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[Kevin Wood]

No problem. Was nice to meet you earlier.

Hmm. :-/ Thinking about it, more flow through the exhaust should mean more flow through the MAF which would mean the ECU would give you more fuel anyway, without extra fuel trim.

Long term trim for both banks seemed to be pegged out at +24% and at times under load it was adding another 10% short term. At idle the total trim was only a few percent. Makes me think it might be an air leak or a fuel delivery problem.

I think I will compare live data from my car to that snapshot. See if anything jumps out as being different.

Kevin

[Albatross]

No problem. Was nice to meet you earlier.

Hmm. :-/ Thinking about it, more flow through the exhaust should mean more flow through the MAF which would mean the ECU would give you more fuel anyway, without extra fuel trim.

Long term trim for both banks seemed to be pegged out at +24% and at times under load it was adding another 10% short term. At idle the total trim was only a few percent. Makes me think it might be an air leak or a fuel delivery problem.

I think I will compare live data from my car to that snapshot. See if anything jumps out as being different.

Kevin

I don't suppose you had a chance to check your readings on your car did you?

I was wondering; do you think that it could even be a very dirty fuel filter?

[Kevin Wood]

I had a look at your datalog tonight and the fuel trim seems to get worse with increasing load. It's not unreasonable at idle but it's winding on quite a lot at heavier load. Having seen that I think it could well be restricted fuel supply. Either a clogged filter or a lazy fuel pump perhaps.

MAF, and the other sensors seem to be reading roughly what mine do under similar conditions. Nothing jumps out at me as wrong, at least. :-/

Kevin

[Albatross]

Thanks Kevin,

I'll change the fuel filter this weekend and try to use some motivational management techniques on the pump.

If the fuel filter change doesn't work, what's the next step? How can I diagnose the fuel pump before going to the lengths of replacing it?

I'll get the fuel pressure checked at a garage like you suggested, but I'll wait now until I've changed the filter.

I've seen the maintenance guide on changing the fuel filter, but that's on a 3.2 estate. Is it pretty much the same with a saloon? Do I need to do the "remove the fuse whilst the engine is running" bit that it mentions to drain the fuel lines 1st?

Fuel filter change (Estate) http://www.omegaowners.com/forum/YaBB.pl?num=1177279323


Fuel pump plate renewal http://www.omegaowners.com/forum/YaBB.pl?num=1186065848

[Kevin Wood]

I would either remove the fuse or loosen the feed pipe union where it connects to the fuel rail under the plenum to relieve the pressure in the fuel system otherwise you're liable to get doused when the filter comes off. Saloon filter is identical, IIRC, and located between the front of the fuel tank and the rear of the diff. Slide under the car just behind the rear offside wheel and look up and you'll see it.

I suspect fuel pressure at idle will be fine, as the fuel trim at idle didn't seem to be going outside sensible limits.

If you still have issues after replacing the filter the thing to do would be to measure the flow rate returning back to the tank. This will tell you how much flow the fuel pump has "in reserve" once it's got the system up to 3 bar of pressure.

Kevin

[Kevin Wood]

Rather worryingly, I have just found this:

http://newsgroups.derkeiler.com/Archive/Rec/rec.autos.makers.honda/2005-12/msg00732.html

It suggests post-cat Lambda sensors can have an influence on fuel trim on certain engine management systems whereas previously we assumed they were only to monitor cat efficiency. I wonder if relocating them has upset something? :-/

Have you noticed any change in fuel consumption since relocating the Lambda sensors?

Kevin

[Albatross]

Rather worryingly, I have just found this:

http://newsgroups.derkeiler.com/Archive/Rec/rec.autos.makers.honda/2005-12/msg00732.html

It suggests post-cat Lambda sensors can have an influence on fuel trim on certain engine management systems whereas previously we assumed they were only to monitor cat efficiency. I wonder if relocating them has upset something? :-/

Have you noticed any change in fuel consumption since relocating the Lambda sensors?

Kevin

Yes fuel consumption is Sh!t now :-/

I used 2/3 of a tank going from Bedford to Worcester and back again!

I reckon it looks like the secondary O2S may have to go backto where they were again. What other optons are there? Can the ECU system be remapped so that the O2S sensors are less sensitive and therefore stop complaining 0430 stylee that the pre-cats are tired?

Do you reckon I should consider replacing the pre-cats?

