Fuel pressure bleed down relationship to breakdown

[precopster]

A nice looking 2001 XC70 with 160K miles came in to my workshop for some suspension and diagnostic work.

The car continues to show low MAF readings of 9.5KG/HR even after a new Bosch MAF and a baseline reset by removing the ECM. No vacuum leaks that I can spot. Car can stall from cold or be on the road for an hour before it stalls and then will sometimes take afew minutes until it can be driven home. Customer complains of a "dead" pedal where car will idle and not rev at all. No codes apart from low MAF code read with Vida. NO THROTTLE CODES.

Fuel pressure check shows 55psi with engine running however the alarming thing is how quickly the fuel pressure bleeds down with key off. Within 15 minutes the pressure is down to 0psi

Comparative readings on my 2001 T5 show a drop of only 10 psi in 2 hours so this leads me to believe something is wrong with the fuel supply. What is even more perplexing is that our own 2002 XC70 has quite bad bleed down of pressure yet continues to run perfectly. Can't quite put my finger on it at this stage however don't want to replace the fuel pump unless there's something else in the fuel delivery that can cause the bleed down. I know that the return line (which is part of the fuel pump) can be kinked & torn however is this linked to intermittent breakdowns?

Would really like some learned hands on this one before I go and order a AUD$300 pump and spend 3 hours replacing it.

[abscate]

Mike ..I think the fuel pressure specs do give a bleed down number and I know that's it's much higher than you are observing. I'll search and post

[precopster]

Thanks so much for the Alldata specs. No the figures are much LOWER than the problem car if you read my post again. My own T5 has almost NO bleed down and the problem car has quite marked bleed down. I think it's all totally not related to the breakdown of the engine and I will report my findings after completing the PCV service tomorrow. Pressure with engine running is 55psi.

I noticed that the ETM to inter-cooler pipe had an odd wear mark where the clamp was located, as if the clamp was seated badly at the front. This may explain the low metered air readings. I had just placed the intake manifold back on before retiring for dinner so not too long until completion.

[abscate]

Can you watch STFT to diagnose the ETM leak, perhaps?

[precopster]

PCV system was replaced and lo and behold MAF readings are now averaging over 12.0KG/hr. I still believe that most of the issue was the seating of the throttle tube over the ETM however original PCV just had to go at 273K kilometres. Interestingly owner had the shiniest set of valve stems I had ever seen after removal of the intake manifold. When I asked him if he used fuel system cleaner he said no; just 98 octane (highest RON rating here) fuel for the past 8 years.

Car idles well and no longer gets upset with the cycling of the A/C. MAF code gone. Long term fuel trim code gone. Owner picked up tonight and very happy with the result and so am I!!

[precopster]

Heard from the customer today. He said the car is still going strong with no intermittent breakdowns; looks like the bleed down of fuel pressure has no relationship to this particular car's breakdown issue. The bleed down was about the same as wife's 2002 XC70 which goes well.