Hi folks,

So I'm pulling my hair out trying to find the cause of my untoward emissions. At idle, everything is in the red. At fast idle, lambda goes green, hc sometimes goes green, and co is around 500ppm (200ppm is the limit).

V8 4.6 gems with a top hatted and rebuilt bottom end a couple of years ago. High torque camshaft. Top end skimmed, stem seals done and valves ground.

Its always suffered a bit from being rich at idle, and idle itself is slightly stumbly. Last year it scraped through the mot with a lot of loud pedal action getting it roasting hot etc.

This year though it is not playing ball.

Stuff I've done:
New plugs. Old ones all looked identical in colouring, couple had slight sooting down the side of the ceramic centre core.
New leads.
Coil pack resistances checked ok.
New fuel filter (genuine).
New air filter (Mann).
Air intake flexible pipe replaced to fix leak.
Lambda sensors tested on an oscilloscope, showing one was sluggish. Replaced and confirmed both switching at the same speed.
Valley gasket replaced (slight oil leak) and resealed, ram pipe and plenum sealed with threadlock.
Vacuum hose to fuel pressure regulator was slightly perished, but not leaking. Replaced anyway.
Fuel rail lifted with injectors in place and pump fired up to check for leaks. None found.
Tested each injector on the rail and no issues found. Not a scientific test but I don't have an injector test rig.
Refitted rail and found slight air leak at the o ring for cyl 1, replaced o ring and problem fixed.
Also found a very slight air leak from one of the LPG stubs, so fixed that (have now actually installed the LPG injectors).
Wurth fuel treatment run through.
Bp ultimate run through.
Oil flush, change and filter.
Nanocom mostly shows the fuel trims are around zero, with the short terms dancing around both sides of zero, more so at idle.
Also shows o2 sensors switching ok (oscilloscope confirmed this though).
Have tried three different gems maf sensors, all seem to give the same results.
Cleaned the idle air control valve (iacv) and plenum ports to gleaming.
Oil strainer checked and is clear. Oil breather hoses both clear and not perished.
In desperation I tried adjusting the idle adjustment screw, but it hasn't really helped, plus nanocom reports the idle steps as a percentage rather than raw steps, probably, so its anyones guess what it should be set to.

Probably more stuff that I've forgotten.

Anyway I'm out of ideas. I really need to get it to run cleanly before I finish off the LPG install, not least for my pocket!

Runs well otherwise, plenty of power and pick up, as Gordon can attest to :)

Any and all suggestions welcome!

You've got them the wrong way round, CO limit on petrol is 0.2% while it is HC that is 200ppm. High HC is showing unburnt hydrocarbons in the exhaust so you have incomplete combustion caused by either a weak spark on one or more cylinders or too much fuel going in on one or more. Which two plugs had slight sooting on them? Were they two that share one coil which would suggest one coil pack is weak. It would also explain the slightly uneven idle. Otherwise you could be looking at leaking injectors that don't shut off fully so are dribbling extra fuel in. As a percentage of how much is supposed to go in, it would be far greater at idle when the injectors are only open for a short duration while when the revs are higher they will normally be open for longer allowing more fuel in and less time for additional fuel to be dribbling in. You ,might have an injector or two that needs a clean. I used this method https://www.youtube.com/watch?v=rUUgR94drxg to clean injectors but used a 12V supply and a 3.3 Ohm resistor in series with it. If you don't have a spare Schrader valve, you can indulge in a bit of bodgery as in this method https://www.youtube.com/watch?v=8rk0tKtiVic

On a GEMS, the Nanocom (under Inputs, Air and Idle) shows idle air valve as a number between 0 and 200 (showing the number of steps), correct being between 15 and 30 at idle when hot. However, if you have a weak coil it will be opening more than it should to keep the idle revs correct. If you find that you can't adjust it down to zero, then it is trying to compensate for something else. .

