S40 V40: Another s40 T4 misfires

[rija]

Hi to all!

It's been 1 year since I bought my T4 and until now I have not solved the Misfiring problem.
The problem:
Idle: fine
cruising conditions: fine
Wide open throttle: misfires begins at 3700 RPM
Throttle <60%: no misfire

What I have done:
Changed the plugs into original volvo: problem not solved
Changed the 2 coils (after market): problem not solved
Changed the 2 coils (original volvo): problem not solved
Changed MAF (original volvo): problem not solved
Changed Water temp sensor: problem not solved
changed the Fuel pump (High flow pump): fuel pressure near the fuel filter is 5.5 bar and at the rail 2.5 bar: problem not solved
Today I took the FPR off and put the fuel line directly into the fuel rail.
Now fuel pressure at the rail is 5.5 bar: the problem disappeared the first 5 minutes I have finished the modification then misfires again!!
Maybe because the engine was not very warm I don't know.


DATALOGGING
Installed my Innovate Motorsport AFR gauge

When the misfire occured the lambda was 0.96 (too lean at 0.9bar)
but after I modified the fuel line, lambda is now 0.76 - 0.8 at WOT but the misfires still happen at 3700 RPM
It was better just after I modified the rail line (FPR removal) then after 5 WOT runs the problem came back. The fuel rail pressure is still 5.5 bar

Boost Gauge shows 0.9 bar when the problem happens

When I disconnect the boost controller valve the gauge shows 0.4 bar - 0.5 bar and there is NO misfire.

Now I don't know what to do.
AFR is good at wot: 11.8 is really correct

If anyone has an idea please help me.

[960kg]

.....you can`t really do a diagnosis by disconnecting other parts thinking that if no mis-fire then that is the faulty part......i see you have an AFR guage but you can`t use that either for diagnosis, you just confuse yourself with random numbers!! those figures are telling you at what ratio it is burning the fuel it is not telling you why! i would put your FPR back in otherwise you may need your own private petrol pump in the boot because the consumption will go sky high........get a Scanner to plug in and read the codes and it would of saved you a whole lot of money, you have spent about £500 and still have the same problem........read the error code thrown up and it will point you in the right direction.......how many miles or kilometres has the motor done you may have an air leak or the front O2 sensor is playing up.....a Memoscan U480 will read and can erase the codes after replacement of the faulty part...

[rija]

Originally Posted by 960kg

.....you can`t really do a diagnosis by disconnecting other parts thinking that if no mis-fire then that is the faulty part......i see you have an AFR guage but you can`t use that either for diagnosis, you just confuse yourself with random numbers!! those figures are telling you at what ratio it is burning the fuel it is not telling you why! i would put your FPR back in otherwise you may need your own private petrol pump in the boot because the consumption will go sky high........get a Scanner to plug in and read the codes and it would of saved you a whole lot of money, you have spent about £500 and still have the same problem........read the error code thrown up and it will point you in the right direction.......how many miles or kilometres has the motor done you may have an air leak or the front O2 sensor is playing up.....a Memoscan U480 will read and can erase the codes after replacement of the faulty part...

I forgot to tell that O2 sensor has been replaced.
When throttle is wide opened, the O2 are disconnected (open loop) so their function is just for cruising conditions.

AFR is very helpful because if you have 16 AFR at boost condition it could mean you have lack of fuel. Fuel pump problem or FPR.

It is normal to have misfire if the AFR shows 15 at boost.

But just before the misfire happens, the AFR is 11.8 (good for turbocharged engines) and no possible lean misfiring.

I have read the codes also (i forgot to tell it) but it only showed the things I had disconnected MAF...
after error erasing the did not come back.

What I suspect is the ignition is not strong enough at high boost because when I reduce the plugs gap, the problem almost disappears but power is slightly reduced.
The wires that go to the coils have some cracks. Resistance grows when they are hot and may cause misfire.
The problem only appears when the engine is hot.

[rija]

I'm talking about the + and - wires not the leads that are also new.

[960kg]

Originally Posted by rija

I forgot to tell that O2 sensor has been replaced.
When throttle is wide opened, the O2 are disconnected (open loop) so their function is just for cruising conditions.

AFR is very helpful because if you have 16 AFR at boost condition it could mean you have lack of fuel. Fuel pump problem or FPR.

It is normal to have misfire if the AFR shows 15 at boost.

But just before the misfire happens, the AFR is 11.8 (good for turbocharged engines) and no possible lean misfiring.

