Porsche 924 Scheiße - knackered fuel accumulator?

[24vdiamond]

Great news you've got it running at last 👍

These sort of motors get very close to being broken for spares when they get temperamental! 

[N Dentressangle]

FTP!!!

Broken fan belt. Sodding thing was new but must have been slipping and lunched itself. Sadly the ECP just up the road doesn't stock the belt I need.

Awaiting the Big Yellow Taxi...

[N Dentressangle]

Belt found round the corner at APD so all should be sorted soon...

[N Dentressangle]

Belt fitted and home again.

But now with some hot start and hot idle problems. Ah well, it's all teething troubles to be expected.

[Peter C]

In almost 16 years' of ownership, the only time my W123 230E suffered a FTP was when the fan belt snapped on the A40, in west London, as I was heading home with my wife and son. And I've driven this car twice across Europe.

[Cento16v]

2 hours ago, N Dentressangle said:

Belt fitted and home again.

But now with some hot start and hot idle problems. Ah well, it's all teething troubles to be expected.

Hot start problem used to be due to fuel vaporising in the fuel pipes in the engine bay iirc?

 

[N Dentressangle]

5 minutes ago, Cento16v said:

Hot start problem used to be due to fuel vaporising in the fuel pipes in the engine bay iirc?

 

Yes, sounds like that could be the issue. It wouldn't explain the really rough running and refusal to idle though - suspect the WUR might be the culprit, so time to do some tests and see what's revealed.

Now it's cooled down everything's smooth again.

[juular]

1 hour ago, Cento16v said:

Hot start problem used to be due to fuel vaporising in the fuel pipes in the engine bay iirc?

 

The accumulator (cylinder next to the fuel pump) is meant to stop this happening as it keeps the fuel at pressure.

If it's knackered it makes hot starting difficult.

When you run a system pressure test, if you turn off the pump and leave it for an hour and the pressure drops to zero, the accumulator is usually gone.

There's also an o-ring on the main pressure regulator that when it's gone allows the pressure to slowly bleed off via the return line and has the same effect.

[N Dentressangle]

Thanks for that - will be doing some pressure tests tomorrow.

Much better this stuff reveals itself now rather than when I've got somewhere to be, so these shakedown drives are serving their purpose.

[inconsistant]

10 hours ago, N Dentressangle said:

FTP!!!

It looks great though!

[inconsistant]

10 hours ago, N Dentressangle said:

Broken fan belt.

Fan belt?!

[N Dentressangle]

13 hours ago, inconsistant said:

Fan belt?!

You know what I mean

[N Dentressangle]

Now working on snagging the hot start issue.

Using the brilliant 924 OC guide, all the pressure tests check out correctly. The warm engine "operating pressure" is at 50psi, so that's good.

What isn't so good is the way the pressure drops away very quickly when the engine and pump are shut off and the tester valve is left open. It should settle to about 30psi ± 3psi. It falls very quickly much further than this.

To diagnose further I shut off engine and pump but closed the tester valve. Pressure now settles correctly at about 32psi, but makes some very odd noises first:

The guide states that "If the pressure now holds, you have a leaking WUR pressure valve (this is internal). See strip down of the WUR".

I did just do this - I wonder if it can be the cause?

The guide also suggests the following culprits for pressure drop with the valve closed:

• External leaks. Check all fuel lines and connections for leaking fuel.

• Pressure relief valve.

• Leaking fuel accumulator. The accumulator can be found under the car behind the fuel tank. Remove the little flat head screw seen from the bottom of the accumulator. If fuel leaks out, then the diaphragm is damaged. It’ll need replacing.

• Faulty non-return valve (or check valve) at fuel pump. The only way is to replace with a new check valve, and carry out the leak test again.

• Leaking CSV (Cold start valve). This valve is found connected to the inlet manifold and is situated near the throttle body. Remove, and with pump on, (engine not running) check for dribbling.

• Fuel injectors. Remove one ay one and check for dribble with pump on

 

Any ideas / suggestions where to start gratefully received!

[juular]

13 minutes ago, N Dentressangle said:

Now working on snagging the hot start issue.

Using the brilliant 924 OC guide, all the pressure tests check out correctly. The warm engine "operating pressure" is at 50psi, so that's good.

What isn't so good is the way the pressure drops away very quickly when the engine and pump are shut off and the tester valve is left open. It should settle to about 30psi ± 3psi. It falls very quickly much further than this.