Gilbertd wrote:

You've got them the wrong way round, CO limit on petrol is 0.2% while it is HC that is 200ppm. High HC is showing unburnt hydrocarbons in the exhaust so you have incomplete combustion caused by either a weak spark on one or more cylinders or too much fuel going in on one or more. Which two plugs had slight sooting on them? Were they two that share one coil which would suggest one coil pack is weak. It would also explain the slightly uneven idle. Otherwise you could be looking at leaking injectors that don't shut off fully so are dribbling extra fuel in. As a percentage of how much is supposed to go in, it would be far greater at idle when the injectors are only open for a short duration while when the revs are higher they will normally be open for longer allowing more fuel in and less time for additional fuel to be dribbling in. You ,might have an injector or two that needs a clean. I used this method https://www.youtube.com/watch?v=rUUgR94drxg to clean injectors but used a 12V supply and a 3.3 Ohm resistor in series with it. If you don't have a spare Schrader valve, you can indulge in a bit of bodgery as in this method https://www.youtube.com/watch?v=8rk0tKtiVic

Neat videos, ta. They're not leaking with fuel pressure behind them, and didn't appear to be leaking after activating them manually, but obviously the rail pressure dropped then as the pump stopped. Cleaning them sounds like a good idea, although between the fuel treatment and the bp ultimate I imagine they probably aren't too bad. I wonder if I can get carb cleaner in a 5 litre tub, rather than spray can.

I might be confusing my quantities, but the CO was definitely way up and refused to come down. I'll check the printout tomorrow, but I think it must have been around 0.5% then. It was double the limit and a bit more.
Will also check the plugs too. I don't believe they were two that shared a coil, but I will recheck that, ta.

My suspicion is that it's running rich at idle (you can smell it), but slightly lean at fast idle - that would cause higher CO levels I think?

On a GEMS, the Nanocom (under Inputs, Air and Idle) shows idle air valve as a number between 0 and 200 (showing the number of steps), correct being between 15 and 30 at idle when hot. However, if you have a weak coil it will be opening more than it should to keep the idle revs correct. If you find that you can't adjust it down to zero, then it is trying to compensate for something else. .

There are three things listed on nanocom under the air/idle inputs (this is from the manual):

Long term adaptive idle: This is the value that the GEMS learns over a period of time to
take into account manufacturers' tolerances on components which affect overall idle
speed. It can be reset, forcing the GEMS to re-learn this value or it can be manually
altered in the settings section.

Short term adaptive idle: This is the value that the GEMS uses to regulate the current
idle speed to take into account current engine load, temperature, etc. It can be
manually altered in the settings section.

Idle air control valve: The Idle Air Control Valve (IACV) has a stepper motor mounted on
it, which controls its position in steps thereby regulating the air flow at idle and thus the
idle speed. The position of this stepper motor is adjustable and should be such that a
warm engine at normal idle should cause the stepper motor to be at between 15 and 30
steps. The value can be between zero (closed) and 200 (open).

Also from the manual, under settings:
Short term idle (steps): This is the value that the GEMS use’s to regulate the current idle speed
to take into account current engine load, temperature etc. It can be manually altered here may
later be changed by GEMS. The value is in steps and it can be a number between 0 and 255.
Long term idle: This is the value that the GEMS learns over a period of time to take into account
manufacturers tolerances on components which affect overall idle speed. This value cannot be
modified, but it can be reset, forcing the GEMS to re-learn this value.

Clear as mud :)
So yeah in theory you're looking for 15 and 30 steps at idle, but the problem is, where does nanocom show this, and in what format?

My short/long term idle inputs usually show up near 255. My iacv input says it's a percentage on screen, and watching it change under load, it's certainly never gone as high as 100.

Short version: Idle figure is the bottom of GEMS / Inputs / Air-Idle / Second Screen "Idle Air Control Valve" and appears to be in the right format for setting to 15-30, or as close-as.

