Does anyone know who or where would be able to check the ecu from my cab? I've just rebuilt the engine and all the cables/plugs were tagged so no confusion when putting back but engine wouldn't start. Ignition has been checked and rechecked and checked again, the double relay has been checked too many times, the fuel pump is putting out the pressure when it's turning over and every wire from the ecu plug to the sensors have been checked but no signal is getting to the injectors. The injectors are not blocked and I am at my wits end and my wife wants a divorce.....so I suppose it's not all bad

Is that the early mechanical injection type? My friend had a bay with a early suby motor in it that needed a valve undone on the fuel rail to purge the air as he had run it out of fuel... took me a while to find it.. worth a try..

That is a later type EFI with vane type AFM if I am not mistaken.

The injector are actuated by the ECU grounding them. One side of the injectors should be live with 12V all the time when ignition is on.

check its live, if not, check relays, fuses and a like. Otherwise there may be a trigger input signal missing to the ECU.

From what I've read no part of the FI is fused and I've checked the relays plus I have also read that the ecu hardly ever is the reason.....mind you that is "hardly ever". As I've said I have checked everything else as far as I can see so it6 just leaves the ecu. Mind you Vlad I didn't know about the eco earthing the injectors so that may give me something else to play with.

I can't see there not being fuses on the power side for the EFI system. They should be before the relays.

On 2nd thoughts, The D jet system have the injectors grounded to the engine case and power it pulsed from the ECU.

If L jet is the same ( I would be surprised if it was) could have injector grounds if it does used them and that is a common issue on the Type 3 with D jet

I worked on D Jetronic (type 3) and K Jetronic ( VK commodore) K Jetronic looks very similar to L jet so I assume ?? it should have live injectors, ground switched by ECU.

Worth checking both scenarios. Can you tell me which grounding system it uses?

Right, I've just checked the injector plugs, with starter turning over I'm getting both contacts in the plugs as continuous live, not on and off as I expected for maybe one of the contacts? So any ideas?

the pulse width may be too wide to actually measure when they are not on as you are in the starting mode (wider pulse width, for starting enrichment). What are are you using to measure the pulse?

At the moment I'm just using a simple circuit tester so 'pulse widths' etc is way beyond my capabilities but the question still is where do I get the ECU checked and/or replaced.

I've checked the injectors and they all work fine (clicking) and they're unblocked. I'll continue to play with it.

Latest!! I've found a broken wire that goes into the series resistance block. There are 5 wires going to the block, one to the centre and one each to the cylindrical parts around it (please excuse ignorance here) and it's one of the cylindrical 'wires' that's busted. 1/ How the f*ck do get to this block without removing the engine? and 2/ Would this one wire stop the whole shebang from firing?

Right having removed this from the car (and a fair bit of skin) would this stop the car from firing up?

Sorted this but still dead Pumps is going when the flap in the air intake is opened just nothing at the injectors, I'm now getting very pissed off at this, the trouble is whenever there's a problem with the FI I'm very tempted to just replace the whole lot with a carb and end the worry but when it's going it's just so smooth plus it's keeping it original.

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Originally posted by ancientbugger Sorted this but still dead Pumps is going when the flap in the air intake is opened just nothing at the injectors, I'm now getting very pissed off at this, the trouble is whenever there's a problem with the FI I'm very tempted to just replace the whole lot with a carb and end the worry but when it's going it's just so smooth plus it's keeping it original.

Try reading thru these to help diagnose

L jetronic manual 1

Manual 2

manual 3

You should remove the fuel rail and turn the pump on cos just cos you can hear it don't mean it's working plus this test the pressure reg is flowing too.

There's only 4 or 5 inputs to the ECU so if the fuel is getting thru then if the inputs are all good it has to be the ECU.

I'm going to take the whole FI wiring loom out and check that ...again. Making sure all plugs are correct and labelled and going to the correct numbers on the ecu plug. I keep reading all over the web that the Ecu very rarely packs up and I have a sneaking suspicion that it's just maybe one wire that's causing it as it was working perfectly before.

The pump does run as it's supposed to Matt, that was one of the first things I checked. I checked the pressure when it was turning over on the starter and that was fine just the injectors not working so back to the start and systematically check everything again. Oh well the loom is out so tomorrows job is checking, oh the joy

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Originally posted by ancientbugger The pump does run as it's supposed to Matt, that was one of the first things I checked. I checked the pressure when it was turning over on the starter and that was fine just the injectors not working so back to the start and systematically check everything again. Oh well the loom is out so tomorrows job is checking, oh the joy

The double relay provides power to the fuel pump on start up and also provides power to the injectors via the resistors.
Just checked a wiring diagram and terminal 86b of the double relay is connected to terminal 43 on the pre-resister block...Dave

Silly as it sounds is the earth wire making a good connection? I used to use a LED plugged into the injector socket to ensure power and if you pull the injectors out of one side you can watch them spray into a bottle whilst cranking as shown in the manual.The other thing to check is the cold start injector,if this doesn't work it is very hard to get going.If you need some copies of the test sequence let me know . Cheers Les

The double relay is working fine, that, I believe was the first thing I checked (I now have 4 relays here!) They seem to be the main culprit for L jetronic mishaps so it seems. The earth is something else I have to look at but the continuity of the wires in the loom is my job for this morning.

right, all the wires check out good BUT the wires for the Throttle position sensor ("Throttle valve switch/ Full throttle switch" depending on which diagram you're looking at) positions 3 & 18 on the ECU plug aren't there? There appears only 2 wires in the plug for the switch one of which goes to earth the other I haven't found the other end yet. One diagram I have downloaded from The Samba appears to be from the Bosch handbook has the wires from the cpu to the TPS then back to the cpu via positions 3 & 18.....now Vlad please explain to me how is this all easier than a carb!!!!!
The other end from the plug in the TPS goes to the EGR valve plug!?!

its still easier imho. when the loom is botched or stuffed or you just want a conversion/modification, I just make my own new looms and systems from the top of my head.

I never been able to work out why carbs dont run right so I gave up on carbs years ago.

learn the system, understand the logic because it is literally logic and its easy!


do you mind posting up the wiring diagram and posting a few pics?

its kinda hard to imagine what you are looking at given the terminology barrier.

http://images.thesamba.com/vw/gallery/pix/931096.jpg 
http://www.thesamba.com/vw/archives/info/wiring/diagram.jpg 
These are the diagrams I'm going from, please note that on the lower diagram there is no wire coming from 3 and 18 on my ecu plug. Hope this makes sense.

I found this on Samba FI diagram

The second link you gave was a very small picture I couldn't enlarge.

Anyhow, looks like when the TPS is active, from foot on accelerator, this activates the EGR and allows the cases gasses be drawn into the air intake. No throttle means no recirc of these gasses. So this ain't a worry for now if it don't work.

88b of the double relay provides power to the injectors and the ECU grounds the injectors to fire them so with ign on 88b should be live.

cranking the starter activates the Thermo/Cold start timer.

27 of the Airflow meter seems to be the potentiometer of the vane within the meter to give engine load data to the ECU. The meter gets power from the ECU but the meter also activates the second relay within the dual relay to operate the Aux air regulator. This will be for engine overrun more than likely.

And then 86c of the dual relay powers the ign coil and either the ECU fires the coil or no1 ECU input gives the engine speed.

So I believe during cranking the ECU will activate the Aux Air Regulator so the engine can breathe properly cos the AFM won't be moving too much. Then so long as the ign coil is giving an engine speed signal the ECU will fire the injectors.

So that's my take on what should fire the injectors