Porsche 911 Do you know the reason why?
Discussion
I need all your help before I go crackers
I have a Porsche 911 1987 3.2 supersport.
It was my childhood pin up car. I bought it 2 months ago. So here is the problem.
Start the car , set off great. park it up lock and leave. return press immobilsier and opens and beeps. great. Turn the ignition, car starts, great. runs for 20 or so secords then dies.NOT SO GREAT
The car will not restart. Get out lock it up. leave 20 minutes return and car starts up and off we go. great.
Now everyone said change the DME relay. Did do but problem remains.
I have a scorpion 1218T2 alarm /imobiliser.
Please can any of you petrol heads offer some advice.
Tony
United Kingdom
>>> Edited by Bullseye123 on Saturday 22 January 15:04
I have a Porsche 911 1987 3.2 supersport.
It was my childhood pin up car. I bought it 2 months ago. So here is the problem.
Start the car , set off great. park it up lock and leave. return press immobilsier and opens and beeps. great. Turn the ignition, car starts, great. runs for 20 or so secords then dies.NOT SO GREAT
The car will not restart. Get out lock it up. leave 20 minutes return and car starts up and off we go. great.
Now everyone said change the DME relay. Did do but problem remains.
I have a scorpion 1218T2 alarm /imobiliser.
Please can any of you petrol heads offer some advice.
Tony
United Kingdom
>>> Edited by Bullseye123 on Saturday 22 January 15:04
[quote=SXS ]Little gremlins like that are a killer...
Definitely an electrical problem.... have you tried wiring up a multimeter to the MAF/MAP sensor and see if its on the blink? just a thought...[/quote]
I would advise not to do this unless you know what you are doing and how the sensor works.
SXS may be on the right track but I know that at least on my old Range Rover even the very low current of a multimeter is sufficient to blow the sensor. (ask me how I know). I later read that I should only have applied the meter for a maximum of something like 2 seconds.
Go find an auto electrician.
Steve
Definitely an electrical problem.... have you tried wiring up a multimeter to the MAF/MAP sensor and see if its on the blink? just a thought...[/quote]
I would advise not to do this unless you know what you are doing and how the sensor works.
SXS may be on the right track but I know that at least on my old Range Rover even the very low current of a multimeter is sufficient to blow the sensor. (ask me how I know). I later read that I should only have applied the meter for a maximum of something like 2 seconds.
Go find an auto electrician.
Steve
I have an '87 Carrera. When I bought it a few years back now, I was dead carefull. I think the bloke that sold it was a bit worried, I spent more time under the car than in it. For nearly a whole afternoon he was paranoid that I was going to find something he didn't know about!
I'm glad I did though, he didn't tell me everything. He didn't tell me about the DME problem.......
The first day I had the car, I went out in the morning and tried to fire her up. She ran for twenty seconds and died. Tried again, same thing, I couldn't believe it! All that effort, and I still ended up with a dud.
All those fears about being a laughing stock, the small todger problem.... Arrrrrrrgh! For a day I was distraught. In the end I decided to be rational and find out what the problem was.
O.K. the DME problem. The Fuel pump is electric, and without fuel your engine won't go. When you turn on the ignition, the Motronic ECU fires into life and decides that since you've turned the ignition key, you must want to go somewhere. It knows that to do this you're gonna need fuel in the engine. It doesn't have the grunt to to drive the fuel pump directly, so it has a relay to do it.
This is where the problems start. There are a number of other factors which affect weather the Fuel pump is going to run, the details of which I can't remember. The bottom line is that the electrics aren't well designed.
There is a condition which the electrics go through every time you start the engine which causes the current through one of the acilliary fuel pump relays to be very high. In the end the relay dies, but the contacts are usually welded shut, so you don't notice the problem. In fact the only way to recognise the problem is to root around under the passenger seat and feel for a hot relay.
Once the electrics are in this condition, the ECU ends up taking the strain, and in the end it gives up. It has an open collector output which can't sink the current that it is expected to when in this erroneous but difficult to spot condition.
The open collector output on the ECU can fail completely, or it can become intermittent. Obviously the first stage is to replace the DME relay, but if that doesn't work, the next stage is to solve the problem of the DME/ECU it'sself. One way of solving the problem is to get a new ECU. :-( another to repair it.
In each of these cases, one is just putting off the problem until it happens again. Another way, is to take the ECU out of the equation, by deciding that the car needs to start on the ignition rather than the ECU. This is a relatively straightforward modification and costs pence. The problem goes away forever.
