508 HDI RHH Cranks but no start

C

crd74

New member
Tadpole
Tadpole
Joined
Aug 15, 2025
Messages
8
Location
Sydney, NSW, Australia
Hi
Car stared running very rough then stalled soon after. A code p12a8 was read in the reader.
Car will now crank but not start after clearing code.

Done so Far
-checked as many electical connections as possible
-checked for fuel to injectors
-replaced battery as voltage was low 11.9 (possibly due to cranking but battery was also old)
-reset BSI multiple times
-tested all fuses
-recent replacement of throttle body. Put old throttle body back on to see if this caused the error.
-checked hoses and vacuum lines for leaks .

Now the code reader does not pick up any codes. The car cranks and almost seems like it will fire but fails. Not sure where to go next. Fuel pump? I'm concerned that it could be an ECU failure but as it seems like it's trying to fire I'm not sure.
Any help would be appreciated.
 
P12A8 is injector 3 (3rd from transmission end) stuck closed. It seems to now be corrected.

ECU faults are very rare.

By throttle body, I assume the doser valve at the front of the engine. It is vacuum controlled. Is it functional?

Is fuel flowing? The RHH pumps from the HP pump.
 
Thanks for getting back to me... and yes I mean the doser valve. It appears to be functional.
It's my sons car and he was driving at the time so didn't see exactly what happened but when I had a look the fuel gauge said it was empty.
I can use the bulb primer to pump fuel to injectors so am thinking it's ok? Is there a specific process to bleed system or just prime with bulb and start?
 
There's a bleed screw on the top of the filter. Slacken it and pump with the rubber bulb. When flowing close the screw. Since the HP pump also sucks, it will complete the bleeding when the starter motor runs, and hopefully it will start.

If you can't get a solid feel at the bulb with the bleed shut, the non-return valve at the bulb inlet is gone.
 
I can pump fuel with the bulb but I wouldn't say it feels particularly solid. I can continue pumping and it never feels as though it will stop pumping fuel. I'm thinking I'll get a cheap non return valve to splice into the line before the bulb to test if it is the valve. I can replace the lines later if it confirms the problem. Does this sound like a good idea or am I missing something?
 
The hand pump is to prime the filter by sucking from the tank and holds fuel there when the engine stops. During running the RHH HP pump sucks fuel in and can handle a small amount of air near the HP pump at start. You can test the bulb for backflow. There is a transparent fuel line section after the filter.
 
Ok so fairly confident that it's not the non return valve. I've been reading about starter motors failing. Could it be possible that the starter motor is on the way out. The engine cranks but does not fire. The last couple of times I tried it felt like it would start but just didn't get there.
 
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