cant work it out strange misfire

[orangepeel]

hi all a couple of day a go my 91 3b coupe developed a strange misfire like it was a pot down so i put new plugs and leads on .still didnt sort it so i thort piston or valve trouble did a pressure test with on problems .but when i looked at spark pug on pot 4 second one from the back it was dry so i took off the injecter rail and you have it the forth injector was dry too. so i cleaned it and swoped it over. put it all back together started it up.still no fuel going in . i only have limited knowlage car electrics so if eney of you members can help me and put a smile back on my face i would been very great full thanks for looking

[djh]

check the plug wiring

[orangepeel]

ive only checked it with a bulb tester and it lights up but do you now if i can tap in to another injector for the pulse to see if it will work or the pin out number on the ecu

[mcandmar]

I would guess its a wiring problem. Wiring diagram can be found here http://www.s2central.net/S2_Schematics/D/D34-04.pdf

First off try moving the injector to another position to confirm its working, then will tell you if it is a wiring issue.

Basically all the injectors get constant 5v power, and the ECU earths each injector to fire it. With a multimeter check you have 5v going to the injector, should be a Blue/Black wire. Then unplug the ECU (i recommend disconnecting the battery first), and do a continuity test between the Brown/Black wire on the injector to pin 35 on ecu connector. That should confirm if your problem is a broken wire somewhere.

If that tests out ok you have a problem inside in the ECU which is a rather specialized job to fix. Prj or S2Central might be able to help you with that.

[4WheelDrifter]

I was once an injector down on my 7A. It was the injector wire on the bend as it turns to run along the cam cover at fault.
I tested the wiring using an LED and checked for a pulse, which there was not. Then I buzzed the cable with a multimeter from the ECU connector to the injector plug and found the break.
I was glad it was a spot that was easy to get at.

[orangepeel]

thanks for the info but i already swoped the injector and pot 4 was stil dry and the rest were wet with petrol and all leads have a good spark

[Kieron20V]

Then you probably have a break in the wiring for injector 4.
Have you pulled diag codes?

check continuity between injector plug and 12v feed from fuel pump relay, and continuity between injector plug and gnd signal from ecu which is pin 35 according to above schematic.

If your bulb tester is a 12v bulb into the plug with its own ground lead then its probably the gnd signal wire from the ecu that is open circuit.

[Knight Rider S4]

As others have said , easy way is to do output check with VAG.com , check each injector by fully open throttle each time when vag.com goes through them , you will here each one pulse (click)

Cheers


Steve

[orangepeel]

what is the pin out number on ecu for injector number 4 the brown/white wire eney one

[Kieron20V]

35 as I said above..

[orangepeel]

well ive done a continuity test with no problems at pin 35 on ecu on the brown /white wire

[Kieron20V]

And you have 12 on the other wire?
Did you move the wires around while you were checking continuity? If there is a break it migt only show up with some movement, like vibration from the engine running.

If it all checks out then it would point to a dead injector driver inside the ecu as far as i know. You said you already tried a different injector?

Maybe a blocked fuel rail at that injector stub?

[orangepeel]

cleaned injector with cleaner and tryed it on the batterayand fuel came throw it ok . when i pulled it out of the rail fuel was there so may be its inside the ecu

[WabTheKing]

do a compression check, could be a cracked valve seat

[WabTheKing]

sorry missed that in your first post my bad