The problem with this is that the ECU also does something else. If the engine stops rotating, it cuts the fuel pump, irrespective of the ignition key setting. I spent a considerable amount wondering why that might happen. In the end I came to the conclusion that it might prevent fuel spilling after an accident. I had visions of being trapped in a burning car. In the end, faced with hefty bill for an ECU, I saw reason. I realised, that in each of the serious accidents that I had been involved in, a car had always ended up running with the throttle wide open even though the car wasn't going anywhere.
Since the ECU only shuts down the fuel pump if the engine stalls, I figured that if you're gonna die, you're gonna die.
A less expensive alternative to a new ECU might be to get you existing one repaired, if it needs it. If you get someone to do this, you might consider getting them to modify the electronics and electrics, to eliminate what I consider to be a design fault.
Andy.....
BEng Electronics!
I'm glad I did though, he didn't tell me everything. He didn't tell me about the DME problem.......
The first day I had the car, I went out in the morning and tried to fire her up. She ran for twenty seconds and died. Tried again, same thing, I couldn't believe it! All that effort, and I still ended up with a dud.
All those fears about being a laughing stock, the small todger problem.... Arrrrrrrgh! For a day I was distraught. In the end I decided to be rational and find out what the problem was.
O.K. the DME problem. The Fuel pump is electric, and without fuel your engine won't go. When you turn on the ignition, the Motronic ECU fires into life and decides that since you've turned the ignition key, you must want to go somewhere. It knows that to do this you're gonna need fuel in the engine. It doesn't have the grunt to to drive the fuel pump directly, so it has a relay to do it.
This is where the problems start. There are a number of other factors which affect weather the Fuel pump is going to run, the details of which I can't remember. The bottom line is that the electrics aren't well designed.
There is a condition which the electrics go through every time you start the engine which causes the current through one of the acilliary fuel pump relays to be very high. In the end the relay dies, but the contacts are usually welded shut, so you don't notice the problem. In fact the only way to recognise the problem is to root around under the passenger seat and feel for a hot relay.
Once the electrics are in this condition, the ECU ends up taking the strain, and in the end it gives up. It has an open collector output which can't sink the current that it is expected to when in this erroneous but difficult to spot condition.
The open collector output on the ECU can fail completely, or it can become intermittent. Obviously the first stage is to replace the DME relay, but if that doesn't work, the next stage is to solve the problem of the DME/ECU it'sself. One way of solving the problem is to get a new ECU. :-( another to repair it.
In each of these cases, one is just putting off the problem until it happens again. Another way, is to take the ECU out of the equation, by deciding that the car needs to start on the ignition rather than the ECU. This is a relatively straightforward modification and costs pence. The problem goes away forever.
The problem with this is that the ECU also does something else. If the engine stops rotating, it cuts the fuel pump, irrespective of the ignition key setting. I spent a considerable amount wondering why that might happen. In the end I came to the conclusion that it might prevent fuel spilling after an accident. I had visions of being trapped in a burning car. In the end, faced with hefty bill for an ECU, I saw reason. I realised, that in each of the serious accidents that I had been involved in, a car had always ended up running with the throttle wide open even though the car wasn't going anywhere.
Since the ECU only shuts down the fuel pump if the engine stalls, I figured that if you're gonna die, you're gonna die.
A less expensive alternative to a new ECU might be to get you existing one repaired, if it needs it. If you get someone to do this, you might consider getting them to modify the electronics and electrics, to eliminate what I consider to be a design fault.
Andy.....
BEng Electronics!
Yep. Mine does. It's supposed to work that way.
There are two fuel lines, out and return. The tank is at the front the pump pushes the fuel direct to the back of the car, where it is filtered. The fuel then goes on to the regulator, and into the main fuel rails for the injectors.
The regulator maintains a constant pressure in the fuel rails, and sends any unwanted fuel back to the tank at the front in the other fuel line.
When at idle most of the fuel goes back into the tank, and when wide open, most goes into the engine.
Andy.
There are two fuel lines, out and return. The tank is at the front the pump pushes the fuel direct to the back of the car, where it is filtered. The fuel then goes on to the regulator, and into the main fuel rails for the injectors.
The regulator maintains a constant pressure in the fuel rails, and sends any unwanted fuel back to the tank at the front in the other fuel line.
When at idle most of the fuel goes back into the tank, and when wide open, most goes into the engine.
Andy.
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