Injection problem Smart Merc CDI. Frankebrick

[touchwoodsden]

I have an interesting problem which I’m trying to resolve with my Mercedes Smart diesel engine BMW K100 .
Just before Christmas, I had been out and written about 40 miles or so. Bike was going great.
It started to get slower and slower and slower estate was overheating and about to seize.
I stopped and the bike ticked over it was fine.
I switched it off and started again, no problem.
I rode off and it was absolutely fine for about half a mile and then gradually started to slow.
I found that by switching the electrical for a couple of seconds and back on again, everything reverted to normal for a while. That’s how I got home.
I put it in the garage when I got back home and thought that I would get back to it a month later when no doubt, it would miraculously have cured itself! (As you do!!).
Well, as you might expect, it hadn’t!
As soon as it gets remotely warm, after even a couple of miles, the problem exists.
Even if I leave it ticking over, it will eventually die and restart but not tick over.
Switch off the fuel pump and back on again and it’s normal for a while until eventually it goes slower and slower.
My first thought was low pressure fuel pump but the low pressure gauge is showing one bar which is fine. It doesn’t change from being cold to hot.
I have to attach the laptop and record what’s happening so that Simon from Specialist Control Systems can investigate.
Whatever it is, it would appear to be something really simple.
What isn’t simple is finding what it is!
I must admit, that the service from Specialist Control Systems is absolutely fantastic.
I have just got to take a break out of work to go out on the bike for an hour on a dry day now. It may be some time!

[coachgeo]

Sounds like an air leak in fuel system. As vacuum builds over time (which it makes it look heat related) a little flap of worn rubber inside a fuel line gets sucked further like and further open like a valve increasing amount of air sucking in. Once your vaccum pressure drops (turn off bike, etc) the little internal flap of old fuel line returns home and covers the air leak.

[touchwoodsden]

Sounds like an air leak in fuel system. As vacuum builds over time (which it makes it look heat related) a little flap of worn rubber inside a fuel line gets sucked further like and further open like a valve increasing amount of air sucking in. Once your vaccum pressure drops (turn off bike, etc) the little internal flap of old fuel line returns home and covers the air leak.

I know that there is no air leak in the low-pressure fuel side because the pressure is a constant one bar.
The other reason is that the low-pressure pump is submersible in the fuel tank (there is no vacuum on that pump, it does not suck the fuel out of the tank). At one bar, there are no leaks.

However the rubber flap theory is really interesting.
For what they cost, and the time involved, it might be worthwhile just replacing the fuel pipes. At least then, that can be eliminated.
Thanks for the input. I appreciate that.

[touchwoodsden]

I have had another idea. I will simply disconnect the fuel return from the tank and repipe it back into the tank so that it’s just going round and round and see whether, after 5 or 10 minutes or so, the flow decreases.

[gilburton]

Good idea and if you temporarily replaced them with clear tubing you would indeed see the fuel flow lol.
It wouldn't be something stupidly simple like a blocked fuel tank cap??

[Stuart]

I remember Neil saying that you must have the correct fuel filter on the engine. Petrol & diesel filters are easily mistaken on the Smart & used in place of each other. Could this be causing slow fuel starvation?

[touchwoodsden]

You know something, the blocked fuel cap vent never even occurred to me.
I had it once on an MZ when my tank bag covered the hole in the cap.
I am going to investigate that.
What would not make sense of course is that turning the fuel pump off and back on again turns things back to normal for a short period of time.
It did occur to me that it may be the fuel filter because this is a petrol filter which is the petrol filter inside the BMW fuel tank.
It’s a substantial piece of kit because it’s designed to run at a couple of bar pressure. I’m not aware that anything else would work inside the tank although I could easily bypass it and fit an external filter easily enough.
When I disconnect the fuel pipe and have it open circuit, I guess it will reveal all.

[touchwoodsden]

Don’t you just love it when it’s something simple?. Unfortunately, it is clearly not something simple.

It’s not the vent unfortunately (I was hoping and praying) and the fuel on free flow continues to go around and around. After five minutes the fuel pump does start to make a strange noise but the fuel continues to flow. I think this may be low pressure fuel pump related and although BMW genuine ones are expensive (about £250), aftermarket ones are cheap enough (about £50) although my understanding is that there are 2 different sizes and so, I will have to get it out to see which size it is before I can get one.

[gilburton]

Forgive me as I am not familiar with your setup but do you need a pump/filter in the tank??
Does the Smart engine have its own pump and would gravity be enough to feed it?
On a car obviously you need a lift pump but now as the tank is higher is it needed?
I was just thinking along the lines of does the Smart pump need more fuel than the tank pump can supply or is the smart pump overcoming the tank pump/filter??
Personally if it needs a new tank pump I might be tempted to get an external car pump/filter.