To diagnose further I shut off engine and pump but closed the tester valve. Pressure now settles correctly at about 32psi, but makes some very odd noises first:

The guide states that "If the pressure now holds, you have a leaking WUR pressure valve (this is internal). See strip down of the WUR".

I did just do this - I wonder if it can be the cause?

The guide also suggests the following culprits for pressure drop with the valve closed:

• External leaks. Check all fuel lines and connections for leaking fuel.

• Pressure relief valve.

• Leaking fuel accumulator. The accumulator can be found under the car behind the fuel tank. Remove the little flat head screw seen from the bottom of the accumulator. If fuel leaks out, then the diaphragm is damaged. It’ll need replacing.

• Faulty non-return valve (or check valve) at fuel pump. The only way is to replace with a new check valve, and carry out the leak test again.

• Leaking CSV (Cold start valve). This valve is found connected to the inlet manifold and is situated near the throttle body. Remove, and with pump on, (engine not running) check for dribbling.

• Fuel injectors. Remove one ay one and check for dribble with pump on

 

Any ideas / suggestions where to start gratefully received!

Start with the easiest and cheapest in my opinion.

A banjo that isn't tight or a nicked copper washer can cause all this. It won't drip fuel and may only look a tiny bit damp as the fuel evaporates really quickly. The easiest way to tell will be by smell.

The injector drip test is a good idea, as is checking the cold start injector as they can drip when faulty. 

The non-return valve attached to the pump can be checked by blowing through it both ways although they don't tend to go.

The next and most likely culprits will be o-rings on the fuel pressure regulator in the metering head.

A hot start o-ring kit can be had here:

https://www.deloreango.com/uk/hot-start-o-ring-kit.html

Likely, but unfortunately the least desirable is the accumulator.

WURs don't tend to leak but I suppose it's worth a check. 

[N Dentressangle]

17 minutes ago, juular said:

Start with the easiest and cheapest in my opinion.

A banjo that isn't tight or a nicked copper washer can cause all this. It won't drip fuel and may only look a tiny bit damp as the fuel evaporates really quickly. The easiest way to tell will be by smell.

The injector drip test is a good idea, as is checking the cold start injector as they can drip when faulty. 

The non-return valve attached to the pump can be checked by blowing through it both ways although they don't tend to go.

The next and most likely culprits will be o-rings on the fuel pressure regulator in the metering head.

A hot start o-ring kit can be had here:

https://www.deloreango.com/uk/hot-start-o-ring-kit.html

Likely, but unfortunately the least desirable is the accumulator.

WURs don't tend to leak but I suppose it's worth a check. 

Totally agree.

Checked the cold start injector and it's fine.

Pressure valve spring looks OK but nothing else came out with it:

Do I need to have a dig around in there? The pics on that O ring set (now ordered, thanks) show there's more to come.

[juular]

6 minutes ago, N Dentressangle said:

Totally agree.

Checked the cold start injector and it's fine.

Pressure valve spring looks OK but nothing else came out with it:

Do I need to have a dig around in there? The pics on that O ring set (now ordered, thanks) show there's more to come.

Hm, that doesn't look right.

Whole assembly looks like this (both parts)

Try a long thin screwdriver or a magnet.

Both o-rings are pictured above.

[N Dentressangle]

Managed to fish the rest out:

Doesn't look right, does it?

[juular]

Ah that's an early type.

So just one o-ring.

Have never actually seen one before.

[N Dentressangle]

👍 had me worried there

Looks like that O ring kit will still fit, and the O ring that's on there certainly looks like it's seen better days.

I'll check the accumulator anyway and make sure the diaphragm's in one piece, plus I can put the new bobbins on the rear silencer whilst I'm under the back end.

[N Dentressangle]

OK, we have fuel dribbling from the vent screw at the bottom of the accumulator when it's loosened:

I think that means it's knackered. New one ordered.

£177 after some handy Ebay discounts, which is a PITA but kind of what you'd expect - the system is 43 years old after all. Plus it's relatively little in the context of the kind of bills modern stuff throws.

[inconsistant]

I think unfortunately most 924s either have a hot start issue or have had the accumulator replaced. Yeah, they’re not cheap. 

[N Dentressangle]

2 minutes ago, inconsistant said:

I think unfortunately most 924s either have a hot start issue or have had the accumulator replaced. Yeah, they’re not cheap. 

Just the way, innit? I would expect to be replacing most of the rubber bits on a 42 year old car anyway, and in my view it's worth working through the fuel system to get a reliable car rather than putting up with temperamental motors. Sooner spend a little on this than £700+ road tax, or a £1000+ bill of the kind moderns produce.