Hi all
I've noticed a few times since it's got a little colder (and a little damper) that I've got a misfire from cold start up. There's a little shudder for each misfire and now I have openSID I see the misfire count up 1 or 2 with each shudder and then it resets to 0, shudders and counts up again then resets to 0 ... and so on.
No CEL and no error codes and after a few mins of running it disappears. Is this just normal for a cold damp start or something more sinister?
I'd started a thread about rough idle some time ago which seemed to be resolved with some new plugs correctly torqued down (I'd found 1 or 2 plugs were basically hand tight). But I'm wondering now if this is an issue linked to cold damp weather. Or maybe a failing DIC or something else?
Cheers
D
Had this again this (slightly frosty) morning and this time seemed more prevalent under load. Again it's odd as it was counting misfires anywhere between 1 to 4 over a few seconds, then run ok for a few seconds, then mifi count reset to 0, then it would miss again and the mifi count goes up again.. I thought the misfire count would only reset to zero after the ignition had been shut off??
Again no error codes. And it's definitely misfiring, with a very very slight jerk when it misses and an audible pop from the exhaust.
Short run, so I didn't get the car fully warmed up but Teng was 76degC...
Whist it was misfiring at about 2k rpm, Lambda was around +1000 to +1600 so quite lean? And Ioff around +24. I've only just done an ECU reset about 30 miles but have done an adaptation run, and Amul is +425. So I don't think any major issue once the engine's warmed up and I'm not seeing misfire under load once warmed up.
I know the colder weather wont be helping but my paranoid side worries there's something up..
I did two things yesterday - I fit the new CPS I've had sitting in my shed since last spring. And I gave the car it's first hoover since August :-[
Whilst hoovering the front passenger footwell I discovered it was soaking wet!
I snapped one of the 4 studs that locks down the ECU cover in the summer and as it turns out 3 studs are not enough to make a good seal and rain water has been peeing in around the ECU!
I removed the glovebox for better access and have used a nut, bolt and a few washers to secure the loose corner of the the ECU cover through the scuttle panel.
The ECU was dry around the plug but I don't know if the moisture and increased humidity around the ECU would have been enough to cause problems. The misfire, not exclusively, does seem to have correlated with wet weather. Although saying that the misfire was present before I broke the stud!
If one of the above does resolve the issue, typically I'm never going to know which one it was :o
If you suspect the ECU, have a look at the big multiplug on the bulkhead, it's a 42 pin connector on the early cars and two 24 pin ones on later cars. Also check the rubber "elephant trunk" is not blocked. It's in the centre and drains the area under the grille in front of the windscreen. If blocked, water gets into the car.
I kind of suspect a number of things at the moment. I think only the ECU since I found water was getting in there but it's a long shot as the fault was there before the water started getting in.
I've checked the earth on the thermostat housing and the intake manifold, sparks have been changed, so it can only really be the CPS or the DIC.
The "elephants trunk" is clear, I did it when I serviced last spring and I've washed water down from the scuttle panel and through the "elephants trunk"..
What about the big multiplug(s)?
Unchecked! I'll have a look tomorrow and at least give them a spray with contact cleaner.
Thanks for the tip :)
Haven't checked the two plugs on the bulkhead yet but since replacing the CPS and sorting the leak (passenger foot well carpet's now dry) I've not had the misfire at idle problem.
Not going to call this one just yet as it's been intermittent since I bought the car..
Must admit I've still not got round to checking the two plugs on the bulkhead that Will mentioned above. I will at the weekend, but for the first time in a good while, the occasional misfire at idle was back again today. I say idle but it became more frequent (1 misfire every 30 to 60 seconds) when i held around 1200>1500rpm. Otherwise 1 misfire every 2 mins or so. I don't see any misfires under load or when underway at similar rpm.
One thing that sprung to mind is that I've only noticed this when I'm waiting to pick the Mrs up from the train station. Possibly as that's the longest time I sit idling, but also struck me that's when I'm always parked on a slight incline, nose up. Could this indicate a weak fuel pump? Considering I'm stage 3, I don't see any issue under load. My fuel trim (Amul) is mostly around +300>600 which indicates a lean state but is near enough within tolerances. However on long runs I have seen Amul drift up to 900 briefly a few times. I'm also thinking maybe an injector that sticks occasionally?
I really need a TechII session to see if the misfire is just one one cylinder or occurs on all. Seriously starting to bug me this one, I'm tempted to book it in with Joe for a diagnostic session but worried it could be money wasted due to the intermittent nature ..
Yes I'm still banging on about this ;D
Car went to Joe's today for a diagnostic session.
He pressure tested the coolant system, no leaks and certainly nothing going into the cylinders.
Compression test, all cylinders "very good" 210psi. This wasn't really related to the misfire issue I just wanted it done for peace of mind.
Tech II showed only a few 100 misfires on each cylinder, I think I last reset the ECU just before Christmas so a low count. There was however about 200 more misfires on cylinder 1. Typically it didn't misfire once during the session.
Suggested it could be injectors or the DIC but try an injector cleaner. So I'm going to eat my words http://www.saabtechtalk.com/forum/index.php?topic=3733.msg29779#msg29779 (http://www.saabtechtalk.com/forum/index.php?topic=3733.msg29779#msg29779) and I've ordered a can of Orio fuel treatment. It's got to be worth a pop.
