Conundrum of the day... Motronic...

[MVX11V]

I'm at a bit of a loss here. I swapped out my fuel regulator and serviced my injectors, put those back on the car and drove it. It was down from hitting 31mpg over 50 miles to 25mpg over the same journey.
The reason behind that may well have been because the afm was set to run the engine to suit the knackered regulator by making the spring load richer by 4 notches. So I had a poke about. (This afm has been played about with and I don't know what's been done on it. I had to mess about with it when the car stopped starting and found the readings/ track contact all over the place and I managed to get a decent reading from it eventually).
The regulator replacement cured the low revs/ stalling issue and it ran ok, just down on mpg.

The last two nights I've had the afm off again and set it back to where the spring load was although my info says the afm resistance should be peaking at 1200, I can barely achieve 1000. I also found as explained in another post that the throttle set up seems to be way out of adjustment.

Long story short, I took it for a run today, 50 miles, and now it can only achieve 24mpg and is very 'lumpy' at 55-75mph cruising on the throttle, pressing the throttle eliminates the lumpiness, it's almost like it's being starved of something.

In a good way, this problem appears to be caused by one component rather than several which I have been battling with over the last few months.
My question is this, will even 1 notch of adjustment on the afm spring tension have such a dramatic effect on the fuelling? Is it running too lean?
I keep telling myself that I will get to the bottom of this!

EDIT: The CO screw is 3.5 turns out as standard right? Mine has always been screwed in tight... you see what I'm dealing with here...!

[MVX11V]

OK, plan of the day to investigate conundrum of the day is to whip off the afm, tighten spring by 7 notches and wind out screw by 4 turns, gaffer tape the plastic bit back on, put afm back on... then drive it home. This is guerrilla mechanics at it's finest... what could possibly go wrong?

I've read so much info on these things today that I have gathered enough stuff to reach an average. It would appear that these metal boxes will cause all manner of running issues, most describe what I have going on right now.

[MVX11V]

Yeah, no, it didn't like that much... not even gonna bother test driving that. Darn, there was a glimmer of hope for a minute but at least it shows the AFM is doing something! Reset it back to as it was before I even touched it as it seems happiest yet slightly miserable in that position. Sounds like some US V8 hardcore muscle lump under there as it ticks over. It'll get me home and then I can revisit some stuff that was changed, I've a sneaky suspicion that it's down 1 cylinder and getting worse. If it's the dizzy cap again, I'll go mad... that'll be the 4th one in as many years. Pesky 635.

[MVX11V]

I don't suppose that if I pull the vacuum off the fuel reg and it has no difference on the stability of the engine at all that it could be a problem right? I just drove the funkiest 50 miles ever!

[GRNSHRK]

Having a great conversation with yourself there squidward

Sorry, don't have an answer for you, don't have a Motronic equipped 6er, but I just thought that you've been responding to your own posts and I found it rather humorous

I hope that some of your comrades step up to the plate with solutions

[MVX11V]

I always talk to myself, I'm usually the only one that knows what I mean...and I have to be a bit bonkers to own this car!

[hornhospital]

You pulled the vacuum line to the FPR and it made no difference? No wonder it's running lumpy. Test the fuel pressure. Methinks you've got a dead FPR, so the injectors are running at whatever pressure the fuel pump can put out, and therefore it's running way rich. It's driving the ECU crazy trying to balance the air/fuel mix.

[MVX11V]

Yeah, that'll learn me. I had a dead fpr, and swapped it with a second hand unit of the more common type for ease of future replacements and that has obviously only worked for 2 miles before wiping out on me.
This is breaking news!

And yes, it's running way rich, trees were collapsing as I passed them.

[Brucey]

there's no need to ever fit a knackered FPR; you can test them with a footpump/bike pump that has a gauge fitted.

Re the AFM; one notch on the spring is worth about half the travel in the bypass screw.

Testing AFMs isn't easy; for various reasons a typical multimeter won't give an accurate reading, even on a good AFM.

