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Constant p0301 code

Help, Advice, Owners' Discussion and DIY Tutorials on Volvo's stylish, distinctive "P2" platform cars.

2001 - 2007 V70
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Constant p0301 code

Post by mikich » Tue Jan 14, 2020 8:26 pm

I've exhausted most of the possibilities with this so I'm coming out of lurking....

2006 V70 2.5T about 174000 on odometer.

Started running rough with CEL on. p0301 shows up
Here's what I've done recently:
Swapped plugs and coils from cylinders 1 & 2
Replaced coil on cylinder 1 with one from junkyard
Replaced injector on cylinder 1 with junkyard unit.
Added a can of Berryman's cleaner to the tank
New fuel filter
New forward o2 sensor

The plugs are NGK and less than a year old. They look okay with grey deposits and no fuel or oil. No white smoke from the tailpipe.
The car runs pretty well at highway speed but rough in park or idling in Drive or Reverse.
The code doesn't come up immediately but appears within a half hour or so.
I'm going to swap the injectors on cylinders 1 & 2 next. If that doesn't isolate the cause, I guess I'll do a compression test. How do I disable the fuel pump on this car? There is no fuel pump relay but there is a pump control module in the back and a fuel pump fuse. Or should I unplug the injectors for the compression test? There are some excellent instructions for doing a compression test on a p80 but I haven't found a good set of instructions for this p2 model.

No matter what I've tried the p0301 comes up It would be nice if I could get it to move to 302 so that I'd know what the problem is but no luck yet.
I'm afraid that it is going to be something like burnt valves.
Thanks in advance


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Re: Constant p0301 code

Post by SuperHerman » Tue Jan 14, 2020 9:48 pm

So far your work has been solid and on the right path. I would do the following:

1) Compression test and if only #1 is low;
2) Leak down test;
3) Test wire harness to #1 if above provides good numbers;
4) Check your fuel trims for signs of an air leak if 1-3 are solid; and
5) Put some solvent in spark plug well with plug out as you may have a sticking oil scrapper ring.

If you have a boroscope you can pull the plug and look at the valve seat with a mirror attachment. Have you checked your PCV system, glove test? Usually the other end of the head causes problems, I have not heard of #1 going first.

If I recall I pulled the fuel pump fuse when I did Volvo compression tests. The leak down test can be your first and only test if you have a tester. It will tell you all you need to know. If you hear hissing from the valves then a burnt valve or damaged seat may be the issue.

Have you shined a flash light and taken a good luck at the piston tops? If #1 looks like the others, it could be wiring or a bad injector.

As far as the delay in the code appearing - this is normal Volvo behavior as the system runs a programmed cycle - so it is a red herring unless you have a hard mechanical fault (although I am unsure here - I suppose if you leave #1 coil disconnected you can test if it will send an immediate hard fault by showing an immediate CEL - and also exclude your wiring if it does)

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