HT leads are my best guess...

[e34.535i.sport]

Hey guys first of all thanks for all your help recently... MUCH appreciated.

Now, I was doing some searching about my 'event' the other day and I stumbled on a few threads that described my car perfectly - Shitty rumbly Idle and BAD fuel economy (i.e. if the guage is correct 1/4tank (20litres) got me <40miles)... This is 9mpg - and at £5.09 a gallon I can't afford it!Their problem was in the HT leads so I found out you test them by running the car and pulling them out one by one to see if the idle changes or not...

My question is can I put them back in and move to the next one while the car is running or do I need to switch off? I am hoping this is not a stupid question, but it seems a bit dangerous messing with the electricals while its on!

It only clicked in my head while reading around that when I changed the sparks I found one of the HT lead boots had a small peice of curved plastic or metal inside that looked out of place. I thought nothing of it. Could I be running on 5 clyinders and not know as such? Would this give me such bad fuel economy?

The idle is rumbly and with the door open you can see it move. I've checked the sparks and for intake leaks and I think fuel pressure is ok as no problems in running... Injectors are noisy and may change them for the Ford 19lb ones soon if I don't find a fix to the fuel economy problem.

[pingu]

I know the HT leads are insulated but I'd still turn the engine off before moving them. I'm concerned that with no plug to discharge into, the spark might track across the outside of the leads and onto your fingers.

Have you got a decent Indy near you? It just seems that replacing the injectors isn't a good way of diagnosing whatever is causing your problems. Unless you want to replace them anyway (so you can sell and get a 540? ;-)

[e34.535i.sport]

If I'm honest there's nowhere I really trust Indy-wise... I was under the impression it was ok to remove them while running from reading old threads... but I can certainly see your point, we think alike.

Have you got a decent Indy near you? It just seems that replacing the injectors isn't a good way of diagnosing whatever is causing your problems. Unless you want to replace them anyway (so you can sell and get a 540? ;-)

I must confess I emailed the guy earlier over that Oxford Green 540i/A... I just keep going back to the ad to look at it! I asked him some Q's about his windscreen and a few other bits... Inc the block number so I can see what the score is Nikasil-wise.

I reckon I could sell mine no problem with the injectors as they are if they aren't causing the fuel consumption. It is in great condition bar this. I wouldn't sell a car while its using this much fuel, its just plain wrong! Going to fill back up later to check if it is using such a huge amount. Its funny because when I bought it the fuel economy was good in comparison to other 535iM owners on here.

I think I've narrowed it down to the injectors or HT leads, hopefully the latter... Anyone else know If I should remove them with the car running?!

[leicesterboy15]

I've pulled HT leads out before while the engine is running with no problem, you can hear the spark quite loudly and sometimes you can feel it but the lead is designed to insulate and you only pull it out for a few seconds. For more protection, wear gardening gloves and wrap the lead in a cloth. Is the idle worse when the weather is damp? Try coating the lead in WD40 to see if it improves, I can see how leads would cause a rough idle but how do they cause a drop in economy?

[DaveVoorhis]

I can see how leads would cause a rough idle but how do they cause a drop in economy?

It will cause partial or no burning of fuel in the cylinder with the bad lead. When a cylinder doesn't fire, it simply pumps raw fuel out the exhaust. That's fuel you're throwing away without using it to move the car.

[leicesterboy15]

It will cause partial or no burning of fuel in the cylinder with the bad lead. When a cylinder doesn't fire, it simply pumps raw fuel out the exhaust. That's fuel you're throwing away without using it to move the car.

Ahh I see, makes sense now!

[whiskychaser]

Try coating the lead in WD40 to see if it improves

Run engine, spray leads with WD40. Before it dries pull/replace each plug lead in turn. The one that makes you jump highest is the worst one. Or just put a meter on each lead and check resistances. Bet somebody has a spec

[e34.535i.sport]

Hey, just filled it back up after doing 75 mile and by my reckoning I'm getting 14.6 mpg... Not sure how bad this is driving mainly city (better than I thought though!), but it definitely used to be much better.

Still thinking I could be running on 5 cylinders, so will try what leicesterboy did... The idle is shite no matter what the weather, why do you ask?!

[leicesterboy15]

Is it connected to anything at the other end ? Is there even another end or does it just wrap around the cable? Best thing to do is go to your local car parts shop and buy a cheap HT lead (about £4), then swap each lead in turn with this new one and see if it improves, if it does on one particular lead, theres your problem, I wouldn't recommend using the cheap lead permanently but its ok to test with, I found the fault lead on my merc like that, it turned out to be the one from the coil to the dizzy cap. Saves having to buy a whole new good set for £80 just to find out its not the problem, or spray the existing cables with WD40 and see if it improves.

Is that thing you took a picture of some kind of ebay'esque fuel saving device or is it definately #9 in the diagram? I know Satnavs use speed pulse to determine how fast they are going, if it is #9 it could be for a similar use here. Maybe.

[e34.535i.sport]

Is it connected to anything at the other end ? Is there even another end or does it just wrap around the cable? Best thing to do is go to your local car parts shop and buy a cheap HT lead (about £4), then swap each lead in turn with this new one and see if it improves, if it does on one particular lead, theres your problem, I wouldn't recommend using the cheap lead permanently but its ok to test with, I found the fault lead on my merc like that, it turned out to be the one from the coil to the dizzy cap. Saves having to buy a whole new good set for £80 just to find out its not the problem, or spray the existing cables with WD40 and see if it improves.

Is that thing you took a picture of some kind of ebay'esque fuel saving device or is it definately #9 in the diagram? I know Satnavs use speed pulse to determine how fast they are going, if it is #9 it could be for a similar use here. Maybe.

It definitely looks like an official part, and it goes on the third lead along like in the diagram... Going out now to trace the other end now, if it is the pulse generator its quite costly for what it is! I'm hoping I notice some improvement for the price of it!

There's copper showing on both sides where the wire has split (looks like cleanly cut with a knife for example) so I don't know whether to splice it see what happens...