PO300 Random/multiple cylinders misfire

Sergio del Castillo · **Posted:** Sun Sep 13, 2020 12:46 pm

Hello members;
Need some guidance. This morning, coming back home in city traffic, 30 t0 35 MPH, I pressed the accelerator to pass a slower car and got nothing, just continued with the inertia that I had created. At the next stop light, the car shacked while idling and had almost no power to move in a flat surface. It did not move when stopped at a slight up incline. By revving up in neutral and shifting to drive, managed to get it moving and the last mile to get home.
In my driveway the CRD idles rough and then I can rev it up to 3,000 rpm smoothing the engine. Plug in the Code reader and got a PO300.
I lost my connection to the tech that looked after it from new, and the his brother at the shop (16 miles away) does not has a lot of experience with this vintage of CRDs. I have some basic tools and have worked and rebuilt some British Triumphs and Mopar's 4 and 6 cylinder gasoline engines, but I feel at lost in this case. :banghead:

Do any one could offer an idea of where should I start looking for a fault? Could it be some open wire in the injectors harness ? I assume that if the ECM is at fault I should have gotten a CEL which I did not.

It is an 05 CRD with 245+K miles and the only engine modification have been the addition of a Provent to the crankcase ventilation system which eliminated all the EGR troubles that I had originally. I do have an in-tank fuel pump to be installed, but waiting for better weather conditions to do it. I work in my driveway with no roof over.

Thanks in advance for the help

WWDiesel · **Posted:** Sun Sep 13, 2020 1:50 pm

Is the engine making any odd mechanical noises when idling or revving?
Have you tried pumping up the fuel filter manual pump to see if it makes any difference in the issue?
Check all the wiring to all the sensors on the engine very closely for any signs of wear or loose connectors.
:idea:

Sergio del Castillo · **Posted:** Sun Sep 13, 2020 3:32 pm

The engine makes no odd noises of any kind. Simply runs rough at idle (740RPM) with no little power to move the Jeep. It does respond to the accelerator and runs smooth and quiet at 2,000 RPM with no load on it.

I will try the pump and will check the wiring for loose connections now that is cooler. It did not overheated nor raised the temperature above normal. Also the manifold pressure, by the Code reader, increased from 28 IGH at idle to 48 IGH at 2,000 RPM.

Will post results

Sergio del Castillo · **Posted:** Sun Sep 13, 2020 4:22 pm

OK;
1. Check the pump; three strokes, first one sort of soft but with resistance, second one lot of resistance, third one hard.
2. Check wiring, could not see or feel any one connector loose or out of place, no signs of wiring harness damaged nor rubbing against any thing.
3. Started the engine, run smooth at idle with some light outorthe ordinary noise. Located the noise to the coolant metalic hose that run across the front of the engine. The bracket that bolts to the head had broken some time in the past and the zip-tie that I used to anchor it in place had deteriorated (brittle) with the heat. Replaced with a new one, noise gone.
4. Took it for a road test with some hilly street in my neighborhood and runs like usual. Did not sensed lack of power.

Will continue to watch of the possibility of air in the fuel system, but for now :BANANA:

Thanks again

WWDiesel · **Posted:** Sun Sep 13, 2020 9:28 pm

Based on your testing, sounds like you had some air in your fuel system? :BINGO:

Time for intank fuel pump install. Air in fuel problems will be gone forever.... :wink:

PO300 Random/multiple cylinders misfire

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