Popping and spluttering

Sat Jun 25, 2005 11:06 am

Since I changed my injectors a week or so ago, (for same inj not bigger ones) I have been getting alot more popping and backfiring etc from the exhaust on overrun... Sounds

,

(it might have done it this much before, but I just not noticed it as I've only had the car 6 weeks'ish !!) could this mean it is overfueling?? unburnt fuel in exhaust.

or is it more likely to be ignition timing slightly out, as the car is slightly underpowered!!

I expect a bit of popping etc as slowing through the gears, bit this seems alot!!!

Sat Jun 25, 2005 12:05 pm

Maybe it's becasue the weather has been nicer the last week..windows open, and you noticing it a lot more? I know I've been hearing the M3 pop and bang a lot more the last week!

Sat Jun 25, 2005 12:07 pm

Simon wrote:Maybe it's becasue the weather has been nicer the last week..windows open, and you noticing it a lot more? I know I've been hearing the M3 pop and bang a lot more the last week!

Definately!!

Sat Jun 25, 2005 12:07 pm

Simon wrote:Maybe it's becasue the weather has been nicer the last week..windows open, and you noticing it a lot more? I know I've been hearing the M3 pop and bang a lot more the last week!

Yep very true.... still sure its more than normal though!!!

Sat Jun 25, 2005 12:46 pm

ignition timing buddy, mine was doing it, took it a bm specialist the other day and fook me mate shes like a brand new car, it pulls like a train now, i actually know ive 325 under there now!

Sat Jun 25, 2005 1:00 pm

just jumping in a bit ,how or what you ask the garage to do to get ignition timing checked ,to find that its spot on ?? and what sort of cost is involved ??

Sat Jun 25, 2005 1:05 pm

i had tappets set propperly, ignition timing done and somthing else but i cant remember what and somthing to do with the fuel line, cost Ãƒ”šÃ‚£120, it was the best Ãƒ”šÃ‚£120 ive ever spent on a car, unleash the beast

Sat Jun 25, 2005 1:21 pm

might get the ign timing checked, i done tappets myself couple weeks ago!

Sat Jun 25, 2005 1:34 pm

yeh i did my tappets 3 weeks ago. must go and get my timing checked i think

Sat Jun 25, 2005 3:57 pm

don't think you can adjust the ignition timing on a 325, they're all motronic management aren't they?

Sat Jun 25, 2005 4:03 pm

Toby_Unna wrote:don't think you can adjust the ignition timing on a 325, they're all motronic management aren't they?

I was gonna ask if you could

Sat Jun 25, 2005 4:03 pm

Toby_Unna wrote:don't think you can adjust the ignition timing on a 325, they're all motronic management aren't they?

I'm sat here with scrunched up eye brows thinking exactly the same thing

Sat Jun 25, 2005 4:09 pm

Can anyone explain the timing on these engines, to help me understand!?

Sat Jun 25, 2005 4:44 pm

Yeah, the ECU keeps an eye on the position of the crank and it's speed.

Then, based on the speed/crank position and the load (AFM signal) it'll look up how much ignition advance the engine needs.

Then, using the crank position as a reference, it'll fire the coil to correspond with the rotor arm passing the relevant contact in the dizzy cap.

This is why there aren't many moving parts in the dizzy compared to old clockwork type affairs

Sat Jun 25, 2005 4:50 pm

Turbo-Brown wrote:Then, using the crank position as a reference, it'll fire the coil to correspond with the rotor arm passing the relevant contact in the dizzy cap.

Superb description,,, thanks

I am not an expert at all, by any means, and have never changed a timing belt (yet) on a bmw, BUT.....

What happens if you need the belt to be between two teeth, if i'm right on the adj style dizzy's (eg rs turbo) you could advance retard the ignition timing by moving the dist...

On these the rotor arm, dizzy etc cannot physically be moved at all, therefore the rotor will always pass each of the six points at the same time no matter what.....

I am confusing myself with vague knowledge, but do I make sense at all????

Sat Jun 25, 2005 5:03 pm

Yaa, with older types, the dizzy / ignition was a little system pretty much independant of every thing else (allowing people to fit carbs to things like 205GTi's and remove the ECU altogether). The dizzy triggered the coil to go off (instead of the ECU) using a little switching mechanism (you hear people talking about 'points').

Also, the rotor arm was free to swing about which it did depending largely on engine speed. Engine load was sensed by vacuum by the little UFO thing you see on old dizzies.

Anyway, the upshot of it all was that if you moved the dizzy round, you adjusted the point of reference it had so if you moved it to advance by 1degree, you ended up with a 1degree advance everywhere in the rev range.

With the ECU triggered system, the position of the dizzy cap is largely acedemic. So long as the arm's pointing at the correct contact when the coil fires, all's well.

You tend to find that the contact on the end of the rotor arm is much wider with ECU triggered system than clockwork ones to allow for different advances without any of the parts having to move.

That's not a very good explanation is it

Sat Jun 25, 2005 5:15 pm

Think i'm with ya,... The roter arm has a wider point of contact, therefore the ecu can tell the coil to fire at any point as long as it is between when the rotor starts to pass the point and when it finishes. the ecu controls what point this is........ which I guess can only be changed by an aftermarket chip?????

If I'm right here I may be getting somewhere....

The chip I have in my car is a zone chip, but was from Taffy's race car... (I wasn't on this site when Taffy was, but others may know him) now could this chip have been changed, and how probable is it that the ignition timing was changed for some very hard race cam, Taffy may have had?????

Am I possibly right, or am I completely off track!!!??

ANT???

Sat Jun 25, 2005 5:37 pm

Wilson wrote:Think i'm with ya,... The roter arm has a wider point of contact, therefore the ecu can tell the coil to fire at any point as long as it is between when the rotor starts to pass the point and when it finishes. the ecu controls what point this is........ which I guess can only be changed by an aftermarket chip?????

If I'm right here I may be getting somewhere....

Yes, exactly that, and explained much better than I manged

The popping etc could just be caused by any extra fuel that your chip puts in passing through the engine and collecting in the exhaust system waiting to ignite and 'pop'. That or it's the same thing being caused by a mixture which is too lean passing through the engine and missing the spark.

Sat Jun 25, 2005 5:51 pm

Turbo-Brown wrote:Yes, exactly that, and explained much better than I manged

Well I didn' have the first idea, before you explained to me, so your explaination, must have been spot on.... Thanks

Turbo-Brown wrote:That or it's the same thing being caused by a mixture which is too lean passing through the engine and missing the spark.

Never heard of that before....!

So conclusion is........

1, too lean, missing spark...

2, chip is not intended for my car, causing the ignition timing to be out.

3, I'm imagining it.

Thanks for your help mate, even if the conclusion is no. 3, at least i've learn't some good info!!!!