TruckinMatt

Hello, I recently replaced the head on my 944 that I bought from a guy who experieced a broken timing belt. I replaced the head rollers tensioners belts and all the gaskets. The car sat for seven years before I got my hands on it. When I first tried to fire her up she puttered at bit and wouldnt fire. She would run for a short bit on ether. I found that the fuel pump was locked up so I replaced it with a new bosch one. I replaced the spark plugs for good measure. I checked for spark and they are firing. It still wouldn't start. Fuel pump is gettin juice and spins while cranking. I cranked for a while expecting to be pretty flooded and only plugs 2 and 4 were wet. 1 and 3 where bone dry. I feel like I am missing something here. Is there a good way to check the injectors. Please give me some place to check that I havnt yet. Thanks Matt

Yarf

Information on a company that repairs the injectors.
https://rennlist.com/forums/924-931-...+injector+test

peanut

they'll need a good specialist clean and spray pattern test after sitting a long time. Injectors are self cleaning to a point but the additives in old petrol turn to laquer in the injector ,blocking the filters and making the solenoids stick.

I have used a 9v+ PP3 battery with wires and disconnected the electrical connectors to the injectors and flashed the injector terminals with the 9v battery simulating pulsing. When you can hear the solenoids clicking loudly they are freeing up.

TruckinMatt

I will try that 9v battery trick tomorrow, if that doesn't work I guess I will give Southbay a call. I think I covered all my bases as far as narrowing down the problem. Does anybody have any thoughts to anything else I should check? If my fuel pump is working I take it my DME relay is ok?

peanut

yes if your fuel pump is working your DME relay is probably ok but you cannot take it for granted.

You need to understand how the Bosch Motronic Fuel injection system works to fault find.

I very much doubt there was a problem with your fuel pump in the first place.

When you turn the ignition on 12v+ is fed through the DME relay to the fuel pump for about 1 second only then shut off. This pressurizes the fuel system for starting.

When you crank the engine ,provided the ECU sees 225rpm crank revolutions it grounds your DME relay providing 12v+ to the fuel pump for continous pumping.
If your engine isn't cranking over fast enough the fuel pump won't be powered nor will the ignition system.

Provided all the sensors feeding the ECU are giving correct outputs then your ECU will ground your fuel pump and ignition system and pulse your injectors and coil.

I would first check that your injectors are working correctly. If two of your plugs are dry then it is unlikely to start.

Connect two wires to the 9v dc PP3 battery
Disconnect the electrical connectors to all 5x injectors including the cold start injector (85.5 onwards)

Connect one wire on one of the terminals of an injector (NOT THE ELECTRICAL INJECTOR CONNECTOR TERMINALS)
Then flash the other wire from the battery across the other injector terminal very quickly. ( DO NOT LEAVE THE BATTERY CONNECTED TO THE INJECTOR )

You will get a little spark and you should hear the solenoid inside the injector click twice . One as it hits the end of the injector and the second time when it returns to rest after you remove the battery wire.


Repeat this at least 10x for each injector or until you can hear the injectors clicking loudly

Then reconnect and try starting. You should see fuel on all the spark plugs .

If no start post back and we'll try the next step

TruckinMatt

I am going to try that battery trick later today. My fuel pump was locked up I took it out and hooked it up straight to a battery and it wouldn't spin. I am sure the car sitting for 7 years didn't help plus the fuel pump sitting at the lowest point in the system any moisture would have ended up there. If I was to meter the connectors to the injectors what am I looking for from the computer? Voltage, ohms? any specs just to make sure they are gettin signal. Thanks for all your help I will let you know later today how far I got.

peanut

do not what ever you do connect a multimeter to the injector connectors unless it is reading dc volts.
You cannot test the unjector supply connectors for resistance. Some of the chips in the ECU run on very low voltages and can easily be damaged .

You are looking for 12v+ to the connectors either or possibly both terminals should have 12v+ with ignition on
If you can get hold of a Noid light test the injector supply with that. You should then see the LED in the Noid light flashing with the pulses from the ECU when cranking the engine.

The ECU does not supply any voltage to the injectors. The ECU grounds the 12v+ supply that is fed to the injectors from the DME relay.

TruckinMatt

ok that makes sense and may have found the problem. I did test the injector connector for dc and I got no reading. I guess I will try to get my hands on a DME relay tomorrow and see if that helps. I have seen the inside of this relay and it actually looks like two relays in one housing which would explain why the fuel pump is working and the injectors are not. Ill see what happens then

peanut

Matt did you check each injector terminal to ground on the car chassis ? or did you check between the two connector terminals ?

Remove the DME relay and check between terminal 30 and the car chassis with a multimeter . You should have 12v+ with the ignition off or on.? That is your 12v+ supply to the fuel pump. It is fed through the DME relay to the fuel pump and then to ground.

If you have 12V+ at terminal 30 (the terminals are marked on the relay base) then use a 3x way bypass wire instead of a DME relay .
Connect termial 87 to 87b then last connect terminal 30 .

Your fuel pump will then run continously. Try start the car now. If it doesn't start with a bypass wire then the problem is not your DME relay.

TruckinMatt

after playing with the 9v battery she finally fired today , She is missing really bad and was running really hot but she started I put some injector cleaner in the fuel system hopefully that will clean out those injectors but now I need to find out why shes running so warm.

peanut

Matt I'm very glad the car is running now but the very worse thing you could have done is put a cleaner into the tank !....

All that will achieve is send all the muck in your fuel pipes along to block the extremly tiny filters in all of your injectors.

944 owners with injected engines should never never use a fuel system cleaner unless you disconnect the fuel distribution pipe first.The best it is likely to achieve is to block your fuel filter or injector filters.


ok lecture over

If your engine is running on less than all 4x injectors or getting insufficient fuel a lean mixture could raise the temperature.
Sounds to me like your car doesn't get used frquently ?

I would take the car on a longish run keeping the revs low in every gear and keeping well back from other cars. maximise the air flow through the radiator and avoid traffic jams. The injectors will probably clean themselves

Keep a check on the temperature guage and if the fans don't cut in to bring the temperature down you might have a problem with the fan, fan fuse or radiator temperature sensor.