I have read the codes also (i forgot to tell it) but it only showed the things I had disconnected MAF...
after error erasing the did not come back.

What I suspect is the ignition is not strong enough at high boost because when I reduce the plugs gap, the problem almost disappears but power is slightly reduced.
The wires that go to the coils have some cracks. Resistance grows when they are hot and may cause misfire.
The problem only appears when the engine is hot.

....what else have you forgotten to mention????...
....after what you have done and with the equipment your doing it with i don`t think there is much hope anyone on here could help you after all the car is sitting on your drive and not on our`s!!....

...."AFR is very helpful because if you have 16 AFR at boost condition it could mean you have lack of fuel. Fuel pump problem or FPR."....i wouln`t take any notice of that pointing to fuel as you have checked that and you have a new pump....i don`t know what pump you replaced it with but are the fuel pickup points and filters all as per original as if they are not the fuel rushes to the back of the tank on WOT and you won`t pick up the fuel and it will mis-fire???... don`t forget the other component for the engine is Air so you may have an air leak somewhere?.......Check the Carbon Canister ,especially the top hoses as they do split where the clamp is also the Purge Valve is not leaking......You could also check the TPS setting ......the plug gaps should be 0.7-0.8mm with only Volvo plugs!.......there is also a hose which connects to the large Turbo hose from the Air Cleaner down by the turbo this also tends to cause trouble and some have araldited the joint to prevent the air leak......the ignition coils have you checked the springs on the end under that rubber sheath they should protrude from the plastic 5mm......those + and - wires you say have cracks because of the work involved to change them just put tape around them to stop any earthing out.......there is a pic. attached so that should keep you busy with some carb. cleaner squirting all the joints that can leak, the pic. just tells you there location as you know check with the engine running and when squirted with the cleaner if the revs rise you have a leak.....after all that why don`t you treat it to some STP injector cleaner as the spray pattern may not be very good......Hope this Helps???

[rija]

I have checked all the hoses and there's no leak. I also unplugged some of the intake hoses to see the effect but it's different. Idle speed varies etc...
Could this be an alternator issue? Micro cuts causing lower voltages?
I also noticed that when I unplug a component eg the Maf sensor, AIT, altitude sensor... the problem disappears for a moment then comes back.
When the maf is disconnected, the turbo pressures is lowered to 0.4bar. To go back to 0.9 I unplugged the wastegate hose then the engine has it power again. But after 1 or 2 pulls the problem is back again.

Alternator?

[960kg]

Originally Posted by rija

I have checked all the hoses and there's no leak. I also unplugged some of the intake hoses to see the effect but it's different. Idle speed varies etc...
Could this be an alternator issue? Micro cuts causing lower voltages?
I also noticed that when I unplug a component eg the Maf sensor, AIT, altitude sensor... the problem disappears for a moment then comes back.
When the maf is disconnected, the turbo pressures is lowered to 0.4bar. To go back to 0.9 I unplugged the wastegate hose then the engine has it power again. But after 1 or 2 pulls the problem is back again.

Alternator?

......you are really doing dangerous things to find out this mis-fire!!......of course your boost will drop as the MAF cannot tell the ECU how much air is going in ,so it is protecting the engine...then you pull off the wastegate hose and the boost will go crazy numbers and then you thrash the car like it ,you are really heading for disaster!!....

....what O2 sensor did you fit exactly?.....make ....type....Volvo?...also what Volvo plugs did you put in 3-prong or 1-prong??..

[allandwf]

Have you looked at the injectors?

[rija]

Originally Posted by 960kg

......you are really doing dangerous things to find out this mis-fire!!......of course your boost will drop as the MAF cannot tell the ECU how much air is going in ,so it is protecting the engine...then you pull off the wastegate hose and the boost will go crazy numbers and then you thrash the car like it ,you are really heading for disaster!!....

....what O2 sensor did you fit exactly?.....make ....type....Volvo?...also what Volvo plugs did you put in 3-prong or 1-prong??..

Before unplugging the wastegate hose, I made a pull with the maf disconnected. It runs very rich on afr (0.6 lambda) then I checked the boost pressure and showed 0.9bar. On third gear (never above and stable) this is why I dared doing this.
The O2 sensors are ntk (original Volvo)
The plugs are 1-prong bosch from Volvo

Remember that 02 sensors are disconnected on open loop (wot) and they work well on closed loop.

[rija]

Originally Posted by allandwf

Have you looked at the injectors?

I have two sets of injectors and both make no change.