740i Emissions Problem

[TonyD]

Hi Guys, the saga continues...

another local BMW trained techie arrived to view the beast on Saturday morning and the following was tried.

Idle valve cleaned, it was filthy inside and a good wash out with thinners got it working smoothly.

Co2 was at 3% initially but we then changed the Lambda sensors and the Co2 reading increased to 11%.......fault codes were flagged up on both sets of lambda sensors, the old BMW ones and the new aftermarket ones

Fuel now present in oil so we changed the oil and oil filter.

No other fault codes present apart from an inoperative charcoal filter on the fuel tank purge system which is hardly surprising as we havent fitted the filter but have blanked the tube off anyway. This we are told by everyone who has looked at the car will have no effect on the engine as its a requirement for smog control legislation not engine management.

Introducing an air leak after the MAF sensor worked for about 15 seconds as the Co2 dropped to 9% and then the bloody car reacted, compensated for the air leak and Co2 went up to 11% again.

All sensors on the engine good with correct temperature readings on both inlet and outlet water temperature sensors.

It appears that the problem, may not be of our making and that the overfuelling may have been occuring in the original 740i.

All hoses and unions and exhaust joints gas and airtight. The induction system is non standard with a huge green cone type filter ( non oiled) feeding through a large flexible leak proof ducting from the front of the car ( cool air) into the throttle body ie no restrictions etc. Taking off the oil filler cap had no effect on the emissions so crankcase ventilation still working ok.....

The plan is next Saturday to get two new BMW Lambda sensors, and borrow another DME, plus key, plus EWS box, to see if its the DME causing the problem........which it very well could be....

More updates later in the week.

Cheers,

Tony

Good news is that all the techies and garages who have looked at the Cobra have not charged me for their time as they cant fix the problem. One had his guys working on it for three days and didnt charge me a penny......I had to promise to take him for a ride in the car when its legal however..... :P

[KingScare]

Um...i have no idea how to solve your problem...

but what i want...



IS PICS!!!!

so whenever you have it fixed you GOTTA post pics... engine, car itself..interior..

WHATEVER

post that dope project.

[TECH]

CO2 is carbon dioxide. That does not indicate a rich running engine. What you need to look at is the CO being too high (carbon monoxide). It the HC is too high, that indicates a misfire, since HC is unburned fuel, or hydrocarbons.

And if taking off the oil fill cap didn't change the way the engine ran, I'd think that the pcv system WASN'T functioning correctly.

[TonyD]

OK Guys heres the news..........

Went down to my local BMW breakers yard and borrowed a couple of lambda sensors and a DME from a 3.5 V8 ( mine is a 4.4 V8) just to see if we could get the car to run anywhere near the required CO levels.

With the two secondhand Lambda sensors in and the 3.5 DME it ran a bit rough but the Co was down to 0.7%

Put the original 4.4 DME in and the ommisions oscillateted around the 0.3 to 0.7 mark but the engine was running really hot......

This proved that the after market O2 sensors were a load of rubbish ( I got my money back from the vendor later today btw).

Investigated why the car was running hot.....transpired that the impellor on the water pump was not turning with the pulley......a very common problem it seems but one which had fooled everyone for the last 10 months........ A hot engine automatically richens the mixture to compensate.........I have a new water pump on order and am expecting the problem to be now cured.

I spoke to Dinan btw who put me onto a guy in the UK as they wouldnt deal with me from the USA. The UK gave me some very useful pointers......eg skip( throw away) the K&N filters as they upset the MAF sensor ..........I took off my filter put on a straight pipe to get laminar air flow over the sensor and lost another 0.5% CO.........

Result is a car that has gone from 11% CO to 0.3% Co and still has room for improvement.....

Am I a happy bunny or what.............but why did the impellor come off within the water pump, why is it a common problem, and why didnt anyone else think of it......... Mind you as I was in the breakers yard I did spot a BMW M5 complete with engine and I thought if I cant get my original engine to run right that buggar is going in next....... I may still do that.....400bhp in a Cobra weighing less than 1200kg......

Cheers,

Tony