Frustrating cold hard starting/no-start issue on 456

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Ooops... Correction... I just realised that the USA cars don't appear to have the two way valve. I tried to make edits to my original message, but it was too late.

Also, item 3 is actually a rollover valve. My memory is failing me.

Here is the Euro diagram showing the two way valve on the Euro 456.

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I usually expect the USA/Canada cars to have more anti-evap hardware. In this case, there seems to be less.

 

Here is the installation on the F355 as a comparison:

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The red item is the two-way valve. The rollover valve plugs into the top of the vapor separator with a tight rubber seal.

I suppose you could check the check (one-way) valves in the system. These are known to fail.

 

The charcoal filters are service items. On our V12s, the replacement interval is 90,000 miles, along with the O2 sensors, but the 456s are at least 34 years old. On the 599, they recommend checking, cleaning, or replacing at 8 years.

 

Maybe a long shot, but do you know if the fuel pumps were ever changed? I remember somebody here with a 550 installed new Bosch pumps and had a cold start problem because the pumps he bought did not have the internal check valve and the system did not hold pressure. I believe the Bosch pumps are available with or without an internal check valve. Since you say it takes about 10 seconds to build pressure and pressure drops significantly within just 2 hours, maybe your pumps don't have a check valve, or one or both check valves have failed. It is unlikely that both would fail at the same time though. Do you have the same pressure drop over time on both sides?

 

Quite a lot of threads on this. Normal, thats debatable, but not unusual on the early 456 cars. When the tank is low the pressure builds up as hot fuel get recirculated back into the tank. The simple solution is to keep the tank full(er) and it will help absorb the heat to keep the temps and expansion down.

The fix would be to see if your carbon cannister and vapor recovery hoses are blocked, but may not be worth the risk, effort or expense. Especially if you have no other fuel smell

 

+1

This is exactly what happens to my 512tr.. the key is a fuller tank(as stated above) and not remaining idle



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You would think so.

Here's an overview of the system:

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The only thing that seems to be capable of holding pressure in the system is the two-way check valve.
I don't think the rollover valve would cause a problem.

The charcoal canister appears to be vented to atmosphere at all times. The fuel vapours will still have to flow through the charcoal however, to get to atmosphere. I can't see this causing a pressure buildup. Even if the canister was laden with fuel, you would still think the pressure would escape. Are there any valves in the canister on the vent to atmosphere line?

Meanwhile, back to your coldstart problem... You would think that at least the engine would start if your tank was not completely full, even if the tank was sealed.... then, as the vacuum built up (as fuel is pumped out), it would then cause problems. You're getting the very opposite. Hard to start, then getting better in time.

 

On the 456 at least, the hoses to the canister are easily accessible. So if you open the fuel filler cap and take off the hose on the canister you should be able to blow through and confirm nothing is blocked. Or is, in which case you can go from there.

 

You said it takes about 10 seconds for the fuel pressure to build to 45psi. The WSM for the 550 with the same pumps says it takes 2 seconds to pressurize the system. So it sounds like your pumps are not operating at full power and the system is not holding pressure when shut down. The pressure has to go somewhere. Either back into the tank, leaky injectors, or a leak in the system somewhere?

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Quit screwing around then.... put a fuel pressure regulator on the (each) Schrader valve, pull the fuel pump replays and put in a jumper wire and see what the pressure in the line is and how it bleeds down. Do it for each side and eliminate line pressure issues. Its a $40 (or less) fuel pressure guage and a jumper wire. All you have to do is turn the key to on. Cheap and easy to identify.

 

Any update. I am having the same issue. sometimes when i reset the ecu by turning the battery disconnect off for a bit it starts up good for a while.

 

Thx. I hope for the same luck


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