'87 Carrera won't start

CarreraRocha · 10-10-2023, 08:34 PM

I have an issue with my 1987 Carrera Targa starting. I started the car and backed it out of the garage to warm it up. The car ran for about 1 minute then stumbled and died.
It cranks over fine but start. I am not hearing the fuel pump turn on with the key and am not getting power to the Fuel Pump fuse; fuel pump will run if I jumper power to the fuse. I have replaced the fuel pump relay under the seat with no change. (the relay does activate with the key.)

I am not sure what to check next. It looks like the oxygen sensor may be in the circuit, but I am not sure if that would keep the fuel pump from running.

Any help would be greatly appreciated.

911obgyn · 911obgyn's Garage

Do you have a timing light to check for spark?
Could be one of the sensors on the flywheel there are 3 plugs on the front left side of the motor on a bracket, if you exercise them it may be a loose connection and it may start. One of them is head temperature sensor. You can do a search and check for continuity on them to determine if one is faulty.

911obgyn · 911obgyn's Garage

If you have a spare DME relay i would swap that out first, every 3.2 should have a spare in the glovebox!
Relays solder joints go bad and it controlls power to fuel pump and the ECM.

911obgyn · 911obgyn's Garage

Oh you did.

romster · romster's Garage

Quote:

Originally Posted by 911obgyn

Do you have a timing light to check for spark?
Could be one of the sensors on the flywheel there are 3 plugs on the front left side of the motor on a bracket, if you exercise them it may be a loose connection and it may start. One of them is head temperature sensor. You can do a search and check for continuity on them to determine if one is faulty.

I had this issue a few weeks ago. Perhaps my thread can be of help in troubleshooting if it ends up being a similar problem. Definitely start by checking resistances at the bracket in the engine compartment.

wazzz · wazzz's Garage

Just a reminder, not hearing the fuel pump run when you turn the key on ignition is normal. It only starts running when you crank. Then it keeps running once releasing the key if the ECU thinks it is right, meaning it gets the right signals from sensors. Otherwise, no go.

This is controlled through the DME relay, so the first thing is indeed to rule it out by swapping with a new relay or using the 3-wire shunt.

GBODY_ · GBODY_'s Garage

Quote:

Originally Posted by wazzz

Just a reminder, not hearing the fuel pump run when you turn the key on ignition is normal. It only starts running when you crank. Then it keeps running once releasing the key if the ECU thinks it is right, meaning it gets the right signals from sensors. Otherwise, no go.

This is controlled through the DME relay, so the first thing is indeed to rule it out by swapping with a new relay or using the 3-wire shunt.

Is this exclusive to porsche? cause otherwise that is simply not true. Im not challenging you im genuenily asking as i am only on my first aircooled 911. And am unsure.

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wazzz · wazzz's Garage

Quote:

Originally Posted by GBODY_

Is this exclusive to porsche? cause otherwise that is simply not true. Im not challenging you im genuenily asking as i am only on my first aircooled 911. And am unsure.

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What is not true? Sorry to ask, but since I made several statements, may be one of them at least is true?

GBODY_ · GBODY_'s Garage

Quote:

Originally Posted by wazzz

What is not true? Sorry to ask, but since I made several statements, may be one of them at least is true?

That the fuel pump doesnt prime when acc is keyed on. Is that true? I didnt think so, but if true thats insane!!

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wazzz · wazzz's Garage

Indeed, there's no FP priming when you turn the key to acc or ignition. Same is true on CIS since the mid-70's when a US DOT requirement made it compulsory for the whole world to have the FP not run (or stop running) when ignition key is on and the engine is not turning. This was as a safety feature in case of accident.

GBODY_ · GBODY_'s Garage

Quote:

Originally Posted by wazzz

Indeed, there's no FP priming when you turn the key to acc or ignition. Same is true on CIS since the mid-70's when a US DOT requirement made it compulsory for the whole world to have the FP not run (or stop running) when ignition key is on and the engine is not turning. This was as a safety feature in case of accident.

Wow! Thank you for allowing me to learn something new today!

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FA-18C · 10-11-2023, 08:06 AM

In the "closed" system, there is a fuel pump check valve that retains fuel in the rails and lines after shutting down. IF this fails, fuel will drain out of the rails which leads to long cranking to prime the system. wazz is 100% correct. There is a solid state DME avail that has a priming option, I have one and it works fine.

mysocal911 · 10-11-2023, 09:33 AM

Quote:

Originally Posted by FA-18C

In the "closed" system, there is a fuel pump check valve that retains fuel in the rails and lines after shutting down. IF this fails, fuel will drain out of the rails which leads to long cranking to prime the system. wazz is 100% correct. There is a solid state DME avail that has a priming option, I have one and it works fine.

1. Isn't better to solve the loss of an initial fuel pressure, than to do a "patch" by installing the "priming option" DME relay?
2. Furthermore, which do you think is potentially more reliable long term; an original Porsche DME relay, which has just 4 internal parts,
and has been re-soldered properly, or a "state state DME" with >10X the internal parts of an original Porsche relay?

wazzz · wazzz's Garage

I have a SSR too but chose to not buy the priming option for only one reason. I don't like my engine to start too quickly when the car hasn't been used for a while.
So I give short successive cranks until I see the oil pressure go up. Then a longer crank for the engine to start. But very often it starts at the second short crank because fuel pressure is already there.

CarreraRocha · 10-11-2023, 12:08 PM

Quote:

Originally Posted by romster

I had this issue a few weeks ago. Perhaps my thread can be of help in troubleshooting if it ends up being a similar problem. Definitely start by checking resistances at the bracket in the engine compartment.

@romster, thank you for that thread. This gives me a good place to start.

FA-18C · 10-11-2023, 03:50 PM

Dave, resolved all of the issues, the solid state was a whim. Works great.i have 2 original DMEs as spares.Did not recommend it, OP was surprised that the fuel pump only runs when cranking not to prime. Just sharing there is an option should he want one. If you immediately crank they work the same.