Issues with warm temp, starting

[mapguy]

My 1999 Boxster has started a weird behavior. When the car is warmed up, gage at 180, and I shut it down it will start no problem. If I wait for about a hour or so, allowing the temp gage to show about 150 or less, it will crank but not start. I must wait for it to cool to about 100 to get it to start. Here are the things I've done.

1) MY Duramatic is returning a 1324 code. (camshaft position) so I replaced the cam position sensor.

2) I've performed the electrical tests(from my Bentley) on the Relays in the trunk, checked all fuses etc.

3) I by- passed the relay for the fuel pump and the pump works fine.

4) I've checked for vaccum leaks.

5) I've replaced plugs and coils.

6) I took the MAF off and it didn't make any difference.

7) I cleaned the TB.

Any help will be greatly appreciated.

Thanks in advance

Mapguy

Edited October 7, 2009 by mapguy

[Loren]

What do you mean by not start?

It does not crank?

or

It cranks but does not catch and fire?

[mapguy]

It cranks but will not start when the temp (gage) is at 150 - 180. I just started the car cold and watched the temp go up to 180 on the gage and it just stalled.

[pk2]

You might want to see if you really have a spark (just ask the guy at checkers how...ahem) . But really. the most direct method is to take a plug out , put it back on the coil/wire, dangle it away from an thin vaporous and flammable and while someone cranks it over to see if it sparks. (you can also do it without removing the plug with a timing light on that plug wire (don't know if that works with coil packs though, same goes for one of little the spark tester pen). If it does you have a fuel problem. If not, trace the circuit back to it's orgin testing al the way.

If you have a spark (I'm going to be flamed for this) spray some starter fluid in to the throttle body mouth, crank it and see if it kicks a bit. If it does you have no fuel supply.

Either one, no spark or it won't kick narrows the possibilities 50%. I'm guessing it's electrical, sensor related, or possibly a screwy security box. Electronics can get screwy with heat. Essentially, over 100 degrees a signal is being sent saying to the dme, "don't spark" or "don't inject while cranking". Part of the security box/system keeps the car from starting but, won't necessarily keep it from running once started.

One weird thing is at least one part of the security immobilizer circuitry is only active (disabling) while cranking Once the engine is running though, any thief is good to go. Case and point, the ignition key immobilizer; Start the car up and if you could remove the head or pill from the key, while running, it will keep running, all day long but, it won't start again till the head or pill is back on. Then once running you can do it again.

So check for a spark, fuel and you have half as much to ponder. Also remember dodgy electronics can be heat sensitive to heat and start throwing out bad signals, Like some sensor on the block.

It's early , food for thought...

PK

Last though; If all the mobilizer stuff works the same as the key, running it on starter fluid for a couple seconds may be enough to get it out of mobilizer mode and let it keep running on it's own. That will tell you more.

Regards, PK

Edited October 8, 2009 by pk2

[mapguy]

Thanks PK2 - I tried the starter fluid and it will not fire. So I assumed it is electronic. I then spoke to "the man" at Rennshop and he is pretty sure it's the Crankshaft Position Sensor. Just ordered one should arrive Friday. I'll update then.

[wvicary]

I wouldn't recommend using starting fluid of any type. It's not worth the risk of engine damage. Can you check for engine RPM while cranking on the Durametric?

[pk2]

Thanks PK2 - I tried the starter fluid and it will not fire. So I assumed it is electronic. I then spoke to "the man" at Rennshop and he is pretty sure

it's the Crankshaft Position Sensor. Just ordered one should arrive Friday. I'll update then.

Smart move, starting fluid first instead of checking a plug for a spark. 2 birds.

So the theory is, the position sensor (electronic (?)) gets effected by heat and stops working. That would stop your spark allright, fits my (dicey electronics spaz when hot) scenario to... sorta.

I don't know what might be special about a Porsche sensor or circuitry to and from it. Someone one can set me straight because there usually isn't that much to these sensors to go wrong (or weird). Why does it (the sensor) work fine and run the motor normally at 100-180, but then suddenly freaks & stops working as soon as you turn it off for a second.

So, all that has happened is: Sensor gets'warmed up + quick power interruption= instant, comatose sensor.

I guess dicey electronics can do any thing...

Regards, Peter

Edited October 8, 2009 by pk2

[pk2]

I wouldn't recommend using starting fluid of any type. It's not worth the risk of engine damage. Can you check for engine RPM while cranking on the Durametric?

Should try it sometime. In my experience, a quick little 3 second, 1500rpm blip on ether pretty much pales in comparison to what your motor goes through screaming around the track at 7k rpm's for hours. Lot of heat, fatigue, twisting, torquing, clashing, gnashing, back and forth, round and round, 720,000 times in that 2 hour romp. Starter fluid is more like put, put, put, ...75 times with little load.

Regards, PK

Edited October 8, 2009 by pk2

[wvicary]

Starting fluid can destroy intake manifold or even worse cause a connecting rod to escape from the crankcase. I've seen it happen to many time as folks around these parts have been using it for years until one day when it goes pear shaped and causes extensive engine damage. It's just not worth risking any damage.

[phillipj]

Gentlemen,

Please don't forget about the poor guy who's Boxster wont start :o

[mapguy]

Gentlemen,

Please don't forget about the poor guy who's Boxster wont start :o

Yes Thanks! I was ready to try anything. I was very careful and I'm not an idiot so I did it and didn't ruin my engine - it just saved me time in my problem solving. The Rennshop has helped me determine that the Crankshaft Sensor is probably the culprit. I ordered one got it today and by tomarrow should know if it worked. thanks to pk2 and Carlos for their help

[mapguy]

Update! It was the Crankshaft position sensor. Runs and starts great.