Pin 8 is the ecu spark output. Is all you're doing is bypassing the ecu. Seems like the issue is ecu isn't seeing trigger from crank. I have looked at the diagram. There should be a few wires bolted to engine sort of under the dizzy near the plate holding the big plug on. Brown and a brown/white. These are sender earth for crank, air and throttle pot coolant etc. They also should go to pin 33 on the ecu. Pin 1 on ecu should go to earth possibly to the battery.
Thanks that helps a lot I'll check pin 33 and 1, the wires are present but it doesn't mean their connected correctly.
Okay I've established that ecu pin 33 is connected to a load of sensors including the crank sensor but not earth. There's a couple of ring terminals in the engine sensor loom but not one that connects to the pin on big plug that ultimately terminates at ecu pin 33. Obviously ill just splice this in so it connects with other ring terminals but where on earth was it originally? I assume I've deleted it from the main loom by accident as there's no evidence that there was ever a ring terminal in the sensor loom for this pin?
the sensors dont earth anywhere except the ecu pin 33 so dont worry about that. the rings on the head are for the dash earth and the speed sensor/breather heater earth
That suggests there's nothing wrong with my loom then and the sensors earth internally in the ecu. That being the case disconnecting the ecu will lose earth to the sensors which is what I'm seeing. Ill try tshirt2ks test to eliminate the crank sensor (however this is new so should be fine) and if its not that then that leaves the ecu?
only when the ecu is plugged in edit: it could be an age difference actually, as the 1st abf i ever built definitely had no direct earth path for the ecu sensors, as when the car wouldn't start I found this with a multimeter and added one in myself. (still didnt start though, immobiliser fault) it could be some others have an earth to the head but I'm pretty sure they do not, from memory non of the engine looms I have repaired had this only 2 rings for the dash earth and the speed sensor/breather heater. my memory could be playing tricks though
Mines a later loom but what your saying is consistent with my findings. Nothing to suggest there was ever a third ring terminal present when I unwrapped the sensor loom. The 12v present on both of the other terminals suggests a problem with the ecu. The crank sensor is new and the ignition wiring has been checked and works.
12v present on both doesn't mean an ecu problem. It could be where the crank sensor is in relation to the crank wheel. You have to test by turning the engine by hand. Regarding the earth. If you can trace where pin 14 goes to on th engine side of the 28pin plug. That will tell you whether it is earthed. I reckon it bolts to the engine. It's a 1mm brown wire.
the diagram is a bit miss-leading earth point '220' is 'in engine wiring harness'. what it means is inside the round plug loom on the engine side, there is one of them vw waterproofed crimp connections but no physical earth to the head. note the earth point '221' for the speed sensor and breather heater shows something similar. but if you follow the diagram to page 3 you can see earth point '221' has a little looped wire to earth point '18' which is 'on cylinder block', but earth point '220' does not
I'm going from memory. There is a join behind the plug. Haven't traced it tbh. But it's earthed anyway. Testing should be done as per diagram to be sure if correct continuity. Crank sensor operation needs checking. And can be done as long as you can supply it with 12v and an earth.
Certainally crimping another earth in wont do any harm. Next ill test the crank sensor I take the point on the position of the sensor relative to the wheel but this is measured with the sensor disconnected.
Have you had a VCDS connected, if I knew how simple it was from the start I'd have done it sooner than later. The crank sensor was one of the items that was hard to test/check, very high resistance reading (from memory). If there was an ECU available that I could have just swapped out and got the engine to fire I may have had a fault elsewhere, so I took the plunge and bought ECU/IMMOB/STEERING SHAFT, it was from ebay .de and I had a friend translate and organise shipping in German. To clarify, prior to the install of the 2nd ECU, I bought a good length of heavy gauge brown wire, crimp rings on them and ran one from ecu housing and one from coil housing as grounds to the block point near dizzy, to insure against any potential difference. Far fetched theory perhaps, but something fried ECU and after the stress of delivering my sons birthday gift on a tow truck and pushing it around our driveway for three months.... It's worth the effort... Once we fired, we had to give our vacuum hoses a once over, HT leads, plugs and an idle valve calibration. Initially we had weird idle issues, so I cleaned the ISV as well, but in hindsight it could have been poor ignition or an air leak of types not sure.
Earths have been beefed up. Tried another ecu and there's no difference I'm still getting 12v on both pins at the crank sensor and this was the case before cranking. Tried testing the crank sensor and I'm getting a change of just less than a volt but I can't get the plugs out so its hard work turning the engine over by hand. I'm correct in thinking that 12v shouldn't be at the centre pin of the crank sensor when static aren't I?
pin 1 is the 12v feed, pin 2 is the signal back to the ecu, pin 3 is the shield/earth. if you get 12v on pin 1 and 2 with just the ignition on this suggests to me there is a short in the wire somewhere? edit: I'm assuming you're testing this with the crank sender unplugged right?
Yes this is with the sensor unplugged. If it is a short then its not between 1 and 2, so I suppose I need to verify whether theres a short in the loom between 2 (67 at the ecu) and and of the other supplies. These would be 9, 23 and 38? The only other possibility is that the ECU itself is outputting 12v at pin 67 either due to the same fault in 2 ecu's which seems unlikely or the loom is somehow tying something to + 12v instead of earth?
right yeah you'll want to follow crank sensor pin 2 all the way back to the ecu pin 67 checking for damage, there are a fair few 12v supplies in the loom so its hard to say which it is but following the pin 67 should reveal the culprit.
What loom have you got? Who made it? Or is it just a standard mk3 loom. There shouldn't be shorts unless it been messes with
I made it so its perfect So yeah its been messed with which makes it the obvious culprit but I'm stuck finding anything out of place.
