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Discussion Starter · #1 · (Edited)
Hello All,

Recently my 1999 v70xc (~200,000 miles) has been throwing a P0304 code and running very rough.

What I have done so far:

- The ETM and MAF were replaced 20k miles ago by me.

- The car has been serviced by a reliable mechanic who deals primarily with Volvos within the last 5k miles. At the time, they did an oil change and standard inspection resulting in only one issue being found (suspension related).

- The error first threw when my wife was driving the car on a trip. I had her check and change the air filter and check the MAF (which was fine).

- Once the car was home I read the code and proceeded to test the plugs, wires, and coils. I ended up replacing the spark plugs as they needed it anyway but the wires seem fine and swapping the ignition coil does not get the code to jump to a new cylinder (I take this to mean that the coil is not the problem).

For note: During this time I cleared the codes between all tests and the only code that has been thrown is P0304.

What I think the next steps are:

- Checking the fuel injectors and attempting the same swap test to see if the misfire moves to a different cylinder.

- Checking the compression

- ???

Conclusion:

With the car being as old as it is, there is a limit to the amount of time/money I am going to be putting into it but any input on if my next test seems like the right choice would be appreciated. Also, if anyone has other things they would check or guesses as to what else it might be and how serve the repairs would be I am all ears.

Thanks for your time.

UPDATE

Thank you so so much for all the great information.

I tested the wire, coil and plug: got plenty of spark.

I swapped the fuel injectors: still getting the same code on the same cylinder.

All the shops around me that lend tools seem to not have a compression test kit available kit now. I have three questions:

1. Is there really any other thing that could be wrong other than bad compression?

2. Is there any cause of bad compression that won't result in a $600+ repair bill.

3. Is there any safe distance/speed that this car can be driven or should it not be used at all?

Thanks again so much for all the great info all (and especially Drivewaytech)!
 

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See if that coil is producing spark i/e let it spark to head if it will not then check wiring on that coil if u verify spark compression is easiest thing to check next odds are it's on the ignition side but can probably rent compression test kit from parts store so you don't spend money unless you know the issue. Swapping injectors would cost you an o ring kit

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Check compression. That’s a cylinder 4 misfire and if plugs and coil swap didn’t make it go away you may be looking at a burnt valve.
 

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Discussion Starter · #4 ·
See if that coil is producing spark i/e let it spark to head
Could you please elaborate how one would do this? I have checked the wires visually and found no patches, fraying, or other damage but I am not sure what you mean by "let it spark to head".

Thanks!
 

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Discussion Starter · #5 ·
I am going to rent the equipment to run the test today. If it does end up being a burnt valve, any idea what the repair cost might range (I would take it in for this).

Thank you!
 

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Put old plug in end of wire touch tip of plug to bolt or ground of any kind and have someone crank car with injector of that cylinder unplugged so it does not fill with fuel and u should see and hear the spark.

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Could you please elaborate how one would do this? I have checked the wires visually and found no patches, fraying, or other damage but I am not sure what you mean by "let it spark to head".

Thanks!
Posted missfire video by Robert DIY he also has video on YouTube for compression test on these cars

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Discussion Starter · #9 ·
Posted missfire video by Robert DIY he also has video on YouTube for compression test on these cars

Sent from my SM-G960U using Tapatalk
Thank you so so much for all the great information.

I tested the wire, coil and plug: got plenty of spark.

I swapped the fuel injectors: still getting the same code on the same cylinder.

All the shops around me that lend tools seem to not have a compression test kit available kit now. I have three questions:

1. Is there really any other thing that could be wrong other than bad compression?

2. Is there any cause of bad compression that won't result in a $600+ repair bill.

3. Is there any safe distance/speed that this car can be driven or should it not be used at all?

Thanks again so much for all the great info all (and especially Drivewaytech)!
 

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Could you please elaborate how one would do this? I have checked the wires visually and found no patches, fraying, or other damage but I am not sure what you mean by "let it spark to head".

Thanks!
Don’t do this. The Volvo could drive about 27kV and that is not a pleasant feeling.

You moved the coil and plug without change if it was a bad plug or and coil the misfire would migrate
 

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I don't know what it would cost off hand however make absolutely sure its a compression issue before making any decisions if u do have compression then I would check injector pulse but compression is next I don't know what it would cost but I'm sure some searching on here will give you the information you need to make a informed decision there is mountains of info. and yes I'm aware u can get shocked it's a very crude test but it even tells you if the wiring to coil is good.

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