Misfire cured ???

[Alan]

I've normally run my 150 Tid on supermarket diesel and never believed it was inferior to branded diesel but....

The misfire initially was only for 10 seconds or so on cold starts, I checked the glowplugs and found 2 were not working.

4 new glowplugs and no misfire, but it came back. This time slight but noticeable through most of the rev range.

No 3 injector wiring changed and no misfire, but it came back. Only on cold starts so checked the glowplugs, all OK but swapped them in pairs with the old ones anyway just to check but it didn't help.

I suspected a temp sensor but as MPG didn't seem to be affected decided to see how it was when the weather got warmer.

It slowly got worse, to the point where it misfired all the time but only below 1500 rpm.

Full throttle below 1500 rpm and no misfire light throttle it misfires made me think blocked injector.

In the last 6 weeks I've done four 200 mile trips and two 100 mile trips towing a 1300kg caravan and two 200 mile trips solo mostly on motorways.

All these miles were done using branded diesel ( mainly Shell ) and since then I've done around 300 miles of mixed running also using branded fuel.

For the last 400 miles it's been running great with no sign of a misfire.

Is it because the 1000 miles towing at 25 mpg cleared the injectors is it because I've not used supermarket diesel or is it something else ?

             Alan

[collywobble]

I have a cousin who works at a large oil refinery on the south coast of England and he tells me that supermarket fuels do not have the additives that the branded fuels do. I personally put a bottle of 'Forte' fuel additive (recommended by Saab) in the tank once a year and only use branded fuels in our 2.2 TiD.  Some years ago we sold a Peugeot 306 diesel to a friend and his wife only filled up at Tesco - they had to have a new injection pump a few months later which I put down to poor quality diesel.

[Audax]

I personally put a bottle of 'Forte' fuel additive (recommended by Saab)

Not true, that was just Saab UK teaming up with Forte in the UK and marketing talk, I once had an argument with a forte rep about this when he told me that Saab recommended you use forte additives in engine oil, but if you look at wis it it very clearly tells you to use no additives.

Anyhow, I can pretty much tell you for a fact that a misfire like this won't be down to supermarket/branded fuel, if it is then there was either a bad batch of fuel or there is something wrong with your car if it can be triggered by the fuel you put in. One the most common cause of misfires on cold starts with the 1.9 diesels was cured by an ecu software update, it might be worth finding out if you have this update applied to your car as weather, temp or similar conditions might have caused the right set of parameters for this to cause a problem. Or, possibly your EGR valve (or manifold flaps) is clogged up or sticky and not working 100% and causing a problem but not enough to put a check engine light on.

[Alan]

I was thinking more of 70,000 miles on supermarket fuel rather than one bad tankfull causing it lol.

It should have all the ECU updates available to last June when it went for it's service as that was one of the things listed on the sheet.

There is no play on the manifold flaps, I had a feel at them when the glowplugs were changed but they could be sticking, under what conditions do they move ? would I see them move if I blipped the throttle or does the engine have to be under load ?

EGR valve is original ( 2007 ) and has never been off so would probably benefit from a clean.

I don't think it was down to weather conditions etc or a temp sensor as it was misfiring all the time ( below 1500rpm ) no matter what the weather was like and has not missed a beat for the last 400 miles.

At the moment there is no problem so nothing to fix. I'm not a fan of additives so I'm just going to keep it on branded fuel and see how things go.

The type of driving it gets, I don't normally go over 3500rpm but often use full throttle to get it there and it has weekly 30 mile motorway runs at 75/80. 

[Max Headroom]

OK my diesel runs extremely noticeably like a bag of nails on supermarket fuel so I stopped using it.

Sometime after occasionally using supermarket fuel (namely Asda) - maybe a coincidence I dont know - the car developed a misfire that was intermittent but could sometimes last a few moments or an entire journey.

Software update had been done at a previous service and also some wiring modification on the injectors, but I still had the misfire.

Sometime later the dreaded flaps on the inlet manifold meant an expensive manifold change, but even after that I still had the misfire.

Frustrated I chemically cleaned a very delicate sensor on the back of the manifold that was unbelievably crudded up with coke  - cant recall what sensor it was but someone here will know. I still had the misfire after that.

Finally, I removed the EGR valve and found that it had actually seized up! It didn't even move! I cleaned it and lightly lubed it with some high-temp aircraft grease, and lo and behold.... misfire seems to have gone.