S60 2.5T 2003. My car misfires, horrible to drive. Local garage no idea. Coil packs and sparks all fine.
Volvo dealership/master technician state that pots 1 to 4 are ‘leaking’ more than normal. The ‘leak test’ showed pots 1 to 4 were leaking close to 20%, but pot 5 was not as bad and was leaking only 7%, (with 10% being the acceptable max for this year of car). They said this was really odd, and had never seen this before. The dealer wrote to Volvo UK for help. Volvo UK came back and said “they have seen previous reports of RPM sensor wiring too close to the B+ cable, also to make sure that the gearbox pickup hasn’t been damaged or dented as this could cause an idle problem”.
Volvo dealer suggest having the car back for a second round of testing, and looking at the above. But if the RPM sensor proves to be working all okay, then the issue is probably internal, and will mean cylinder head removal, and another large invoice!
I look forward to some responses on what my issue could be!

 

are you getting misfires on all cylinders, some or random? Not sure what the tech is referring to as a "leaky pot". I would be looking at the end connectors/cabling into the coil packs. I'd think if the RPM sensor was acting up, it would throw a code... did you get a check engine light? Anything internal to the engine would show up on a compression test (wet/dry to see if you are losing compression via the valves or the rings). Has the tech done a compression test yet?

 

When the misfiring started I took it to a local general mechanic. His snap on diagnostic tool came up with 'misfire cyl 2'. He then swapped the coil pack and the spark with cyl 3 then ran the diag again. It apparently came up with the same message, 'misfire cyl 2'. He then did a compression test and said the compression was down, so it was probably a burnt out valve. I then took it to another local mechanic, who did his own diag, and said that all 5 pots were fine, he tested them engine hot and engine cold, all fine. Their diag tool indicated there was an issue with the ECM, and therefore suggested I take it straight to main Volvo dealer. Of which I did.
Volvo firstly came back and said that the ECM was not cooperating with the reboot, or reset of the original software, so it was deemed faulty. They then replaced the ECM (Ł700)! The issue then was that there were no fault codes coming up, and the engine management light that was ON, was now off, and not picking anything up.
The tech apparently spent 9 hrs looking for the fault, and like the previous mechanic, he said yes, compression was good across all 5 cyl. However, he seemed to think that it wasnt missing on just cyl 2, he seemed to think it was missing randomly on various cylinders. That then led to them doing a 'leak test'. I too had not heard of a 'leak test'. That seems to be the same as a compression test.
I picked the car up last weekend and we are no further forward. However, on driving the car home some 12 miles, the engine management light came back on. So, this should now throw up a new fault code right?

 

still don't know what tech#2 means by "pots" lol (coils??). The idea of swapping out the coils is a fast way to see if a specific coil pack is bad. If you move it and the fault remains on the same cylinder, it suggests either the connector/wiring is bad or something mechanical is wrong. To check for mechanical issues, the common test is a compression test. All 5 should be relatively close (say 150 PSI). If one is low, the next test is a "wet compression test where a couple of tablespoons of oil are dropped in the spark plug hole. The oil helps the rings seal - so if the compression goes back up, its the rings. if it stays low then its either a valve or perhaps a head gasket (I suspect you'd hear a blown heat gasket...). So if you suspect a valve, the next test is a "leak down" test where compressed air is forced into the cylinder via the spark plug hole - bubbles in the coolant means your head gasket, hissing in the intake means your intake valve etc. So to your woes, If the car is only missing on one cylinder and all the mechanical tests appear good, they it would only leave a wiring/connector into the coil. If you are in fact getting random misfires on all cylinders (the new check engine codes will help here) then that opens up a lot of other possibilities - ie anything that can mess with the mixture... lots to choose from and sort out...

 

Thanks for the reply, great help. I am going to liaise with Volvo again tomorrow. I know their tech spent 9 hrs on the car, but the first part of that was spent working on and then replacing the ECM.
I wonder whether their term of 'Leak Test', is the same as you describe below, with the oil down the plug hole, and then compressed air into the cylinder. I will ask them tomorrow and let you know.
In anticipation of my car going back in to them, they have also now obtained (from Volvo UK) a camera probe. Similar to the thing used in surgery on humans. They suggest they can take the inlet manifold off and then be able to look at the valves close up with this camera. But it does come with additional cost. Which brings me to ask, how much money should I be spending with no solution being found?! How many possibilities are there that could cause a misfire?!
(By the way, a 'pot' is another word for cylinder :-)

 

In addition, I am sure that either the previous general mechanics, and/or the Volvo technician confirmed that there; was a spark coming from the plug, and that there was fuel going into the cylinder.
The mechanic prior to Volvo also replaced the injector on cylinder two.

 

Must be a "British" term. In almost 50 years of playing with cars and airplanes, I have never heard of a cylinder called a pot!