Yet another MOT failure....emissions:(

Adam fc · February 14, 2011, 09:02:27 PM

Hi all, Ive recently had my fc3s turbo 2 put through an mot to find out \'surprise surprise\' the emission\'s were way off!

Ive recently installed a front mount intercooler and new fuel pump along with all the filters and a new set of plugs with magnacor leads. I allso swapped the after market ecu out for the standard one hoping it wouldnt run so rich in preperation for the mot.

From the results it seems its running rich and isnt burning the fuel and its hunting like it has an air leak which i was half expecting from fitting a front mount intercooler as theres plenty of chances for air leaks on the new connections.

Im guessing this issue is a collective of of problems rather than an single fault?

If anyone has any info or knowlage please share as i dont know where to start:( cheers Adam

Prof · February 14, 2011, 09:28:58 PM

What fuel pump did you go for?

Walbro pumps are much more efficient than the stock pump, and hence they produce more pressure than the stock one when running through the resistor at idle. It seems that this can increase fuel to air during idle, and this isn\'t corrected by the lambda as it\'s not used below about 1500rpm.

You can probably correct it a bit by adding another resistor in series with the standard fuel pump resistor (this will be safe, as both resistors will be out of the circuit when you are under load).

Other things to try:

New Plugs
Make sure it\'s fully warmed for the MOT
Ask him if it will pass on the fast idle test (if HC or CO test is a pass at normal idle, they can run the car revs higher to see if the other reading will come good.)
Make sure water temp sensor on the back of the water pump is properly plugged in - if not, the car will overfuel to correct an apparent cold condition

Adam fc · February 14, 2011, 09:35:48 PM

Its running a walbro 255lph pump at the moment. My mate was following me and he said he could smell how rich the car was running and could see fumes coming from the exhaust. All this was before i fitted the walbro pump so kinda hoping it might not be related to that

That temp sensor sounds like a likely culprit as i assume the system will be in closed loop if its not recieving info from that sensor?

Since putting the FMIC on and a larger exhaust would this increase the HC count in the exhaust?

Brett · February 14, 2011, 09:36:16 PM

Are you still running the airpump?

Prof · February 14, 2011, 09:55:03 PM

At idle, the car will be running off fixed maps for fueling - with an overide for water temperature - running richer when cold.

As you open the throttle, it will adjust fueling based on the airflow meter signal, but at idle this is assumed to be closed, and any air coming in is via the small bypass adjustment - a little screw usually capped off on the AFM - you can remove the cap and gain access to the adjuster - that might help you a bit.

Adam fc · February 14, 2011, 09:56:17 PM

No the air pump is long gone im afraid,it wasnt plumed in when i removed it.

Prof · February 14, 2011, 09:59:56 PM

Quote from: Adam fc;742819No the air pump is long gone im afraid,it wasnt plumed in when i removed it.

That\'s an impressive CO figure then - mine is usually at or near the 3.5% (higher when cold) !!

I had assumed you\'d still got that plumbed in.

Adam fc · February 14, 2011, 10:02:11 PM

Okay well ive got an afm gauge which came with the car plumed in so ill have a tinker with this AFM adjustment screw and see what effect this has to the running.

Im allso going to have a go at setting the TPS tomorrow. Could this be a factor in the emissions as i was told the MOT tester will also check fast idle and half of the engines maximum rpm?

Adam fc · February 14, 2011, 10:03:47 PM

Quote from: Prof;742821That\'s an impressive CO figure then - mine is usually at or near the 3.5% (higher when cold) !!

I had assumed you\'d still got that plumbed in.

No sorry forgot to mention that! My understanding is that HC are produced by unburnt fuel?

Prof · February 14, 2011, 10:16:46 PM

yep - HC is unburnt fuel - it could be poor ignition either because the mixture is rich or plugs are bad / fouled, or coils not giving a good spark. It could also be down to rich mixture - giving a lot of unburnt fuel in the exhaust. I suppose it could also be down to excess oil not getting burnt off.

