Last chance saloon

[7 Seat Sports Car]

Baffler, I am of the opinion that aftermarket cats have a higher flow rate due to less monolith material but are harder to heat up and get them to work hence the regular efficiency code. One thing I did try was run the car with the front O² removed to relieve exhaust pressure in case a blocked cat was causing my low manifold vacuum and it actually dropped to around 10/11...

Not sure what this means if anything. I thought less back pressure would allow higher manifold vacuum. Am I fixated on the wrong thing here and vacuum will likely be low as it's a high miler.


Steve, if I can definitively prove it's my cat at fault then I would be grateful of first refusal for your known good one. I'm assuming that they all had angle flange turbos after a certain year, mine has.


Thanks again folks for your input. I had the turbo and exhaust manifold off yesterday. While some of the nuts didn't put up much of fight the gaskets were still sealing as there weren't any signs of blowing past any of the gaskets. No cracks on the manifold either. Turbo also seems in good condition. The "tiniest" amount of axial play that's barely detectable in the shaft. I don't think I need to worry about that as I'd need a DTI to measure it as it's not even close to ½mm. Certainly no signs of oil getting out of the core anyway.

[ITSv40]

If it was me I would fit a known good cat, if only to eliminate a possible cause. If it isn't the cat you could refit the aftermarket and sell the genuine one to get your money back - there is a market for them. Given the time spent on the issue, changing the cat isn't a big job in the grand scheme of things. If the cat is the issue, then hopefully problem solved.

[Luxobarge]

Originally Posted by ITSv40

If it was me I would fit a known good cat, if only to eliminate a possible cause. If it isn't the cat you could refit the aftermarket and sell the genuine one to get your money back - there is a market for them. Given the time spent on the issue, changing the cat isn't a big job in the grand scheme of things. If the cat is the issue, then hopefully problem solved.

Totally agree, that makes so much sense. I'd buy SteveSarre's one, I've had several parts from him in the past and he's a top bloke and totally trustworthy. As above, if it doesn't sort the problem then you've got a spare cat you can sell on, given how many are being stolen at the moment you'd be doing someone else a huge favour if you sell it to an owner rather than weighing it in. Either way the cost in the end will be minimal.

[Pidgeonpost]

While I wouldn't have a clue where to start with the level of diagnostics you've done so far, eliminating the cat does seem to be a necessary step if only to eliminate it, as others have said.

[SteveSarre]

Hi Drew

You said
"When it gets overwhelmed I can see maf climb to between 17 & 20 kg/hr and injector pulse goes up to 2.6/2.7ms"

Do you get that same increased MAF reading if you simply rev the engine (either load or no load). If it is working correctly you would expect the MAF reading to go up directly in line with air flow, ie with revs and throttle opening.

The MAF simply measures airflow - it is not controlled by anything (except the airflow).
Injector pulse width is controlled by the ECM (which increases pulse width to increase fuel delivered). If that increased reading does not in your opinion correspond to true increased air flow then something about the MAF is faulty.

So maybe a faulty MAF is causing the problem by falsely reporting a high air flow.
Then the ECM responds by increasing the pulse width intending to keep the mixture right.
So then more fuel is being delivered (and so the engine runs rich because there is not actually as much air flow as the MAF is falsely reporting).
Then O2 sensors give extreme readings.

Is there anything at all about the MAF that could be faulty? What Volvo or Bosch part number are you using? Have you cleaned the MAF yourself, and what did you use to do that? Have you substituted a known good MAF? etc etc

HTH
Steve

[SteveSarre]

PS

I believe that if you change or plug or unplug O2 sensors, you need to do a reset. I think you can do this through VIDA or unplug the battery for 10 minutes. Others may be able to give more info.

I assume that if you don't do that the ECM will lose track of what is going on and what it needs to do.

[7 Seat Sports Car]

Steve, every time I fit a sensor I've pulled big fuse 8 which kills battery voltage to the main relay and ECU system effectively disconnecting the battery without having to reset the time on the clock and radio code constantly. I always start with a fresh adaptation and wait to see what it does.

MAF and map readouts correspond with throttle movement fine. As mentioned previously with airflow approximately 14kg/hr and measuring 1.31V across the maf sensor which Vida says is correct I'm getting about 2ms pulse which all points to healthy idle stats but rear O² says 0.8 to 0.9V so reading rich. I've tried another rear O² and get same results. I've basically got 2 front O², 2 rear, 2 mafs, 2 ECUs, all Bosch, all correct part numbers and regardless of combination I get the same results. Surely they can't all be wrong!

If I disconnect the rear and start afresh the car still goes into closed loop and after a while the trims start to add fuel until it hits the max and after another 5 minutes or so of that I start to get codes for the front O², either heater circuit fault or no activity fault. Car won't run closed loop again unless I "reset" the ECU. If I leave the rear connected it rarely goes closed loop and spits out codes quicker.

Randomly it'll start to increase maf and injector pulse times.

On maybe 2 or 3 occasions in the last year the fuel trims have swung max negative instead and it's borderline undrivable and close to cutting out. Wife won't get in it now. She takes the 240 cos it's more reliable!!!

I've got some gasket sheet material that I made to blank off intake manifold from head and managed to pump over 10psi into the charge air pipes from compressor outlet to head. No leaks. I'm double checking all the vac lines tomorrow while the engine bays in bits but I'm positive they're all ok. I also double checked the exhaust manifold, turbo and cat/downpipe for leaks while off the car, system is airtight. Rest of exhaust is 3 yr old 2.5" stainless so not much to go wrong there. Sounds sweet without being obnoxiously loud.

[7 Seat Sports Car]

I've managed to source a leak down tester and compressor.

Cylinder 1 to 5 results are:

26%
13%
33%
8%
4%

Nothing coming out of the intake, exhaust or coolant tank so either rings are gubbed or the HG is. Either way it's the end of the road and will be getting broken up as it's just not financially viable to keep it going anymore.

Thanks for everyone's input along the way.

[Jas16]

Sorry I am coming into this thread now. With a scan tool, did you manage to record live data from cold to hot. You are more experienced than me.

I presume that you haven't played with your injectors?

would a blocked PCV have any influence with oil burning affecting emissions and causing any o2 sensor readings to go off?