Ignition Fault

Merry Christmas everyone, let's hope next year is a better one.
I drove to a funeral today of my 32 year old cousin and as he was a petrolhead his wife (just married) asked all of us to turn up in our classic cars.
After the service we left the Crematorium and she wasn't idling very well and the rev counter was not working. I pulled over and switched off the engine to check leads & coils were all tight as I thought it was only running on one bank (big smell of fuel).
Anyway I called out the AA who when trying to diagnose the fault used a length of wire from the one of the coils and shorted it out whilst I was cranking the engine (after checking for voltage both the coils).
He thought it could be the hall sensor so ordered a truck to take us home.
When the truck arrived I tried to drive onto the bed but it would not even start on the other bank, and hasn't started since. Before the AA guy did anything she would always start but only on one bank.
My question is do you think he has fried the Digiplexes as I checked when we got home with a strobe light and I am not getting a spark on either bank, and I have swapped over the Digiplexes.

 

Thanks for your replies. I will test at the Digiplexes with a scope to check hall sensors are working, and test coils.

 

Thanks John. After testing the at the Digipexes yesterday I found one dead sensor (bank 1-4) but I am confused about the signal from the Bank 5-8 and the replaced 1-4 sensor. The speed sensor gave me a uniformed sine wave , but on the 5-8 bank it did not (1-4 no signal and infinite ohms with multimeter) I after tested today again the speed gave a uniformed sine wave but both 1-4 & 5-8 signal were similar to each other but not the same as the speed sensor. (I am still getting to grips with the scope as I was given a second hand one Vellman HPS 10).
I have tested the coils and both are the same reading. Primary to Primary 0.3 Ohms. Primary to Secondary 3.7K Ohms which seem good to me.
I put the scope on the coils earlier but did not get the same sine wave that you had on the picture, what was the time you had it set at please ?.
So I now know why it was only firing on one bank (before the AA man used a long H.T test cable) but have a horrible feeling that he has taken both Digiplexes out when trying to fault find by grounding out the coils.
I will carry on testing tomorrow and practise a bit more with my scope.
Thanks again.
Glen

 

Thanks again Steve. Do you know how easy it is to damage these Digiplexes ?

 

I saw him pull a HT lead from one of the coils & connect a longer HT lead into a coil and then he asked me to crank the engine. I think he held the end of the HT cable on the engine to see a spark.
The reason I called them out was I had lost a bank and didn't want to drive it home, I thought it would be best to have the car transported home. So before he tried this the car would fire up instantly albeit on one bank. After he tried this I did not try to start it again until the recovery truck arrived (ordered by the AA guy).It didn't start so we had to push it onto the flatbed truck. I said to the recovery guy (2nd guy) at the time I think the AA guy has damaged the ECU's, and he said that he himself wouldn't of tried anything like that, incase anything was damaged. I reckon the AA have damaged both of the Digiplexes.

 

Once again thank you, will have another look tomorrow & let you know how I get on. I really appreciate your time and knowledge.
Glen

 

Ok I have completed my testing and here are the results

Crank Sensor Banks 1-4 TDC 665 Ohms
5-8 TDC 649 Ohms
Speed. 642 Ohms
Tested at the Digiplex
(Replaced 5-8 sensor as it was very high impedance and tacho was not working when the bank was not firing before the AA tech shorted the HT lead)

Both 1-4 & 5-8 giving similar signal on the scope
Speed gives constant ripple signal.

Voltage tests at the Digiplex during cranking
1-4 & 5-8 TDC 0.2v AC. (Pins 1 & 5)
Speed Sensor 2v AC (Pins 1 & 2)

12v at Digiplexes on Pins 8 & 9

12v at Coils between Pin 15 and Chassis
Coil resistance Pins 1 & 15 1 Ohms
Pin 1 or 15 to Secondary (HT output) 3600 Ohms on both coils

Coil terminal 15 to chassis 10.05v DC bank 5-8
10.03v DC bank 1-4
Pin 1 to Pin 15 80mV AC whilst cranking bank 5-8
100mV AC bank 1-4

Here is a picture of the signal when cranking, scope connected to Pin 1 & Pin 15 on coils

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Could the transistors have been damaged when the AA engineer shorted the HT leads down to ground as the signal looks ok to me but I think the transistor in the Digiplex has blown as the signal is only 100mV when I believe it should be much higher between terminal 1 & 15 at the coil.
When I put a timing light on the HT leads it does not light.

Thanks again.
Glen

 

Thanks again Steve
I thought John had connected his scope from Pin 1 & Pin 15 in post #5. Pin 1 coming from the Digiplex and Pin 15 from ignition switch (12+).
I will try again tomorrow, so you are saying put probes of scope on Pin 15 of the coil (12v) and on the chassis. And I assume selecting DC ?
Thanks
Glen
p.s. the AA have agreed that if the fault was due to their engineer, they would cover the cost of repairing/replacing the Digiplexes. We shall see.

 

Thanks Gents for the explanation, I will have another go tomorrow.

 

Ok so I have taken more readings with both the scope and multimeter.
I took the readings from Pin 1 of each coil and chassis ground.
Coil bank 5-8 on multimeter showed 0.2mV AC but on scope was 1.163v AC if I used the Marker Function and set Marker 1 at top of wave and Marker 2 at lower part of wave. Hopefully I am using the scope correctly. Using this method I set the Marker 1 and 2 on the Timebase at the repeating part if the signal which gave me 0.3 seconds whilst cranking .
Coil 1-4 on Multimeter showed 0.3mV but using scope, freezing the frame using memory again and moving the Markers top and bottom of sign wave gave a voltage of 1.105 v AC.
So I am assuming that the scope is giving the correct voltage as apposed the the multimeter due the the frequency being too high for the multimeter to capture, and that just over 1v is not high enough to fire the coils. If this is correct then I again would assume that the ECU's power transistor was blown due to being shorted by the working coil when grounded .

 

Here are the images of the coils signal.

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