Another common cause of rich running is that the CTS is up the spout, but there are plenty of others.

cheers

[MVX11V]

Wow, that's quite a bit of change with the AFM there, cheers for the info! It's a new CTS for that very reason.
I still need the car and despite chucking tonnes of cash at my other two cars this month on much needed bits I learnt on Sunday that I can't use my Discovery this week because the wife needs it... every day. Come on man!
Well, that mean't I needed to go put the old fuel rail and regulator back on and hope for the best.
It runs and drives with it on, it was getting lumpy and stalling and I couldn't get the revs up at idle. Previously changing the FPR changed that but after it died and I swapped it back the car idled bang on... until it got warm and then it shot up to about 1050rpm and now it seems to want to stay there. It drives fine though so it'll have to do as I have 0 time this week to spend on it because I'll be rolling around under the green E36 in the rain bolting many things to it. I'm not spending out on it this month, it'll come out of service this weekend so long as this storm gets gone!
I could mess about with the position of the throttle switches and get the revs down at idle but with the FPR on the way out I'll still be fighting a lost cause.
Whatever I touched when I swapped the fuel rail/ reg over has made my MPG needle gauge work as it should. Unless that is a coincidence as well! It worked when it felt like it for about a year and then packed up altogether recently. Now it's alive again. What did I touch? Position sensor plug, speed sensor plug, all injector plugs, afm plug, tps plug... hmmm, it's a strange one.
The car used to hit 36mpg on the obc, then it struggled to hit 32 recently, swapping the FPR for the now dead one saw it just about reach 24mpg and now with the old one back on it all I can get is 28... all on the same run! But I'll give it some slack as it's not well. Still, got a spanking new battery for it gratis so something is going well!

[Devildog0341]

WOW, I have had my 635csi for two months now and the MPG has never averaged more than 22mpg. I would be shocked to see 30mpg. I live 10 miles from my shop and its all highway driving. I am now going to start looking into this and why mine isnt getting awesome mileage. Thanks for occupying my weekends now. LOL

[hornhospital]

20-ish mpg is the norm, I'm afraid. I am thrilled when my 633 gets over 18, but I drive the crap out of it.

[ron]

Don't forget that a UK gallon is 4.54 litres against a US gallon that is 3.78 litres.

[MVX11V]

Yes, plus I do 50 miles on the highway with virtually no traffic for 30 of those. Even my V8 Landrover can hit around 30mpg on a long run, with the AC off, and with a good tail wind and that's like trying to push a dinosaur. Around town... forget mpg

[MVX11V]

WOW, I have had my 635csi for two months now and the MPG has never averaged more than 22mpg. I would be shocked to see 30mpg. I live 10 miles from my shop and its all highway driving. I am now going to start looking into this and why mine isnt getting awesome mileage. Thanks for occupying my weekends now. LOL

I'm up for totally swapping the Motronics on our cars if you want... international post?

[Brucey]

do bear in mind that our gallons are bigger than yours, which makes a difference. Nonetheless some folk have reported 30 (US) mpg on a long run with a US spec 6er.

Having driven mine in vary conditions and distances whilst keeping an eye on stuff like this, I can report that it usually takes about 50 miles for a 6er to (fully) warm up; it makes a noticeable difference if the engine, gearbox and diff oil are not up to temperature.

cheers

[MVX11V]

You know I said I'd spend no money on it... saw an AFM didn't I... no dinner for the rest of the week... stupid ebay/car!

[Devildog0341]

20-ish mpg is the norm, I'm afraid. I am thrilled when my 633 gets over 18, but I drive the crap out of it.

Whew, Thank God as I was about to start disassembling my car. Not really as I too actually drive the crap out of it. Isnt that what they are built for? lol

[MVX11V]

I love driving the crap out of mine, the last time I burst a rear damper but sadly it's been on the 'poor little fragile unicorn' list for a while. The worst thing anyone can do to these is NOT drive them. They self destruct on the driveway!