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I had thought about a vapour lock. But I recently put a pressure gauge in the hp fuel line which indicates all is well on that side.
Robin
I don't properly understand the 'Vapour Lock' phenomenon but unless the vapour lock is in the pump, I would expect the test pressure to be OK, but for some reason the injection mechanism (or carburettor) seems unable to function properly to feed vaporised fuel into the induction side of the engine.
I need to read up/research this because it seems pretty fundamental. I am in correspondence with somebody who seems to have some experience of temperature control in IC engines.
I know my carbs are being supplied with cool (liquid) petrol but the engine refuses to fire, when a few seconds before, it was running well. I know this isn't exactly your problem but it's similar, it seems to me that as soon as the engine stops and induction ceases, the carb venturi heats up, or to put it another way, ceases to be cooled by the passage of air in depression, which cools the air and the carb venturi. The latent heat in the carb body then immediately warms the venturi and the vaporises the fuel in the jet, apparently preventing the venturi from sucking liquid fuel from the jets.
Allowing the engine mass to cool below a critical temperature, allows the engine to start, because the liquid fuel is no longer vapour, the main jets which are not designed to pass vapour therefore the mixture isn't rich enough to start the engine.
That's the rough bones of my theory but it needs some meat, in the form of accurate temperature monitoring at the critical points. Some research as to what temperature ethanol bearing fuel vaporises, also what effect atmospheric depression has on all this, the boiling point of liquids varies with atmospheric pressure, therefore the depression in the venturi may affect the boiling point therefore the formation of vapour which seems to stop the show. Wish I was a chemist! LOL
A fueling problem was my first suspect. So I changed the fuel "route" so that the high pressure return goes straight back to the tank without the possibilty of it recirculating through the hp pump and getting overheated. It may still be worth trying a tank of the more expensive stuff though. I'll try tyat next time I fuel up.
I just came back from a run without the alternator working. Still has the missfire - so that eliminates that.
One other thing that is odd though is that the characteristic of the missfire has changed since I changed the ECU. Something else to think on....
I have done some thinking and poking arround on the E30 zone web site. It seems the only transducers that really affect the engine management are the Crank Position Sensor and the AFM. The other various sensors are only use to tweak the fuel mapping depending on temperature etc. It shouldn't be possible for them to cause a missfire. I have changed the CPS. And I don't see how the AFM could cause the pattern of missfire that I have. So on to new ideas...
Next step is a new set of leads - although that seems to be grasping at straws as the existing leads look fine. But I didn't replace them when I built the car so they could be the originals which makes them 25 years old!. They are Beru which is one of the OEM brands. I have decided to DIY them as a new OEM set is ££££ It's cheaper to buy the proper crimping tool and the various bits required.
At this rate I'll have a complete new engine management system.....
There is a very easy check for the integrity of the plug leads, lift the bonnet after dark and blip the accelerator, if you have a minor firework display they are leaking.
The other thing is to get another, known good ECU. I had the Devils own job with the original motronic 1.1 system I had, and when I finally swapped all the engine loom and management for 1.3, I opened up the old ECUs to find and absolute horror show:
I have done some thinking and poking arround on the E30 zone web site. It seems the only transducers that really affect the engine management are the Crank Position Sensor and the AFM. The other various sensors are only use to tweak the fuel mapping depending on temperature etc. It shouldn't be possible for them to cause a missfire. I have changed the CPS. And I don't see how the AFM could cause the pattern of missfire that I have. So on to new ideas...
Next step is a new set of leads - although that seems to be grasping at straws as the existing leads look fine. But I didn't replace them when I built the car so they could be the originals which makes them 25 years old!. They are Beru which is one of the OEM brands. I have decided to DIY them as a new OEM set is ££££ It's cheaper to buy the proper crimping tool and the various bits required.
At this rate I'll have a complete new engine management system.....
Robin
Robin
Have you considered fitting new plugs/sockets to the loom wires that connect to all the sensors? I had a broken connector to my TPS which caused me problems similar to yours, and I only found it by luck - I caught a wire with my sleeve while poking around at something else and it disturbed the engine revs.
There was a fractured wire/pin contact inside the connector which gave an intermittent fault that was impossible to diagnose.
My £5 is still on it being an electrical fault..........!
Yesterday, for some reason, I decided I would strip down all the fuel system just in case there was some odd problem or obstruction. I lined up an old icecream box under the swirl pot in attitipation of 1 litre of petrol pouring out and removed the bottom fuel union. Only a teacup of fuel came out. The rest of the contents was air. Err - that's odd...
It turns out that the low pressure pump, an expensive Facet Red Top, is completly dead. Open cicuit in fact implying some catastrophic failure of the internal electronics.
So - the Walbro HP pump had been sucking fuel directly from the tank through the empty swirl pot and the dead LP pump. Very impressive - but I am guessing responsible for at least part of my problem. It begs the question of course whether the LP pump, swirl pot, HP pump set up is really necessary. Anyway rather than redesign the fuel system I have ordered a new LP pump (more ££££). Should arrive next Tuesday - I can't wait.
I have to say though I am not convinced that this is 100% the problem - but it must have been at least a contributary factor.
Well at least you have something to go on, and I almost got it right when I suggested a fuel problem.
The down side is, and I really don't want to spoil your weekend, but the extra strain put on the HP is the reason for the cutting out and restarting a few minutes later. This is something I have experienced myself and even though my HP was only a few months old it would cut out through overheating. In my mind the pump was brand new it could not possibly be that but the extra strain on it meant that it would run, get hot and then stop, but you could leave the engine running all day. So even after changing the LP you may still experience the cutting out problem it depends on how overworked the HP has become. At least you can easily access your pump, mine is in the tank and a right pain in the backside every time I was fault tracing. Don't get despondent at last you know you are on the right track,and my apologies for the bad news.
