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[feeutfo]

http://www.obd-codes.com/trouble_codes/
The above link, which you may have seen on here before, from Entwood, gives seperate codes for lean and rich. So, are we "assumeing" your "fuel trim malfunction" is giving a rich mixture? Do your codes encompas lean and rich? Or does 0170 and 0173 mean something else. Yes the "trim" is out of limits but if its rich why is there not a rich code? or whatever.

On the Maf subject, i dont mean to be rude, but do you have a cone/oiled filter? They can oil up the maf (as you probably know tbh), is it worth cleaning the maf anyway just to eliminate it?

You will see also in the link, the site has its own forum. Might be worth a go...

And you probably mean coil packs in your list above rather than ht leads? A very minor, rather picky point...

[Kevin Wood]

Fuel trims are going positive so I assume adding fuel to correct a lean condition. The output of the MAF does appear to "flat top" on the datalog when you view the calculated volume but the raw voltage doesn't, and this doesn't co-incide with huge fuel trim. I must get a log off mine and see if it does the same.

I doubt it's ignition related as it would misfire before throwing obscure codes IME.

At the end of the day, the ECU is calculating the volume of fuel to inject but the engine needs more than it's getting, so either the inputs to the ECU are faulty or the fuel calculated by the ECU is not being injected due to a fuel system problem.

MAF is the primary input into the ECU in addition to throttle positition, temperatures, etc. Temperatures look fine on the log. Throttle position is controlled by the ECU and very carefully monitored for errors on a DBW so I doubt a problem there. There don't appear to be air leaks, and the behaviour (more trim under heavy load) suggests it's not a leak into the vacuum side which only leaves the ducting from MAF to throttle body. Nothing visibly wrong there.

I agree the MAF is a possible candidate and I'll have to get a datalog from mine and see if the readings are broadly similar.

Failing that it still points to fuel system. It's exactly the same for both banks so I think clogged injectors are unlikely. Could be a poor fuel pump (might explain why a filter change helped a little). :-/ Could be the fuel pressure regulator I guess. :-/

I keep coming back to the fact that it happened when the exhaust was changed, I must admit.

Kevin

[Marks DTM Calib]

Is the vac pipe to the fuel pressure regulator on and ok?

[Kevin Wood]

Is the vac pipe to the fuel pressure regulator on and ok?

Front end of it certainly is. Might well be worth lifting the plenum and checking the back end.

Kevin

[Albatross]

Is the vac pipe to the fuel pressure regulator on and ok?

Front end of it certainly is. Might well be worth lifting the plenum and checking the back end.

Kevin

I'll have to have a look to make sure when I get back from Newcastle. I suspect it will be this weekend. I won't need to replace any of the 'O' Rings etc will I as these were done when the cam-belt was done recently.

[Albatross]

http://www.obd-codes.com/trouble_codes/
The above link, which you may have seen on here before, from Entwood, gives seperate codes for lean and rich. So, are we "assumeing" your "fuel trim malfunction" is giving a rich mixture? Do your codes encompas lean and rich? Or does 0170 and 0173 mean something else. Yes the "trim" is out of limits but if its rich why is there not a rich code? or whatever.

On the Maf subject, i dont mean to be rude, but do you have a cone/oiled filter? They can oil up the maf (as you probably know tbh), is it worth cleaning the maf anyway just to eliminate it?

You will see also in the link, the site has its own forum. Might be worth a go...

And you probably mean coil packs in your list above rather than ht leads? A very minor, rather picky point...

No cone filter, just a new standard air filter. I think cone filters are $hite because they draw warm air (Put an oiled sports panel filter in if you must). Yes I do mean coil packs and they weren't changed; I just got away with myself a bit on the list.

As for :http://www.obd-codes.com/trouble_codes/

P0170 Fuel Trim Malfunction (Bank 1)
P0173 Fuel Trim Malfunction (Bank 2)

Come up simultaneously and Kevin has answered most of your questions above^^

Thanks for all your thoughts and input though, they are appreciated and will only add value.

[feeutfo]

in relation to the exhaust on your car, iirc Steve (sp32) has the same system/car/age/mileage ish? And presumably does not have any issues?
Has he had the cat codes/lambdas moved.
Is it safe to assume his car is set up the same and does not have the fuel trim issue? Mark dtm plugged in tech2 to his car at the rolling road day but i cant remember the outcome...

[Entwood]

Daft question .. from one who knows nowt.. and is struggling to follow kevins excellent arguments .. .. but ...

Is the fuel trim actually doing/achieving anything .. I mean the code is a trim malfunction, not an overfuel or underfuel ??  Is the "system" sending a small signal to fuel trim that does not happen, so a bigger one is sent, then another bigger one etc etc until the limit is reached and the light comes on ??

