75 P6 V8 - Bye, this car

[LC Torana]

  On 17/07/2015 at 20:23, Junkman said:

This is mine:

 

 

Haven't had a problem ever.

That fuel pump seems to be in the wrong place.

[Conrad D. Conelrad]

 

FFS

[phil_lihp]

Oh dear.  Same again?

 

If it's any consolation, it still looks very pretty sat there decorating an otherwise ugly stretch of carriageway.

[Alan_Green]

^^Yes. After seeing them my whole life I've suddenly realised that these cars look absolutely stunning. And the engine sounded great on that video. Wonder what they drive like. 

[Conrad D. Conelrad]

  On 23/07/2015 at 14:39, phil_lihp said:

Oh dear. Same again?

No, it just started losing power. Revs fine in neutral, but as soon as it's under load it goes to bits.

 

It limped off the motorway but is currently abandoned in a layby. Because it vapour locked again while we were trying to diagnose it. (Eye roll)

[Pillock]

When can we expect your "laybys of the British Road System" book to appear in Waterstones?

[Skizzer]

Bugger.

 

On the bright side, at least next year's calendar now has a front cover.

[LC Torana]

From my experience of 30 years' P6B ownership, here is my checklist for this circumstance:

 

Fuel pump

 

Timing (turn the distributor)

 

Dwell (the hex adjuster)

 

Condenser could be on the way out

 

The points - some cheap moderns have the nubbin that the cam hits is made of butter so it wears too quickly and so the points don't open enough

 

A loose wire in the distributor

 

Less likely but possible:

 

Fuel filter blockage

 

Carburettor settings - mixture etc.

 

Needles & seats - if these get too worn the sump will fill with petrol! Check the dipstick.

 

Spark plug gaps

[LC Torana]

  On 23/07/2015 at 14:57, Conrad D. Conelrad said:

It limped off the motorway but is currently abandoned in a layby. Because it vapour locked again while we were trying to diagnose it. (Eye roll)

With that symptom, just thought of something else to check.

 

The P6 fuel tank has two outlets, the "reserve" outlet at the side of the tank near the very bottom, and the "main" outlet an inch or so above this.  These pipes go to the reserve tap, high up above the driver's side back wheel.  The tap is operated by a bowden cable from the dashboard, and if the inner stretches or kinks too much, the tap can stick near the half-way point, letting not enough fuel through for hard acceleration, and of course putting a strain on the fuel pump.

 

This can let enough fuel through to allow the car to tick over at idle, but not enough when you give it a bit of welly.

 

(There is also a fuel shutoff tap next to this, and I suppose that could be partly shut off, too.)

 

One last thing - you've mentioned vapour locks - have you serviced your charcoal canisters?

[Conrad D. Conelrad]

[Inspector Morose]

You're getting the composure of your pictures quite nice. I reckon a few more breakdowns and you'll have cracked it.

[Jim Bell]

The last pic is so lovely that I couldnt help LIKEing it.

 

Its a shame tat the subject matter is so infuriating.

[Junkman]

What the picture doesn't tell is that this happened on the test run after an electric fuel pump was installed today. The car did perform beautifully for about an hour, then all of a sudden started to play up again. The diagnosis revealed, that there is definitely petrol arriving at the fuel pump, the pipe from the tank is not blocked or anything. Also, when petrol is actually arriving at the carburetters, it runs like a fucking new car. But sometimes and rather suddenly, no petrol arrives at the carbs, or rather, very little. When this was acute, I felt the fuel pump and it was a bit too hot for my taste. On my car, it's only ever merely lukewarm at best. Equally suddenly, the petrol resumes flowing and the car ultimately performed flawlessly from where the pic was taken to home. Much head scratchage is currently happening. I can't bring myself towards believing in new fuel pumps being borked.

[captain_70s]

The adventure never ends.

[LC Torana]

  On 02/08/2015 at 23:58, Junkman said:

What the picture doesn't tell is that this happened on the test run after an electric fuel pump was installed today. The car did perform beautifully for about an hour, then all of a sudden started to play up again. The diagnosis revealed, that there is definitely petrol arriving at the fuel pump, the pipe from the tank is not blocked or anything. Also, when petrol is actually arriving at the carburetters, it runs like a fucking new car. But sometimes and rather suddenly, no petrol arrives at the carbs, or rather, very little. When this was acute, I felt the fuel pump and it was a bit too hot for my taste. On my car, it's only ever merely lukewarm at best. Equally suddenly, the petrol resumes flowing and the car ultimately performed flawlessly from where the pic was taken to home. Much head scratchage is currently happening. I can't bring myself towards believing in new fuel pumps being borked.

