T4 engine diagnosis

[Old Painless]

If I touch the throttle at all the engine will stutter, drop revs to almost cut out

That doesnt sound normal as i understand it. I think my v40 just drops a tad then recovers, it certainly doesn't almost stall. What's your steady idle rpm speed ?

If the injectors were partially blocked or worn would that give a different error code to the one the OP is recieving ?

Coolant temp seems good.

I know a rough idle or stalling can sometimes be presented with a bad battery, the car is pulling some current from the battery as the revs are low at idle iirc. Can you check the battery voltage:

1. When the engine is switched off
2. When the car is idling
3. When the engine is reving around 3000 rpm

Should be around 12.5v - 13.5v - 14.5 v i think.

[960kg]

......Sorry....Old Painless..."The rear lambda sensor is the one which measures the content of the burned exhaust gas, if that was not working properly you would have an engine warning light and the ecu would default to a rich stock fuelling map".......this incorrect it is the first O2 Sensor on the down pipe from the manifold that does this procedure......the Rear O2 Sensor at the back of the cat. makes sure only that the cat is efficient and doing it`s job, you will still get a light though as i had one, but my problem was the sensor gone kaput........the Fuel pump pressure my be alright stationary with a tank of fuel not being jossled about but when at 100mph and the tank being thrown everywhere if the pump cannot grap the petrol then the fuel pressure will suffer....

.....jtravers, you have got me in a spin, the number pump you mention is the Litres per minute that pump can deliver and not the actual pump number....as you have now said it was the 342 that i fitted, you have fitted......the number pump that they fitted in the States is the 340GSS with the large pickup spigot in the centre, Pic.....You will not get any noticeable difference in running with the rear sensor light on situation...UNLESS your cat is actually faulty......as you say, you did your compressions the wrong way or procedure, but it doesn`t matter as the end result will still give you an indication of the condition, because you are not allowed more than 29psi variation on any one cylinder.....what model is your S/V40 you say 2000 T4 but what engine.....the vacuum at hot idle should be about 14lbs on the 1855 turbo as the compression is only 8.5 to 1 ...the 2 litre T4 may well be 20lbs as the compression is 9.1 .... you said yours is 20, BUT are you the 2litre......if it satifies you with your temps. my T4 runs at 90 to 91C all day what ever i do!...except idling when it will creep to 105 then the fan will bring it down to 95, open road again 90 to 91.........

......because now so many words have gone under the bridge....what exactly in practical terms is the problem???...

[Old Painless]

I should have said exhaust lambda sensor rather than rear, bad choice of words. I thought there was only one sensor in the exhaust. Sorry folks.

[960kg]

......i have been on Vadis .......your Volvo DTC`s are clear that it is your front O2 Sensor that has a permanent fault which then gives this error code.....the EFI 512 is merely a subsequent error because you have a EFI 435 which is the main error......or in other words, you have a Permanent Faulty Signal from the Front O2 Sensor which gives a DTC of EFI435 and that in turn has caused an EFI512 DTC......so if you fork out for a new Volvo front O2 Sensor all should be well again!!..

......i replaced all of my sensors as a sort of a "Mission" for the car to be reliable after it`s 115000mls it had done when i purchased it.....the sole sensor that made all the difference to performance and speed and general well being of the engine was this O2 sensor, so do not regret the 100 or so quid it will cost, you will get your money back on MPG alone.....

[jtravers]

The engine is the B4194T2 1855cc. Regarding the DTCs, when I looked at the description on Vadis and saw front H02S, faulty signal, etc. I immediately thought the same and replaced the front oxygen sensor to no avail. I then combed through it again and found that the wording is slightly misleading. What it seems to mean by "faulty signal" is that the signal does not behave as expected, not necessarily that the sensor generating the signal is faulty. In other words the signal doesn't alternate between rich an lean as it should, but just goes in one direction (only enriching in my case). There is a diagnostic procedure for these codes on Vadis and the common checks it recommends are:

• Check MAF (done)
• Pressure test intake system (done and no pressure builds up)
• Pressure test exhaust (not done but visually inspected for holes upstream of the sensor)

I don't think it even mentions replacing the sensor itself. 960kg, do you not find it strange that there is free airflow between the MAF and the crankcase?

[960kg]

......some sensors throw up error lights on the dash and some don`t......every sensor i fitted made a performance difference but only the front and rear O2 sensors gave a light...the DTC EFI435 on vadis for this engine 1855cc as my own shows a PERMANENT fault so therefore it needs replacing to overcome it......the airflow is only one way from the MAF to the engine and not vice versa......you say you replaced the FRONT O2 sensor but with what?.....a copy, a universal one which you have to splice the wires?......you cannot use these sensors as one of the four wires sends back to the ECU the AMBIENT temperature of the atmosphere and that also decides what mix to adjust to....so therefore if you splice that particular lead you are destroying those certain measurements and the ECU won`t get them......you should only use the Volvo sensor which has the correct length of lead and also the clips and correct plug on the end...£146 including VAT......don`t believe in Vadis where the rear sensor plug goes in to it`s connector as it is not next to the front sensor on the bulkhead behind that plastic shield, but it is in the cabin behind the centre console......the problems you are getting can only come from faulty sensors as these run the parameters for the engine via the ECU....if the sensors are replaced it MUST work........i believe you are being blinded by your own science....take a practical view or approach.......

