Why does my car keep dying

[Radraddad]

I bought a great looking 84' 911 with a few things that needed to be addressed.

The first one that I'm sure you guys can figure out quickly is what causes my car to die after it's warmed up and at idle. It's happened almost every time I've taken it out. Today I stopped some traffic while I tried to turn it over for a few minutes. The battery is good and is pushing power to the starter. The starter is trying to crank but it takes about 1-2 minutes to decide to start.

The car will start up cold with no problem. I'll drive it conservatively for 10-20 minutes, and then when I stop and idle (stopsign, parking lot, etc), it will just anti-climatically stop and not start for a bit. I won't pretend I know what I'm doing, but I assumed fuel line or filter. Oil temp, pressure, and volume are all good. The fuel in the tank was filled up by the last owner.

I'm a new Porsche owner with much to learn from my last post. I would appreciate any advice.

Lastly, there is tape keeping the brake line into the brake booster from leaking. I will figure that out when I get some time, and it looks like a pretty tough/tight space.

[EC900]

How long had the car been sitting or stored?
Fuel delivery and/or pressure problem seems likely, perhaps as simple as a vacuum leak. Bad fuel, stuck injector? What is the rpm at idle, smooth or rough? Any tailpipe smoke and what color at startup if any?
You might be able to tinker here and there to find some obvious fixes but that depends on so many other things that could be related the culprit beyond changing filters and tweaking the idle speed.

As for the line/hose leading into the brake booster; the hose is likely taped to seal a vacuum leak (no fluid), any lines from the resevoir or master cyclinder would be leaking brake fluid, no tape would fix that.

I would take a newly purchased car to a dedicated mechanic for a overall inspection rather than rely on tips and clues to sort mysteries myself as this could get complicated since I don’t have many tools, meters and garage space.

[EC900]

https://www.pelicanparts.com/techarticles/101_Projects_Porsche_911/35-Motronic_Fuel_Injection/35-Motronic_Fuel_Injection.htm

[911obgyn]

Multi meter and a test light,timing light are good for most of the sensors, if you have a timing light you can check for spark when it doesnt start. Head temp sender, crank senser and timing sensors have 3 plugs on left front side of the motor, perhaps exersise the connectors and look at wire to see how crunchy they are.

[917_Langheck]

This appears to be a heat-induced issue, not initially a failure to start issue.

Coil is often cited in situations like this.

Was hoping that "Dave" would chime in. He's got a check list posted here someplace.

I would replicate the failure condition someplace where you can assess the condition of the spark from coil to cap and cap to plugs.

Another suspect place is the dme relay can open short with time/heat on the circuit, so assessing cracked/cold solder joints is in order.

Fuel pumps can also pack up, so you can look there as well.

[pmax]

Agree with being ignition related as best bets ... coil as mentioned above or perhaps CPS sensor ?

[PeteKz]

I'd bet on the coil too. But get a bottle of Chevron Techron and pour it in the tank, then drive the snot out of it. Next, I'd look at the temp sensors.

[Radraddad]

Gotcha and agreed. The car had a PPI done before I bought it and only listed a few things, including the vacuum leak.

I do need to find someone to check it out.

I read the other post about Motronic, wasn't super clear as if that would solve anything from the responses below the article.

[grb008]

Do you have the Bentley manual? It has the check for the coil and the temp sensor. Real easy and will tell you if you have issue with just a multimeter. If you have an issue with the head temp there is a tool on amazon for under $10 that is a cut away socket that makes it easy to take out and replace with the car jacked up and wheel off.

Threads on Coils

Test Ignition Coil
Carrera Coil resistance values?

[GH85Carrera]

New coils that work for 3.2 Carrera is really hard to find with the proper voltage and fit. I gave up and found an used original old 1980s black coil.

I still want to find a new coil designed to be the right one for a 3.2.

[Radraddad]

Would that prevent it from starting as well? It usually starts up just fine from cold, but after driving a while and stopping/turning off it takes a few minutes of trying to get it to turn over.

[PeteKz]

Sometimes. What can happen is the coil heats up, starts acting up, and then when it cools back down it operates normally. Then you restart the cycle. But because it seems to be temperature related, check the temp sensors too. There is a spec chart somewhere on here for the resistances at different temperatures.

Of course, if someone nearby has a 3.2 and will swap coils with you for testing, that would be a good way to see if it's the coil. Another option: Although the exact same Bosch coils are hard to buy, any 12 volt coil with the same internal resistances will work. That coil may not produce the same maximum energy, but you should be able to test with it.

[grb008]

Ohm readings for sensor:

Verify my CHT sensor test results

[mysocal911]

Originally Posted by 917_Langheck

This appears to be a heat-induced issue, not initially a failure to start issue.

Coil is often cited in situations like this.

Was hoping that "Dave" would chime in. He's got a check list posted here someplace.

I would replicate the failure condition someplace where you can assess the condition of the spark from coil to cap and cap to plugs.

Another suspect place is the dme relay can open short with time/heat on the circuit, so assessing cracked/cold solder joints is in order.

Fuel pumps can also pack up, so you can look there as well.

Read here; 911 3.2 No-Start Troubleshooting

[Radraddad]

How is it that there isn't a 3.2 coil replacement that works?

Been reading another thread with a guy that has a similar issue. Reading his troubleshooting teaches me what I probably need to dig into this weekend.

There are no Porsche mechanics in my area, so I will have to fumble through this.

[Radraddad]

So I worked through much of the recommendations on this thread and others to include a replacement coil, replaced fuel filter/pump, plugs, DME, etc. but recognized I didn't know what Im doing. I learned from fumbling through things in and under the car. In the end, I gave up and had it towed to a mechanic with a good reputation and recommended by a friend.

He checked the fuel pressure, injector pulse, and ignition system. He found a weak injector pulse and sometimes no pulse, low reading on the reference sensor, and eventually replaced crankshaft sensors and adjusted the clearance. This got it started.

My ignition coil wire was bad and ended up getting replaced.

He mentioned that the inline fuel pump fuse needed repair. I'll have to figure out which one that is and why it would need to be repaired rather than replaced.

He found a couple of other things: my vacuum line was disconnected from the fuel pressure regulator, and the car was constantly blowing in hot air because the AC hoses were routed next to the heater boxes and needed to be re-routed.

The car starts, runs great, and didn't cost me all that much to get back on the road. I figured this could help someone else in a similar situation.

Thanks for the help and expertise.

[Radraddad]

[otto_kretschmer]

There is a screw in filter screen on the bottom of the tank so its best to just change it. My car is a 76 and the screen was clogged and it was causing problems.

[FA-18C]

Agree with Otto - change the tank screen, and new fuel filter. Would also do a hot lap on all of the grounds. My car would start and run well, and then occasionally would drop RPM and die at a stop. The strainer in the tank was 34 years old an horrible. I drained the tank and cleaned it, new strainer, new check valve, and filter. The filter was nasty as well, despite having been changed 3 months previously. Ran Techron in every tank since and thankfully have been in good shape since.

Also may be worth having your injectors cleaned or serviced.

[Radraddad]

Not sure I can afford to drain all of the non-ethanol fuel. It costs me almost as much as California gas. I'll try and change that out once I run out of fuel. Looks easy enough to swap.

Can anyone recommend a source for a replacement coil? Also, are the off-brand coils (flame throwers) worth installing or having as a backup?