I am quite tempted to use this as an excuse to upgrade the injectors to 'Green Giants' and I'll pick up a DIC to keep in the boot.
Joe also gave the suspension a once over and gave it the thumbs up.
So no real outcome to the misfire issue but a few things ruled out and fair amount of peace of mind..
Forte fuel treatment is decent stuff............ branded is probably better than repackaged OEM distributor with a badge tax.
Going to have to resurrect this thread. Can't say I've really been monitoring misfires since I sorted an earthing issue and no longer experience any loss in performance but also can't say I've noticed any. Distinctly noticed the odd pop from the exhaust whilst doing a fast idle to warm the engine up post giving the car it's annual service today (plugs were changed.). Sure enough the Miss count on openSID was going up 1 for each pop then dropping back to zero again. Same on a test drive, hit a string of 5 misfires at one point but the count (on openSID) goes back to zero immediately afterwards.
I'm 99% sure I've sorted my earthing issue and no longer have any performance reduction issues.
Doesn't appear to be a classic failing DIC symptom since they're not occurring en-mass under high load, rather just the odd misfire whilst holding a steady rpm but I'm starting to think I do have a dodgy DIC, or maybe have a dry connection somewhere.. Maybe just bad batch of fuel??
Plugs all look clean and as it's not actually causing any major issue, I'll probably just ignore it for now .. just annoying ..
Do you use dielectric grease on the plug connectors ?
I think you are supposed to, but I don't have any, and have never got round to getting any, so guess what.
This just happens when on a constant / light throttle does it ?
I still have a tube of silicone grease that I bought from Maplins before they stopped trading. It has a very high electrical resistance and is a perfect substitute for dielectric grease.
One common cause of apparent DI problems is the earth wire connected to the thermostat housing. It connects to one of the bolts and reconnection is often missed when a thermostat is replaced.
I've had a tube of silicon grease in the shed for a few years, it come out each year for this very purpose. However i just smear it round the top of the rubber boots on the DIC connectors. I'm sure Ive read in WIS that this is what you're meant to do, to keep moisture out and prevent arcing to the head?? Seems counter intuitive to me to put a dielectric grease on the actual connectors, I just clean them with IPA.
Thermostat housing earth is good Will, my issue was with the intake manifold earth, stripped thread, high resistance when the engine was up to temp, that's now sorted..
That makes much more sense to me now, I had never looked into this at all, thanks.
I know some people put vaseline on battery terminals...... I won't and remove any I see, horrible stuff for interfering with a good connection
I see you have already changed the CPS, and assume all the cabling / connections were fine.
Have you any basis for believing it is ignition rather than fuel ?
Can you identify that the misfire is on one particular cylinder, rather than being spread across them all.
Just a couple of ideas for you
From the last techII session the count was higher on one cylinder by a factor of 10. Could be a dodgy injector, that's also on my list.. Fuel filter already replaced, pump a possibility too..
What you are doing with the grease on the rubber boot ends is correct. The last new Saab DI was pre-greased on the rubber only.
I doubt it is fuel pump related. The system runs at a pressure with injectors open for a certain duty cycle to provide fuel that the ECU calculates.
Let's say that the fuel pump switches off for a second, then restarts. The result for that second would be a drop in fuel pressure as residual pressure allows fuel to flow through the open injectors. With the drop in pressure there will be a corresponding reduction in the amount of fuel actually delivered, which would make the mixture a little lean across all cylinders, rather a single misfire on one cylinder.
Of course T7 being what it is, it will then try to adjust idle speed and increase fuelling based on the lambda readings.
Does that make sense ?
The fact that you have one cylinder where the problem is greater would have me looking at swapping plugs and injectors between cylinders, to see if the misfires follow either of those changes. Just an idea.
Injector issues can of course be as a result of problems with the wiring, so even a fuel misfire becomes electrical
Thanks Will, I try to follow the WIS service guide and thought I was on the right track.. In fact I was worried I'd managed to somehow contaminate the terminals with silicon this time so took the DIC off and gave them another clean with IPA..
Makes perfect sense carrera the pump would of course affect all cylinders, I'd not actually thought along those lines to be honest.
The fact it's intermittent makes me thinks it's electrical, or dodgy fuel.
The manufacture date on my DIC is 09 so obviously new to the car, but that doesn't necessarily mean it was 'new' when put on the car.
Injectors is top of the list and I wish I'd known about switching to green giants when I went stage 3 as opposed to the 3.5bar fuel reg. Obviously if it is electrical new injectors wouldn't solve the problem.. I didn't replace the pollen filter today as I ran out of time but when i get the chance to do that I may see if I've got time to swap the injector round on the dodgy cylinder too.
If you send the injectors off to get cleaned (normally about a tenner each) you will get a before/after flow test result, which could confirm or not a possible cause. Of course you need to label them individually when you send them...
Think I'd sooner just replace the injectors if it came to that, being our only car I can't have it sitting immobile for any great length of time.
I've just got back from the Gower, so a few hundred miles, and I've not seen any more misfires on the motorway using cruise control or under load. Only a few misfires registered on overrun, which I believe I'm right in thinking is to be expected.. Really think I may be getting bad fuel from my local Shell garage. Might switch to Esso and see what happens..
V-Power or regular ?
always V-Power
Well, there's that suggestion flying out of the window then :)
Try some regular - good enough to eliminate the bad fuel, I would expect the injection system to be clean if you only use v-power