odd no start behavior on '88 3.2

[terryb]

I checked the archives and don't see anyone describing the no start symptoms I experienced. This has only happened twice in the last year.

Turned key to start and engine *immediately* stumbles, misfires and dies. When I say immediately I mean there's no turning over for a second or so and then firing. After 5 or 6 tries with this same immediate stumbling and dying, it then started right up normally, and by normally I mean the engine turned over for a second or so without firing then fired and started.

The no-start behavior is odd to me because the moment the engine starts turning over it's firing and stumbling.

Last year when this happened, it was early morning in the garage before heading out to an AX. The following day a fellow Pelicanite and I cleaned the Idle Control Valve. It didn't look very dirty. This time it was late afternoon outside in the sun after an AX. After 6 tries I popped the hood to see if anything looked obviously wrong. I slightly wiggled connectors just to make sure nothing was loose. Tried it again and it turned over for a second or so and then started right up. Ran fine, no problems on the way home.

Any ideas? I've never felt nervous about being stranded before but this has me worried.

Thanks,
-Terry

[stlrj]

Possible loss of residual fuel pressure due to leak in fuel pump check valve or fuel pressure regulator?

[Quicksilver]

Originally Posted by stlrj

Possible loss of residual fuel pressure due to leak in fuel pump check valve or fuel pressure regulator?

Same knee jerk answer I had.

[terryb]

Thank you very much for the suggestions. I'll look in the Bentley manual to see where the check valve and pressure regulator live. Are they easy to test?

If you wouldn't mind explaining, why does failure of these components cause the immediate stumbling while turning over behavior?

[stlrj]

Vapor forms in the fuel lines unless pressurized ( that's where residual pressure comes to play) causing air to be injected instead of fuel.

[Quicksilver]

Originally Posted by stlrj

Vapor forms in the fuel lines unless pressurized ( that's where residual pressure comes to play) causing air to be injected instead of fuel.

The DME doesn't start the fuel pump until it sees that the engine is cranking which would be quite a delay on startup. To make fuel available as soon as the DME sees that the engine is cranking it retains pressure in the fuel rails.

There is a pressure test port on the rear end of the driver's side fuel rail. It is a bit goofy of a thread to hook a common gauge to. There should be about 20psi in the system when it is off. If you open it and there is noticeable pressure after it has set for quite a while it should be ok. (Fuel WILL squirt out if the pressure is there so be careful.)

[terryb]

Thank you very much for the explanations. It's been sitting for about a week so I'll have a look at the fuel pressure tonight.

Please pardon my lack of understanding but how does vapor causes the immediate firing? Is it that much easier for the vapor to combust? Or is the DME tricked somehow? When it clears is it because after the half a dozen cranking attempts the vapor is flushed through?

At the risk of over-explaining, here's what I hear:

Good start: (Key START) ruh, ruh, ruh, ruh, ruh, ruh, VROOM! (Key ON)
No start: (Key START) ruh-stumble, sputter, stumble, sputter, stumble, (Key ON), die

[wwest]

Start injector leaking.

[stlrj]

Originally Posted by wwest

Start injector leaking.

Does not exist on DME, cold start injector on CIS only.

[ischmitz]

Good though never the less. Maybe one or more of the main injectors are leaking. When the engine fires without even turning over a full rotation this suggestes there is a combustable mixture already present. So there must be fuel in at least some of the barrels.

Maybe try the simple stuff first and run something like Techron through the engine to see if that helps. Next, check the fuel pressure after shutting down the engine. For that you need a special pressure gauge that connects to the fuel rail port.

ingo

[terryb]

Thank you ingo. I've used Techron in the past but it's been a while. Thank you for the reminder, I will dump some in tonight. Family stuff has taken precedence this week so I won't be able to check the fuel pressure until the weekend. It's been such an intermittent thing (only twice in 1 year) so I'm not sure a good fuel pressure result will be entirely trustworthy.

So I'm on the right track that firing without turning over completely is kinda weird right?

[ischmitz]

Well the only time I get this is when I crank a lot and stop just before it fires. Then when I try the second time it sometimes fires right away because now there is fuel in the barrels.