No-start/"vapor lock" condition

Bad gas? water in the line or tank may cause this. Try running Stabil with your fuel and see if the problem returns. Just a guess but worth a try.

 

Tom, I have no ideas about your problem but sometimes these cars just stop to be admired for awhile then proceed along going about their business.

One thing it is not is vapor lock. the 550s have a fuel return system, no possibility of vapor locking

 

Mine began doing that just before I pulled it down for its major, and I suspect it was the check valve in the fuel pump not holding pressure. I put a fuel pressure gauge on each rail, and one wouldn't hold pressure for more than 5-10 seconds.

When you turn the key on the first time after shutting the engine down, the ECU's will run the fuel pumps for a couple of seconds to "purge" the system and ensure there's pressure at the injectors for a good start. This is a one shot deal, however; if you turn the key off before starting, then turn it back on, the pumps won't run again.

I'd check the fuel pressure at the rail if I were you. The fitting at the rail is a -4 AN and it has a Schrader valve in it, so you should be able to spin the outer cap off without leaking fuel, however I'd still be careful and take the cap off and put the pressure gauge on without the engine running, and with plenty of rags handy, in case the Schrader isn't holding......

FWIW, the combination fuel pressure/compression test kits usually have the right adapters for the fittings on the rails.

 

Tom,

Also with heat you always have to suspect electrical connections that expand and contract with heat. Check obvious connections like the ground wires on the top rear of the valve covers and the circular connectors that feed the fuel injection harness. While conventional wisdom is does it lack spark or fuel sometimes it is not that easy. When this happens again spray some starter fluid in the intake and see if the car fires. If it starts on first glance that would indicate a fuel problem but it could also mean an inefficient spark. You are still going to want to put a gauge on the rail looking at idle and psi at rpm. There are some specs in the WSM. Even bad injector spray patterns or leaky injectors can make this worse.

 

Tom, it appears the check valves in your new pumps are holding, so fuel pressure apparently isn't the issue.

You mentioned both fuel pumps were replaced in the last 5000 miles; why was this?

 

I have had the same problem a number of times. It seems to happen when ambient temps are hot. I have found a fix that works for me Press gas pedal all the way down, and crank until it starts. It sometimes take around 5 seconds or so, but it always starts. Problem goes away for months at a time and then reminds me occasionally that the car is Italian...

 

I think it might have something to do with the heat soak after the car is shut down. Mine also runs cool, but the problem seems to happen after stopping and parking for a while. Sometimes, when I drive the car hard, and then stop for gas, I have the problem once filled up. Once started, all seems to run ok.

 

Try pulling the Motronic ECUs and make sure you do not have corrosion or a bent pin at the connectors.

 

Thanks, that's why I asked, as the next question/suggestion was whether you'd experienced that problem and if the fuel system had been thoroughly flushed out afterward, including a deep cleaning of the injectors. So are you fairly confident all that's been done and you don't have any stray bits still in there that could be causing this intermittent starting issue?

It would be good to get codes from the ECU's; those would at least give you some hints on where to start looking. It may be that one or the other crank sensor is failing intermittently, or as Taz said, perhaps there's something dodgy in one or the other ECU.

Had you washed the car just prior to taking it out, or done any other maintenance work recently, ie within the last week or so?

 

"Maybe" the tank still had some rubber bits in it, but those should have been trapped by the new fuel filters.

The day it wouldn't restart, was that the first time you'd driven it since washing it? If so, you might want to look at the ECU in the passenger foot well and see if there's any moisture or corrosion in the connector, as Taz suggested. That passenger side ECU apparently is fairly exposed due to bad weather stripping, as FBB discovered awhile back and enlightened us all.

If you find any on the right side, it might be interesting to check the left one too.