engine cuts out under hard load

[redhouse53]

Hi, recently got our P6 up and running and set up by a local mechanic who served his time on these cars.

We've taken it for a quick run and everythings fine if its driven nice and gently, but if you push it, it starts to cut out on tickover and struggled a little on the slope into my garage.

Before I try and get the mechanic back does anyone have any ideas, many thanks

[a15htn]

Fuel starvation? when it dies switch off whilst it's dying and check to see if there is anything in the floats..... If there isn't I'd suspect the fuel pump..... Don't the v8's haves an issue with these?

If there is plenty of fuel I'd be suspicious of the condenser as a car can idle and rev really nicely with a dodgy condenser but will struggle to drive away or do anything under load.

Hope that's some help - but bear in mind im not a v8 person so could be completely wrong

Good luck.

[rockdemon]

could also be the coil - they have a habit of being fine on startup and going tits when they get warm...

[chrisyork]

Yep, my first suspect would be the coil - or if you are still on points ignition - a duff capacitor in the distributor. Yes, I know your mechanic will have just changed the capacitor for new; that's why I suspect it. There have been some duff batches around recently that misbehave straight out of the box. Cheap enough to try, anyway; or better, use an old one from your magic box of spares that lurketh in all good garages!

After those two, I too would be on to fuel starvation. With a recent re-commission, the first port of call would therefore be the cooling system. Spend a long time flushing out the radiator with a hose pipe on full bore, then move to the engine for the same treatment, and finally spend a while with the hosepipe running through the heater. A nice quiet days entertainment for a hot day with the grandkids! It may be as well to be prepared with a full set of coolant hoses, as you will disturb most and old hoses don't like that!

When done, don't put any antifreeze in the system just yet, there are a couple more checks to do. First check is to see if there is water flow into the top of the radiator from the pipe that runs from the "tower" between the two carburettors. You should be able to see this with the help of a very little engine revs with the cap off the radiator. If not, then this is almost certainly the primary cause of fuel starvstion. Take the hose off the "tower" and unblock the hole into the manifold. Some serious aggression with a hammer and a jewelery screwdriver or equivalent is likely to be needed.

Second check is to inspect the thermostat by removing its top cover casting. There is some chance of snapping a stud here, so don't force things too much unless you feel up to coping with the consequences. The thermostat should have a pilot hole - about the size of a 1/8 drill bit (clue for if it hasn't!) positioned at roughly 12 o'clock as you look at the stat. It might even have a little dumb bell shaped "jiggle pin" through it. If not change the thermostat, or if you are confident it is working properly, drill your own hole.

Now you are ready to finally refill the system, including the antifreeze. When full, run the engine up to temperature with the radiator cap off. When the top hose to the radiator gets good and hot, demonstrating that the thermostat has opened, rev the engine moderately for a lengthy period. Then top up the radiator. Repeat this until you are quite sure that all the air has been purged from the system. You might well take 20 mins to 1/2 hour doing this. Then top up the radiator finally at idle and fit the cap.

Report back to us how the car now performs and we can sort out any other attention required from there.

If you don't feel up to this yourself, print this out and give it to your mechanic.

Hope that helps!

Chris

[rover100rich]

how far do you have to drive to get fuel vapourisation , he mentions using the car hard , maybe hes sitting in traffic ,i dont know but a car running perfectly well suddenly starts running badly , does the car run ok again when cold , i agree with the coil , my p4 had this recently , ok when cold then cutting out when warm, please remove the carb elbows and check that the carb pistons are rising and falling freely, im thinking one may be sticking open when the car is hot and used hard,and check the dashpot oil level , cheers rich

[redhouse53]

Thanks guys, interesting stuff, I never thought fuel starvation could be caused by coolant issues.

To answer a few questions, the engine has had a new coil and condensor, the coolant hoses are all new, as is the rad and thermostat, but I didn't flush the heater. I havent checked the pipe from the carb tower either. This I will now do.

The car is going for its first MOT tomorrow (its been a project for the last 8 years!), so has only been run around the industrial estate so far.

We have fitted a facet fuel pump (in the boot) with all new hoses, but did have a problem early on with the filter/ non return valve so I'll check this again.

thanks again, I'll let you know how I get on

[chrisyork]

If the thermostat is new, do check that it has the bleed hole. Normal over the counter one's don't. Without the bleed hole the thermostat will be very late opeing on the V8, so the coolant in the top of the heads and inlet manifold will already be overheated and causing vaporisation.

Chris

[redhouse53]

thanks for the replies, I'll check the thermostat.

Well the car made it to its MOT, failed on handbrake, fuel lines not secure enough and a twisted flexi hose, so, while I was re-routing the fuel lines I thought I'de take the sender out as it wasn't working and think I've found the problem.

In my haste I hadn't flushed the tannk and it was full of crud, from sitting for a number of years with fuel in the tank, so I think this was causing starvation. As soon as we get another sender I'll put it back with a clean tank and new filter at the pump and see were we're at.