Rich running BX 16 Valve

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bx16v
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Rich running BX 16 Valve

Post by bx16v »

Hi all

After a bit of advice if anyone has had experience of it previously.

My 16V seems to be running a bit rich on fuel, it's failed it's MOT on high Carbon Monoxide amongst other things today, nearly at 5% with the limit being 3.5% on the test.

Any unusual places to check? Other than the usual injectors, air filter, breather hoses etc.

It's the non-CAT version, I haven't had a decent look into it yet because...the weather and work, but it can be difficult to start sometimes, 10 seconds of cranking over to get it to start and when that happens the engine managment light (K light) comes on, but when I read the codes by eathing the connector (as I can't get Lexia to connect up for some reason), it's flashes the no codes stored number 12 and then 11. So not sure if I've got a dodgy ECU perhaps?

Cheers

Brian

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Re: Rich running BX 16 Valve

Post by RobC »

Hi Brian
Could be many things! And it’s usually very tedious methodically working your way through all the variables to track down what’s causing the issue. And In 30 year old cars the chances are that there’ll be more than one thing faulty, and they’re compounding things even further!

First off tho there is an idle mixture adjustment screw on the airflow meter. All things being equal this will adjust the CO level at idle, but if other components are faulty then there’s not much point messing with it. Worth a go tho.

Does it idle smoothly or lumpy? Any lack of power or misfires noticeable?

Check usual service items such as plugs, leads, dizzy cap etc.
Do the plugs show signs of running rich?
Also check for air leaks.
The wiring to the AFM is easily broken, which can cause unusual running problems.
A faulty coolant temperature sensor (or the wiring for said sensor) can fool the engine into thinking it’s always cold, leading to rich running. This is the sensor near the thermostat with two wires coming from it.
I’m sure others will have some more suggestions.
Good luck!
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Re: Rich running BX 16 Valve

Post by Jaba »

/\ Mixture adjustment. If you have a flow meter adjustment I reckon 4 turns out/anticlockwise will weaken the mixture to give you a lower CO and MOT pass. I am saying turn anticlockwise from memory so it may be you need to turn it the other way or get the garage to tweak it with the sensor up its fundament to set it to 1.5 or thereabouts. Someone else may know better than I.

By the way the K light always comes on after prolonged cranking so that is not a fault.
Last edited by Jaba on Wed May 05, 2021 12:02 am, edited 1 time in total.
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Re: Rich running BX 16 Valve

Post by rutter123 »

My gti emissions were up at 6, two turns out on the airflow meter screw brought it down to just under 3 for a pass. There maybe an anti tamper cap yellow or orange? on the screw which is easily removed.
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Re: Rich running BX 16 Valve

Post by bx16v »

Hi Rob

Thanks for the reply.

It's annoying, not having an emissions tester to hand, you can't tell if you are making things better or not!

I didn't realise there was an idle screw on the airflow meter, thought it was all ECU controlled, thanks for that, I'll have a play.

I would say it does run slightly lumpy on idle, has every since I bought it, it's hard to tell without a nicely running one to compare it to, but I would say it's not quite right. I'm going to order a new idle control valve, guessing the one that is on there is original and 30 years old, so won't hurt to stick a new one on. I would say given it's supposed to be 160BHP it's not quite as powerful as it should be, I've put that down to age and 130k on the clock until now.

It was recently missfiring, I started it last week after 6 months of hibernation over winter and one cylinder wasn't firing, turned out there was moisture on one of the spark plugs/HT lead, dried and cleaned that all out, that all sorted and it's not missfiring now.

I pulled off the dizzy and HT leads when I was checking for the missfire, they are all clean, HT leads are fairly new and dissy and rotar has only done about 3,000 miles, pulled the spark plug out to clean on the one that was misfiring, no surprise it was covered in petrol, didn't bother pulling the others out at the time, but I'll give them all a check the weekend now see if anything obvious going on.

I did happen to buy a new water sensor recently, just because I was ordering some other parts a couple of months ago and was only a fiver so why not keep it on the shelf just in case, the coolant temperature gauge seems to be reading ok, but won't hurt to change it anyway.

Hopefully it is just the idle mixture screw, as you suggested, but will give it all a good going over as well.

Thank you for the advice, much appreciated!

RobC wrote:
Tue May 04, 2021 9:59 pm
Hi Brian
Could be many things! And it’s usually very tedious methodically working your way through all the variables to track down what’s causing the issue. And In 30 year old cars the chances are that there’ll be more than one thing faulty, and they’re compounding things even further!

First off tho there is an idle mixture adjustment screw on the airflow meter. All things being equal this will adjust the CO level at idle, but if other components are faulty then there’s not much point messing with it. Worth a go tho.

Does it idle smoothly or lumpy? Any lack of power or misfires noticeable?

Check usual service items such as plugs, leads, dizzy cap etc.
Do the plugs show signs of running rich?
Also check for air leaks.
The wiring to the AFM is easily broken, which can cause unusual running problems.
A faulty coolant temperature sensor (or the wiring for said sensor) can fool the engine into thinking it’s always cold, leading to rich running. This is the sensor near the thermostat with two wires coming from it.
I’m sure others will have some more suggestions.
Good luck!

