Cranking but motor won't stay on for more than 2 seconds!

[dkkim81]

Bought my 1984 Porsche S just a few weeks ago. After performing delayed maintenance from the previous owner (spark plugs, rotor cap, wires, brake pads, brake rotors, new fuel injector hoses, all 4 struts), I decided to put in a car stereo to replace the head unit. I take it into the shop on Tuesday, leave there all day, and at the end of Tuesday, the car cranks, but it won't start. When it does start (stay idled), it won't stay on for more than 2 or 3 seconds!!

I replaced the fuel filter and fuel pump thinking that it might work, but to no avail. I checked the spark plugs and 2 of them were blackened even though they were very new! I will next try to replace the ignition coil. Everything mechanical seems ok?

Could the ignition coil prevent the motor from staying on? Or do you guys think that the installers at the audio place could have crossed some wires or cut ones they shouldn't have? Could a bad wire connection or small electrical problem prevent the car from starting and staying started??

Has anyone had this problem happen before??

[tedward515]

Congrats on the new car. Looks good. First we need more pics

I would rather doubt that your ign coil is the problem. Its most likely to be an electrical problem like a relay or poor ground. I wouldn't be surprised if your car has an old alarm system or two that might be rearing its ugly head after the stereo install.
I would also go through and clean all of the ground points. There is a chart with there locations here or on Rennlist I can't remember, maybe someone else can post it. by cleaning the grounds it will help eliminate that has a potential problem. I think most will agree that the 928 can do some strange things when you have a bad ground. That should get you going down the right path to diagnose the problem.

[Mrmerlin]

get a fuse chart here 928gt.com , find page 2 then tips and links, print one off.
Go check the fuses make sure that the correct fuse in the in the correct position and clean the ends of them with a pencil eraser.

Next if the car was running before the install of the stereo, then that is probably the reason it is now not running, as the installer either damaged a fuse or another wire has been shorted, do the fuse check first

[dkkim81]

I changed the fuel pump, got new spark plugs and will change the fuel pressure regulator tomorrow. It is still cranking, but not starting!

How many fuel pressure regulators are there in the 1984 Porsche 928S??

I will also take the car into the audio spot on Wednesday so they can take their time to check their installation...

[Mrmerlin]

how do you take a car thats not running to the audio store??
This seems like it could go different ways , your taking the car to people that dont have a clue on how its wired and you expect them to check their work?????

My suggestion is find a good 928 Mechanic and have the car towed there, if he is a good mechanic he should be able to figure out the radio install

Follow the advice in link 3 and figure out the fuses, first,
also swap out the fuel pump relay with the horn relay

[JhwShark]

Originally Posted by Mrmerlin

how do you take a car thats not running to the audio store??
This seems like it could go different ways , your taking the car to people that dont have a clue on how its wired and you expect them to check their work?????

My suggestion is find a good 928 Mechanic and have the car towed there, if he is a good mechanic he should be able to figure out the radio install

Follow the advice in link 3 and figure out the fuses, first,
also swap out the fuel pump relay with the horn relay

Follow the advice...check the FP relay by swapping as suggested. It can get fried if the pumps were working to hard to deliver fuel. Then do the others...

Jon

[Alan in AZ]

The fuel pump fires for 2 reasons - a short initial priming pulse when the ignition is turned on, then it won't turn on again until it detects engine rotation.

sounds like you may be getting the priming pulse but nothing else.

Does the radio install include a speed ralated connection... if so suspect that.

Workaround - remove the relay and insert a fused jumper from the socket 30 to 87 terminals - if the car starts & runs this way - that is your problem.

You cannot leave the car is way - the fuel pump will always be on... and safety features will be disabled

Alan

[dkkim81]

The audio guys checked their installation, jogged something back into place, and now the car works, albeit with a rough idle. But it will do for now!

[ptitquick]

Hi,
I am currently experiencing the exact same problem on my porsche 928 - 1983. My car will not start for more than 2-3 seconds. I was wondering if you have succeded to fix your problem on your car ?
Please contact me, I would really appreciate the help. My direct email : lucnadeaumaster@gmail.com

[JhwShark]

piti,
I suggest you invest some time and get the information previously recommended in this post.

Get a WSM cd and or the wiring diagrams and apply the knowledge shared by others. Also, for rough idle look into vacum componenets, A/F ratio, fuel pressure, fuel filter...even timing. How is the compression?

Owning and maintaining a classic is applying art and science, patience, as well as pro-action...we must get to know our "rigs" from putting our hands on them.

The audio guys jogged something and it worked...I'd rather see the audio girls jiggle something...
Having anyone that does not know a 928 electronics, touch the circuitry is messing with trouble...have them show you exactly where they wired the radio (ground, hot, security), get pictures of the connections and evaluate against the schematic for any protagonistic connections! Post the pictures and we may be willing to give more precise input.

I am uncomfortable with it's good enough for now approach...never liked being on the side of a snowy mountain road at night...or even on a local highway...sometimes a bandaid is not what it seems when what is really needed is a stent...
I am sure there is a better metaphor...

[Danglerb]

Once you've poked around in the dash of a few cars ever letting an "audio shop" mess with your car loses its appeal. They are generally clueless, cutting wires until they find one at random to tap into, total objective is in and out fast and what the customer doesn't see doesn't matter.

Sooner or later we will all need to sort out some mess in there, might as well make it our own mess, do it maybe slowly, but cause no harm.

Ptitquick needs to start a new thread, introduce themselves and no expect people to contact them via direct email. What makes a forum work is that if I give you stupid advice, everybody sees it and somebody will correct it. Also if I fail to give a complete answer, others can pick up the slack and fill in the missing information.

Check your GREEN WIRE. it goes from the distributor to the area of the 14 pin connector on the passenger fender, and its bright green.

[EIPtuningR32]

help me out on this guys but, when a spark plug is BLACK after just being changed doesnt that mean its running rich? maybe your issue is your running so rich its flooding the motor at startup....

[Fredfox]

Do these cars have a starter relay and a resister wire from the solenoid? If so, the starter relay may be bad. It will give it full voltage to crank, but when you let go of the key, it will stop.
This is just a thought.

[Danglerb]

Unless the motor actually runs, fine points like rich or lean aren't going to be easy to tell since fuel could be going in the cylinder or not, during cycles with no spark.

[DPW928]

Originally Posted by Fredfox

Do these cars have a starter relay and a resister wire from the solenoid? If so, the starter relay may be bad. It will give it full voltage to crank, but when you let go of the key, it will stop.
This is just a thought.

Good thought! Actually there are two resistors that feed the coil. During cranking the circuit is routed through 1 resistor which supplies a higher voltage for starting. After starting the circuit is routed through both resistors which reduces the voltage to 3 to 5 volts. If the connections on the second resistor are corroded, the voltage would drop to less than 3 and the engine would die. The resistors are located on the panel in front of the drivers side wheel well.