Fuel pump pressure?

[Maggo54321]

Hi, does anyone know roughly what PSI the fuel pump should produce on an 89 carb turbo?  I'm just tested mine and the pressure (on ignition before cranking) just before the fuel pressure regulator is 27 PSI which to me seems a lot for a carburettor car?

Just checked and it's a Lucas 4FP

[Maggo54321]

Scrap that, I've just read that the fuel pressure regulator will keep it at around 4.5 PSI by dumping the excess fuel back down the return pipe to the tank.  Even on full boost, it's unlikely to get above 12 PSI, so it does seem excessive for 27 PSI to be coming from the pump though.

[drdoom]

Doesn't the regulator have a pressure line connected to reference the output in harmony with boost?

[Maggo54321]

Yes, and I'm wondering if this is to do with my issue.  Basically, the car wouldn't start (another story - ignition related) but the carbs and ultimately the plenum filled with fuel (dripping out of the bottom of both).

I would have expected the floats in the carbs would have stopped the fuel intake (along with the fuel regulator valve) but I've check both and both are working fine.  So the only conclusion I'm left with is the pipe from the 4 way tee into the top of the fuel pressure regulator is forcing an awful lot of pressure onto the fuel pressure regulator and preventing it from opening and dumping the fuel back into the tank, then ultimately the carbs have flooded as it's too much pressure for the float valve (27 PSI).

So now left with investigating what pressure should be coming out of that tube and where it is getting it from.  Does anyone know?  It's the circles below.

Also, does anyone know which direction the 'non return valve' goes (in red also on the picture below).

Thanks all for any help.

[Sparky]

In 15 years I have seen 2 catastrophic FPR failures on Turbo Esprits.  Both failures overpressured the entire system and filled the plenum with fuel.  FPR replacement solved both.

[Maggo54321]

Fair enough, I will as a matter of course replace the FPR as they're a relatively cheap item (£60).

Has anyone any comment on the non return valve direction?  The manual is no help other than to say that the black end needs to go towards the carbs (which is no help if you don't have an original black and white part).  I'm guessing the black is in and white is out for the flow direction?

[Chillidoggy]

Zoom in to the diagram you posted.

[Maggo54321]

I have, what am I missing?

[Sparky]

If you don't have original colour-coded NRVs, then ensure they're open towards the engine.

[Chillidoggy]

Eloquently put, as usual.

[Escape]

The non return valve is there to prevent pressurised air from the turbo to be blown into the crank case. But on idle or overrun, fumes should be sucked out of the crank case. So the the valve needs to allow air from bottom to top (crank case to carbs), but not top to bottom.

[Maggo54321]

Excellent thanks.
 

So flow should be allowed white ——> black (i.e cold enrichment valve ——> carbs) and not allowed the opposite way. 
Thanks to everyone for help as usual. 

[Maggo54321]

Hi guys, well the new FPR hasn't worked, and I'm still getting petrol flooding through into the plenum after say 10-15 seconds of trying to start it.

I've had the carbs apart and checked the float and replaced needles etc and all looks good there too.

I'm at a loss now.  From what I can see, the petrol only goes from tank ---> fuel pump ---> FPR ---> carbs float chamber?  So there is no way fuel should be in the plenum unless there's an glaring issue I'm missing.

Can I attempt to start the car without the plenum on?  Should it start without it on?  I want to have a look into the carbs upon starting to see what's going on, but with all the plenum parifinalia attached it's impossible.

Any other ideas?

[Sparky]

So this doesn't happen if engine isn't running, only after starting it?  Are you absolutely sure the carb top gaskets are intact, or even correct?  A breach between chambers could possibly cause this.  Also, do you know the float needles are correct and floats adjusted?  There are slightly different profiles, and they should be viton-tipped.

Have you tried running it with the tank caps removed?  Not that I'd dare run it at all.

[Maggo54321]

I can't start the car currently, it's just turning over, I now have a spark at plugs (having replaced the faulty distributor), but after turning it over for 10-15 seconds I find petrol coming out of the plenum bottom and seemingly from the bottom of the front carb (although I can't quite pin point it but it looks like it).  I daren't attempt to start it again until I've stripped it all back again and dried out the fuel.

It was doing this when it wouldn't start 2 weeks ago (before I replaced the old distributor).  So whilst the carbs were off, I serviced them with the kits from Dellorto, so I'm confident the carbs are fine, and given it was doing this before the carb service, I can't even blame myself for messing something up.

I have fuel pressure of 4 PSI after the (new) FPR and I've got spark at the plugs.  Timing should be ok as I set the cylinder 1 at TDC before installing the new distributor.  Compression is good too.

So I have 2 problems.  One it won't start, and two, (I believe as a result of one), I've got fuel flooding into the plenum.  

This might have beaten me...............and time to get a low loader to take to the professionals

[Sparky]

OK, so if you just  turn the ignition on, after a number of seconds it's dripping out of the plenum?  If so, after FPR change and ensuring the return isn't blocked, your next area of interest is floats etc.

[Maggo54321]

Ah right, I've not tried just turning the ignition on to see if this happens, I've just tried it on cranking.  Give me 5 mins and I will confirm if it does it on ignition on only.

[Maggo54321]

Yes I can confirm that upon ignition (not starting) I can hear the fuel pump whirring and after 10 seconds, petrol is coming out from underneath the front carb and into the plenum also.

Hmmmm blocked return......not checked that, I will do now though. 

[Sparky]

And try it with the tank caps off.

[Maggo54321]

ok return pipe not blocked, double checked and there's definitely only 4 PSI on the 2 carb lines from the FPR.  So like you say it must be float/needle related.  It does seem it's isolated to just one carb (front), I've had the float and needle off again just to check it wasn't stuck etc but all seems fine (needle is brand new).

So I will take the plenum and parafinelia off it and see if I can work out where the leak is coming from and then report back. 

BTW thanks for taking the time to assist Sparky, much appreciated

[Sparky]

No worries!  What colour is the tip of the needle?  Preferred is brown, not black. Also different sizes are numbered and matched so worth checking the stamps on them. Also take and post a pic of the float chambers immediately after removing the carb tops, to show fuel level.

[Maggo54321]

Wow.....so I have news.

With the plenum off and everything stripped back to the carbs (see pic - yes I know a stud came out) there is NO LEAK and everything seems normal!  I left the ignition on with the fuel pump running for a good 30 seconds and not a drop.......What a strange car this is lol.

So I guess the float and needles are not in question anymore, but what on earth would cause fuel to come through just because the plenum was on?

[Sparky]

Nothing whatsoever, to my knowledge.

[Maggo54321]

Maybe I was mistaken when I saw the fuel coming out with the ignition on then. It could have been residue from before when I was cranking it then I guess. 
 

I’ll put it all back together tomorrow and try it again. 

[Sparky]

Just be super careful with this!  I've seen these catch fire with exactly this issue.  This doesn't just happen then go away.  I can't see how the plenum can affect fuel delivery to the carbs.  I would definitely have those carbs off for a detailed check.