[jtravers]

.....you say you replaced the FRONT O2 sensor but with what?.....a copy, a universal one which you have to splice the wires?......you cannot use these sensors as one of the four wires sends back to the ECU the AMBIENT temperature of the atmosphere and that also decides what mix to adjust to....so therefore if you splice that particular lead you are destroying those certain measurements and the ECU won`t get them......

Bit of an unnecessary rant as I didn't use one of those sensors - I got one of these from LambdaPower:
http://www.lambdapower.co.uk/partsea...Dlist=LP-19416
They supply OEM sensors at a decent reduction (I don't work for LambdaPower)

Here is the exact text from Vadis on the possible causes of the error codes I get:

EFI-512:
Possible source
...
Lean limit:
-Defective mass air flow (MAF) sensor
-Low fuel pressure
-Air leakage in the intake system.

and EFI-435:
Possible source
...
Faulty signal:
-Air leakage
-Uneven compression
-Defective mass air flow (MAF) sensor
-Defective front heated oxygen sensor (HO2S).

So it is a permanent fault, but not necessarily a fault of the oxygen sensor. I tested the MAF, tested for low fuel pressure, air leakage, uneven compression, and replaced the front oxygen sensor with an OEM part - I think this was a practical approach. Anyway, Vadis describes the procedure for testing intake air leakage and it involves pressurising the intake from the MAF and checking for leaks - as all the air was coming out the oil filler cap / dipstick tube this was not even possible. This is the point I am at now where I am asking for advice on whether this could be the oil trap thing behind the manifold letting air into the crankcase.

[Old Painless]

Just remind me here.

1. The cam chamber has an air outlet which leads to the air intake somewhere which lets leaked air get burned by being reintroduced into the intake system.

2. The crankcase has an air outlet which leads to the air intake somewhere which lets leaked air get burned by being reintroduced into the intake system.

If 1 and 2 are correct then they may be the way the compressed air is getting to the dipstick and oil filler cap. Didn't think of that earlier.

Can these air lines be clamped off to do the test ?

The more i learn about these engines the more complex they become. Kinda cool but it makes my head hurt. lol

[jtravers]

Yeah, there's actually a good picture of the unit on this thread:

http://www.volvoforums.org.uk/showthread.php?t=89992

Looks like the one from the top vents the cam chamber and the one on the side vents the crankcase. Think there is also a hose on the bottom to release the separated oil back to the sump throught the crankcase. The hose the poster has removed is the one going back to the intake before the turbo so might try to root that out and clamp it - see if that makes any difference.

I did manage to clamp the top hose for the test but didn't make any difference.

The more i learn about these engines the more complex they become. Kinda cool but it makes my head hurt. lol

Same here, seems almost every system is now interconnected and mostly by emissions control gadgets. The number of things feeding the intake air especially is crazy.

[960kg]

......first of all that wasn`t an "unnecessary rant" as you aren`t the only person reading this and it was to help those that don`t understand that using copy or cheaper O2 sensors can lead you up the garden path maybe for 6 months before it packs in again....you only get what you pay for.....also i don`t even "rant" when my car plays up but it is going fine with no problems, i am just trying to help you with yours!!....by being forward it can help one see past the tree`s and see the wood......you don`t say if you renewed your rear O2 sensor as this also works in tandem with the front one,do you have a light upon the dash or just these two DTC`s?, see pic...the crankcase emissions has it`s own set of DTC`s so in theory should not be posing any problems as you do not have there codes up.....the engine is only a form of pump so therefore it has to have breathe holes in the crankcase otherwise the pressure would build up and if the PCV valve didn`t work then you would blow oil seals and you haven`t done that either........they are really thick pipes that are in this emissions system and shouln`t pose any threat for leaks unless they have been punctured by useless mechanics.....if you look at it another way, that chap whose "link" you have has blocked the emissions pipe leading to the large turbo intake and just let it to the open air under the car so even if the crankcase is open to the actual atmosphere it is still not classed as an induction leak......older vehicles use to just have a canister on the side of the block and the fumes were just vented straight out ...but it did not misfire........you only misfire on the induction side of things because that is your mixture and it is critical, whatever it may be.......the emission side of things will not give you a misfire unless you have a lot of oil fumes getting in the intake side...but your compression is fine, so it is not that either.......i still believe you have a malfunction with the O2 sensors, ok so you have a new front one, fit a new rear one as well.....if you needed a new front one then the time is the same for the rear one about 100000mls, unless one had faulted?.....getting back to the Walbro 342, which way did you point the inlet spigot?......