Diesel question

[Max Headroom]

Okay as a bit of a noob to the world of diesels, I have a question.

I experienced a bit of a lumpy idle recently, so while the car was at Oxford Saab for other work, I got them to look into it but nothing untoward was found, and I pretty much decided that it was caused by putting cheap diesel in the car from Asda because the car has been fine ever since I topped it off with half a tank of BP Ultimate diesel.

However...

This morning on my way to meet up with colleagues in Witney I was aware of a fairly profound misfire while the engine was still cold (about a mile into the journey) this did eventually clear after the engine had warmed up.

I was wondering if this is caused by my bad habit of coasting down long Cotswold hills?

Late last night on my way home I coasted about a mile to a set of traffic lights where I had a brief wait before going off up the hill the other side. On leaving the lights I was aware the car didnt seem to be pulling as well as I expected and so dropped it down a gear and went on up the hill very nicely, but was aware that I could see what appeared to be a cloud of smoke behind. Shortly after going up the hill I was home and parked up.

OK I know coasting is a bad habit and I probably shouldnt be doing it, but the car is well maintained and I wouldnt do it if I thought the engine would stall. But that aside, is there any other reason I shouldnt do this with a diesel,  am I 'oiling' something up by coasting last night that has caused my misfire this-morning?

[dustydes]

Hi

And welome neighbour (Wantage)

If you do short jurneys or slow drives a lot it will cause a few problems with diesels.
Your egr valve will start to stick, causing the car to slow and eventually not be able to pull away. Can be cleaned, search threads.
Swirl flaps will fall off, should have been checked
Map sensor becomes dirty and needs cleaning (poor tickover, hunting) Does your car idle evenly, Revs stay at a constant speed?? if not clean Map with proper Map cleaner.
As for clouds of smoke it is probable the DPF (Diesel particulate filter) was doing a regen (normal)
Have a read here. http://www.saabscene.com/forum/threads/131536-Diesel-Particulate-Filter-manual-regeneration (oneill875 half way down)
If you do not drive long jurneys at a good speed and good revs these happed sooner or later being a diesel.
I would remove fuse no4 in engine bay (10A) and leave out for 5 mins (dont try and start car)  to reset ecu. Replace fuse and take the car for a long drive 20 miles + (A34, M40) keep revs at 2500 + for 20min's.

have you looked on this site as well   http://www.saabcentral.com/forums/index.php

Good luck enjoy the sun while we have it.

des

[Petemate]

Agree Mark with the above. I also filled up last week with Asda, a complete departure from my normal "Nothing but Shell in MY car chaps", temped by the very low price. Can't say there were any misfires during the week, but the car didn't have the usual 'sparkle'. Consumption just now brim-brim since last top-up (at Asda last week) worked out at 43.9, compared with the previous top-up which revealed 44.9. On this stretch, I went to LHR from Oxford Mon & Tues, Wed the wife took the car in for the air-con gassing and did about 35 miles running round, don't know what speeds but she doesn't hang about when out & about. Then I went to work Thurs & Fri in it, stuck 20 litres of Shell in it yesterday, went to Bovingdon & back today, and filled up just now. My journeys were conducted on the naughty side of 80 most of the way, so MPG no real concern with the Asda in but I did read somewhere that s/market fuels do not have all the additives that major brands do. BUT - I have seen Shell tankers on one or two occasions in the past at non-Shell filling stations, eg Sainsbury's, and recently at a small Gulf one in Horspath. ??

[Max Headroom]

Thanks for the replies Des and Pete.

The other night when the car seemingly chucked out the smoke at the bottom of the hill, I had driven up from Uxbridge, dropped a colleague off in Witney and carried on home to Stow. The cruise back on the M40 had been twix 75 and 85 but it was dark and with the roof down and both wearing tee shirts was getting a tad nippy around the shoulders, so after the cutting by the B4009 I backed the speed off.
The drive from Witney was at legal road speeds.

Today when I experienced the misfire was a "short" journey from Stow to Witney where I dropped my car off and went to work in a colleagues car.
On returning to Stow tonight I did the exact same thing and coasted down Wyck Hill (the distance clocked is about 1.5 miles). A brief pause for the traffic lights to change, and then gave it a good bootfull of the 'loud pedal' to go up Stow hill - and guess what? No smoke!

I was always of the opinion that the fuel was all the same - the different oil companies just pay for a quantity and it arrives by truck from the refinery all the same stuff.

[sgould]

I don't know if the diesel is the same as the petrol, but if you want to save fuel on a petrol car, don't coast. 

If you coast a petrol car, the engine will carry on on tickover using fuel.  If the revs are above 1200 rpm on overrun the petrol car the fuel is automatically cut off for you.   So just change down to keep the revs up above 1200 rpm.

I think it's 1200 rpm, it was on one car I had, but it may be a bit higher on a Saab, but not much.  I'll check in the morning if I remember.

[littlebasher]

Injector 3 wiring?

[Petemate]

Really worth doing as a matter of principle. Cured the missing on mine, which was a definite misfire!!

[Audax]

Wiggling the connector on injector number usually shows if it's the fault or not. There is also a software update for the engine ecm that can help with some misfires.

[Max Headroom]

I got a software update done last October.

The wiring snag is interesting but why only injector #3? I'll take a look.

However this misfire hasn't happened since, and I took a drive up to Worcester yesterday and experienced no rough-running or misfires at all.  I'm hopeful that this was just a one-off glitch  but nevertheless very
grateful for all your ideas.

[Audax]

It can be other injectors that give a problem but i think it's due to the location of injector 3 on the engine that it gets more muck blown over and through it which causes the problem.

[Max Headroom]

The blithering misfire is back 

It's been absent for some time, but on the drive into work on Monday it came back. Yesterday it was behaving itself, but this morning it continued again, and despite stopping and restarting, it stayed.

I'm going to get the wiring looked at... or is this something I could deal with myself? I'm no electrickery injuneer but if I know where to look and what to do when/if I find it, could I give it a go?

[Audax]

I'm going to get the wiring looked at... or is this something I could deal with myself? I'm no electrickery injuneer but if I know where to look and what to do when/if I find it, could I give it a go?

You can deal with it yourself, the simple test is to open the bonnet and find the connector for injector number 3 and wiggle it when the engine is running (and the other connectors too) if the misfire goes then it's fairly simple to say it's that injector. As for replacing the connector, I'd say it was simple enough if you can join 2 wires and undo some plastic clips. If that's too tricky for someone who works on planes then I'm going to start walking on my holidays

[Max Headroom]

Thanks for that - a connector change?  I think I can manage that! Will source some and get it done. probably as well to do the lot. Is this likely to occur again or is there anything else that I can do to reduce the likelihood of it happening again?

I fix the frame, the hyds and oxy systems - not the bits that get wiggly amps through them - thats all still white-mans magic 

[Audax]

Thanks for that - a connector change?  I think I can manage that! Will source some and get it done. probably as well to do the lot. Is this likely to occur again or is there anything else that I can do to reduce the likelihood of it happening again?

Don't do any of them until you're certain that is the fault, due to the nature of how you're fixing it you may introduce problems and it's a bit of a messy fix too. I wouldn't do the lot as it'd end up being an untidy mess, if it isn't broken don't fix it!

[Max Headroom]

if it isn't broken don't fix it!

Okay thanks for that - will do some wire wiggling ( ) and see how it goes