Compression query

Author
Discussion

Mark Hulme

Original Poster:

35 posts

74 months

Saturday 27th January 2018
quotequote all
Thanks for your replies guys !
The engine would reluctantly tick over very unevenly , but when I removed no 1 HT lead , it made no difference.
When I removed the rest of the leads , one at a time , the engine cut out .
Problem only seems to affect no. 1 cylinder.

liner33

10,641 posts

201 months

Saturday 27th January 2018
quotequote all
Pop the plug out and see if the its sparking on no1

Mark Hulme

Original Poster:

35 posts

74 months

Saturday 27th January 2018
quotequote all
Well , as intended, I tried the compression tester on my wife's car , which runs fine , and the readings were really low on that one too !
I used the (Gunson) tester in conjunction with a Laser adapter for deep seated plugs. The adapter had a Schrader valve screwed in the threaded end presumably to retain some of the pressure. I repeated the test after removing the Schrader valve and the compression reading rose to a much more feasible 165 PSI !
I've just learnt that this valve is , indeed , intended to retain pressure.
The theory is that if this valve was not there , the volume in the hollow adapter , together with the volume in the compression tester's flexible hose , would add to the volume into which the cylinder contents were squeezed , thus giving a lower true reading. Maybe the Schrader valve is faulty but I think I'll leave it out !
This tool has REALLY cost me a lot of wasted time !
I feel I've been barking up the wrong tree for the last week !
Back to the old drawing board tomorrow !
I think need to source a wiring diagram for the sensor/ECU circuits so I can carry out some multimeter tests.

stevieturbo

17,229 posts

246 months

Saturday 27th January 2018
quotequote all
Doesnt matter how long the hose is ( without getting daft ) the readings should still be sensible.

And the next cource of action is to do what has already been asked.

Check spark, check for fuel on what you believe to be the offending cylinder.

Mark Hulme

Original Poster:

35 posts

74 months

Saturday 27th January 2018
quotequote all
Yes ! I'll be straight onto that first thing in the morning !
I was thinking about buying a set of these HT testers.
Any good ?

GreenV8S

30,149 posts

283 months

Saturday 27th January 2018
quotequote all
Mark Hulme said:
Any good?
Yes, that's exactly useful to diagnose ignition related issues. For single cylinder diagnosis, an ordinary cheap passive strobe light works as well, and has the advantage that the leads let you position the lamp where it is convenient to see.

While you're in a buying mood, get yourself some NOID test lamps too.

stevieturbo

17,229 posts

246 months

Saturday 27th January 2018
quotequote all
A spark tester where you can create a gap and view a spark is better, but the above are cheap and handy to have too.

ie, this sort of thing, but there are a few different designs

http://www.accelerationkarting.com/bikemasterignit...

As for noid lights....I've never been a huge fan of them. A decent multimeter with dwell, pulse width etc is more useful. Many times I've seen noid lights do nothing...but plugged into a healthy engine ! lol So IMO they can be misleading.

If you want a good injector test...and some vehicles will lend itself better than others...pull the injectors and rail away from the intake manifold and crank the engine over to get a visual.
Or if it is easier, lift the intake manifold away from the head, complete with injectors still fitted and do the same.

Then you can see if each injector is spraying fuel in a half decent manner, and it's an almost free test. Not always practical though, and obviously taking caution regards fuel etc etc


Mark Hulme

Original Poster:

35 posts

74 months

Sunday 28th January 2018
quotequote all
Looking at the Laser set of four in the photo which I uploaded , I'm not so sure they'd be situated too far down the spark plug recesses to be of any use.

liner33

10,641 posts

201 months

Sunday 28th January 2018
quotequote all
You know cyl 1 doesnt have a spark , and you have fitted new coil packs , leads and plugs , I dont see how further confirmation of no spark will help

Arnold Cunningham

3,758 posts

252 months

Sunday 28th January 2018
quotequote all
Nah. They glow like lightbulbs, so as long as you can see down the hole, you'd be fine.

