Cleaning alternator...

[Deluks]

Unplug the SPI
Switch ignition on
With the -ve test lead on the -ve battery terminal(helps if you can wedge this into it so you don't have to hold it)
Now test the voltage on each of the terminals in the plug, as I say I think one of the wires should be live. Let us know how you get on.

Following the above, I get 11.3v on the green/red cable in the plug. The other 3 are all 0.01 or 0.02

With ignition off, they all fluctuate every couple of seconds between -0.00 and 0.01

With battery negative (and it's earth strap) disconnected they all show in the region of 11-12v

Burnerman: I have already double checked the timing and seen that the dizzy is on plug no.1, as it says in the Haynes. And would timing being out affect the fuel injection or disable the fuel coming from the nozzle?

 

[Deluks]

Anyone got any wild theories? Went down to a VW dealer today and spoke to one of the mechanics, who wasn't very helpful. All could say was bring it in a we'll run some checks.
Chargeable work of course, I'm thinking that the money may be better spent on a replacement ECU from scrappy/eBay.

 

[Burnerman]

Bring us up to date with the engine type, will you, and the age of the car?
Its so easy to throw new parts at the thing, and we've all been down that road!
Have you tried a push start?
John

 

[Deluks]

Bring us up to date with the engine type, will you, and the age of the car?
Its so easy to throw new parts at the thing, and we've all been down that road!
Have you tried a push start?
John

1991 1.3spi AAV engine code. Bosch mono-motronic ECU

Looks like this:

Haven't tried push start, bit tricky due to location. But my lack of fuel problem is unlikely to be solved by giving it a push, is it?

Reading up on the system in the Haynes:

1 The Bosch Mono-Motronic system is a self-
contained engine management system, which
controls both the fuel injection and ignition.
This Chapter deals with the fuel injection
system components only - refer to Chapter 5A
for details of the ignition system components.

2 The fuel injection system comprises a fuel
tank, an electric fuel lift pump an electric fuel
line pump, a fuel filter, fuel supply and return
lines, a throttle body with an integral
electronic fuel injector, and an Electronic
Control Unit (ECU) together with its
associated sensors, actuators and wiring.

3 The fuel lift and line pumps deliver a
constant supply of fuel through an
accumulator/coarse mesh filter and a fine
mesh cartridge filter to the throttle body, at a
slightly higher pressure than required. The fuel
pressure regulator (integral with the throttle
body) maintains a constant fuel pressure at
the fuel injector and returns excess fuel to the
tank via the return line. This constant flow
system also helps to reduce fuel temperature
and prevents vaporisation, aiding hot starting.

4 The fuel injector is an electromagnetically
operated pintle valve, which is opened and
closed many times per second by an
Electronic Control Unit (ECU). When the valve
is open, fuel is sprayed in conical pattern onto
the back of the throttle disc. The ECU
calculates the injection timing and duration
according to engine speed, throttle position
and rate of opening, inlet air temperature,
coolant temperature, road speed and exhaust
gas oxygen content information, received
from sensors mounted on the engine.

5 Inlet air is drawn into the engine through the
air cleaner, which contains a renewable paper
filter element. The inlet air temperature is
regulated by a vacuum operated valve
mounted in the air cleaner, which blends air at
ambient temperature with hot air, heated by
the exhaust manifold.

6 Idle speed control is achieved as follows.
An electronic throttle positioning module,
mounted on the side of the throttle body alters
the amount of air entering the engine and
hence the idle speed. The ignition system
provides idle speed stability by increasing and
decreasing the engines torque through.

 

[Burnerman]

This is very similar to the AAU engine that I had much dealings with years ago.
The diagnostics are somewhat crude for this engine, and relate only to the ignition system and lambda sensor, if I remember correctly.
My theory about a push start is only based on the fact that some electrical systems like a full battery voltage, and as you crank it over some of that voltage is lost. A push start takes this issue away.
The only problems I have had with these are the throttle body (would behave for ages and then give misfiring or cutting out; the coil on the bulkhead breaks down and sparks from underneath; the ignition switch is very prone to failure and can cause cutting out or no start.
Hey, I'm not saying for a moment that any of these theories are correct but how I wish you were getting somewhere!
Have you tried a compression test? You need around 200 psi minimum on each pot.
John

 

[Deluks]

This is very similar to the AAU engine that I had much dealings with years ago.

Not much in it, very similar.

The diagnostics are somewhat crude for this engine, and relate only to the ignition system and lambda sensor, if I remember correctly.

I have read similar, you can download software and get a cable from ebay but not worth it unless you have a later Polo, '95 onwards.

My theory about a push start is only based on the fact that some electrical systems like a full battery voltage, and as you crank it over some of that voltage is lost. A push start takes this issue away.
I have been charging 2 batteries alternately, so it has had full charge going through.

The only problems I have had with these are the throttle body (would behave for ages and then give misfiring or cutting out;
Have swapped this over.

the coil on the bulkhead breaks down and sparks from underneath; the ignition switch is very prone to failure and can cause cutting out or no start.