Phil.
Hi Robin,
I feel like I'm becoming the Harbinger of Doom, but the LP must have failed for a reason as most pumps go on for years. Are you sure there is no obstruction of the pickup pipe in the tank, certain that the pickup pipe isn't touching the bottom of the tank and therefore covering the end of the pipe which in turn will cause premature failure of the LP and the snowball effect on the HP.
I'm beginning to feel I should be there to help you as I am becoming as frustrated as you in solving this problem.
Phil
If the HP pump could drag sufficient fuel to run the engine at all then the suction pump can't be that restricted. Normally a suction pipe is cut at an angle to prevent that sort of blockage. Reasonable point though. Is it possible to peer inside the tank or pull the dip pipe? Gently blowing on it should say if it's restricted... Does it have a filter on the end?
In order to check the flow it should be a simple matter to run a temporary pipe into a container and run the pump for say one minute, then measure the fuel?
My mind keeps coming back to this being a temperature related fault. The symptoms occur when the engine has been running for some time on a warm day and it has been gradually getting worse?
I think it's important to keep that at the top of the mental whiteboard.
This is the first concrete fault that has been discovered, until it's rectified no further solid conclusions can be drawn.
Having eliminated most if not all of the electronics, we seem to be left with the fuel system components and perhaps the fuel.
Given the pump seems to be US, why not slice it open and try to establish what has happened inside. That might be good info for us all, I think many of us rely on these Facet pumps, although I have fitted two, not trusting these new fangled things!!! The SU's were notoriously unreliable. That said, my understanding is that the Facet pumps work in exactly the same way just that they don't have the mechanical contacts. A plunger is pulled by magnetic pulse against a spring. The spring pressure presses on a diaphragm and pressurises the fuel through a one way output valve. So the pump shouldn't be overloaded by being unable to suck fuel, it should just lie idle, or pulse normally, as though trying to suck fuel, that shouldn't overload or over load the windings or circuit.
As Robin has already stated, the sportster fuel tank is very basic. There is no pick up tube - just an outlet but welded on to the bottom, and a return slightly higher up the wall of the tank.
I can catagorically state there is no blockage in tge tank - the rate at which the petrol pissed out when I disconnected the LP pump is testiment to that lol.
I agree its unusual for a LP pump to fail specially as its a genuine facet. Its completly open circuit so its the electronics that have failed. I am in the process of taking it to bits but it is very well made and seems to be filled with some potting compound.
I am using a sytec swirl pot. I have stripped it and its clean as a whistle.
New pump arrives Tuesday. Just in time for the heat wave :-)
Sytec told me that their HP pumps will burn out their vanes in seconds if they are allowed to run starved of fuel (the petrol acts as a coolant): so though your HP pump may run, it would be a good idea to test the pressure it puts out after you have fitted your LP feeder.
MartinClan wrote:
I can catagorically state there is no blockage in tge tank - the rate at which the petrol pissed out when I disconnected the LP pump is testiment to that lol.
I agree its unusual for a LP pump to fail specially as its a genuine facet. Its completly open circuit so its the electronics that have failed. I am in the process of taking it to bits but it is very well made and seems to be filled with some potting compound.
I am using a sytec swirl pot. I have stripped it and its clean as a whistle.
New pump arrives Tuesday. Just in time for the heat wave :-)
I have fitted the new LP pump. And - what a surprise (not) - the HP pump is much quieter in that you can no longer hear it. (Just as when I first built the car.) Fuel pressure looks healthy - as one of my efforts in diagnosing the problem I have a tee fitted for a fuel pressure gauge. I hope I haven't damaged the HP pump as I already replaced it once when first starting to trace the problem.
So far the damage to the wallet has been:
HP pump, filter and non return valve (£££)
Crank position sensor (£)
Coil (Borrowed from Peter)
ECU (££) actually would have been (£) but I bought the wrong one first time - oops.
HT leads and distributor cap (£££)
LP pump (££)
I discovered the LP pump problem just after I bought the HT leads and distributor cap which is a bit of a bugg€r. I haven't fitted them yet so they could well end up on Ebay.
On the plus side I found the coolant leak that I have had since the car was first commisioned, and the coil is now mounted in a far better (cooler) location. And the new fuel pump had a big note with it saying it was E85 compliant.
Drove to work this morning. I didn't experience the big missfire but I still not convinced things are 100%. As I started to suspect, and the reason for it being so difficult to diagnose, there may have been two problems. Which means there still is one....
Tomorrow I have a longer run planned - weather permitting.
Cheers, Robin
BTW - I checked the old LP pump (4th time!) and it is definitely US. This time I just did it the simple way of wiring it to a battery. I checked the new pump before I installed it and I discovered a continuity check is a waste of time as the electronics in the pump means you don't get any sensible resistance readings. Indeed in one direction it is infinite. I guess the pump has an internal blocking diode to stop damage if wired the wrong way round.
Sounds good, and a nice ride out in the rain never hurt anyone. I have had a read through the previous posts and notice that your plug leads are quite old, or have you changed them, I would get out the old multimeter and check the resistance of all the leads, copper ones seem to last a lifetime but the carbon leads break down with age.
If you have new leads take them for a run out, and if the problem starts again swop the leads and see what happens. Your manual will tell you the ohms for the leads.
Phil.
My trip out yesterday went without a hitch. Round trip of about 60 miles in temperatures up to mid upper twenties. So I think I can conclude that the major issue was the low pressure pump. Only time will tell if there is/was a secondary problem but right now I intend to start enjoying it again!
