308 QV european spec: another warm start issue

Yes, your mechanic (or you) should measure the residual fuel pressure at warm engine shut off to see if the residual fuel pressure is falling too quickly, or not. In addition to the fuel pump check valve not working and the Accumulator leaking, a third item is there are two o-rings in the K-jet fuel distributor pressure regulator plunger assembly that need to seal well to prevent the residual fuel pressure from dropping at engine shut off. Additional, no guarantee that the new fuel pump check valve isn't leaking. You need to measure the residual fuel pressure at warm engine shut off BEFORE doing anything else.

1.4% CO is nothing terrible. The Ferrari "spec" is intentionally set to be very lean. On a car with no cats, 1.5% CO is A-OK IMO.

 

This is good, but you still haven't answered the basic question: Is the fuel supply pressure falling too quickly, or not, at warm engine shut off?

If it is falling too quickly = you have to keep investigating that until it isn't.

If it is not falling too quickly and meets the specification = could be something like a bad thermo-time switch or the wrong thermo-time switch has been installed, but there's no reason to go there until you answer the basic question (i.e., make a functional measurement of the fuel supply pressure at warm engine shut off and monitor it for about 20 minutes). Early 308QV (SN 49601 and before according to the 308QV SPC) use a CIS fuel pump that wasn't available for a while, and we've had many cases of people using the wrong (later) CIS fuel pump that doesn't have an internal check valve (and leaving out the external check valve of the later CIS fuel pump) -- so when you post "the pump...are brand new" that can be meaningless. Can you post a picture of your brand new fuel pump and its plumbing?

 

Its a little rich but fuel mixture is not the problem. There really is only one valid test to be done here. There is a specific piece of test equipment for this and it is not expensive. It will test system pressure, control pressure and residual pressure. If you want this fixed, do that test. Anything else at this point is a waste of time.

 

Seems like a plausible way to confirm the check valve is functioning. If one found the supply pressure test not to spec then would this not be a way to assess the check valve other than just replacing with another, possibly flawed replacement?

 

I am not suggesting to avoid the pressure test. But if the pressure test shows a problem, there are still a number of things that could cause that. The check valve would not be the only possible cause, so it would be helpful if there was an agreed way to test this verses just replacing parts and hoping new spares are of consistent quality.

 

I had a warm start issue on my 83 QV. I looked up past posts from Rifledriver, and per his advise changed the checkvalve first. On my car it's part of the pump. You are saying you already changed pump, so did it have valve attached or not? He says the accumulators are rarely the problem. On my car, the checkvalve was the issue. He is correct, you need the cheap pressure tool to know if pressure is even your issue, and if you are fixing it.

Also, per his advice(or was it someone else?), I added an aftermarket inline filter between the fuel tank and pump. This is likely why the checkvalve failed; little particles in the fuel coming from the tank. I could see them when draining the fuel for the pump install. It's been more than a decade since I did this, with no further problems.