Fuel Pressure Problem

[Kevo_6]

Good Afternoon, I’ve been having problem lately with the car getting richer on every trip. So I thought I would go through everything (a service), I’ve done the tappets, ordered new points, cap, rotor and condenser from the dizzy doc, replaced the fuel filter and I thought I would check the fuel pressure and it’s only about 70psi. So I adjusted the PRV many times and nothing changed, I then removed it to give it a clean but there was nothing noticeably wrong with it, bunged it back in and still I can’t get more than 70psi. Pump checks out ok.

Cant think of anything else apart from something wrong with the fuel filter.

Any help will be much appreciated.

Cheers Kev.

Edited June 10 by Kevo_6

[TR NIALL]

Bypass the Filter and try it.

[Kevo_6]

Great idea, thanks Niall

[TR NIALL]

2 hours ago, Kevo_6 said:

Great idea, thanks Niall

Kev are you on the old type PRV if so it maybe time for a change to the newer type but try the Filter bypass first.

[Kevo_6]

35 minutes ago, TR NIALL said:

Kev are you on the old type PRV if so it maybe time for a change to the newer type but try the Filter bypass first.

Hi Niall, yes I’m on the original Lucas system. The PRV was refurbished about 6 to 7 years ago and the rest about 10 years ago.

[Rob Salisbury]

I'm a bit surprised that the car runs with a fuel pressure of 70psi, maybe it's time to check with another pressure guage?

Cheers Rob

[Kevo_6]

39 minutes ago, Rob Salisbury said:

I'm a bit surprised that the car runs with a fuel pressure of 70psi, maybe it's time to check with another pressure guage?

Cheers Rob

Hi Rob, I don’t know what the pressure was before I changed the fuel filter. The gauge is relatively new and of good quality. The only time the pressure went up was when I inadvertently left the return pipe clamped, it then went up to about 95psi and I thought I cracked it but then I realised my mistake.

I’ve not tried to start the car with the pressure as it is.

Cheers Kev.

Edited June 10 by Kevo_6

[Mike C]

If the pump and its electrical feed are ok it could be the pump throughput has increased due to more fuel flowing through the PRV or MU, moving its operating point to the right of a typical pump curve..

What's the flow from the MU return look like? It should be close to negligible. MU internal problems might also contribute to the rich running.

[Kevo_6]

7 hours ago, Mike C said:

If the pump and its electrical feed are ok it could be the pump throughput has increased due to more fuel flowing through the PRV or MU, moving its operating point to the right of a typical pump curve..

What's the flow from the MU return look like? It should be close to negligible. MU internal problems might also contribute to the rich running.

Hi Mike, the pump’s electrical feed is good. I beefed the cables up and with a relay years ago. I can hear a constant dribble back , don’t think it’s anymore than it used to be BUT I could be wrong.

Could it be an air lock somewhere any way I will try Naill's idea today by looping out the CAV filter and see where we are then.

Cheers Kev

[Mike C]

2 hours ago, Kevo_6 said:

Hi Mike, the pump’s electrical feed is good. I beefed the cables up and with a relay years ago. I can hear a constant dribble back , don’t think it’s anymore than it used to be BUT I could be wrong.

Could it be an air lock somewhere any way I will try Naill's idea today by looping out the CAV filter and see where we are then.

Cheers Kev

I hope something simple like  the filter is your problem. If you want to avoid air locks try and grade the suction line into the pump as much as possible- so that the air bubbles flow along the line and  are pumped out rather than being trapped in the  line.

[stuart]

3 hours ago, Kevo_6 said:

Hi Mike, the pump’s electrical feed is good. I beefed the cables up and with a relay years ago. I can hear a constant dribble back , don’t think it’s anymore than it used to be BUT I could be wrong.

Could it be an air lock somewhere any way I will try Naill's idea today by looping out the CAV filter and see where we are then.

Cheers Kev

What filter have you used as apparently diesel fuel filters are being sold by some suppliers for the CAV filter and they are breaking down in petrol.

Stuart.

[Kevo_6]

1 hour ago, Mike C said:

I hope something simple like  the filter is your problem. If you want to avoid air locks try and grade the suction line into the pump as much as possible- so that the air bubbles flow along the line and  are pumped out rather than being trapped in the  line.

🤞

[Kevo_6]

1 hour ago, stuart said:

What filter have you used as apparently diesel fuel filters are being sold by some suppliers for the CAV filter and they are breaking down in petrol.

Stuart.

Hi Stuart, I use the Delphi Fuel Filter HDF296 which I’ve always used but the only difference I can see is that the older ones were always white with black and white stripes but the new one is white with blue lettering.

Cheers Kev.

