Suddenly my 911 won't start ???

[byuhog]

Hello All,
I have a 1984 911 Carrera 3.2
Really nice car. It given me 6 years of reliable performance.

A couple of weeks ago I took it into my friend's shop (he only works on Porsche) to have the Schrader valve replaced and recharge the A/C. Which we did.
Since then I have only driven the car about 3 times and each time it took 4 or 5 times cranking the engine for 15 seconds or so each time before it would finally fire. It was acting like there was no fuel pressure and it took the cranking to get the fuel to the engine.

Today, no such luck! 4 minutes of cranking on and off and it never even thought about firing. I didn't drain the battery, but that was coming.

In the 6 years I have had it, it has always fired on the first crank, even if it had been sitting for 8-10 days. But today nothing.

Could something have been missed after the Freon re-fill, or maybe a fuel pump failure? I'm going to check spark tonight to rule that out. But it's really puzzling.

I was hoping to attend a show on Saturday, but I guess that's out. If its not going to run I'd rather have it in the garage that stuck somewhere.

Any suggestions would be helpful.

Thanks

Stephen

[Discseven]

Stephan... Will suggest checking fuel pump before spark---is easier. With ignition is ON, you should hear the fuel pump buzzing when standing next to the front tire... or put your head by ground next to front tire. If no buzz, 1. bad fuse 2) bad connection at fuse and/or pump 3) pump died. Given progressive decline, probably not bad fuse. If pump is working... I'd do spark next.

Good lookin car

[jlex]

Time to pop in that spare DME relay under the driver's seat.

[cabmandone]

Originally Posted by Discseven

Stephan... Will suggest checking fuel pump before spark---is easier. With ignition is ON, you should hear the fuel pump buzzing when standing next to the front tire... or put your head by ground next to front tire. If no buzz, 1. bad fuse 2) bad connection at fuse and/or pump 3) pump died. Given progressive decline, probably not bad fuse. If pump is working... I'd do spark next.

Good lookin car

I don't believe that's accurate for a Motronic with Speed/Reference and DME relay. The pump will only go while the engine is cranking as I understand it. I have a tune in my car that will prime for 3 seconds but then it shuts off and waits for cranking.
You can jumper the fuel pump fuse and see if the pump is working. I think you can also jumper at the DME relay. I'd guess if you haven't installed a new DME relay, now would be a good time.

[proporsche]

Hi Stephen
here is how to test your fuel pump...with the key of...
Ivan

[Crude Rudy]

If its not the DME check the resistance of the speed and reference sensors in the engine bay per the SM, easy to check and eliminate

[mysocal911]

Originally Posted by Discseven

Stephan... Will suggest checking fuel pump before spark---is easier.

Actually, checking initially for a spark is the easiest on most engines, i.e. especially on a 911 3.2.
Remember, the fuel pump may run but it may not provide the correct pressure or not be powered,
i.e. the pump relay may not be getting a signal - so running it directly is of little value.

[proporsche]

Hi Dave the test for fuel pump has only value if you want to know, as Porsche manual book said ,that the fuel pump is working
Kinda test to eliminate one thing at a time...the problem above is most likely heads sensor...
Ivan

[mysocal911]

Originally Posted by proporsche

.the problem above is most likely heads sensor...
Ivan

Guessing not good! The engine will usually start (cold) with a bad temp sensor.
It can be eliminated by just jumping it with a paper clip. Use of carb cleaner into
the intake will easily determine a fuel shortage problem.

[drauz]

Have you tried jumping it? Worth checking if your batt is not strong enough output for the Motronic to be happy, though adequate to turn the starter.

[proporsche]

Dave, as i said one thing at a time;-)

Ivan

[cabmandone]

Folks! You're going to get him going sideways. Start with the known trouble spots on the 3.2 that being the DME relay. Once you're sure the fuel pump is working if you question spark, use a spare spark plug, pull a wire and see if you have spark. If no spark, move to speed and reference sensors.
I will just go ahead and rule out the CHT (cylinder head temp sensor) because yes the car will start and run albeit very poorly with the CHT disconnected and yeah I'm sure because I did it once by accident. The car ran like hell, coughed and backfired but it ran.

[Drisump]

Originally Posted by jlex

Time to pop in that spare DME relay under the driver's seat.

Agreed. Symptoms are classic and DME relays go on these cars quite frequently. Even if it doesn't solve the problem, you should have one in the glove box anyway. Cheers

[gomezoneill]

Seems odd that you never had a problem until it was worked on. I would talk to the tech that worked on the car and see if he did more than replace the valve for the A/C.

[proporsche]

Hi Cabmando...good point ..but he said "Today, no such luck! 4 minutes of cranking on and off and it never even thought about firing"..............

Ivan

[cabmandone]

Originally Posted by gomezoneill

Seems odd that you never had a problem until it was worked on. I would talk to the tech that worked on the car and see if he did more than replace the valve for the A/C.

He does have a point here. While I think most of the work would have been done on the right side of the engine bay for the A/C, it would be worthwhile to check the speed/reference/CHT connections just to make sure they are making good connection. That's actually how I figured out a 911 will run with the CHT disconnected. It looked connected but I bumped it off to a point where it wasn't actually making contact. I still think though that it's displaying a need for a new DME relay.

[Rodsrsr]

If you have spark, fuel and compression the car should start. Pretty sure you have compression so its either spark or fuel. Check for spark first as others have said. There's no reason to go any farther until you determine if its fuel or spark..

[mysocal911]

Time for the OP to start troubleshooting based on all the info provided!

[crustychief]

Originally Posted by jlex

Time to pop in that spare DME relay under the driver's seat.

This.