure yesterday and it was 48psi at idle down to about 42 when driving down the road. It doesn't cut out or bog down when driving just seems a little weak, but I've never had a 454 before. It starts right up no issues. No check engine light(bulb is good as it lights up with key on, not running) , but when I use scan tool it shows "P0327 Knock Sensor 1 Circuit Low Input (Bank 1).  Any suggestions?

 

Here at the things I've replaced:

Plugs

Wires

Distributor

ICM

Coil

MAF

Fuel Pressure Regulator

Both O2 sensors

Both Knock sensors

 

Did you checked and cleaned idle control valve?

And if EGR open when idle can also cause rough idle.

 

But if you say it seems weak while driving, maybe not ICV and EGR.

Edited June 30, 2020 by Tom_1991

[ChevroletTough]

That knock sensor made my 2004 silverado run like trash. Way under powered. I'd imagine that's your problem.

[jjdward]

On 6/26/2020 at 6:29 PM, CamGTP said:

A knock sensor code can make the computer pull a lot of timing, so you may want to look into that further. A new sensor could be out of spec or faulty. And you could have a harness issue.

 

Watch your fuel trims on the scanner, see what they read. If they are very positive, it's a possible vacuum leak and negative means it would be running rich.

Is it odd that the knock sensor code doesn't make the CEL come on? 

[CamGTP]

Most knock sensor codes are set to "MIL on Second Error". So it needs to report the same error within a given amount of time or key cycles to set the light.