[touchwoodsden]

No need to apologise.
The setup is not that different than on the Smart car apart from of course the Smart uses a vacuum pump which then feeds the high-pressure injector pump whereas on the bike there is no vacuum, it’s all pressure..
There is a low-pressure pump which is in the tank and the high-pressure injection pump.
The high-pressure injection pump needs a low-pressure fuel at one bar /15psi although the bike was running satisfactory with a pressure of about 1-2 psi.
I have played around with the pressure and it doesn’t make any difference.
It seems most unlikely (confirmed by the ECU manufacturer and designer) that the very small head of fuel which, with an almost empty tank is only going to be about 50 mm, would be enough to supply the high-pressure pump.
I would have thought that any pump would be better than no pump at all.
Because injectors have such tiny spray orifices, the filter is absolutely imperative of course.
I have thought of an external pump although it would mean rejigging the piping inside the BMW tank and there would be no going back. It would also mean mounting it somewhere in the BMW pump is not known as being problematical. That’s why, for now, I’m inclined to stick with the BMW pump.
Please bear in mind that the bike has been running brilliantly for about 1000 miles and this problem happened all of a sudden

[Crazymanneil]

Sounds weird to me. Which side of the fuel filter is your low pressure gauge on?

Is the issue isolated to resetting the low pressure pump or could it be that resetting the ecu is actually what resolves it each time?

Neil (still occasionally here)

[touchwoodsden]

Well gentlemen, I have news.
The FrankenBrick rides well once more.
I emptied and removed the fuel tank and removed the fuel pump and the filter.
Please bear in mind that this was a completely clean installation with a new filter.
The very fine gauze on the bottom of the fuel pump (which actually needs replacing) was full of some kind of a very fine fluff. I don’t think it was enough to stop the fuel flow completely but I think it was probably contributing to the problem.
The only way I can think it got in there was from the polishing mop when the tank was polished and some of the fluff went inside the tank.
Probably more importantly, I decided to take the filter apart. That really surprised me. Although it was clean enough, the element had been crushed clearly by some kind of great pressure. How, I have no idea. Why, I have no idea other than (I cannot remember) what I may have done was to turn the ignition on with the fuel outlet tap (I have taps on the in and out line to facilitate tank removal) and hence, the full fuel pressure would have gone on to the fuel filter although I cannot see why it would crush it because the pressure would be all around. The filter element itself does not look particularly dirty but without a microscope, it would be very difficult to tell.
And here is the offending part.

20170325_151248

I had a new filter already on the shelf and I have bought another couple. If it happens again, I reckon I will just have to look for another filter arrangement.
I would like to take the opportunity of thanking people for their thoughts.
Kind regards.

[Crazymanneil]

Looks like combination of flow, pressure and partial blockage over time to me. As the filter becomes more plugged it resists the fuel flow. Then when engine demands more fuel the pressure drop across the filter becomes larger and crushes the filter. Also explains drop in power at higher demand but OKish at idle

Do you have a fuel pressure regulator? Where is it in your system?

Similar happened to my bike but it was cutting out due to fuel starvation since my fpr was installed upstream of the filter (and is still in same place for this reason). Whatever filter you use must also stop water.

Neil

[gilburton]

I still think that the engine pump is trying to demand more fuel than the standard bike filter can supply and is collapsing it inwards.
As has been suggested before it may be because the petrol filter can't handle the viscosity of diesel?
If I remember correctly the filter is just a canister with a tube each end so would it not be posssible to replace it with a larger disposable high flow filter if it happens again?
Would it be possible to eliminate the internal filter with a simple loop of tube and place a proper diesel filter/ water trap outside the tank?

[touchwoodsden]

UPDATE: The new petrol filter has been removed from the tank now that I have ascertained what the problem is. It’s a pain in the backside inside the tank to get at anyway and I’m now going to put an external filter on. The problem of course is that there is an acute shortage of places to locate it and an acute shortage of bracketry.
For now, I’m just going to probably zip tie it to “something” while I do a bit more figuring out.
I still have the whole instrument thing to resolve yet because at the moment, I’m running using a bicycle speedometer!
I need a water temperature gauge. Peace of mind.
We have a credible explanation for the very fine fibres in the mesh of the fuel pump screen. The breaking up of the filter.
I just don’t think the filter element is up to taking the more viscous diesel fuel which is why it collapsed.
If you look at diesel filters on cars, they are huge.
I don’t have a regulator but I do have a pressure gauge and a small clamp on the pipe with which I can tweak it.
To be honest, the high-pressure pump is not particularly sensitive to low pressure supply. This constriction clamp is just before it returns to the tank.
Looking at the moment at car filters

[Stuart]

Probably best to mimic or use what was on the original car setup if possible. As Neil knows, our filters are zip tied under the Tiger's tank.

[touchwoodsden]

I have fitted a full-size car filter
http://www.ebay.co.uk/itm/260357383770? ... EBIDX%3AIT
immediately behind the fuel injection pump between the frame rails and held with a jubilee clip to a bracket on one of the frame tubes.
You will note that the inlet and outlet go in opposite directions which would have been great if I was using it sort of in-line there was nowhere to mount it and when it’s full of fuel it’s not going to be particularly light.
Because I need one of the fuel lines now to do 180° and I don’t trust the robber pipe not to kink, I put some quarter-inch copper fuel pipe the inside with the 5/16 rubber pipe and that allowed me to put quite a nice bend in it without it kinking. The copper stays in place.
When I come to replace the filter, I will replace it with this one
http://www.ebay.co.uk/itm/351839961251? ... EBIDX%3AIT

Because it makes the pipework neater