83 944 will not stay running

[steves83944]

I have a 83 944, it will start but as soon as the key turns back to run it stops running. i have replaced the coil, ecm, s&r sensor and the fuel pump relay. i even made a jump wire for the fuel pump relay and the fuel pump stays on but still will not stay running. with the fuel pump relay in i check if there is power going to the fuel pump with the key on and there is no power there, turn the key to the start position and the power is there the engine starts let the key go to run engine stops and no more power to pump, not sure what to do now, thanks for your help

[nynor]

bad ignition switch?

[steves83944]

Originally Posted by nynor

bad ignition switch?

Thanks ,i will try it today and let you know.

[DeadPorsche944]

Have you jumped the DME/fuel pump relay so that both stay powered?
If so, the FP should stay on. I have a similar thread with these issues. Search on my posts. I'm using my phone right now, otherwise I'd give you the link.
This will bypass the ignition switch.

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[v2rocket_aka944]

Originally Posted by DeadPorsche944

Have you jumped the DME/fuel pump relay so that both stay powered?
If so, the FP should stay on. I have a similar thread with these issues. Search on my posts. I'm using my phone right now, otherwise I'd give you the link.
This will bypass the ignition switch.

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DME relay jumper won't give any power to the ignition system, only fuel.
You need the ignition switch for the spark to work...there is a black wire at the ignition switch that runs straight to the ignition coil.

[steves83944]

tried new ignition switch and still the same. it will stay running with starter fluid, so i checked if i was getting fuel to the rail and i am, injectors do not seem to be opening, checked injector wiring and they are tell them to open. cleaning the injectors to night

[DeadPorsche944]

Originally Posted by v2rocket_aka944

DME relay jumper won't give any power to the ignition system, only fuel.
You need the ignition switch for the spark to work...there is a black wire at the ignition switch that runs straight to the ignition coil.

Yes, but if you notice in the message, the fuel pump turns off when the key is released. It won't matter if there is power at the coil if the fuel pump is off. By jumpering the DME and fuel pump on, you can then eliminate DME/FP relay from the debug equation.
If the car keeps running, then you've isolated it pretty quickly. It's an easy thing to do.
Also, if the DME isn't getting power, you won't get a spark.
The DME relay also supplies power to the fuel injectors.
Yeah, go ahead and check the power at the coil, that's easy.

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[DeadPorsche944]

There's a lot of stuff needed for the car to keep running. Power to ignition switch, ignition switch supplying power to turn on the DME/FP relay, a signal from the AFM, power to the fuel pump, signals from the reference & speed sensors, ...

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[v2rocket_aka944]

what you might try is jumpering the DME relay socket to power the fuel pump and DME, and also unplug the harness from the ignition switch and use another "jumper" to start the car and take the switch out of the equation entirely.

[steves83944]

put new injectors and still will not stay running, any one?

[DeadPorsche944]

Have you jumpered the DME/FP relay? It takes a 3 wire spade ended jumper. One end goes to the battery power input, one to the DME, and one to the fuel pump. If your not sure which is which, just look for the larger slots that have wires coming to them. The small slots are the control inputs that turn in the DME and fuel pump.
You should hear the FP turn on as soon as it is jumpered.

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[djnolan]

It could be a harness problem.

I won't get into the details , short or open or intermittent, Injectors, Sensors, coil.

Intermittent is the real killer...

[steves83944]

yes i have jumped the DME /fp relay to death, the fuel pump runs just find but will not stay running even jumped it will not stay running. i put a new Throttle body postilion sensor in and nothing.

[Ga 951]

I hate to suggest something so easy!! Is the AFM plug FIRMLY seated?

[DeadPorsche944]

Originally Posted by steves83944

yes i have jumped the DME /fp relay to death, the fuel pump runs just find but will not stay running even jumped it will not stay running. i put a new Throttle body postilion sensor in and nothing.

When you jump the DME/FP relay, you are sending power from the battery, through, through the jumped relay, through a 15 A fuse, through the fuel pump and to ground. If the fuel pump is turning off, ONLY something in that path is not working (including wiring). Since the fuel pump does run, you can rule out the battery and the fuse. If you have jumpered the relay correctly, you can rule that out. That ONLY leaves the wiring and the fuel pump. The fuel pump does run, and you have probably verified pressure.

