T4 engine diagnosis

[jtravers]

I appreciate your help and advice but don't think I was blinded by my own science as you put it. I simply worked throught the possible causes listed on Vadis and tried to detail the whys and hows of the tests I did hopefully also for the benefit of others on the forum.

Anyway, I agree that the rear oxygen sensor can have a part to play in a problem like this but the engine hasn't actually passed the air intake test detailed on Vadis yet - so would like to get this out of the way. If you look at the test procedure listed for one of the codes I had, it shows the intake being compressed to 0.3 bar to check for leaks. If it is open to the atmosphere through the crankcase ventilation or some other path then this test isn't possible.

I know the engine must breathe and in the case of this engine the normal path is through the air intake - in older cars the crankcase ventilation (to the atmosphere) and intake were completely separate so one couldn't effect the other. I did a search on the forum for PCV issues and it seems that normally the valve gets blocked so pressure builds up, oil seeps through gaskets like you describe. In my case, and I haven't seen this fault described anywhere else so I could be way off the mark, I think the PCV valve is blown through and is open in both directions.

So I will investigate air intake test over the next couple of days and then on to the rear oxygen sensor.

[960kg]

.....perhaps with your Air Intake Test seeing as the required pressure is as low as 4.41lbs per sq ins then you could put the filler cap half on or something like that to try and make it show a leak somewhere.....however i am sure you will find a way and i hope you are successful in finding the cause of the problems...

[LevL]

Originally Posted by jtravers

I appreciate your help and advice but don't think I was blinded by my own science as you put it. I simply worked throught the possible causes listed on Vadis and tried to detail the whys and hows of the tests I did hopefully also for the benefit of others on the forum.

Anyway, I agree that the rear oxygen sensor can have a part to play in a problem like this but the engine hasn't actually passed the air intake test detailed on Vadis yet - so would like to get this out of the way. If you look at the test procedure listed for one of the codes I had, it shows the intake being compressed to 0.3 bar to check for leaks. If it is open to the atmosphere through the crankcase ventilation or some other path then this test isn't possible.

I know the engine must breathe and in the case of this engine the normal path is through the air intake - in older cars the crankcase ventilation (to the atmosphere) and intake were completely separate so one couldn't effect the other. I did a search on the forum for PCV issues and it seems that normally the valve gets blocked so pressure builds up, oil seeps through gaskets like you describe. In my case, and I haven't seen this fault described anywhere else so I could be way off the mark, I think the PCV valve is blown through and is open in both directions.

So I will investigate air intake test over the next couple of days and then on to the rear oxygen sensor.

Have a look on my datalog attached. Compare it with yours and you may find what sensors are misreading...Hope this will help

[jtravers]

That's great info, thanks a lot. Most of the readings look very similar to mine apart from the trims (19.5% long-term and up to 19.5% short-term). One thing that stands out apart from that though is a MAF reading of 183 g/s - the highest I've got is 156. Is that from a standard setup or have you increased BHP somehow, and is that the highest reading you've logged?

What did you use to gather the data, by the way - looks pretty useful? I have just been watching live readings from a OBD scanner, which apart from being hit-and-miss, is pretty scary for measuring maximum load, etc.

Should have a chance to look at the oil trap thing tomorrow anyway - think it's a wild goose chase though as I already tried clamping the hose going from it to the intake and no difference.

Originally Posted by 960kg

perhaps with your Air Intake Test seeing as the required pressure is as low as 4.41lbs per sq ins then you could put the filler cap half on or something like that to try and make it show a leak somewhere

Unfortunately the oil cap doesn't hold positive pressure so even when it's tightened it leaks. Will try the test with the oil trap breather clamped though and see what happens

[jtravers]

Well, just had a look at that oil trap thing and it wasn't anything to do with a PCV being blown open as I had expected - it just IS open. The oil trap component is literally a box with 5 holes in it for hoses - no PCV valve or any mechanical components for that matter. Does what it says on the tin I suppose, nothing else. So, if you see an Intake Leakage Test on Vadis treat with suspicion.

I clamped the hose coming from this box anyway and tried the compression test through the MAF again - no leaks. I then swapped out the rear oxygen sensor with the one I had replaced on the front and ran the car to closed-loop - still no difference to the trims. The replaced one could be bad as well, but I'd expect some change in the trims if this was the cause. Then tried the fuel pressure test again when the car was actually stuttering to see if there was some intermittent probem with the fuel system - readings bang-on again.

So, I am thinking of getting a second hand set of injectors and sending them to be professionally cleaned. Could the injectors have degraded to an extent that their fuel delivery is 40% down on the MAP values while the engine still runs quite smoothly - i.e. there doesn't seem to be a major variation between cylinders?

[zerosub]

jtravers,
i've read through the whole thread and it is very interesting.
Have you ever sorted out what the actual problem was?

I have a 1,9 T4,too.
My engine runs fine, but every 2nd week i get the same errorcodes that you described.

I've changed most of the sensors and i even paid 500€ for a new Volvo MAF.
But still, the engine light will turn on from time to time.

I would love to get rid of this light.

[Sorry4myEglish]

Hi everyone!

I have a 1998 v40 T4 and i've been trying to solve that efi-512 for more than a year now. So far i've replaced fuelpump, maf, O2 sensor and fuel pressure regulator and still the car wont act normal on open loop.

Couldnt find a solution here in Finland so how about you UK fellows, any luck with that efi-512 solution?

Cheers from Finland

[960kg]

Originally Posted by Sorry4myEglish

Hi everyone!

I have a 1998 v40 T4 and i've been trying to solve that efi-512 for more than a year now. So far i've replaced fuelpump, maf, O2 sensor and fuel pressure regulator and still the car wont act normal on open loop.

Couldnt find a solution here in Finland so how about you UK fellows, any luck with that efi-512 solution?

Cheers from Finland

Hope this helps?......

[Sorry4myEglish]

In my ear it sounds like the exhaust pipe is leaking from somewhere. The exhaust manifold was replaced when the turbo was replaced so i think that part of the exhaust is fine. Leak in the air intake, could be.. Any tips how to find if its leaking?

[960kg]

Originally Posted by Sorry4myEglish

In my ear it sounds like the exhaust pipe is leaking from somewhere. The exhaust manifold was replaced when the turbo was replaced so i think that part of the exhaust is fine. Leak in the air intake, could be.. Any tips how to find if its leaking?

You cannot have the slightest exhaust leak in the exhaust system along the length of the car.

For finding air inlet leaks the easiest way is to just gently squirt some WD40 or Carb cleaner around each nylon or rubber vacuum hose or joint when idling....when you have a leak the revs of the engine will rise.....also bend gently the 90 degree rubber bends to see if they have perished or not.

One of the main places for leaks or splits is on the EVAP canister the hoses on the top tend to split if old.
Also check the nylon vacuum hose under the fuel rail for the FPR make sure it is clear of obstruction by blowing through it when disconnected.