cappy46

I have a 1984 Porche 911 Targa 3.2, it only starts when the engine is cold, after it has ran for a little while then turn it off. The engine will turn over, but not fire, it has a full tank off fuel. Please Help i need a starting point to troubleshoot.

Thank you

old man neri

Does it turn over at the same speed or is it a slower turn over?

cappy46

It turns over at the same speed.

3.2SLANTNOSE

Welcome to another, in Mississippi!! We are few and far between.

After you make an attempt to start the engine, and it just turns over, but does not start, can you smell raw gas at the exhaust? If so, that is a good indication that your fuel pump is actually working and the engine is getting fuel. Have you checked to see if you are getting spark to the plugs, or out of the coil? Get back with an update, because, your answers will determine the next things needing to be checked. Good luck!! Tony.

J. Brinkley

flywheel sensors

3.2SLANTNOSE

Yep, that is sort of where I am headed with this, but... only after the DME relay, fuel pump, a possible no-spark condition, etc. have either been ruled out or found the be working correctly from his testing. Tony.

cappy46

I check previous repair records, the last time my engine don't hot start, the speed sensor was replaced according to the repair receipt. Is there another name for speed sensor?

spececurep

I think you have a problem with the cylinder head temperature sensor

Ed Hughes

Well it sounds like this issue isn't new? It also sounds like "the last time your engine didn't start hot", that whoever did the "repair", really didn't. Why not go back to them for discussion for starters? Could be the cylinder head temp, could be DME, or some other wiring that is doing bad things when warm.

J. Brinkley

another name for speed sensor is reference sensor, or impulse sensor. But they're both the same, and there are two of them there.

I'd change the cht and dme relay. Resistance on the cht should be 2.2 to 2.8 k ohms at room temp
Resistance goes down as engine temp goes up. Check it after a run when it's hot. I should be less.

scarceller

First, to verify the DME has power check for 5 volts on the AirFlowMeter at the Blue/GreenStripe wire (center wire on the connector) do this with key in 'RUN' position. If you have 5V here then the DME is alive and well, so is the DMERelay. You may also want to see that you have 12V at one of the pins on a fuel injector as a second test.

Then, the speed and ref sensors (both of them are the same) should read about 1000 ohms +/- 20%. Check these with engine cold then again when it's hot and won't start.

The Cyl Head temp should read as follows:
50 deg F. = 3.3 - 4.1 Kohms
68 deg F. = 2.2 - 2.8 Kohms
104 deg F. = 1.0 - 1.3Kohms
176 deg F. = 290 - 350 ohms
212 deg F. = 160 - 210 ohms

Also with car running:
1) if you unplug the CHT sensor the mixture should go very rich.
2) if you short the sensor the mixture will go very lean.

If you have a test light place it across the 2 coil posts '-' and '+' and the test light should flicker while cranking, if it does not you don't have spark.

Do the same for the injectors: unplug injector #1 then place test light across the 2 pins in the harness and while cranking the test light should flicker.

I have a 12V LED test light and these work better than the standard buld test lights because they don't need much current to turn them on.