 

I refer the honorable member to post #99.

[Junkman]

1. Our cars are the domestic market versions with the reserve tap at the bulkhead in the engine bay. They also don't have the fuel shutoff tap.

2. The reserve tap works a treat.

3. There is more than sufficient fuel arriving at the pump.

4. The problem occurs between the pump and the carbs.

5. The domestic market cars never had charcoal canisters or any other emission control devices.

[Junkman]

Oh, and the previous reason for breaking down was a defect of the carburetter, which was found and repaired.

[LC Torana]

  On 03/08/2015 at 01:04, Junkman said:

1. Our cars are the domestic market versions with the reserve tap at the bulkhead in the engine bay. They also don't have the fuel shutoff tap.

2. The reserve tap works a treat.

3. There is more than sufficient fuel arriving at the pump.

4. The problem occurs between the pump and the carbs.

5. The domestic market cars never had charcoal canisters or any other emission control devices.

 

Oh, I see.  Suitably chastened.

[brownnova]

And I thought my old MG Midget broke down alot!

 

But... It did once get too hot, and following that did the same power loss thingy. It turned out it was a mixture of carb needing setting and the throttle cable needing adjustment. As in sometimes it would underfuel for no apparent reason and it turned out the throttle was sticking.

 

You may well have already checked this of course!!

[Junkman]

No, I haven't, but I measured temperatures today.

When up to operating temperature, the fuel pump in my car is 30° warm, the one in Mr Conelrad's car 90°. At 60° petrol boils and this is the reason why nothing is pumped by a pump 90° hot.

I cooled the pump with cold water and it immediately resumed pumping as normal. I can only think of two reasons why this happens:

 

1. The heat emission from Mr Conelrad's engine is at least three times higher than from mine.

2. The return pipe is clogged, preventing the petrol from circulating properly. This would lead to

 

a. the petrol becoming more or less stationary inside the pipework and thus be heated

b. the pump working against maximum resistance at all times

 

which in combination might lead to the pump becoming so hot.

 

I hope it's 2.

[alf892]

or partially blocked pick up pipe?  (Had this before and spent long time fucking about with (electronic) ignition bits thinking something breaking down with heat. It will not be timing or mixture setting causing breakdown that is for sure)

 

Blocked= no fuel but lot of suction in pipe

 

Sit there a while=suction overcomes the blockage and broom she goes........till next time.

 

Repeat with differing time intervals until owner shoots himself or the car. If only he had fuel he could set fire to it......................

 

When there is no fuel it is worth just trying to blow from pump back to tank.

[Junkman]

We did blow from the pump back to the tank many times. There is no resistance in the pipe and the bubbling in the tank can be heard clearly.

[Sloth in a bowl]

  On 02/08/2015 at 19:11, Conrad D. Conelrad said:

[David Attenborough] In the wild the P6 is an ambush predator. It waits still and patient for the unwary AA man to wander by. [/David Attenborough]

[Inspector Morose]

Just a thought but if you've a bit of rust in the tank, it'll blow through nicely but when the pump sucks fuel the other way, a flake or two would be enough to impede progress. Tell me how I know. Chased that one for ever.

 

Blocked return sounds very plausible though, especially as the pump is running that hot.

[twosmoke300]

I knew of a tractor with an intermitant hyd problem which was traced to a crisp/ sandwich packet getting sucked into the pick up every now and again

[Junkman]

  On 04/08/2015 at 19:46, FPB7 said:

Just a thought but if you've a bit of rust in the tank, it'll blow through nicely but when the pump sucks fuel the other way, a flake or two would be enough to impede progress. Tell me how I know. Chased that one for ever.

 

Blocked return sounds very plausible though, especially as the pump is running that hot.

 

It looks like both of these things are the case.

The blockage of the feed pipe seems to be temporary, which could be sediment in the tank, which now more and more accumulates around the take off, which makes the problem getting worse.