The other thing I've done before is use a gunsons colourtune on a single cylinder.
I had a carbed V8 once that flat refused to run on one cylinder. 4 barrel carb, but open into a plenum underneath. Good valve lift and timing, good compression. New leads & plugs, dizzy cap etc. Checked and replaced the intake manifold gasket too - no joy.

So I used the colour tune to verify that the spark was firing under compression - it was, nice and fat spark.

Never did conclusively get to the bottom of that actually - I think there was some issue with the head since I switched another pair of heads onto the motor and it ran perfectly.

GreenV8S

30,149 posts

283 months

Sunday 28th January 2018
quotequote all
liner33 said:
You know cyl 1 doesnt have a spark , and you have fitted new coil packs , leads and plugs , I dont see how further confirmation of no spark will help
I might have missed it - has the OP reported that there is no spark? All I saw was that one cylinder wasn't firing.

liner33

10,641 posts

201 months

Sunday 28th January 2018
quotequote all
GreenV8S said:
I might have missed it - has the OP reported that there is no spark? All I saw was that one cylinder wasn't firing.
P0351

stevieturbo

17,229 posts

246 months

Sunday 28th January 2018
quotequote all
Naively following fault codes from a cheap code reader can often lead to lots of parts replaced for no good reason.

And does this vehicle use 4 individual coils or a coil pack of some sort ?

And it's easy to use the little spark testers above on almost anything, you just need to adapt some HT lead and stick the tester where it is visible. Either at one end or somewhere in the middle.

Arnold Cunningham

3,758 posts

252 months

Sunday 28th January 2018
quotequote all
Steve makes a good point.
This is them on the coil end of a wasted spark setup, sanity checking the coils were firing on the right channels.


Mark Hulme

Original Poster:

35 posts

74 months

Monday 29th January 2018
quotequote all
Just a quick update guys.
I have now eliminated low compression as a possible cause for my problem.
Overall compression figures range from 150 to 175 PSI , so I guess removal of the Schrader valve in the compression tester adapter was the right thing to do !
Incidentally , I thought I had discovered the problem yesterday when I went to put the HT leads back in the coil !
I noticed that where the HT lead numbers are embossed next to each coil turret , there are three sets of numbers ( presumably for different makes / models) Each set of numbers is enclosed in a circle , square or triangle.
I had just assumed that the leads just follow ed the same order as they were in on the original coil !
I tried out each of the other two sets of positions but to no no avail !
The strangest thing was when the engine was idling ( very unevenly and lumpy ) I repeated the test of removing one spark plug cap at a time.
As before , removing cap 1 made no difference ( I always suspected this cylinder as the problem one )
Removing cap 2 rendered the engine unable to start. The same when removing cap 3 , so I guess the engine won't idle on only two cylinders.
But when I removed cap 4 , the engine idled , albeit poorly , exactly as it had done when I removed the FIRST plug !
Given that cylinders 1 and 4 share a coil (wasted spark) and a pulse wire going to the PCM , does this mean I could be on the correct trail at last , not forgetting the original fault code P0351 ?

liner33

10,641 posts

201 months

Monday 29th January 2018
quotequote all
You have already replaced the coil havent you so some testing of the wiring to the coils is in order next imo

Mark Hulme

Original Poster:

35 posts

74 months

Monday 29th January 2018
quotequote all
👍🙂

Jack_and_MLE

620 posts

238 months

Tuesday 30th January 2018
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Hello

Not sure how practical is it, however, if cylinder 1 and 4 share a coil and are not working, but 2 and 3 are working.
Can you swap the coil round?

After the swap, if cylinder 2 and 3 are working fine then it would be safe to assume the coils are ok therefore it is something controlling the coil which is at fault

Jack

Mark Hulme

Original Poster:

35 posts

74 months

Tuesday 30th January 2018
quotequote all
Thanks for your reply Jack.
The problem is that the primary coil and the two secondary coils are encased in a sealed block.
Also , the coil is a brand new unit.

liner33

10,641 posts

201 months

Tuesday 30th January 2018
quotequote all
There are a few how-to's on youtube on how to check the pcm with a meter

A quick google suggests that the wiring pcm-coil can sometimes be the culprit