1977 530i "no ground to the injectors"

CBradio · Post by **CBradio** » Mon Jun 11, 2012 2:05 pm

my dad forced me to take the car to his mechanic friend,
and now the car is stuck there, hostage.

I wanted to get the car started again myself, but my dad insists I leave it there.

The mechanic has been through 3 ECUs, claiming they are all bad.
There is a slight burnt smell and an orangish film on the circuit boards,
he tells me they are "rusty."

The combo relay, fuel pump, and injectors were all swapped out.
He says "THERE IS NO GROUND TO THE INJECTORS" so the ECU must be bad.

I'm thinking he may be wrong about the ECU as well as the "rust" he sees on them. Everybody keeps telling me they just don't go bad so easily.
The mechanic says they were exposed to moisture somehow.

I don't know what to do, can anybody tell me if that orange film is normal on the circuit boards?

Anybody know other reasons why there may not be a ground to the injectors?

He says everything is going fine INTO the ECU, but that the injectors are not getting a signal..

Please help! I'm going nuts and dying to drive this car already!

CBradio · Post by **CBradio** » Mon Jun 25, 2012 2:50 pm

SO: here is an update, for anybody that is interested:

After two months of the car sitting at the mechanic,
and having the fuel pump, combo relay, ECU, and injectors all swapped,
the mechanic has finally given up.

They are telling me the injectors are not firing, and they can't figure out why.

I'm going to have it back home soon.

I need a checklist of things to check as to why this might happen,
does anybody have any suggestions, please?

1977 530i

Trevor M · Post by **Trevor M** » Mon Jun 25, 2012 6:42 pm

I'll take a stab at it.... what can you lose at this point.
I'm thinking your mechanic doesn't really understand Bosch L-jet injection too well. On the 530i, when the key is turned on to the run position, the combo relay clicks on and feeds power to the resistor bank which in turn feeds through to the injectors. In short, when the key is on the injectors are live.
To fire the injectors they must be grounded, this task is done by the ECU.
It's the ECU's job to calculate when and how long to fire the injectors according to numerous input signals. One of those input signals would come from the ignition system. The ECU needs to know how fast the engine is spinning so it can time the injection pulses. Also, if the engine were to stall the ECU needs to know this so it can stop dumping fuel into the engine.
Pin #1 on the ECU is the input signal from the ignition. There should be pulses on this wire when cranking the engine over.
Now, I'm assuming everything is ok with the ignition system and you have spark. If so then I would check the wire on Pin 1 of the ECU for breaks.
I'm not familiar with the breaker point setup in the older cars so I don't know where this signal is taken from.
I think I remember a wire with connector that runs between the ECU and tach. Maybe somebody else can confirm that.

HTH

Jeff Dennis · Post by **Jeff Dennis** » Mon Jun 25, 2012 8:20 pm

There was another post recently with a car in AZ that failed to get a signal from the tach and would not fire the injectors. If you do a search you should find that no start issue or the owner may post his trouble shooting.

CBradio · Post by **CBradio** » Mon Jun 25, 2012 10:30 pm

thanks a lot guys

I was confused about this and I'm a noob so it clears things up for me a lot.

I did not know that the ECU needed a signal from the ignition system-

the car is back with me now and I will investigate in the daylight.

I think he may have overlooked it, and I need to learn the pinout on the ECU a little better.

CBradio · Post by **CBradio** » Tue Jun 26, 2012 1:26 pm

besides the input from the tach, what other inputs are required for the ECU to signal the injectors?

If the AFM is not plugged in, will the car start at all or just start and die?

CBradio · Post by **CBradio** » Tue Jun 26, 2012 6:41 pm

Anybody know where the crank position sensor is located on a 1977 530i?
Is it in the distributor?

I got the car started somehow for about 3 seconds but only one time.
That was really exciting.

Any input is appreciated!

72Koop · Post by **72Koop** » Wed Jun 27, 2012 5:31 pm

was part of Motronic, a later version of FI.

You "fire" comes from the distributer if still stock. Below the cap, on the side is a point system that sends a signal to fire the injectors in batches. Those are low voltage and tend not to be a problem. You can look at them to make sure they're not oiled up or noticeable something wrong. Under the cap is the normal points for firing the spark plugs. So your distributer does double duty.

Since it fired for 3 seconds, it probably means you've got spark and a little fuel. There's a cold start valve on the log manifold with a fuel line that works like a choke to send a bit of fuel.

Hook the AFM back together again.

Go back to the distributer area. Follow the injector harness to find a connector by the distributer. Check that connector which sometimes gets loose, etc.

Grounds- check every ground wire related to the engine and battery. Many have added another ground to the engine.

CBradio · Post by **CBradio** » Thu Jun 28, 2012 3:42 pm

SO: all this information was very informative and helpful to me.

My cold start injector was working all the while, on its own, and I tested the ground on the motor and it read 12v...

As it turns out, I fit another distributor in and it started right up!!!!!!
FINALLY!!!

Seems that something wasn't right in there-.
Now I just need to put the rest of everything back together.

THANKS EVERYBODY FOR YOUR EXPERT HELP!!!!
(^_^)

Jeff Dennis · Post by **Jeff Dennis** » Thu Jun 28, 2012 8:57 pm

good job..

Firstfives.org

1977 530i "no ground to the injectors"

1977 530i "no ground to the injectors"

Crank positioner