Longer Verson: The Nanocom shows the short term idle and long term idle under settings, and under Gems / Inputs / Air-Idle, which is where I tend to check the throttle position stored vs actual, the intake temperature sensor reading and so-on. On the second page along, this has, amongst other things, the short term adaptive idle, long term adaptive idle (these seem to change more readily than, for example, GEMS LTFT - or at least on mine) and the Idle air Control Valve figure.

Last MOT (another one's due in two weeks so I'm looking at all this again, along with the O2 readings etc etc) it got through OK after cleaning the stepper motor and airways in, plus adjusting the idle % which was up around the 40's at least. It's the last one on that nanocom screen which the bypass valve under the plate affects - the stepper value listed as Idle Air Control Valve, it's not stalling at idle after a reset now it's adjusted - still think I need to fit a new stepper though.

The Bosch passed its MOT 6 months or so ago smelling fairly rich, I don't have a Thor option on the nanocom to look at it, only for the GEMS as it's the one I mostly use (and prefer tbh).

As far as I can tell, the Nanocom seems to be reporting the GEMS figures fairly correctly, my calculated load is usually 20-something but that's likely the car - it's a work in progress, and in mine the O2's switch 0-6.5v but that could be the ECU chip. When I put the tornado in it went to -160 LTFT on adaptive reset, but I suspect it's because it's based on the earlier tune ID (9619 instead of 9625) which did that anyway.

My ST/LT air values usually seem to end up higher on the air side of things. The Iacv % I can't get to much over 60 odd, maybe they don't or maybe my stepper motor's nadgered - it's on the list to replace at some point.

Really dumb question.... if it's not on the input site, or IACV, or injectors... then how are the O2 sensors looking - if they are out and reporting to rich/lean (when it's not) then it could also be throwing things out.

Other really dumb question... do you definitely have cats in there? I swapped my cats when mine failed emissions (because they'd done a petrol test instead of LPG, but despite arguing with the numpty on the counter, I figured it was just as easy to change them and then it would pass on whatever they tested it as.

I was somewhat surprised when I took the old Y pipe out that there were actually no cats in there - they had been hollowed out.

With new cats, my emissions reading was actually 0%, 0ppm. It was up a tiny bit this year (but only marginally - nowhere near the limits - and they tested it properly the first time) - with 1 year old exhaust.

So maybe it's possible that everything 'up front' is working OK, but the cats aren't doing their job properly anymore and that's why it's failing?

Martyuk wrote:

Really dumb question.... if it's not on the input site, or IACV, or injectors... then how are the O2 sensors looking - if they are out and reporting to rich/lean (when it's not) then it could also be throwing things out.

One of the two O2 sensors is brand new. I replaced it after putting an oscilloscope on both sensors and spotting that it was switching slowly. Now both switch around once a second, which is about right by my understanding (at fast idle).

Other really dumb question... do you definitely have cats in there? I swapped my cats when mine failed emissions (because they'd done a petrol test instead of LPG, but despite arguing with the numpty on the counter, I figured it was just as easy to change them and then it would pass on whatever they tested it as.

I was somewhat surprised when I took the old Y pipe out that there were actually no cats in there - they had been hollowed out.

With new cats, my emissions reading was actually 0%, 0ppm. It was up a tiny bit this year (but only marginally - nowhere near the limits - and they tested it properly the first time) - with 1 year old exhaust.

So maybe it's possible that everything 'up front' is working OK, but the cats aren't doing their job properly anymore and that's why it's failing?

My cats are rattly, so I imagine they're there, but not in the best of condition. That might account for a high CO reading, but it doesn't explain high HC, as the cats are after the O2 sensors.

Will post pictures of the plugs in a second.

Plugs 1, 6, 8 and 5 all look spot on. Plugs 2 and 3 show some slight sooting on one side, and 4 and 7 show slightly more.

That's a very good question. If it was bought already converted to LPG it is quite possible the cats have been gutted and will still sail through the LPG emissions test but fail if tested on petrol.

