rough idle, CEL P303, No visible air in the fuel (Help)?????

adrianmiura · **Posted:** Sat Dec 08, 2012 8:27 pm

Ok I'm getting totally frustrated with the rough idle and CEL and the P303 code.
I thought this was being caused by air infiltrating the fuel, so here is what i have done:
1. added an external lift pump.
2. removed the quick connect on the pickup side of the fuel line.
3. two bottles of PS Diesel Kleen.
no difference.
Today spliced in some clear vinyl tubing on the input and output of the fuel filter assembly to check if I'm getting any air (was actually hoping to see bubbles) . No luck the lines were full of fuel and no bubbles.
Another note: When the motor is cold the idle is smooth. when it is at operational temp that when the rough idle starts. The vehicle runs smooth at speed and no black smoke.
Forgot to mention i have the "new" factory fuel filter assembly.

Help :furious:

Sir Sam · **Posted:** Sat Dec 08, 2012 11:12 pm

Have you tried an injector kill test?

adrianmiura · **Posted:** Sat Dec 08, 2012 11:57 pm

No have not tried it.
I don't have the software to do it.
For my Duramax I do, and also have the ability to check balance rates and command fuel rail pressure. I'm not aware of any way to do these tests on a crd with out the correct software. Please let me know if I'm incorrect.

Also forgot to add new fuel filter (crappy WIX next mod once i get this issue fixed is to go to a CAT) to the original post.
thanks
Adrian

adrianmiura · **Posted:** Wed Dec 12, 2012 1:20 am

More background info

GDE eco tune
new timing belt ~12k miles ago.
getting about 24mpg mixed city /hwy @ 5500'

Thanks
Adrian

TJ2 · **Posted:** Wed Dec 12, 2012 2:08 am

I've got PO303 listed as cylinder #3 misfire. If I'm reading that right it doesn't seem like air in fuel. Have you found a way to test #3 injector?

dirtmover · **Posted:** Wed Dec 12, 2012 8:57 am

There are prior posts here outlining procedures to test the injectors. The search on this forum isn't the best. I usually use :google:

restricting the results to this forum using the site: token.

adrianmiura · **Posted:** Mon Dec 24, 2012 1:36 am

Ok did some more testing still no solution, hopefully someone out there has had this same problem and solved it.

Tested the return rate of the injectors and they seem to be ok. the test procedure i found was to measure the total output of fuel at the return line at idle for 1 minute. If the output was greater than 100ml then check each individual injector to determine the one that has an issue. My total output was 60ml.

I removed the fuel rail pressure sensor plug and the Idle smoothed out, i ran the test again and got a total output of 65ml Hmmmm?

also dont have the normal diesel smell at the exhaust.

Thanks for any help.

adrianmiura · **Posted:** Thu Dec 27, 2012 8:37 pm

Ok more diagnosis
swapped injector 3 with injector 2 today and still the same issue. good idle when cold when then when the engine reaches operational temperature i get a CEL it still sets P303.

If I disconnect the fuel pressure sensor the idle smooths out. If the sensor is failing shouldn't there be a code?

Someone must have ideas??????

Thanks
Adrian

rough idle, CEL P303, No visible air in the fuel (Help)?????

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