I'm guessing that fuel trim is "achieved" by varying the injector open timing, or is there something else

Kevin wrote

Fuel trims are going positive so I assume adding fuel to correct a lean condition

I'm wondering if the fuel trim read is an increasing voltage TRYING to add fuel but failing to do so

Tell me to shut up if I'm making no sense ...  

[Kevin Wood]

Fuel trim is a correction added to the fuel value that is calculated by the ECU, based on the corrrection it has had to apply to keep the Lambda sensors happy.

Essentially, the ECU calculates the amount of fuel it should be injecting based on the engine operating conditions and this determines the injector duration. Feedback from the Lambda sensors tell it this is too lean, so it adds "fuel trim" (lenghtening the injector duration) until the Lambda sensors are reading a little rich, then backs it off a little, and so the cycle repeats.

All that has happened in this case is that the fuel trim value has exceeded a reasonable value. 24% looking at the data from Albatross' car.

This is normally indicative of some sort of fault, but of course the fault can be in the metering of the engine operating conditions - temperatures, MAF, etc. It can be due to unmetered air entering the induction system, misreading Lambda sensors due to an exhaust leak, and it can also be because the fuel system is not delivering the correct flow rate through the injectors for some reason - weak fuel pump, clogged filter / injectors, incorrect fuel pressure. A poorly mapped LPG system will do it too.

So, to answer your question, yes. The fuel trim is achieving something. It is keeping the air fuel ratio correct, but it is having to apply a suspiciously high correction to do so, and that's what the fault code is telling us.

Kevin

[Kevin Wood]

.. or to put it in aviation terms, the trim is fully back, but you're still having to pull on the stick to stop the nose dropping, so something is not right.   :-?

Kevin
  

[feeutfo]

so, as you (Kevin) where saying about the exhaust, if it is more free flowing, fuel trim would increase to get the mixture correct again...?

[Entwood]

.. or to put it in aviation terms, the trim is fully back, but you're still having to pull on the stick to stop the nose dropping, so something is not right.   :-?

Kevin
  

Love that analogy .. one I understand !!

Taking it on then .. what if the trim indicator SAYS the trim is fully back but the trim tab hasn't actually moved.. you now have to move the stick more than expected ......  (equiv to fuel trim saying to injectors change opening times but they don't ?? )

I'll guess your answer will be that as the lambda readings are in limits then the fuel trim must be working (analogy: .. stick loading reduces as indicator moves but still remains excessive which confirms trim tab has moved therefore trim tab system functioning)

[feeutfo]

in relation to the exhaust on your car, iirc Steve (sp32) has the same system/car/age/mileage ish? And presumably does not have any issues?
Has he had the cat codes/lambdas moved.
Is it safe to assume his car is set up the same and does not have the fuel trim issue? Mark dtm plugged in tech2 to his car at the rolling road day but i cant remember the outcome...

For what it worth, i pm'd Steve (SP.32)  re his exhaust, and he only has the back box. Not the full cat back system as Albatross has.
So that wont be a fair comparison. I wonder if Albatross has the middle boxs on his exhaust or is it straight through to the rear silencer? Would that then run more freely and need more fuel to balance the mixture?

[Kevin Wood]

so, as you (Kevin) where saying about the exhaust, if it is more free flowing, fuel trim would increase to get the mixture correct again...?

Well, not in an ideal world. :-/ In theory the MAF measures all the air that gets into the engine, so the ECU knows how much air is going in and knows how much fuel to add. A freer exhaust would result in more air, but the ECU would know about it so it shoudn't be corrected by fuel trim. It shouldn't have an effect on fuel trim but the fact remains that the fuel trim problem co-incided with the exhaust change.


EDIT: Abatross' exhaust does have a centre box (although I think just a single large box raher than two boxes?). It looked about as close to a standard system as you could get, TBH

Kevin

[Albatross]

so, as you (Kevin) where saying about the exhaust, if it is more free flowing, fuel trim would increase to get the mixture correct again...?

Well, not in an ideal world. :-/ In theory the MAF measures all the air that gets into the engine, so the ECU knows how much air is going in and knows how much fuel to add. A freer exhaust would result in more air, but the ECU would know about it so it shoudn't be corrected by fuel trim. It shouldn't have an effect on fuel trim but the fact remains that the fuel trim problem co-incided with the exhaust change.


EDIT: Abatross' exhaust does have a centre box (although I think just a single large box rather than two boxes?). It looked about as close to a standard system as you could get, TBH

Kevin

I've been offline at a customer site for much of this week so have missed out on these debates. Very interesting too.

As Kevin says, my exhaust has a pretty standard set up. The "single large box" that Kevin refers to is a single box with two seperate segments one for each bank. It is a 2 in 2 out box. The 2 banks' exhaust flows never actually meet as both through the centre box and the back box the pipes (flows) are through their own discrete flows.

I'm a bit stuck now, as I don't know what to look out for next. All air pipes are good.

If I want to get the fuel pressure checked, what do I need to do? Should a good mechanic / garage know what to do? What should the pressure be?