Fuel pressure rough idling and won’t rev?

Yes, does the engine make a ticking sound at idle from the area of the high pressure fuel pump? If so the problem can be the camshaft lobe is worn out which will cause low pressure. The pump will need to be removed and the lobe inspected to confirm, also I have seen problems with the lift pumps inside the fuel tank starve the HPFP. If you have a check engine light on the fuel pressure sensor on the fuel rail on the engine can be bad and cause the pressure dump. Lets run the codes to see if any are present.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please go over this guide and get back to us. Also, upload a short video in your response of the problem, so we can see what's going on.

Thanks Ken, I can’t say I can hear a ticking from the HPFP. I did a pressure test of the low pressure feed to the HPFP and it’s 5.5 bar holding strong so happy that the feed to the HPFP is sufficient. I also ran the starter for 20 seconds and I’d delivered probably 2 litres into a petrol can.

See error codes attached. Suspicious of hp fuel pressure sensor tho although replaced it 3 months ago.

What is the error code I don't see it? It is good that the lift pump is working well, but it does sound like the HPFP is out or the lobe on the camshaft is worn and not working the HPFP correctly. I would remove the pump and inspect the cam lobe and if okay replace the pump. But, please type out the code number here first.

Hi, sorry maybe photo of codes didn’t send. Codes are P1026 P1031. I have done a compression yes too. All cylinders are around 225 psi except cylinder 1 which is about 190psi. I’ll take pump off tomorrow and take photos of lobe if I can. Thanks for all your help. I’ve been working on this off and on for 6 months!

Hi Ken, just remembered something. When I put the China pump on a few months back, I didn’t fit the white plastic stopper that holds the clutch onto the end of the crankshaft. It was broken from what I remember but stupidly thought it was just there to help with assembly. I have been reading that it is very much needed! I also remember the remaining part of the plastic had slipped further into the hollow end of the crankshaft :(. I just left it in there. I think that might have been the problem all along! I will take the pump out tomorrow and remove what remains of the plastic stopper.

Yep, I think you found the problem, the pump must have the stopper on it, also I would get a an OEM pump for it, (they barely work as it is) for the best results if the camshaft lobe is okay. Try uploading a short video that should work.

Hi Ken, so the plastic stopper arrived today. I fitted it but still no joy! only getting 5600 mbar pressure at rail. even swapped back to the old porsche HPFP but the same result. I am getting a P1031 fuel high pressure sensor stuck at start - limit exceeded error. After Googling this error i see a few results, one is pointing towards O2 sensor. Confiused! :(

Failing High-Pressure Fuel Sensor (MOST COMMON)

The sensor at the end of the fuel rail sticks or reads incorrectly during cold start.

So I would replace the sensor which should fix the problem, did you notice the camshaft lobe when you had the pump off? Here is the location of the sensor and I will email it to you as well. Check out the images (below). Please let us know what happens.

Thanks Ken, I replaced the high pressure sensor back in May. I suspect the replacement was faulty though but only realising this now. I have the old one off the car but can't see anywhere online on how to test its resistsnce (if thats how you test it) put ohms meter accross all 3 pins in every variation but get no reading on my multimeter. i have raised a warranty replacement that should arrive next week. Will let you know how i get on. I have had that inlet manifold off and on about 3 times now lol! thanks again for all you help. i feel a fix is near!

Yep, you are on the trial, it will be difficult to test the sensor unless you test it in operation since that is when it fails, unless it has an open circuit which most do not. I would get a new part because the old one sounds defective. Please let me know.