MPG still looking no better. Doing 1200-1500 miles over a long weekend, so I'll know for sure by then. I wonder if running a bit on the rich side has caused the cat to block up. I think that's my next point of investigation. Air filter, fuel filter, pump timing, intercooler are all checked and good. I now have an MOT, so I'll go ahead and customise the catalyst.
About 45 on the trip to Scotland a few weeks ago. Driving very sensibly about 75 on the motorway. I'm running Miller's diesel additive in it at the moment - 1/2 bottle to a tank of fuel. Based on the miles driven before it got to the 3/4 mark (190ish instead of 150), I'd say it's improving a bit, but it's not 100% clear till you get to the end of the tank. Will keep monitoring. Idle is slightly improved but still rough - not sure if the improvement will disappear when I stop using the additive.. I think there's a part-blocked injector problem too. I was going to buy some BG fuel system cleaner and run that through as well. Need to wait till the end of the month, as I've spent too much already this month, between Xmas credit card bills and buying a welder.
Would the pump timing being at the advanced end of the spec hurt MPG, or is it fine as long as it's not pinking?
Im not sure to be honest, i need to do my cambelt and get my timing checked and adjusted because i only have the free vagcom. But mine has done 206k and im getting 57mpg without trying. Its improved slightly since m1ke sorted me a tuned 16bit ecu conversion. It could be that my timing is spot on though, i dont know. The bum dyno says the car feels fairly spot on with pull and feel, and my gps dyno states 111bhp. So perhaps its ok. Yours could still be injector related mike.
I had my pump timing adjusted the other week.... Setting the basic timing on VCDS sets injection timing for cranking and also establishes the timing window.. One the car is idling it should take its SOI (start of injection) trigger from the lift sensor on injector no.3. The IP does have an advance mechanism but again if the static timing is wayy too far retarded the advance mechanism may reach its full advance position whilst it still be short of what is required. Chaps on tdiclub reckon it is best to set static timing towards the top line of the graph. A more advanced injection does increase bmep at the expense of increased CO emission. I'm happy to have slightly higher CO, no EGR and better mpg thanks! This does not affect your MOT test as diesels have a smoke test and the gas mixture never comes under scrutiny.
Thanks for the input. Sounds like mine is about right then, and I should stick to injectors as the next thing to try. Sorry, what's BMEP?
I think injectors are a likely cause. Out of interest, was the mpg better/worse or the same before the head work?
Better, if anything, which was surprising, as I cleaned out all the ports and inlet manifold, relapped the valves, and blocked off the EGR at the same time. Cleaned out the intercooler too, although there didn't seem to be much goo in it. However, the MPG was steadily getting worse as the weather got colder (stuck thermostat) before its little cambelt 'incident' There are a lot of variables though - pump timing, cam timing, etc. I'm pretty sure the cam timing is right as I have the right tools, and packed out the cam lock with feeler gauges. I split the cam pulley from the cam end and fine tuned it too. There is a smidge of movement in the pump locking pin, but the timing has been rechecked with VAGCOM. Used the same type of head gasket as well (2-hole), new manifold gaskets and injector seals, etc. I was running it very gently for a few weeks after the rebuild, so I'm wondering if it just blocked up the cat with soot. Latest tank is a needle width above halfway at 300 miles. Recent tanks have had less mileage at halfway (260ish) - only recent change is running miller's diesel additive. So things may be improving. It could be that the injectors have been gradually gumming up, and I didn't really notice till after the rebuild. Just picked up some BG244 fuel system cleaner. Will finish the current tank on Millers, and then chuck that in with the next full tank - or would you recommend half a tank to get a stronger mix of the cleaner fluid? I think you said you used to sell it? I don't believe in additives, generally, but the Millers stuff does seem to be making a difference. Whether that's injector performance or just fuel improvement, I'm not sure.
Thats interesting. Im just about to do a cambelt change but in borrowing the tools from a garage. Fingers crossed i dont mess it up. Im looking at paying for a mild head rebuild and getting the inlet and head polished. Iv done the turbo elbow myself. Out of interest you didnt use a bga head gasket did you? I put bg on a 1/2 tank but im lead to believe by the rep although a full tank is recomended, half a tank is fine. If you use less than 1/2 a tank it wont do any damage atall, it just doesnt get enough time to work before it runs out.
It's an Elring head gasket - bought from GSF. If time to act is more of a factor than concentration level, I'll wait till I refill the tank. It gives me a chance to collect the MPG figure from this full tank as well, in that case. Gives me more of a before/after comparison. I don't think polishing inlet ports makes any difference. When I had the head off, it looked to me like there was a restriction in the asymmetric inlet port, around the nose of the valve guide. I opened that out a bit, and tried to open out the port at the back of the valve head. I tried to get it fairly smooth, but only with 80 grit paper - no polished finish. It was all guesswork, and I could have made it worse just as easily as better, but I thought I was probably doing some good.
Cool. Good to know. Im very sure the polishing the the turbow elbow made a difference. Although that could be my imagination. I ask about the headgasket because bga are terrible. Elring are good. Have you checked compression?
Maybe the turbo elbow would help. I guess the air doesn't have to be made to swirl till it hits the ports, where the asymmetric design should take care of that.
Perhaps the gasket, although marked as the correct cutouts, was wrong, and too thick, incorrect at the factory? A compression test would show up that.
Interesting idea. I'll see if I can measure it compared to the old one - where the lip sticks out of the head. I think it's unlikely, but should be quick and easy to check.
Thats ok then, having worked for a motorfactor until recently, i have seen a fair few wrongly packaged head gaskets. Not alot else it could be is there? Im stumped, im not an expert or a mechanic, but all i have said is just my deductive thought process so im not sure where else to look. I guess injectors are the only unknown at the moment. And if the spray pattern is worn and the holes have been elogngated by age and general wear and tear, they could explain the poor mpg. TDi's are quite good at hideing worn injectors compared to a mechanical diesel. If you have not already, and dont have it from factory, might be worth fitting cruise control to help mpg on your longer runs.
