Help with injectors test

[mmasse]

The injector on cyl 6 seems not to be working. Engine is a '97 993., EURO -OBD1 DME

I run a test with a diagnostic tool for OBD1 Porsche engine. The tool allows you to run a test to detect failure on injectors and other sensors, by sending signals to them in a sequence. On all injectors, except nr 6 you can hear the clicking noise when the test is run. On cyl 6 there is no clicking. The problem seems not to be the injector, because I switched the wires between 5 and 6 and the run the test. In this case you could hear the injector in cyl 6 (with the wire of cyl 5) clicking.

I tried to test for signal at the connectors of the injectors, but i dont think I understand how this is supposed to work. I tested with a multimeter and a test lamp. I turned the ignition on (motor not running) and connected the lamp to the injector connectors, but the lamp will stay on all the time. Then I tested with a multimeter and I got 11.59 volts on all injectors, except on number 6 where I got 11.98 volts, but again I got voltage all the time on all cylinder and it seems not to be a different when the test is run. so, when an injector should be clicking I got the same voltage as when it was supposed not to be clicking. I thought you were supposed to get 12volts, only when the injector is activated.

Can anyone explain me how this should work?

Thanks

[mmasse]

Well, there is DEFINITELY something wrong with fuel injection on Cyl 6.

I pulled the fuel rail and crancked the engine to check the spray pattern on the fuel injectors. The is clearly something wrong with the signal to injector number 6. On the other injectors you can see clearly the sequence of the fuel spray with short interval of spraying. On cylinder 6 the spray is a LOT larger and duration is very long. It looks like it is spraying all the time. Again, the problem is NOT the injector because I run the test switching wires from injector 6 to 5, and then the same problem will show up on injector 5. Something is screwed with the signal going to injector 6.

Any ideas --PLEASE!!!

Thanks

[Bill in OKC]

It is correct that you will see ~12V at one side of the the injector connection all the time. The other side of the injector connection gets grounded when it is time for it to inject.

edit: If you have spray all the time then the injector could be stuck open (it happens for a short time -but stuck closed- on one of my bikes cylinders when running e10) or the low side is shorted to ground. Check continuity from cyl 6 connector low side to chassis ground. If you get zero ohms then you'll have to track down where it is shorted.

If you have sequential injection then it could be in the ecu as well - hard to know over the internet.

[mmasse]

Originally Posted by Bill in OKC

..Check continuity from cyl 6 connector low side to chassis ground. If you get zero ohms then you'll have to track down where it is shorted.

Could you clarify what you mean by low side? The connector has two wires, which one are you refering to?
Thanks

[Bill in OKC]

Originally Posted by mmasse

Could you clarify what you mean by low side? The connector has two wires, which one are you refering to?
Thanks

That is the side that does not have 12V on it. It would have to be constantly grounded to allow the current from the 12V side to flow through the injector and keep it turned on. It should normally have a large resistance to ground - 1M ohms or more . A short, less than 1 or 2 ohms, from this wire to ground would cause the problem you are describing, measured with the ecu disconnected.

[mmasse]

Thanks Bill

I was actualy measuring voltage between the two wires on the injector connector. That' s where I was getting 11.5 vlt?

I will measure as you mentioned and see what I get

[Bill in OKC]

Compare the reading against a functional connector like #5.

You can also try a 'noid' light. It would plug into the connector instead of the injector and then see if it ever turns off (ecu connected).

[mmasse]

Biil

I am not sure I am doing this right

I disconnected the 55 pin connector from the ECU. Then I disconnected the connectors at the injectors. I measure for ground with a multimeter between each individual wire at the injector connector, and ground ( chassis). On one wire I got no measurement at all ( meaning no ground) on the other wire I got 17 K ohm (17 on the 20k ohm scale).. I got the exact same reading for all injectors.

Does this sound right to you?

Thanks

[Bill in OKC]

I think you did it right. It looks like your wiring harness is OK since they all measured the same. That leaves 2 things that I can think of. I would hope it is a bad injector -stuck open- but the other thing I would do now (if you are sure it is not the injector) is to try a different ecu, maybe borrow one for a test? With sequential injection, each injector would have its own driver, a power transistor I would assume, and it is possible that the one transistor driving injector #6 is bad.

If you plug a noid light into the #6 position and it blinks then the injector is bad. Otherwise I would suspect the ecu.

[dshepp806]

Noid light would be a big help here,..that ECU may be hosing you...

[fastfredracing]

Here is how I would diagnose this. Borrow, or buy a noid light. The light should flash while cranking. The ecm basically pulses the ground signal to the injector off and on once per revolution. If you determine that the ground signal to the injector is indeed always grounded, then I would unplug the big harness connector from the ecm. If the ground side of the injector is still grounded, you have a short to ground in the harness. If not, the injector driver in the ecm is probably toast.
I just went down this road with a Volvo XC 90. I know, Volvo, but still a bosch ECU. Best of luck, and keep us posted