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

The engine sounds like running in 5 cylinders and when I pulled out the plug from cylinder 6 it is wet with fuel.

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

 

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
__________________

 

Check the wiring from the ecu to the injector. Unplug the harness from the ecu & check for a short to ground. The other less likely possibility is that the injectors driver in the ecu has failed.

 

I will look at my service manual, but is likely 12v is always present and ground is switched on/off to complete the trigger to each injector. If you have a harness short on cyl 6 or a bad trigger to off the ECU to cyl 6, then this will leave cyl 6 always open. I have had an injector stick wide open (by coincidence cyl 6), but not an electronic issue.

 

a bit of info:

red/wht stripe wire on each injector is central. br/blue wire on cyl 6 injector leads to pin 16 on the ECU. remove the ECU and check for a short on this wire coming from the harness to the injector plug. A good check on this is compare the other cyls at the ECU end. cyl 1 is pin 17, cyl 2 is 35, cyl 3 is 5, cyl 4 is 34, cyl 5 is 23. BTW unplug the injector when check for the short.

If you had stuff apart, make sure you do not have a harness plug mixed up. The injector plugs match each other on each side of the engine: cyl 3 and cyl 6 have the same color plugs.

 

I disconnected the harness from the ECu and tsted for ground with a multimeter. I measured between each injector valve pn and ground and got the same figure (17.27 K Ohms) for all injectors, included injector valve number 6.

any suggestions on what to do next?

 

bobt993

ours posts went at the same time. I did not dicopnnect the injector when measuring, so I will do the measurements again and report back

 

Done, tested again with injectors disconnected and there is no ground on any of them, including number 6

Any other suggestions?

What about the following. Can I connect the OBD1 diagnostic tool and run the test and capture which signal is being sent to the injectors valves, WITHOUT connecting the harness? This would imply that I need to turn on the ignition without connecting the harness. Is this possible? or will this damage the ECu, somehow?

 

sounds like a shorted output from the ECU. Can you borrow an ECU from someone that has had the immobilizer deleted? FVD may be able to have the ECU serviced in Germany for you. I don't know of any US based outfits actually servicing the ECU. The ECU switches the ground back on and off on the ground lead. You can read the activity using an oscilloscope or an in line injector tester. I have a clever little tool you can buy that has an LED light in it that flickers to the pulse of the injector being fired. It plugs between the injector and harness. I think you have already ruled that out. Looking more like a bad ECU output because you can duplicate the problem using a different injector that is known to work.

 

So can I do pull the injectors on my 993 and test the spray patterns? I own a 1996 OBDII 99.? I've always wanted to know how good my injectors spray. I even have a PST-2 if that helps.


(Don't mean to hijack a thread but I take it you figured out your problem as this was posted over 6 months ago.)

 

It is not that expensive to your injectors tested, cleaned, and calibrated with a report from RCeng.com

Highly recommended!!!!