Running stupidly rich ... any ideas?

RG.net · Postby **RG.net** » Mon Jul 20, 2009 12:35 pm

hi guys,

it has come to my attention that my car is running abnormally rich. It stinks on start up, and when giving it a fang. Theres also a buildup of soot around the exhaust exit too.

The 02 sensor was changed a while ago. last engine mod was a cold side intake before it started running really rich.

i will unplug the ecu today and see if that helps.

Anyone had this problem before? maybe its time for a air/fuel adjuster.

Edit: fuel consumption is okish, 350 for 38 litres, roughly.

Postby **Okibi** » Mon Jul 20, 2009 12:46 pm

MXHEVN wrote:...i will unplug the ecu today and see if that helps...

That will not only stop it running rich, will stop it running at all. :lol:

Sorry can't be more help, perhaps get Mazda to stick it on their diagnosis machine?

RG.net · Postby **RG.net** » Mon Jul 20, 2009 12:54 pm

Okibi wrote:
MXHEVN wrote:...i will unplug the ecu today and see if that helps...

That will not only stop it running rich, will stop it running at all.

Sorry can't be more help, perhaps get Mazda to stick it on their diagnosis machine?

lol smartass, mazda in my area are a bunch of douches

JBT · Postby **JBT** » Mon Jul 20, 2009 4:45 pm

Dodgy coolant temp sensor :?:

matt9111 · Postby **matt9111** » Mon Jul 20, 2009 10:42 pm

Maybe AFM?

But I would have thought your fuel economy would be worse.

RG.net · Postby **RG.net** » Tue Jul 21, 2009 12:07 am

yeah consumption isnt that bad.

on cold start you can see the excess fuel coming out of the exhaust and onto the ground.
and once warm, and i give it some juice, it tends to blow bleck smoke.

i was on the dyno a few months ago, and i noticed some of the other mx5's blew out a fair bit of smoke too, so maybe that is normal ... but i wouldnt think leaving a shitload of fuel on the floor on a cold start is.

StanTheMan · Postby **StanTheMan** » Tue Jul 21, 2009 8:00 am

MXHEVN wrote:
on cold start you can see the excess fuel coming out of the exhaust and onto the ground.
and once warm, and i give it some juice, it tends to blow bleck smoke.

That would most likely be CO2 or water......most cars have that..... Its some kind of biproduct of the gasses, exploding inside the engine & exhaust. Not sure how it works . I've never been good a chemistry. Maybe someone like JBT or AJ can explain that process.

mine is a little rich on start up too.....Its been like that for some time come to think of it.

JBT · Postby **JBT** » Tue Jul 21, 2009 8:11 am

The water is just a by product of combustion - hydrogen + oxygen. Normally invisible as a vapour once things heat up properly.

I'd check the coolant sensor(s). As I recall, the NA8 system (probably the same as NB8A) had two elements to the sensor. One for the temp gauge and another for the ECU. If the ECU input is wrong and the ECU thus thinks the engine is cold, it will keep the mixture rich.

MX5CHIC · Postby **MX5CHIC** » Tue Jul 21, 2009 11:03 am

Intake air system changes ? My NB ran slightly rich with the standard intake, then I fitted an aftermarket cold air intake with a K&N filter - the car then ran quite lean.
I changed back to the original air intake and the car is running slightly rich again. The length of the intake, position within the intake of the sensor, and type of filter media used.

RG.net · Postby **RG.net** » Tue Jul 21, 2009 11:20 am

StanTheMan wrote:
MXHEVN wrote:
on cold start you can see the excess fuel coming out of the exhaust and onto the ground.
and once warm, and i give it some juice, it tends to blow bleck smoke.

That would most likely be CO2 or water......most cars have that..... Its some kind of biproduct of the gasses, exploding inside the engine & exhaust. Not sure how it works . I've never been good a chemistry. Maybe someone like JBT or AJ can explain that process.

mine is a little rich on start up too.....Its been like that for some time come to think of it.

i'm not sure, but whatever it is it stains the floor, its a musty bleck colour, much like the sh*t on my rear bumper.

It never used to do this before, and none of my other cars do either =/

RG.net · Postby **RG.net** » Tue Jul 21, 2009 11:24 am

JBT wrote:The water is just a by product of combustion - hydrogen + oxygen. Normally invisible as a vapour once things heat up properly.

I'd check the coolant sensor(s). As I recall, the NA8 system (probably the same as NB8A) had two elements to the sensor. One for the temp gauge and another for the ECU. If the ECU input is wrong and the ECU thus thinks the engine is cold, it will keep the mixture rich.

mmm, where are the coolant sensors attached to, the block somewhere?

JBT · Postby **JBT** » Tue Jul 21, 2009 12:14 pm

MXHEVN wrote:mmm, where are the coolant sensors attached to, the block somewhere?

On the NA8 it was at the rear of the head. Not sure about NB.

ampz · Postby **ampz** » Wed Jul 22, 2009 12:31 pm

Bevan had the same problem when he went with the 'shorty' CAI on his NB.
It is because of the relocation of the air temp sensor from the old airbox to the new spot.
Maybe because the air is cooler or the shorter intake tract. But i do remember his fuel consumption sucked with the shorty cai.

38l/350km :shock:

that's my fuel consumption on 10psi and a spirited drive :shock:

you should be getting at least another 50 - 80 km (maybe the auto chews more)

Do you still have the stock piping to do a comparison for about a month?

It would also be a good idea to check the coolant sensors, they are at the rear of the head next to the coil pack (drivers side) for an NB.

RG.net · Postby **RG.net** » Wed Jul 22, 2009 5:59 pm

ampz wrote:Bevan had the same problem when he went with the 'shorty' CAI on his NB.
It is because of the relocation of the air temp sensor from the old airbox to the new spot.
Maybe because the air is cooler or the shorter intake tract. But i do remember his fuel consumption sucked with the shorty cai.

38l/350km that's my fuel consumption on 10psi and a spirited drive

you should be getting at least another 50 - 80 km (maybe the auto chews more)

Do you still have the stock piping to do a comparison for about a month?

It would also be a good idea to check the coolant sensors, they are at the rear of the head next to the coil pack (drivers side) for an NB.

Thanks for that ampz, i have my old intake setup that i will chuck back on and see if that helps. I remember i used to get 400-450kms+ back in the day.

With the coolant temp sensor ... is it one of those things where you wont know if its stuffed or not whilst looking at it?

ampz · Postby **ampz** » Wed Jul 22, 2009 6:07 pm

You won't see any difference on the sensor visually.
The only way to test it is to measure it's resistance when cold, then when hot.
If it's within certain levels (I don't have an NB manual sorry) then it's either good or bad.

I usually just look for a different ohm reading between hot and cold, but that doesn't guarantee it's not within specs. The only temp sensor that died on me went short circuit (0 ohms) and stayed that way hot or cold, so was easy to diagnose (wasn't an mx5).