I'll see if the other coil is similar and maybe swap that out (what does it do???). Ignition lights up ok on turning key, and of course starter motor turns over.

Hey, I'm not saying for a moment that any of these theories are correct but how I wish you were getting somewhere!

Me too!!! I've come a long way with yours and others kind help.

Have you tried a compression test? You need around 200 psi minimum on each pot.
Can get a comp tester for under a score, likely to be an issue?.

Ultimately though, the injector isn't injecting, finding out why this is will likely solve everything.
Reading up on the Haynes info above, it would appear than the ecu tells the injectors when to open /close. As I have replaced throttle body and the injector unit, the problem must lie with the wiring back to the ecu, the ecu itself, or one of the sensors that feed into the ecu. Have changed water temp sensor, now need to find out what others are replaceable and where they are located. All suggestions welcome!

 

[Burnerman]

Your theories are absolutely impeccable and I have nothing to add.
These engines have so few sensors / triggers they should be simplicity itself.
Like you and countless others, I just can't see why it shouldn't start up as before - unless you've unwittingly created a spark across a critical ECU related component. ECU's I find are remarkably reliable.
There are quite a few earth ring terminals around the top end of these engines....none missing? Not being patronising mate.
John

 

[Whitworth]

If it was me I would start by disconnecting the multiplug from the ecu and checking continuity of all the wires to wherever they go on the wiring diagram. Also check the 12v feed. Not unknown for a hidden wire to break in the loom. (I have had this happen to me!)
It seems the ignition side of things is ok as it will run on easystart, so if the wiring is ok then there must be a fault on the signals affecting the injection.(or indeed the ecu as John mentioned)
Now you have a distributor so it would make sense that the spark side of things is generated there with a hall sensor or similar. Does the engine have a separate crankshaft or camshaft speed sensor for controlling the injection side of the ecu or does this signal come from the distributor? Could you remove all sensors from your 'spare car' and try replacing them one by one to test?
As an example;- I had an old Rover once which had a system built into the oil pressure gauge circuit that cut fuel supply if the oil pressure dropped too low to protect the engine. It also cut the fuel if the sensor was faulty (which I found out in the middle of nowhere )
Faulty sensors are probably one of the biggest cause of modern engine breakdowns. Could be worth investigation.

Edit: just a thought, could you have mixed up the flow and return banjo fittings to the throttle housing?

 

[Deluks]

Excellent ideas there chaps, on the back of the head there's a couple of sensors, one is the oil pressure switch, not sure what the one next to it is but is near identical. I left these one when I cleaned up the head, so they have both been exposed to moisture, degreaser and neat petrol. Oil switch is an easy one to replace, I'll have to find out what the other one is.

The other motor is also an AAV, but it's a '94, there a a few differences that I've noticed.

ECU is a later type, more compact, different plug

Fuel relays are in a different place (no biggie)

No sign of an oil pressure switch! Where it should be there is just a blanking plug with a hex socket. The other sensor to the side of this is still present. Will have to dig around...

Fuel pipes were left connected throughout the work, I only removed them (one at a time) to check the flow as requested on here.

 

[MrTinker]

Unplug the SPI
Switch ignition on
With the -ve test lead on the -ve battery terminal(helps if you can wedge this into it so you don't have to hold it)
Now test the voltage on each of the terminals in the plug, as I say I think one of the wires should be live. Let us know how you get on.

Following the above, I get 11.3v on the green/red cable in the plug. The other 3 are all 0.01 or 0.02

With ignition off, they all fluctuate every couple of seconds between -0.00 and 0.01

With battery negative (and it's earth strap) disconnected they all show in the region of 11-12v

Sorry for not getting back sooner, been a bit busy to say the least!
Well at least you have got a live feed to the SPI, so it's not something silly like a fuse thats blown. unfortunately I haven't been able to get the test data for it yet I am still trying to though.
As Burnerman says(which has just joged my memory) there are,if I remember correctly four negative(brown) wires running to a bolt on the head, the thinnest of these has a tendency to fall down out of sight when it's removed, and this is i think a neutral for the engine management system, and if it's not connected will cause a no start, so definitely worth double checking this is connected.

 

[Deluks]

Three of those earth cables into the bolt on a bracket, I'll check for a fourth, but the other motor only has three. Pretty sure there were only three.

 

[Burnerman]

It could be a sensible move to whisk the injector off to a specialist who can get it to perform on a bench, and there are specialist firms who will check the ECU also for a reasonable fee. Car Mechanics mag have some adverts for these.
I've bought parts from dismantlers before and they claimed that they were good - but in reality they were worse than the originals.
Time honoured quote - 'when the car came in, it was running fine'.
Yeah, right.
John

 

[Deluks]

None round here that I know of!
Tried swapping over oil pressure switch today, also the 2nd temp sensor in the stat housing. Neither of these cut the mustard.
The 'spare' car still starts fine with the suspected bits I've tried from the 'patient'
I think I'm gonna get the spare up n running and run that instead. The only issue is that it needs a new headgasket, (plus tax and insurance!) so I'm back at square one taking an engine apart Should be able to do it all quicker this time, it's all still fresh in the mind.