Also, the return pipe appears to be blocked. However, when I tried blow into the one on my car today (we use my car as a reference), there was quite some resistance, too. It appears that the return pipe is somehow calibrated for reduced throughput, thus ensuring that there is fuel pressure building up. I always thought this is achieved merely by the smaller diameter.

[mat_the_cat]

When I was plumbing the fuel system in for the Stellar (with the same engine and fuel pump) I initially went for an 8 mm feed and 6 mm return, thinking this would be sufficient restriction. However I suffered fuel starvation under load, so figured the pump was not up to the job of circulating back to the tank AND supplying a V8 at full chat.

What I did was solder up the return line, and drill out with a 1 mm drill bit. This seems to give a reasonable compromise between circulation to prevent vapour lock, and still giving priority to the carbs. Maybe a MIG welding tip in the return line would also work OK? It certainly sounds like some restriction is designed in, and perhaps this is what has become blocked.

[Junkman]

  On 04/08/2015 at 20:36, mat_the_cat said:

When I was plumbing the fuel system in for the Stellar (with the same engine and fuel pump) I initially went for an 8 mm feed and 6 mm return, thinking this would be sufficient restriction. However I suffered fuel starvation under load, so figured the pump was not up to the job of circulating back to the tank AND supplying a V8 at full chat.

What I did was solder up the return line, and drill out with a 1 mm drill bit. This seems to give a reasonable compromise between circulation to prevent vapour lock, and still giving priority to the carbs. Maybe a MIG welding tip in the return line would also work OK? It certainly sounds like some restriction is designed in, and perhaps this is what has become blocked.

 

That's exactly what I as well think is the case. It appears that the return line of my car is restricted on purpose, probably in a similar way you did with yours.

My car permanently pumps around fuel, thus cooling the fuel supply. You can observe this in the clear fuel filter, which is almost always full. Only when you give it serious bootage, the level drops a bit, with full resuming instantly when maximum demand is eased off.

 

On Mr Conelrad's car however, the fuel filter always shows maybe three quarters full and if there isn't a huge demand for petrol, it doesn't look like the fuel is properly circulating.

It stays put and gets heated. At the same time, the pump is probably pumping against full restriction when the needle valves are closed.

 

The second symptom is, that suddenly no fuel arrives in the filter and it empties, which of course stalls the engine. At the same time, the pump becomes very noisy. This is IMO caused by the fuel feed line being clogged in the tank and no fuel arriving at the pump. Once you blow into the pipe, it clears and once reconnected, it'll continue to pump fuel until the issue repeats itself.

As I wrote earlier, the dirt might now have more and more accumulated around the fuel take off, hence the issue occurs after ever shorter periods of running.

 

One thing is for sure, though. As long as we manage to supply fuel to the carbs, the car is running like new.

[Conrad D. Conelrad]

Whole weekend of P6 ACTION!!! By which I mean...

 

 

By Saturday morning the fuel return line had been unblocked. I forget what happened next, because I'd need a Memento style system of tattoos and Polaroids to keep track of exactly what went wrong and when with this car.

 

The car was running almost nicely when we pointed it towards the Peak District and started driving. We thought the drive would improve it, and, for a while, it did. A nice drive (during which I terrified Junkman by mistakenly thinking the brakes were failing) turned sour as soon as we found a road with steep hills and no stopping places, which is where the car decided to start intermittently running on one carburettor and cutting out. 

 

We eventually rolled into a picturesque lay-by (above), and found that one of the carburettor needles had fallen out. By pure miracle, the retaining piece had not been swallowed by the engine. We bodged it back together, and the car was instantly transformed back into a wheel spinning, gravel spraying terror. 

 

For a bit. 

 

Within a few miles it was spluttering and cutting out again. Only this time it wasn't the carb needle, it was fuel starvation. 

 

So, after a day's worth of work on this, the TL;DR is: there's dirt in the tank which is periodically clogging the fuel line. This isn't going to be fun to fix, not least because although the P6's fuel tank is conveniently mounted in the boot, all the connections and pipes are on the bottom, under the car. Great. 

[Jim Bell]

It still looks fucking marvellous though.

 

Needs more photos with the bonnet closed.