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Re: Rich running BX 16 Valve

Post by bx16v »

Nice one, cheers Jaba. Reasonably friendly with the MOT garage, so sure I can get them to stick the probe up it's rear end and adjust to get it through, and adjust accordingly.
Jaba wrote:
Tue May 04, 2021 11:35 pm
/\ Mixture adjustment. If you have a flow meter adjustment I reckon 4 turns out/anticlockwise will weaken the mixture to give you a lower CO and MOT pass. I am saying turn anticlockwise from memory so it may be you need to turn it the other way or get the garage to tweak it with the sensor up its fundament to set it to 1.5 or thereabouts. Someone else may know better than I.

By the way the K light always comes on after prolonged cranking so that is not a fault.

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Re: Rich running BX 16 Valve

Post by bx16v »

Thanks Rutter, looks like the airflow screw might be the quick and easy answer!
rutter123 wrote:
Wed May 05, 2021 8:53 am
My gti emissions were up at 6, two turns out on the airflow meter screw brought it down to just under 3 for a pass. There maybe an anti tamper cap yellow or orange? on the screw which is easily removed.

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Re: Rich running BX 16 Valve

Post by xantia_v6 »

Assuming that the fuel pressure regulator has a compensation hose to the inlet manifold, ensure that the vacuum hose is not blocked and connected before attempting to adjust the mixture.

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Re: Rich running BX 16 Valve

Post by Dave_16v »

If you have a previous pass certificate to refer to, see what the pass readings were on that. If it passed well within last time, I would think there is something more to it than adjusting the mixture screw unless it has been moved between MOT's. It must be virtually 1.5 higher
on the fail and if for example it passed under 2% last time, you would be looking at a 3% rise. Moving the screw may work but it could be disguising something else at fault that shows up under different conditions if there is a big difference in pass and fail readings.

So still check all the items covered above by Rob and xantia. I would look at everything before attempting to adjust the "sealed" (if it still is) screw if it was previously fine.
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Re: Rich running BX 16 Valve

Post by bx16v »

Thanks Dave, I'll dig out last year's certificate and see what the reading was.

Maybe I just didn't give it enough of a run before the test, had it sitting running 5 minute on the driveway and then not even a 10 minutes drive to the MOT center, probably wasn't enough to get the engine temp up and clear it out after sitting for 6 months.

Dave_16v wrote:
Wed May 05, 2021 2:03 pm
If you have a previous pass certificate to refer to, see what the pass readings were on that. If it passed well within last time, I would think there is something more to it than adjusting the mixture screw unless it has been moved between MOT's. It must be virtually 1.5 higher
on the fail and if for example it passed under 2% last time, you would be looking at a 3% rise. Moving the screw may work but it could be disguising something else at fault that shows up under different conditions if there is a big difference in pass and fail readings.

So still check all the items covered above by Rob and xantia. I would look at everything before attempting to adjust the "sealed" (if it still is) screw if it was previously fine.

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Re: Rich running BX 16 Valve

Post by rutter123 »

My mot tester told me about the mixture screw and let me adjust it whilst on the ramp, maybe if a friendly tester you could do the same.
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Re: Rich running BX 16 Valve

Post by Vanny »

Maybe a bit late to the show, but I'd strongly recommend NOT messing with the AFM settings.

Unless you've put in an AFM off another car, it's not your problem.

The last garage that decided, without my agreement, to mess with the AFM settings wrecked the AFM and it had to be replaced. In my case, one of the HT leads had gone off. They passed a spark on their own, but as soon as they went into the car they weren't happy. A new AFM, grrr, and a set of Bosch silicone leads, and its been fine ever since.

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Re: Rich running BX 16 Valve

Post by bx16v »

Trying to figure it out today funnily enough, putting it in for another MOT next week.

The screw might have been messed about with as the cap is missing. But I've never touched it and looking back at last years MOT, it's CO level was 1.6% so to jump to nearly 5% the next year suggest something's broke. Unless it's just because it hardly got driven last year, did less than 600 miles and so maybe it just needs a good run.

While the air filter isn't too bad, I've got a new one to whack in to help it breathe slightly better. Checked all the vacuum lines I can see and they look clear and intact. I cleaned up the MAF sensor as well just in case it's because it's a bit grubby.

ECU/K light still comes on almost every time I start it, it is difficult to start, it takes 5-10 seconds with my foot on the accelerator pedal to get it to start. Last time it said no codes were stored, but I'm just about to have another go at reading them with the earthing trick and see if anything comes up.

Cleaned all the spark plugs up, took the dissy off and gave that all a good clean, other than that can't really think of anything else at the moment.

Going to give it a VERY good run before it's MOT and get it properly hot and hopefully it might help lower it's emissions.

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Re: Rich running BX 16 Valve

Post by Pcheaven »

Sounds like it’s beyond repair - sell it to me 😂
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Re: Rich running BX 16 Valve

Post by Vanny »

Have you checked the throttle position sensor, and that the TB butterfly valves are set correctly?

My logic being, if the throttle position sensor is always partly open it will fuel up with not enough air flow. Could equally give the same result with sticking TB valves. I'm far from an expert though, if you can't plug a laptop in, i'm out of my depth :D