2006 XC70 2.5T miss fire headscracher

driesbabe · Post by **driesbabe** » 01 Apr 2014, 05:49

Hi Guys,
I am here for some advice as I don't know what else to try.
Recently bought a very nice 2006 XC70 with 138000 km and full service history. After looking thru all the history I found a service invoice for a refurbished cylinder head. Fearing that this car had overheated I immediately phoned the garage that did the job (Volvo specialist) and was told that the car had burned a valve due to a faulty coil pack and a resulting miss fire and that the owner had neglected this.
I can live with that. The car received 5 new coil packs and the problem was solved.
About two weeks ago I took the car for a longer drive and noticed that the car was misfiring under slight load accelerating from 80-120 km/h. Next day I took it for a drive again and the same thing happened with the Engine check light now blinking while the car is misfiring. I took it to my Volvo indy to read the codes and.....NOTHING. He suggested that we do a fuel pressure test and told me to come back the next day. That evening I went thru all the invoiced history again and notice that the car had not for the past 70000 km received any spark plugs. So the next day before I went for the fuel pressure test i got my wrench out and a new set of Volvo plugs and replaced them. Plug nr 3 looked very bad with signs if very lean running and even some small aluminum pearls stuck to the electrode. All other plugs look fine and where in good condition.
The car now runs very much better and the misfire is almost not noticeable with no engine check light blinking.
However the problem is still there. I suspect that it might be a air leak and have done my best to find the leak using Carb cleaner and also a water test but i can not find anything.

Now for some things that seam strange to me.
1. On a cold start the car idles at -+2000 RPm before settling down to a normal idle about 20 second later.
2. When revved in park and the throttle is released quickly the engine makes a loud hissing / sucking noise. This is almost like a blow off valve on a tuned Turbo car.
3. The PCV needs replacing as it dose blow smoke from the dipstick. (parts are on order)
4. An Oil change is due (the oil looks disgusting, almost diesel like)
5. I own other 2.4T and T5's and this thing goes like a bat out of hell with power matching the 2000 T5 that I own.

I would really appreciate some advice, as I still don't have any codes and I am hesitant to look at fuel pressure as it's only one cylinder.
I look forward to all the great suggestions that you guys will come up with.
Kind regards
Andreas

huzzsaba · Post by **huzzsaba** » 01 Apr 2014, 15:48

I would start with the easy stuff first like cleaning the throttle body with etm cleaner. Second, I would clean the maf sensor with maf sensor cleaner.

Try those and see if it helps.

draser · Post by **draser** » 04 Apr 2014, 16:44

Hi Andreas,
I'd be concerned more about that cyl #3, since you discovered it ran lean. I'd check the electrical connector to the fuel injector to make sure it's clean looking and tight. You can unplug and look into the contacts to assess condition. The other thing would be the wires going into the connector, I'd give them a slight pull to make sure they're still intact. If that passes I'd suspect the fuel injector for that cylinder. Perhaps you could get a good used injector of same type and swap. As you can imagine after seeing the AL droplets, it's dangerous to run very lean since temperature gets hight. I'd hate to swap the injector to a different cylinder only to find out that the symptom moved. Another thing you can do, if you suspect previous overheating, is to have a compression test on the engine. One question: can you hear any pinging or knocking noise under acceleration?

driesbabe · Post by **driesbabe** » 09 Apr 2014, 09:03

Hi Draser,
I have had the injectors on a flow bench and they all seem fine. I actually stood next to the guy testing them and had a look for myself. The theory that the wiring might be faulty is a very valid one. and I have not thought of that. I will go and check that out. I have driven the car allot in the past two days, and I can't get it to ping or knock, my Wife has however reported some strange noises and loss of power in the past.
I am almost suspecting a over-boost situation. My thinking is that cylinder nr 3 is directly above the ETM and where the boost pressurized air enters the manifold. Maybe it is getting most of that air and messing up the mixture on # 3 the most?
I just don't know, with no codes it is hard to tell.

driesbabe · Post by **driesbabe** » 14 Apr 2014, 07:55

Guys I need help here please.
What I have done.
I have connected my Scan tool that shows boost pressure live. I have then driven the car and according to the readout I am getting 220 Kpa of boost (30psi) under full acceleration. The car dose not show a CEL.
I have replaced the TCV with a known good one, problem persists.
I have replaced all vacuum lines with new ones, problem persist.
I have checked the waste gate operation, it is in good working order.
I suspect that the boost pressure sensor is giving a faulty reading to the ECU and therefore the ECU is not telling the TCV to open the waste gate. I don't know if this could be correct though, because as far as I know, the boost pressure sensor is also supplying the data for the scan tool?
I am starting to think I am looking in the wrong spot?

Help.

draser · Post by **draser** » 15 Apr 2014, 06:30

You'll need to know what voltage reading you get at the boost pressure sensor for a good working engine and compare to yours. Does the connector look ok?