eyeball kid

This has happened thrice now. After car sits in the sun all day (it's black) and ambient temperature gets above 80, car won't start. Cranks, stumbles, fires briefly and dies like there's no fuel. Repeated cranking, nothing happens.

Get in next morning, fires right up.

Tach bounces.

I'm stymied. Any suggestions?

Thanks,

Dan

eyeball kid

Looking for wild guesses at this point.

Cyberpunky

Had same issue and was fixed by jiggling speed and ref sensor connectors at back of block. Cleaned the contacts up and now once every cpl of weeks I might need to give them a jiggle and that's only if I stop once engine is up to normal temp and then try to start a few minutes later, like if I stop at a 7-11.

eyeball kid

Thanks I'll try that next time. Makes sense.

blown 944

My guess would be the S/R sensors or their gap.

Rogue_Ant

S&R sensors (or the wiring), or coolant temp (or its wiring), are the most likely culprits.

968turbos2

The EGR system may have a vacuum leak. Drivers side right next to the firewall in front of the fuse box. Start there with those valves. Follow those lines as one of them goes to a thermo valve that only allows vacuum to hold open the canister valve. Thermo switch is on back of head near the ref sensor connectors. Two tubes coming off what looks like a sensor body. Often they break...or one of the lines leads to a leak. This would cause a lean condition that would affect your AFM (can't suck as hard kinda like a 4 dollar ***** at dusk) and hence meters less fuel (car can't start or runs like crap and cuts out).

Also, unless you were first owner you may want to check your hose routings to make sure someone did not 'upgrade' you to an issue some time back by eliminating or rerouting something wrong.

What you describe is a fuel metering problem but may not be the AFM due to an air leak after it.

Hope some of that helps.

shortyboy

my money is on either the speed reference sensors or wiring to them. Had the same issue, cold starts were fine but after a warm up and short pit stop at a store or something, it would not start.

Ronin-951

Small chance the DME Temp Sensor might be failed in the 'cold' state, but that would normally just be pig rich.

eyeball kid

Great ideas. Thank you all. Got a wide band AFM, and it is where it's supposed to be pretty much all the time.

jvillanueva944

Take out s/r sensors and clean them out.. they can get covered in oil and debris causing weak signal.

jmj951

Tach bounces in the no-start condition, so why is everyone thinking S/R sensors and connections? If a 951 has tach bounce, doesn't that always rule out S/R sensors?

FYI if needed, a quick way to rule out S/R sensors post-DME is to hook up a 12V light bulb to the DME connections on the coil (borrow the glove box light assembly and run long wires from the DME connections on the coil to the connectors on the bulb assembly). If the light blinks when you crank the engine, then your S/R sensors are fine and the coil is getting the signal it needs. This test doesn't guarantee spark, just that everything is good electrically from the S/R sensors through the DME and up to the coil.

Also, you probably have a spare DME relay on hand, right? Swap it the next time you have a no-start condition.

Black51

Plugs, plug wires, no fuel pressure, DME relay(cause of no fuel pressure), cracked solder joints in DME, injector harness, ICV, TPS, etc...

You should install a fuel pressure gauge on your rail to rule out fuel pressure. It's a very cheap and simple upgrade. Change your plugs, but only when the problem shows up. That will rule out that. The contacts inside the DME relay might be going kaput. Again, swap it only when the problem shows up.

To me, it doesn't sound like reference sensors if you're getting tach bounce.

Basically, you need to start ruling things out one by one. Start with the simple and cheap things first, then go from there.

Rogue_Ant

I read it quickly, and didn't see the tach bounce part.

Check the fuel injector harness. Just had this happen two days ago with one of Dave's cars..

968turbos2

Next time it does not start, take a small screw driver or anything metal with a little mass to it and tap on your fuel pressure regulator while starting if you can or just do it then try to start the car. Had similar situation as a result of the FPR sticking when warm randomly and causing very high fuel pressure so the injectors could not open. Found out the hard way taking off the plug for a pressure gauge and the check ball was stuck so I tapped on it and was sprayed eyes and face with gas.