740i Emissions Problem - BMW Forum

TonyD · 01-30-2004, 03:57 PM

Hi guys, new member here who is at his wits end.

I was stupid enough to put a BMW 4.4 V8 from a 1996 740i into an AC Cobra replica.

The car is complete, working and goes like a train but I cant make it legal until I get it inspected. The problem is that at idle the emissions are off the clock its running so rich, and yet put the revs up and all is hunky dory. It has the correct cats and sensors etc. There are no fault codes showing.

Unfortunately the UK goverment inspection includes an emissions test so I am a bit stuck.

So far it has defeated two specialist BMW technicians and BMW tell me that they wont let it into their workshops as its not a BMW. My argument that it was just like a Williams F1 car in that it was a special chassis powered by BMW engineering didn't move them one iota.

Can anyone out there help? Does anyone know a friendly BMW techie or garage owner n the UK who can help ?

I'm getting desperate now as this has been dragging on since last October !!

Cheers,

Tony

ghead

EXtech · 01-30-2004, 08:58 PM

what have you changed? Is everything just like it came out of the 740?

TECH · 01-30-2004, 09:33 PM

Wow, sounds like a can of worms........

How do you know it's rich? What are the CO readings?
What gases are out of spec?

TECH · 01-30-2004, 09:37 PM

There could be any number of things wrong, but you can try doing a fuel injector cleaning/flush. Try and find a flush kit that taps into the fuel rail inlet hose, which feeds a super cleaner through the rail and injectors.
You'll block the return line, pull the fuel pump fuse, and run the car straight off the cleaner.
We have a BG system that works good.
If the injectors aren't spraying a proper pattern, it'll be most noticeable at idle. It's a possibliity.........

TECH · 01-30-2004, 10:40 PM

Is there a vacuum line on the fuel pressure regulator?

TonyD · 01-31-2004, 06:39 AM

Thanks for the input guys.

The engine and gearbox was removed as a whole from the BMW together with the complete and intact engine loom.

The technicians tell me that they have checked everything but when I get the car back on Monday from the latest workshop who have tried and failed to cure the problem I will check the vacuum pipe is on the fuel pressure regulator. I can see where the thinking is here, excess pressure at idle = too much fuel......

All the injectors have been checked and pronounced good, all the temperature sensors have been checked, the last workshop even brought in a perfect '96 740i and kept on swapping parts such as sensors etc they knew were good to see if the EMS was not ignoring erroneous readings. They tell me that even swapped the EMS and that didnt cure the problem.

The techies are telling me that it must be either a software problem in the EMS ( in which case why didnt the "borrowed" EMS cure the problem) or a wiring fault given the fact that we have dumped 98% of the original BMW car loom with links to its computers etc.

I am given to understand that this combination of Cobra Replica powered by a modern BMW V8 linked to the Tiptronic gearbox is unique in the World, now I think I know why!1 The beemer ensemble is far too technical for even BMW to fix them. God knows whats going to happen when the I Drive equipped cars start to get onto the second hand scene. The fact that no one can fix them will be a big disincentive to buy secondhand and residuals will plummet as a result.

keep the ideas coming,

Cheers,

Tony

TonyD · 01-31-2004, 06:46 AM

A couple of pics to give you an idea of how the BMW V8 fits into a Cobra

Cheers,

Tony

TECH · 01-31-2004, 10:11 AM

Very nice.

TECH · 01-31-2004, 10:12 AM

Hell, if you have to, maybe you can create a small vacuum leak to bring the mixture down at idle. It won't affect it much above idle, so it may work..........hehehee....

TECH · 01-31-2004, 10:13 AM

Try cleaning out the idle valve as well.

EXtech · 01-31-2004, 11:01 AM

Looks good tonyd. Why don't you try giving the folks at Dinan a call. Steve Dinan could probably shed some light on software programming for unique transplants such as yours. Dinan is God when it comes to BMW Software. You're going to need specific DME software for your application. The other option that I suggest is contacting the folks at Haltech ( www.haltech.com ). These guys' work is wonderful. I have used their engine management software many times and implemented onto many cars. They can provide you with a wiring harness and the software.

TonyD · 02-02-2004, 12:51 PM

HI guys,

Drove the beast back from the workshop today, still running far too rich at idle but the tecnicians are at a loss to explain it.

There was a vacuum pipe connected to the fuel pressure regulator so it looks like its going to be a slog to get it fixed. There were a couple of leaks in the induction pipework which would have put a little less air over the MAF sensor but still not enough to explain the huge overfuelling problem.

Having said that driving the car home was enough to get me re enthused about solving the problem, boy does this Cobra fly when you floor it.......

If all else fails I will call in the Dinan connection but as the engine, gearbox etc were removed in one lump and nothing was changed apart from the air inlet truncking and changing the strangled exhaust headers for something that breathes better, I would like to get it running as standard before I start tweeking the software.

Cheers,

Tony

EXtech · 02-02-2004, 06:31 PM

unfortunately Tony, I believe your issue lies within the programming and the only way to cure the problem is with custom tuning. The fact is, the DME was programmed for exactly the way it was in the 740 and and in more than just a few ways you have changed that. You have taken the beast from it's environment and now you have to program it to think differently. Save yourself some frustration, time and money. I would at least call Dinan to get their opinion. These guys are better than the BMW's engineers who program the factory software. Just some friendly advice.

TECH · 02-04-2004, 11:16 PM

Is the CO too high or is it the HC?

Waiting for a bone............. :P

makdolby · 02-06-2004, 09:42 AM

Check all the air/breather pipes are not perished/split or blocked. Make sure the PCV (Purge Control value) is working (Should be a one way value), and that the Carbon Filter is not clogged. Also the pipes from this PCV valve tends to clog up.

The ECU is pretty good at compensating for loss of air/pressure by over fuelling without any fault codes present.

The Lamda probe (O2 or oqygen sensor) would normally thow up an error code, but not necassarily. Apparently you can check to see if the resistance is varying during a differential in revs. If this is giving a false reading, then it will instruct the ECU to over fuel.

The Idle control valve maybe clogged up. It can be cleaned to make it run a little more efficiently.

Do you have any after market filters. This can effect the ECU/engine management. After market filters for example can cause a thin film of oil on the Air Mass Meter coil, causing the differential resistance to read slightly highter/lower than the current condition, thus sending the wrong value to the ECU and overfuelling.

These are a few idea's to think about...

Good luck.
MAK