get your thinking caps on....what could cause this problem?

Tried starting my engine for the first time in ages.....newly built 1776, not yet run in fully...

Anyway, it ran like a pig and wouldn't idle....last time I ran it, it was bob on...been through the usual suspects, checked and rebuilt the carb and dizzy, checked for vac leaks etc. etc....couldn't find a thing....very frustrating

Anyway, I've swapped out the stock fuel pump for an eleccy one (half decent Webcon, with the correct pressure for the carb) Power to the pump is supplied from a 3 way Oil pressure switch (link here) as fitted to late '79 buses. It's a nailed on modification so this isn't the issue....the problem is, as a fail safe, power to the pump is disconnected when the oil pressure hits 4 psi, thereby cutting the fuel supply...

Sooooo, this is why my fffing engine won't idle....low oil pressure (even on start up)....the question is, what's the most likely cause of low pressure (oil light fully on....not flickering)?
Prior to today, the engine has been standing....turns freely, starts but cuts

Any helpful suggestions, as always, most welcome....

I've spent a good 13 hours breathing in noxious carp, up to my eyes in petrol today and my love for all things Aircooled is at an all time low....

 

Pm me your postcode
A road trip would do me good at the moment

 

Put it back how it was when it ran right. Ie put a standard oil pressure switch in to check the light. Wire pump direct suck it and see!

 

think I might do this ^^^ to rule it out....total arse of a day tbh...

Trust me...i'm no company at the moment....but appreciate the offer

 

Neither am i but ...............................

 

Cystitis. It's obvious.

 

Thanks Snotty...thank goodness it's not terminal

 

Slightly more sensible, then: has it ever run well? Valves? Camshaft one tooth out?

 

yep....it ran really well on Dells and/or Weber prog, with either 009 dizzy or an electronic 034...so pretty sure it's a good build....just can't fathom why the oil pressure should be so low (according to the sensor) at start up....substituted a new (known good) 3 pin sensor and still have the same issue....going to try a stock 1 pin and wire the fuel pump direct as suggested, but there's no reason why the three pin set up shouldn't work....

 

Air lock? Do you have external filter? Disconnect and spin it over until your assistant tells you oil is coming out then reconnect.* I've had same with one new external filter install. Don't run it with no oil pressure!!!!!! 13 hours faffing about with no pressure!!!! Time for a rebuild...

* Edit, or remove the oil pressure switch and wait for oil to come out here.

 

Knowing bobbins about these engines.....

You've confirmed it's low oil pressure engine side?
You've confirmed there is no issue with the oil pressure switch?

From what I can tell, you are saying it's running roughly due to the fuel pump not receiving the correct signal from the oil pressure switch?

 

I thought it may have been an air lock...had the same problem with a golf....I undid the filter a few turns (oil peed out), but I didn't turn the engine over with the filter loose....will try that, Ta!

 

that's the quandry....I don't actually know if the oil pressure is too low...I'm going off the warning light, which takes it's cue from the pressure sensor and cuts the power to the fuel pump....tried two sensors, both good quality, same issue, so either it's a fault with the wiring (which is doubtful) or the sensor is right, and the start up oil pressure is too low....which is a big worry

 

it's feasible that the fail safe pressure on the sensor is a couple of PSI higher than the equivalent stock sensor and as it's only idling, it's 'failing safe', but the oil light seemed to stay solid, rather than flickering, when I gave it some more beans on the throttle...besides which, the pressure should be right up there as the engine/oil wasn't especially warm...
I'll go and throw some spanners at it...fingers crossed

 

Really? I'd be extremely unhappy if any form of sensor had a tolerance of around 50%!

I take the oil light uses a different sensor? Or at least, what did it use before you put the new one on it?

Logically - you have an oil light sensor stating low pressure, you have an additional sensor demonstrating it thinks you have low oil pressure, and a replacement of this showing low oil pressure.

Is there a way of simply measuring for low oil pressure?

 

the new sensor was specced to earth on at 4 PSI, same as stock, but if it's marginal and linked to the fuel supply then that'd cause the stalling....my main concern was why the sensor should be reading such a low pressure
Anyhoo....just fitted a stock sensor and re jigged the wiring to the fuel pump and relay...oil light comes on with the key and goes out when running....
So it runs and idles (badly) which is probably down to the dizzy/carb/usual suspects.....feckin' frustrating

 

Probably due to wrong oil being used

 

Your idle speed is too low or you have forgotten something.
Like if you have an external filter added it needs about another litre of oil above stock. And if its like my setup it needs about 4 litres and turning over for about 30 seconds before the oil light goes out the first time after refilling with oil .

 

Have you got the idle bypass valve and/or run on solenoid wired up? It's on the left hand carb on my twin solex.
You can test them dead easy by putting the ign on and touching the wire on, they should click loudly...

 

Could it be crappy fuel if its been sat a while?