TBH, where I'd really like to get to is to de-cat the car completely and then only refit the main cats on MOT day once a year, but not at the expense of fuel consumption.

What sort of place does this sort of bespoke remapping on a OBDII DBW engine?

[Kevin Wood]

Hmm. :-/

I wish I could get my head round what's going on. I've been reading through a few patent documents relating to the use of post-cat lambda sensors and they do have a role in calculating fuel trim in some of the schemes. I can only assume that putting a bigger cat in the loop throws the calculations out, but, having said that, your pre-cat lambda sensors look like they're behaving perfectly normally for a closed-loop system with the correct mixture - cycling between lean and rich. :-/ With a load of extra fuel trim they would be indicating a solid "rich".

I think it'd still be worthwhile checking the obvious things like fuel delivery but equally it'd put this one to bed one way or the other to swap the Lambdas back and see if the fuel trim returns to normal.  :-/

Kevin

[Kevin Wood]

To answer your other question, Yes, in theory the code in the ECU could be modified to completely disable the cat efficiency monitoring. The trick would be finding someone who's hacked the ECU code to that level. I suspect it's far less easy on these flash based ECUs than it was on the old M2.7.1 devices that are EPROM based.

A mate of mine used to hang out on http://www.diy-efi.org/ and hacked an older GM ECU to the extent that he is now using a Corvette ECU on a C20XE in a kit car. Unfortunately I don't think anyone is that active anymore.

Kevin

[Albatross]

I am moving my sensors back to their original position this morning to establish root cause. I'll be clearing tthe codes and will be able to confirm whether my current 0170 & 0173 problem is then replaced by 0420 & 0430 again in the next few days.

I am building up quite a case of evidence on sorting this 0420 pre-cat isue and I WILL FIX IT, but the movement of the secondary O2 sensors has co-incided perfectly with no further 0420 codes and the start of the 0170 codes.

[feeutfo]

watching with interest gents...

can the ecu be re-mapped/hacked to give the correct fuel trim with the 02s in the current(behind big cat) position? Is it a set value or does it "learn"?

As said, interesting to see if problem swaps when 02s returned to original location.

[Albatross]

watching with interest gents...

can the ecu be re-mapped/hacked to give the correct fuel trim with the 02s in the current(behind big cat) position? Is it a set value or does it "learn"?

As said, interesting to see if problem swaps when 02s returned to original location.

As stated I will be "testing" as of later this morning, but if it transpires to be that the movement back to behind the main cat causes the fuel trim issue then I am considering two options:

• An ECU remap / hack as suggested, but I consider this to be a bit over complex and perhaps expensive.

So, working on the principle of Okham's razor...

• On reading the link that Kevin Wood posted (Click Here) it seems to me that the fuel trim acts based on the voltage sent back by the secondary O2 sensor. I have an idea which might counteract this: If I were to add a peice of electrickery (I can't remember what they are called, I know it isn't a resistor because that would constantly reduce the voltage, but there is such a thing that "clips" the voltage to a certain amount), this should, in theory, then allow me to stop the higher voltage being sent back to the ECU from the O2 sensor. If the O2 sensor sends more voltage back on higher emmissions then this should work against the 0420/0430 issue with the sensors in the original position, if it is the other way round and voltage sent from the O2 sensor increases as the air in the exhaust is cleaner then this should work agaisnt the fuel trim issue 0170/0173 when the sensors are moved behind the main cat.

I hope that makes sense. I just need to test 1^st by moving the sensors back today to be sure about where we're at at the moment and then take it from there with an electronics wizard when I can find one.

[feeutfo]

will you change the fuel filter first? Or after. I suppose if you move the sensors and you have fuel trim AND pre cat codes then... You have a fuel issue? If just a the cat code then the position is relevent to fuel trim...

[Albatross]

will you change the fuel filter first? Or after. I suppose if you move the sensors and you have fuel trim AND pre cat codes then... You have a fuel issue? If just a the cat code then the position is relevent to fuel trim...

I'm going to move the sensors 1st, so as to isolate each change. That way I won't muddy the waters at all whilst trying to analyse the root cause.

Like you say, if the 0420/0430 & the 0170/0173 all occur when I hve moved them I can then look at fuel filter.

I also need to get the fuel pressure checked, but I'm very confident that that is good and also that there are no air leaks. Reading Kevin's posts above I think that we have eliminated those anyway in a process of his logical reasoning.

[Albatross]

Sensors now moved back and codes cleared.


Let's see where we go from here...