ROUGH IDLE QUESTION

DIESELIB · **Posted:** Thu Sep 29, 2011 4:27 pm

Got a question concerning the idle caracteristics of my CRD..... When the engine is cold, there's no problem at all BUT once the engine reaches operating temperature the idle becomes slightly rough in park/neutral. If I place a slight load on the engine...by putting it in gear or simply turning on the A/C the engine smoothes right out and idles perfectly. Like I stated...this problem ONLY seems to happen with the engine fully warmed up in a no load senario....NEVER when cold or before it's fully warmed up and NEVER with any type of load on the engine.... No other running problems exist....the engine runs EXCELLENT otherwise. The roughness can be described as lopey...like a v-8 engine with a bigger cam....and the only code I have is a PO403 which is EGR related.... Any help would be appreciated!!
Thanks!!
Tom

papaindigo · **Posted:** Thu Sep 29, 2011 4:42 pm

Could be a variety of things but the first thing that comes to mind is weak fuel delivery at low rpms after getting out of the warm-up cycle. Take a look at the fuel bleeding video in Sir Sam's NOOB guide. Once that's done: 1) do you have a 1st gen fuel head, if so pull the heater electric connection on the driver's side and check for leaking diesel, if you have a leak stop right there and replace the fuel head and pigtail, if you don't have a leak consider replacing anyway; 2) if it has been a long time since you replaced your fuel filter then replace it; 3) bleed the fuel head for air. See if that helps.

Ajamant · **Posted:** Thu Sep 29, 2011 11:27 pm

Seriously there are so many problems directly related to fuel head. We should sticky that number one for all new owners. Get the second gen head ASAP.

warp2diesel · **Posted:** Fri Sep 30, 2011 6:56 am

When my original filter head leaked, it leaked air into the fuel, but did not leak any fuel until I installed my lift pump. Dealer swapped it out under the 3/36 warranty.
Another problem with the air leak was crappy running at higher RPMs that went away with the lift pump.
Upgrade the filter head with at least the new Mopar, or better yet the Racor with a 2 micron filter.
Type, "Eureka Boy" into Google and navigate Stan Wright's web page to the fuel filter upgrade for his CRD. Easier than trying to find it with the LOST search function.

DIESELIB · **Posted:** Fri Sep 30, 2011 11:23 am

PAPAINDIGO: aftermarket fuel filter with a fresh filter AND a lift pump....it doesent seem to be a fuel supply problem since other than the sometimes rough idle she runs GREAT!! Plenty of power and the idle clears up with ANY slight load applied....like the A/C compresor going on or putting it in gear.....as soon as the computer calls for an idle increase from the load....
ON A SIDE NOTE...all the lights surge when this happens as if the alternator wasn't being spun fast enough and causing it to quickly bounce between a charge/no charge senario....perhaps from the idle dropping too low OR my alternator starting to go bad...

Thanks for the replies!!!
Tom

papaindigo · **Posted:** Fri Sep 30, 2011 11:44 am

It's not the fuel filter that's at issue it's the fuel head itself although a lift pump is often the solution unless you have a definite fuel leak in the 1s gen head at the fuel heater plug. I'd still be inclined to bleed the fuel head to make sure you don't have any air in the system.

That said what's your warm engine idle speed not under load. I don't know how to set it but if the idle speed is just a bit on the low side it could be rough.

A too low idle speed could cause lights to flicker but I'd also wonder about 1) the alternator clutch which has been known to fail often with lots of red dust in the area and 2) your battery as a battery on the way out can cause odd electrical problems, including strange ECU behavior, in today's computerized vehicles. If the battery is not recent a load test might be in order.

DIESELIB · **Posted:** Fri Sep 30, 2011 11:51 am

PAPAINDIGO: TOTALLY different filter/head assembly... battery fairly new....tests real good.....no red dust or any other reason to suspect the clutch goin south....but I'm considering replacing the alternator since I've seen what you're talking about with electrical surges causing wierd problems with the ECU..... truly a wierd problem..... THANKS FOR THE INPUT!!!

DIESELIB · **Posted:** Sun Oct 09, 2011 4:58 pm

*************UPDATE***********

Just installed the ECONO/MAX TORQUE tune from GDE......PROBLEM SOLVED!!!!

ROUGH IDLE QUESTION

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