Edited June 11 by Kevo_6

[Kevo_6]

Well I by passed the fuel filter and got an increase to about 80psi. So my next thought was that maybe the pump wasn’t providing enough umph so I swapped it to another one which was working a few years ago but that just screamed like a banshee. Put the other one back on and also removed and refitted the feed to the metering unit to check the filter in there, buttoned everything back up and then I had 90psi. (Air lock maybe) I then went to start the car which started on about the second turn, which is usual and the pressure is now between 100 and 105psi. The engine seems to be running sweet enough. 
Now to sort out my running rich problem which i will start with timing, new points etc.

Thanks for everyone’s help and suggestions so far.👍

Cheers Kev.

Edited June 11 by Kevo_6

[Waldi]

Hi Kev,

have you checked the (free) flow from tank to filter/pump? There could be a restriction in it.

And maybe compare your gauge with another?

Low pressure and high fuel consumption seems contradictive if the system operated ok before.

Waldi

[Kevo_6]

3 hours ago, Waldi said:

Hi Kev,

have you checked the (free) flow from tank to filter/pump? There could be a restriction in it.

And maybe compare your gauge with another?

Low pressure and high fuel consumption seems contradictive if the system operated ok before.

Waldi

Hi Waldi, I will check the flow from the tank this weekend. Niall suggested this to me via PM.

I think I must of had some sort of air lock from changing the CAV fuel filter which caused the low pressure because it’s running and starting really well.
I’m not sure why it’s running rich though, so my thoughts were to make sure tappets, timing, plugs, points, condenser, rotor arm and distributor cap are set (replaced) correctly along with checking/balancing the butterflies and then take it from there.

Cheers Kev.

P.S. I will also check the vacuum level. Is it best to check from the metering unit tube or the servo(booster) tube?

Edited June 12 by Kevo_6

[Mike C]

I might be missing something but I don't see how faulty  ignition components can make the engine run rich.

I check my vacuum level from the brake booster tube. 

[Kevo_6]

6 minutes ago, Mike C said:

I might be missing something but I don't see how faulty  ignition components can make the engine run rich.

I check my vacuum level from the brake booster tube. 

The ignition parts needed (maybe not the condenser) replacing anyway and my thought was that if everything was running spot on I could work from there.

Thanks for the booster tip.

 

[TR NIALL]

11 minutes ago, Kevo_6 said:

The ignition parts needed (maybe not the condenser) replacing anyway and my thought was that if everything was running spot on I could work from there.

Thanks for the booster tip.

 

Kev try and solve one problem at a time if you go at everything at once you won’t know what caused your problem and you may cause even more problems for yourself.

[Steve-B]

Just a thought....

When was your rubber tubing parts of the fuel system last checked/replaced? When we first bought our '73 I discovered the rubber fuel lines were NOT e-10 compatible when the MU had a series of hiccups. Replacing them, a clogged Lucas fuel pump, with new removed that problem.

I know many a MG owner who've also reported similar and it came down to e-10 eating the rubber from the inside out. Can't be seen their perishing.

 

[Kevo_6]

2 hours ago, TR NIALL said:

Kev try and solve one problem at a time if you go at everything at once you won’t know what caused your problem and you may cause even more problems for yourself.

Yes will do Niall, thanks.

[Kevo_6]

1 hour ago, Steve-B said:

Just a thought....

When was your rubber tubing parts of the fuel system last checked/replaced? When we first bought our '73 I discovered the rubber fuel lines were NOT e-10 compatible when the MU had a series of hiccups. Replacing them, a clogged Lucas fuel pump, with new removed that problem.

I know many a MG owner who've also reported similar and it came down to e-10 eating the rubber from the inside out. Can't be seen their perishing.

 

Hi Steve, I replaced all the fuel hoses a few years ago with Gates Barricade but I did notice that the hoses that were connected to the CAV filter when removed left a sticky black residue on the metal tubes but the fuel filter had been in there for about 3 to 4 years and was quite clean as was the filter in the prv.

Cheers Kev.

[Steve-B]

1 hour ago, Kevo_6 said:

Hi Steve, I replaced all the fuel hoses a few years ago with Gates Barricade but I did notice that the hoses that were connected to the CAV filter when removed left a sticky black residue on the metal tubes but the fuel filter had been in there for about 3 to 4 years and was quite clean as was the filter in the prv.

Cheers Kev.

Personally that sticky residue doesn't sound good Kev. Is the hose you went to listed as e-10 compatible - asking as a quick DuckDuckGo search left me wondering.

[Kevo_6]

3 minutes ago, Steve-B said:

Personally that sticky residue doesn't sound good Kev. Is the hose you went to listed as e-10 compatible - asking as a quick DuckDuckGo search left me wondering.

Hi Steve

It’s supposed to be the best you can get. Works with multiple fuels (approved for use with leaded and unleaded petrol, diesel, biodiesel up to B-100, E-10, E-15, E-85, 100% methanol, ethanol and gasohol fuels).

The sticky stuff is a bit concerning though.

Kev.
 

[Waldi]

22 hours ago, Kevo_6 said:

 

P.S. I will also check the vacuum level. Is it best to check from the metering unit tube or the servo(booster) tube?

That is how I do it Kev.