Moomin has sleepy sickness

[Laird Scooby]

That was how i was taught and have always worked too - a fault is only found when you can take it away and put it back again, often difficult with intermittent faults though.

[Rversteeg]

Radio suppression relay

You are correct, the relay also powers the ignition coil. I should have checked the electric diagrams before stating so baldly that it only powers the fuel injectors...

[aardvarkash10]

You are correct, the relay also powers the ignition coil. I should have checked the electric diagrams before stating so baldly that it only powers the fuel injectors...

Ha! We all have a bad day now and then - thanks for your suggestions so far

[aardvarkash10]

update - so after a night of shenanigans with family and friends, an outdoor fireplace and whiskey, today was moominday.

First, I built an indicator box to be able to see whats going on in the ignition system. Go/No go lights show the state of the 12v supply, the earth, the coil switched side and, I hoped, the pulse signal from the EZ-K box.

Dammit, that pulse signal is both low voltage (5v ttl) and low power. Even a 5mA LED pulled the signal so low it wouldn't trigger the ignition amp.

So I had to pull out the big guns - I haven't played with the 'scope since ages ago, and really should have gone there first. Aaaaaanyway, out it came.

Now I could track the EZ-K trigger pulses in real-time, and the indicator box showed the rest of what was going on.

Annnd, *drumroll* we are pleased to advise that the ignition amp module showed faulty. EZ-K pulses in, no coil switched side coming out. All else stable and luverly.

So I pulled the amp out and, as predicted by many, it lacks thermal paste - or more honestly, the thermal paste on it is u/s.

My local electronics shop is closed, I'm clean out of it, so it'll be tomorrow for refit and test. Meantime, I have a tested s/hand unit on its way from a wrecked '93 940 estate down country.

[Laird Scooby]

Glad you got to the bottom of it! Looking forward to the "fixed it" report now! ;) :D

[aardvarkash10]

bugger.

Well, thermal paste didn't do it.

[Laird Scooby]

Hopefully the replacement ignition amp will get things up and running! ;) :D

[Dirty Rooster]

The CPS is new so I'm eliminating that ...

You won't want to hear this but I've seen threads before where a brand new CPS was fitted but it turned out to be dead, i.e. not working despite being new.
Go down the scrapyard and get an old one or more, taking your new 10mm spanner.
Swap in an old one that isn't cracked.
If it is still the culprit this will save time and possibly damage to old wiring joints as you investigate everything ...

[aardvarkash10]

You won't want to hear this but I've seen threads before where a brand new CPS was fitted but it turned out to be dead, i.e. not working despite being new.
Go down the scrapyard and get an old one or more, taking your new 10mm spanner.
Swap in an old one that isn't cracked.
If it is still the culprit this will save time and possibly damage to old wiring joints as you investigate everything ...

Cheers for the advice, but I've already confirmed the CPS is ok. I get an ignition pulse signal all the way to the igniter module, no output from the module to the coil.

[aardvarkash10]

He's well again!

Moomin is a happy boy! The replacement (but second-hand) igniter did the business. Just to be sure, a new one is on the way from the USA - $18USD to buy, $18 to get here...

For future reference, here's the fault and the diagnosis technique.

The initial fault was like the fabled Crank Position Sensor fault - drives fine until warm, engine suddenly cuts with tacho dropping like a stone, restarts after a short period.

Secondary to this though - relatively hard cold starting. Especially when the battery voltage gets low (but not flat).

Diagnosis - you need a dual trace oscilloscope and just a little skill in using one.

1 - Test the CPS output. This is a magnetic reluctor pattern - looks like a sine wave that had a stroke. To do this, break in to the wiring to the sensor. The easiest way to do this is to strip back the wiring on the body loom side of the CPS connector. Push a drawing pin through the output wire - one pin into each of the output wires. Hook one probe of your o-scope onto the pins.


Magnetic reluctor pattern

Set the engine up on a fast idle (1750-2000rpm) and stabilise the o-scope image, then wait for the engine to die. If the CPS is faulty, as the engine dies and winds down the o-scope will show no pattern. If the fault is elsewhere, the CPS will continue to put out a signal even as the engine winds down to no RPM.

2 - If the CPS is ok, break into the wiring to the igniter. You need to get to the wirte carrying the pulse circuit from the EZ-K module (grey), and the wire carrying the coil -ve (red with a white trace). Use the same drawing pin technique. Connect one probe to the grey wire, the other probe to the red/white wire.

Again, start the engine and fast idle, then stabilise the image. You will have a square-ish wave 5v pulse (from the EZ-K), and a 12v squarish wave with some ringing (from the coil -ve).

When the engine dies, look for which trace stops. If the 5v pulse continues while the engine winds down, but the 12v pulse stops, the igniter is faulty.

IF the 5v pulse stops immediately, there is a fault between the CPS and the EZ-K unit. If you have followed this far and understood, you probably have the skill to work further if you get this fault.

Hope that helps. Shout out if you find this thread and post and need help with a similar problem.

And again, thanks to everyone for their suggestions and advice.

[Laird Scooby]

Glad you got it sorted!

The diagnostics makes for interesting reading too, been thinking of one of those portable 'scopes for some time now (little hand-held jobbies) or using one of those audio to USB interfaces on my laptop and one of the freeware programs to turn it into a 'scope.

Might have to think more seriously about that if i get any problems that warrant it. ;) :D

[aardvarkash10]

Glad you got it sorted!

The diagnostics makes for interesting reading too, been thinking of one of those portable 'scopes for some time now (little hand-held jobbies) or using one of those audio to USB interfaces on my laptop and one of the freeware programs to turn it into a 'scope.

Might have to think more seriously about that if i get any problems that warrant it. ;) :D

The laptop path is a good one - it gives you data logging ability as well usually and that makes diagnosis a LOT easier! Cheap as chips these days too.

[Laird Scooby]

The laptop path is a good one - it gives you data logging ability as well usually and that makes diagnosis a LOT easier! Cheap as chips these days too.

I already have a "dedicated" car-related laptop, it's an old one running XP with a proper RS-232 port for connecting the LPG diagnosis/tuning cable to.

I've since added an el-cheapo (but still quite good) £6 ebay borescope to it and somewhere i have an audio to USB interface i bought for using as an oscilloscope interface.

Granted it would probably be as much use at aligning an FM Front End at 10.7 Mhz as a chocolate teapot but for most other tasks, particularly diagnostic on automotive and audio frequencies, it should be more than capable.
Just got to find the audio interface now................. ;) :D

[Joe of Loath]

And learn from my mistake - don't use your matte white laptop to look up parts when you're filthy. The oil will never come off.

[Laird Scooby]

And learn from my mistake - don't use your matte white laptop to look up parts when you're filthy. The oil will never come off.

https://www.amazon.co.uk/d/c84/Gloves-Bodyguard-GL8973-Disposable-Black-Nitrile-Large/B00864OWHO

Been using those for many years now. Used engine oil is carcinogenic and easily absorbed by the skin and ........... oh yeah, when you take them off you should have nice clean paws with which to prod your laptop or any other search device. ;) :D