No, it never had LPG before. I'm slowly (2 years and counting) fitting it.

Posted my last while you were posting pictures of the plugs. 2 and 3 share a coil as do 4 and 7 so I suspect a replacement set of coils might be a good idea.

When you say the cats are rattly, do you mean you can hear something rattling inside or does it just sound like a rattle? Gutted cats without adding a tube inside do make a rattly sort of noise as the empty boxes act like some sort of reasonator box.

SamH wrote:

Short version: Idle figure is the bottom of GEMS / Inputs / Air-Idle / Second Screen "Idle Air Control Valve" and appears to be in the right format for setting to 15-30, or as close-as.

Longer Verson: The Nanocom shows the short term idle and long term idle under settings, and under Gems / Inputs / Air-Idle, which is where I tend to check the throttle position stored vs actual, the intake temperature sensor reading and so-on. On the second page along, this has, amongst other things, the short term adaptive idle, long term adaptive idle (these seem to change more readily than, for example, GEMS LTFT - or at least on mine) and the Idle air Control Valve figure.

Last MOT (another one's due in two weeks so I'm looking at all this again, along with the O2 readings etc etc) it got through OK after cleaning the stepper motor and airways in, plus adjusting the idle % which was up around the 40's at least. It's the last one on that nanocom screen which the bypass valve under the plate affects - the stepper value listed as Idle Air Control Valve, it's not stalling at idle after a reset now it's adjusted - still think I need to fit a new stepper though.

If it is a percentage, then I reckon it wants to be around 11%. I don't think that's my problem though, as it wouldn't cause a very slight stumble at idle. Another thing maybe worth noting, my RH rocker assembly is a bit tappety. Again, has been like that forever. Seats didn't look recessed when I rebuilt the engine two years ago.

The Bosch passed its MOT 6 months or so ago smelling fairly rich, I don't have a Thor option on the nanocom to look at it, only for the GEMS as it's the one I mostly use (and prefer tbh).

As far as I can tell, the Nanocom seems to be reporting the GEMS figures fairly correctly, my calculated load is usually 20-something but that's likely the car - it's a work in progress, and in mine the O2's switch 0-6.5v but that could be the ECU chip. When I put the tornado in it went to -160 LTFT on adaptive reset, but I suspect it's because it's based on the earlier tune ID (9619 instead of 9625) which did that anyway.

My ST/LT air values usually seem to end up higher on the air side of things. The Iacv % I can't get to much over 60 odd, maybe they don't or maybe my stepper motor's nadgered - it's on the list to replace at some point.

I've only seen mine get to maybe 70% or so under load, so yours is probably about the same as mine. I would imagine there's no real point in opening up to 100% as it would just delay how quickly the ECU can close it if the car drops to idle.

Gilbertd wrote:

Posted my last while you were posting pictures of the plugs. 2 and 3 share a coil as do 4 and 7 so I suspect a replacement set of coils might be a good idea.

Any way to test them, other than a resistance test? I'd prefer to pinpoint the actual fault rather than parts cannon it if possible. :)

When you say the cats are rattly, do you mean you can hear something rattling inside or does it just sound like a rattle? Gutted cats without adding a tube inside do make a rattly sort of noise as the empty boxes act like some sort of reasonator box.

Couldn't rightly say, to be honest.

I've only seen mine get to maybe 70% or so under load, so yours is probably about the same as mine. I would imagine there's no real point in opening up to 100% as it would just delay how quickly the ECU can close it if the car drops to idle.

I reckon you're right - I must admit I'm guilty of typing without thinking there, Im sure that the Idle figure is a step-number rather than a %, as Gilbertd wrote, way up the top of the thread. I set mine around 22 on the Nanocom with A/C and fans turned off generally, there seems to be a balancing act between that and the LT and ST idle adaptive steps but on mine it seems to be best to concentrate on the 15-30 range and get that in the right place rather than worry about the other two. Something else that happened when I first adjusted the bypass is that the (high) calculated load went down a bit, although it's still up near 20 (indicated) %. After the next MOT I will have a good dig around the GEMS system if it all goes according to plan.