So let's check voltages from start to finish. You are going to take two measurements at each location. One while the key is turned to the start position and the other when the key is in the run position. Keep the telay jumpered
1. At the battery. Let's just make sure their isn't any large drop offs in voltage that would keep the fuel pump from running
Probe the following at the wires coming out of connector. These are the fat wires.
2. DME/FP relay: the power input
3. DME/FP relay: the power output to the FP
4. DME/FP relay: the power output to the DME
5. At the FP.

With the relay jumpered, you should be getting battery voltage at all these points, all the time. If you are then their are only three possibilities of what is wrong
1: the fuel pump is weirdly bad
2: their is a bad ground somewhere
3: you are measuring incorrectly

One last clarification, when you say "it will not stay running", you are referring to the fuel pump and not the engine, correct?

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[DannoXYZ]

Originally Posted by steves83944

yes i have jumped the DME /fp relay to death, the fuel pump runs just find but will not stay running even jumped it will not stay running. i put a new Throttle body postilion sensor in and nothing.

You must test voltages at various places as previously outlined. If not, you will end up replacing all parts in car, up to and including the engine before you get a running 944. These cars are old and parts do wear out, usually just one at a time. So you have to figure out which part it is that's bad. Otherwise, you'll end up replacing A LOT of perfectly working parts with perfectly working NEW parts and end up with a large box of spares won't need for 10-years or if ever.

Measure those voltages at various parts of starting sequence of events.

Also.. .measure the line going from AFM-air-flow meter to DME. Without a valid AFM voltage signal, the DME will shut off engine. Make sure that voltage is the same at AFM and at the DME connector. Make sure you have an early 0-8v AFM as well, not the later 0-5v unit. And make sure you have the early DME that works with that AFM.

[DeadPorsche944]

Originally Posted by DannoXYZ

You must test voltages at various places as previously outlined. If not, you will end up replacing all parts in car, up to and including the engine before you get a running 944. These cars are old and parts do wear out, usually just one at a time. So you have to figure out which part it is that's bad. Otherwise, you'll end up replacing A LOT of perfectly working parts with perfectly working NEW parts and end up with a large box of spares won't need for 10-years or if ever.

Measure those voltages at various parts of starting sequence of events.

Also.. .measure the line going from AFM-air-flow meter to DME. Without a valid AFM voltage signal, the DME will shut off engine. Make sure that voltage is the same at AFM and at the DME connector. Make sure you have an early 0-8v AFM as well, not the later 0-5v unit. And make sure you have the early DME that works with that AFM.

Great point in the AFM. If you got a replacement, the newer models send a 0 - 5 V signal to the DME. Older ones 0 - 11. Also if you replaced your DME, make sure out was with the older model, NOT the newer.

DannoXYZ WAS GREAT HELP IN GETTING MINE RUNNING. Listen to what he suggests.

Also, after I got mine running, something else died and I had to fix that. All is well now, I even have the AC working great. You can do it, these are not really that complicated, just a bear to work on sometimes.



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[DannoXYZ]

Just to be clear in case the info wasn't discovered in other threads, the fuel pump only runs under the following conditions:

1. Key is in START position or
2. Engine is running

With key on ON position and engine OFF, pump NEVER runs. This is an intentional safety feature. You don't want to be in wreck, trapped upside down with ruptured fuel lines and have the pump happily running along spraying fuel all over your hot exhaust and catalytic!!!

Now, when you turn key to START (#1 condition above), the DME turns on fuel pump, pulses injectors blindly and ignites the plugs to start car. AFM, O2-sensor, TPS, etc. are all ignored when key is on START.

Then when you release key back to ON, the DME checks the input signals to determine how much fuel to inject and when to fire spark. Critical in these calculations are:

- AFM signal, determines how much air is flowing into engine
- Speed signal, determines how long to hold injectors open to match air-flow measured by AFM
- Reference signal, determines when to fire spark relative to TDC

So.... if your car stops running when you release key, lack of fuel is just the symptoms of your problems, not the cause. The DME has cut fuel because some condition is not correct.

1. Test AFM output voltage when cranking at the AFM connector and at the DME connector. Report that voltage back here.

2. Test speed & ref sensor impedance, report that here

3. Measure S & R sensor waveforms with oscilloscope. That will determine if they are adjusted above triggers properly

[DeadPorsche944]

Status?

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