CO is down to partial burn - so not enough oxygen in the fuel / air mix for complete combuston. This would normally be converted to CO2 in the cat with a supply of air (air pump).

It\'s worth checkng a lot of things - vac leaks, air leaks, spark quality, plugs, temp sensor, fueling, fuel pressure (if you can monitor it), idle air adjustment (AFM / BAC), timing.

Adam fc · February 14, 2011, 10:34:55 PM

Okay well thats given me a direction to start looking in as before i didnt know where to start!

Ill report back tomos! cheers Adam

Adam fc · February 15, 2011, 07:03:14 PM

Well ive been through pretty much all the vacuum conections today allong with all concections and earths.

Ive reset the TPS to within the the given parameters using the multi meter method and ive allso run the car with the aftermarket ECU but this had litte or no effect of how rich she was running at idle.

Ive booked her in at RX Motors for next monday with Tim so ill hang on and see what they make of it.

Be interesting to find out what the issue is though. Cheer Adam

Adam fc · February 18, 2011, 01:33:42 AM

Quote from: Prof;742806What fuel pump did you go for?

Walbro pumps are much more efficient than the stock pump, and hence they produce more pressure than the stock one when running through the resistor at idle. It seems that this can increase fuel to air during idle, and this isn\'t corrected by the lambda as it\'s not used below about 1500rpm.

You can probably correct it a bit by adding another resistor in series with the standard fuel pump resistor (this will be safe, as both resistors will be out of the circuit when you are under load).

Other things to try:

New Plugs
Make sure it\'s fully warmed for the MOT
Ask him if it will pass on the fast idle test (if HC or CO test is a pass at normal idle, they can run the car revs higher to see if the other reading will come good.)
Make sure water temp sensor on the back of the water pump is properly plugged in - if not, the car will overfuel to correct an apparent cold condition

Just been trawling through the US site rx7club.com and there have been issues of people adding the walbro 255 and thus overwhelming the stock FPR and making the car run rich at idle and light throttle.

So by adding another resistor in series with the existing one this should bring the voltage down and thus reduce the flow rate on idle??

If so should i go for another resistor the same as the stock one allready fitted?

Ive allso noticed that the stock fuel pump resistor gets bloody hot. cheers

Prof · February 18, 2011, 07:59:34 AM

The following link on the GTO / Stealth 316 site is all about fuel pump upgrades:

http://www.stealth316.com/2-fuelpumpguide.htm

The FC pump isn\'t listed, but from my measurements, it flows less than an FD pump which is in the comparison, and also draws a little more current.

Basically - at 40 psi (stock idle pressure) and 13V the FC pump would draw around 10+ Amps compared to the 7-8 that a Walbro would use.

When Mazda sized the resistor for the fuel pump they had that higher current draw in mind, and the resistor is designed to drop the voltage to around 8-9 volts. This resistor only drops the Walbro to about 10-11 volts (depending on wiring quality in the car), and hence the drop isn\'t as much. Couple this with the fact the pump will flow a lot more at this voltage / pressure than the stock (at 13v comparison for Walbro and FD pump is 265 to 229, but this would be even worse for the FC pump comparison).

So the problem is two fold:

1) The Walbro flows more at any given voltage
2) The more efficient pump drops less current, so would effectively run at a higher voltage on the same wiring / resistor settings as a stock pump.

You could try running 2 stock resistors in series - that should bring the voltage down and help reduce that difference - the added advantage is that the resistors will only have 1/2 of the power dissipated in them, so run less hot

Adam fc · February 18, 2011, 11:50:19 AM

I think ill go for that first then and see if it brings the mixture ratio down abit. You were saying that these resistors arnt used under load or boost?

Last noob question to conect the two resistors together i assume id unplug the origional and just splice the other resistor into the existing resistors wiring?

Im guessing it doesnt matter which wire id cut into on the origional resistor then?