Mine is quite tappety especially from cold, has been since I got it - the Bosch is less so, even at a higher mileage (I think the oil pressure's higher, maybe helps) although it has its own problems at the moment.

The idle step figure - I agree, it doesnt answer what's up with yours, doubt it would be running at all normally by the time it did enough to throw the emissions out. Cheers.

SamH wrote:

I've only seen mine get to maybe 70% or so under load, so yours is probably about the same as mine. I would imagine there's no real point in opening up to 100% as it would just delay how quickly the ECU can close it if the car drops to idle.

I reckon you're right - I must admit I'm guilty of typing without thinking there, Im sure that the Idle figure is a step-number rather than a %, as Gilbertd wrote, way up the top of the thread. I set mine around 22 on the Nanocom with A/C and fans turned off generally, there seems to be a balancing act between that and the LT and ST idle adaptive steps but on mine it seems to be best to concentrate on the 15-30 range and get that in the right place rather than worry about the other two. Something else that happened when I first adjusted the bypass is that the (high) calculated load went down a bit, although it's still up near 20 (indicated) %. After the next MOT I will have a good dig around the GEMS system if it all goes according to plan.

It's supposedly 200 steps for one of them, and slightly more for the other. 11% puts it bang in the middle of both ranges by my reckoning, so should be good for either, assuming of course it really is a percentage :)

mace wrote:

It's supposedly 200 steps for one of them, and slightly more for the other. 11% puts it bang in the middle of both ranges by my reckoning, so should be good for either, assuming of course it really is a percentage :)

22 is what the Morgan plus 8 GEMS guide says is right for the steps to adjust it to, and is also 11% of 200 of course - I have only just made that connection, must be having a slow brain day.

(My rpm seems not to take off 'on its own' under the idle stepper motor's control until around 11-1200 rpm, which is why I think there's something out on it it ought to be more like 8-900 -probably- but that's not really helpful to your emissions situation).

From watching what it does when driving and the affect a TPS that hasn't been calibrated has, I think the IACV adjusts to maintain the idle speed but also acts to raise the revs at very small throttle openings. So it will sit around the 15-30 steps figure at idle but if you give a very small amount of throttle, rather than relying on a tiny movement of the butterfly, the operation of the TPS causes the IACV to open up to raise the revs and give a clean transition from idle to above idle but not by much (a bit like the progression jets in a carb). I had an iffy TPS which meant I could not hold the revs at around 1,000rpm, it would idle fine and it would run at 1,300 rpm but no way could I hold the revs anywhere in between. The TPS wasn't reacting to the small throttle movement so the IACV wasn't opening at small throttle openings and there wasn't enough additional air getting past the butterfly to raise the revs until it opened a bit more. Once you are running normally, it closes back down to the idle opening ready for when you come off the throttle.

However, that isn't going to give incomplete combustion and a high HC figure but a weak spark would.

Gilbertd wrote:

However, that isn't going to give incomplete combustion and a high HC figure but a weak spark would.

So do you reckon the slight sootiness on those plugs is significant then?

I've ordered up a set of coil packs anyway.

Well, it's showing that those 4 pots are running differently to the others and they do share coil packs so I would think it has some sort of bearing on things.

Nod. I need to figure out some way to analyse the HT side to see if there's any obvious differences on a scope.

What plugs are you using and how old are the leads? I reckon on NGK BPR6ES and change every 10,000 miles and generic 8mm HT leads (Island specials) and change every couple of years. On the old school Crypton tuner that had a proper CRT scope, that would show a higher voltage on cylinders that weren't running as efficiently as others. Might be worth a try if your scope can handle the voltage.