Compression query

Author
Discussion

Krikkit

26,500 posts

180 months

Tuesday 30th January 2018
quotequote all
Might also be worth checking the coil open circuit resistance (old and new) to see if you can see any difference. Sounds like a wiring fault to me.

Mark Hulme

Original Poster:

35 posts

74 months

Wednesday 31st January 2018
quotequote all
Really ? I'll certainly look into that !
If I could carry out some basic tests , that would be great , but I'm hoping to find a problem in one of the conductors which carries the trigger signal between the LT coil and the PCM.
I understand that certain resistance tests are not possible when using a multimeter to test electronics due to the amount of current applied by the meter , so I guess I'll have to do some research beforehand !

Mark Hulme

Original Poster:

35 posts

74 months

Wednesday 31st January 2018
quotequote all
Oh , forgot to say that I can now test all four plugs simultaneously because these turned up yesterday !
Thing is , I forgot to find out if they will be useful on a 'wasted spark' Ignition system !
Anyone know ?

GreenV8S

30,150 posts

283 months

Wednesday 31st January 2018
quotequote all
Why wouldn't they?

stevieturbo

17,229 posts

246 months

Wednesday 31st January 2018
quotequote all
4 leads...4 testers.....it really shouldnt be difficult to figure out.

Mark Hulme

Original Poster:

35 posts

74 months

Wednesday 31st January 2018
quotequote all
I was wondering whether the fact that each wasted spark ( TDC on the exhaust stroke ) is reverse polarity would make a difference .
I don't know if these testers only work with the HT current flowing in the conventional direction.

PositronicRay

26,958 posts

182 months

Wednesday 31st January 2018
quotequote all
Mark Hulme said:
I was wondering whether the fact that each wasted spark ( TDC on the exhaust stroke ) is reverse polarity would make a difference .
I don't know if these testers only work with the HT current flowing in the conventional direction.
I think I've heard of everything now!

stevieturbo

17,229 posts

246 months

Wednesday 31st January 2018
quotequote all
It's mostly just an enclosure with a gap so you can see the spark jump visibly.

If there is high enough voltage present and the circuit is complete....you should get a visual.

Mark Hulme

Original Poster:

35 posts

74 months

Wednesday 31st January 2018
quotequote all
Thanks Stevieturbo , that's that cleared up !

Mark Hulme

Original Poster:

35 posts

74 months

Wednesday 31st January 2018
quotequote all
PositronicRay said:
I think I've heard of everything now!
Not quite sure what you mean !
Please elaborate !

PositronicRay

26,958 posts

182 months

Wednesday 31st January 2018
quotequote all
Mark Hulme said:
PositronicRay said:
I think I've heard of everything now!
Not quite sure what you mean !
Please elaborate !
The HT only flows in one direction, it has too, does the earth to your block change?

The spark can jump in either direction however, a spark is just a spark.

GreenV8S

30,150 posts

283 months

Wednesday 31st January 2018
quotequote all
PositronicRay said:
The HT only flows in one direction, it has too
The voltage on the HT lead can be above or below ground potential - with a typical wasted spark setup, each coil would produce a positive voltage on one end and negative on the other.

Arnold Cunningham

3,758 posts

252 months

Wednesday 31st January 2018
quotequote all
@Mark - in the pic I showed above, that's an 8cyl, 4 coil wasted spark setup with 4 of the jobbies - the answer was staring you in the face - so you have "plenty" biggrin

Edited by Arnold Cunningham on Wednesday 31st January 22:30

Mark Hulme

Original Poster:

35 posts

74 months

Thursday 1st February 2018
quotequote all
Fair comment Arnold !
I have carried out the test now on all four plugs simultaneously.
2 and 3 are firing with a good spark , but 1 and 4 are very dim !
Tomorrow I will test the 2 signal leads which run from the coil to the ECU.
Thank you all once again for all your help !

E-bmw

9,106 posts

151 months

Friday 2nd February 2018
quotequote all
More likely to be the "coil pack" for 1 & 4, are they individual, or is it one moulded unit that plugs into all 4 or can you swap 1/2 & 3/4?

Mark Hulme

Original Poster:

35 posts

74 months

Friday 2nd February 2018
quotequote all
This model uses the moulded block type . I fitted a new one but to no avail .

Mark Hulme

Original Poster:

35 posts

74 months

Saturday 3rd February 2018
quotequote all
I have now removed the ECU from the car and carried out some very basic circuit tests.
I identified the two pulse wires which run from the coil connector to the ECU (BK/GN and BK/OG ) which earth out the primary coil when required .
Having disconnected the 60 pin connector block from the ECU , I connected the two pin sockets for the two coil wires with a paper clip so I could conduct the test from the engine bay .
I disconnected the wiring block at the coil and put 12V from the (disconnected) battery on one wire and ran my circuit tester between the other wire and earth.
The test lamp lit , proving a complete circuit through the two wires.
I also tried slightly pulling and wiggling the wires where they enter the connector block but the tester lamp shone without any flickering , so my guess is that they are sound .
My next step now , I guess , is to get the ECU tested ,
Incidentally , I read that a fault code which puts an engine into ‘limp mode’ needs to be deleted from the ECU memory before the engine will return to normal , EVEN if the problem which caused the fault has been rectified ! I wondered if this could apply to my problem ?
Thanks in anticipation guys !

E-bmw

9,106 posts

151 months

Saturday 3rd February 2018
quotequote all
I can't see it being the ECU from what you say, if you have a spark the ECU output is more than likely correct, have you tried re-doing your spark test to see that what you saw isn't just a slight issue between the "testers"?

There could just be slight differences that make the sparks look better on one than another, do the test & then re-do it with the testers in different positions.

A simple & quick test that COULD mean you don't need to do the ECU.

Mark Hulme

Original Poster:

35 posts

74 months

Saturday 3rd February 2018
quotequote all
Well , with my ignition set up , inside the coil block is a primary coil and two secondary coils.
The primary coil has a conductor at each end which is connected to the ECU.
Depending on which conductor the ECU earths out , the HT is induced in the coil on that particular side. Each secondary coil is responsible for two spark plugs , 1 and 4 , and 2 and 3 .Each pair of plugs fire simultaneously . One cylinder will be at TDC on compression and the other , on exhaust, (wasted spark principal)
Having tested the ignition system from the plugs right back to the ECU several times , and finding that the two plugs affected are controlled by the same coil , I believe that the ECU is failing to earth down the LT on one side of the coil.

GreenV8S

30,150 posts

283 months

Saturday 3rd February 2018
quotequote all
It's plausible, but if that was me I'd like to confirm that theory before spending potentially a lot of money repairing the ECU.

If you can exchange the connection between the two wires from the ECU to the coil LT circuit and then swap over the corresponding pairs of HT leads at the coil, if your theory is correct then the problem will still affect the same cylinders.

You could exchange the connection either by backing the terminals out of the connector housing and putting them back in the other positions, or using separate wires to make the connection between those terminals and the coil.