Moomin has sleepy sickness

[aardvarkash10]

The common 700/900 series fault of sudden engine stopping associated with tacho dropping to 0 but dash lights all staying out...

So Moomin, the '95 940 LPT developed his first real fault (as above). He's been fine then suddenly got the sickness. No obvious connector or loom issues, so we ordered a new CPS from IPD and waited for it to travel 8,000km to reach us.

It did, along with a bunch of filters and stuff that cost and arm and leg here, but thats by-the-by.

We fitted the new sensor today (having lashed out on a 10mm rachet ring end spanner for the task - well worth it!).

And the problem got worse.

So now I'm working my way through the EZK/LH2.4.4 system attempting to understand the system and then isolate the problem. This is not helped by excellent Bosch connectors that completely seal all terminals making probing the terminal for voltages a nightmare.

Has anyone got a link or a post-able scan of a quality testing sequence?

[Laird Scooby]

It used to be common practice to have a box full of "breakout leads" with probe sockets built in at some point - unplug the suspect sensor, fit the breakout lead between the vehicle plug and sensor and you can effectively back-probe it.
However i've not seen them for a long time, probably since the advent of OBD-II.

You could try an insulation piercing type probe but that in itself is destructive, another is the "paper clip trick" where you unravel a paper clip and firkle it in under the rubber boot into the back of the plug to enable measurements to be made.

If you haven't got a spark at all it might be worth checking the Hall Effect cable, i've known them to break where they pass through the grommet that holds them in the side of the dizzy - this causes these symptoms. Might not be the answer but worth checking anyway. ;) :D

[stephend]

Just for info, if you have a crank position sensor, then afaik you don't have the Hall effect sensor in the distributor, and vice versa. (The latter was used on the 200E/230E with K-Jetronic fuel injection, which doesn't have a CPS.)

Sorry to contradict, Laird S! Hall sensor would certainly be a prime suspect on models that have one, so it's good advice in any case.

[Laird Scooby]

Good point Steve - wasn't quite awake when i wrote that! :err::nah:

Besides - my Jeep had both, CPS to actually time everything from/tell the engine where the ECU was (t'other wat round i mean! - still half asleep!) and the Hall Effect to provide the signal for the coil to fire.
All the advance of ignition, fuel injection timing etc was then done from the PCM (Powertrain Command Module) with interaction to/from the auto box ECU as well.

That said it may well also be worth investigating the cables running to the CPS just in case. ;) :D

[Rumbo]

"That said it may well also be worth investigating the cables running to the CPS just in case"

Good point,mine was stripped to the silver foil at the top of the wire ;)

[Steve940estate]

You mention no dash warning lamps coming on when the engine stopped. That would suggest to me that there was a cut in battery power or possibly ignition switch.

[aardvarkash10]

thanks all.

Yes, replaced the cps yesterday as I said in the op. The old one was suspect with damage to the cable at hte connector, so on a precautionary basis a new one went in.

I've been working my way through the 1994 940 wiring diagram to identify test points and expected voltages, so thats helping understand the circuit and its operation.

Last night I got it down to a "wiggle" test finding in the loom near the ignition amplifier. Cutting the loom open, the wire that reacts most readily is the blue ignition live supply feed (+12v when ign is on). My plan today is to set up an LED signal light to identify when (or if) it loses this supply.

And paint the deck. I'm told I have 125 square metres of deck to paint today. Lots if thinking time available...

[Laird Scooby]

That's either a big boat or a large garden feature! :err:

Reckon the tell-tale LED is a good idea, after all it is an intermittent fault so anything that can help monitor the supply and/or signals in real time is a bonus. ;) :D

[aardvarkash10]

a boat would be nice, but no, landscaping.

[Laird Scooby]

Very nice too! Cheaper than a

Break
Out
Another
Thousand

as well! :lol:

[Rversteeg]

No spark

The rpm gauge gets its signal from the ignition coil. So a dropping rpm gauge and a dead engine means that you have lost the ignition.
The ECU gets the information about the position of the crankshaft from the CPS and sends firing signals via a power stage to the ignition coil. If the CPS is not the culprit, have a look at the power stage. It is mounted onto an aluminium base with heat transferring paste, to get rid of the heat it generates. A hot power stage can also (intermittently) fail, so check the paste first, before exchanging the power stage itself. The power stage is part 4/15 in the Volvo electric diagrams.
On my 98 LPT the power stage is located on the inner wing, behind the battery.
In Europe the original Bosch PS costs about 80 Euro, two times the price of an imitation.
Rob

Check Ebay, it seems the PS is pretty generic stuff for Volvo, Saab, Porsche etc.: http://www.ebay.com/sch/sis.html?_nk...d=390144013580

[Laird Scooby]

Something else worth noting here, if it is the ignition amplifier/power stage - if it is throwing its toys out of the pram because it's getting hot, removing it, cleaning the back of it (the heatsink) with something like isopropyl alcohol, carb/intake or brake cleaner or a similar solvent and also the mating surface where it lives in the car then applying new heatsink compound can often prolong its life and get rid of faults like this.

Don't use anything abrasive to clean the surfaces of the heatsink and where it mates as this will decrease the surface contact area.

I haven't done mine yet (but only had this one for about 3 months) but did all my previous 740s, both my Rovers, any and all Vauxhalls (think Holden down under) that used a similar system and any other cars that had a separate ignition amplifier/power stage.
It takes ten minutes to do it and saves a lot of grief, even if it isn't the fault it's a worthwhile precautionary preventative maintenance task, especially for the minimal cost involved. ;) :D

[aardvarkash10]

cheers guys - thats my next port of call already!

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

Therefore the crank signal must be reaching the LH/EZ-K units.

I've had the radio suppression relay off and apart - no sign of any damage or fault in there. All solder points are clean and tight, contacts are in good condition etc.

The next most likely point of breakdown is the ignition amp - it carries the highest current load. So this is where I'm inserting a set of indicator LEDs which will show me the state of the four key inputs and outputs: 12v ign supply, 0v earth, ignition trigger signal from the EZ-K unit, and coil switched side.

LEDs provide almost no load on the circuits so won't disrupt the normal operation. I wish there was a conventient break-out cable available, but since there isn't I'm just going to"pin" straight into the relevant wiring.

[Rversteeg]

LEDs

The radio suppression relay only feeds the fuel injectors, nothing to do with the ignition.
Usually I do not like to just exchange components, but for the relative low cost of an exchange power stage it seems a lot of work testing it with LEDs. Even if it turns out the PS wasn't the culprit, you have made your car a little bit more reliable again by putting in a new component....

[aardvarkash10]

The radio suppression relay only feeds the fuel injectors, nothing to do with the ignition.

It also provides the 12v+ feed for the ignition coil. Same circuit.

Usually I do not like to just exchange components, but for the relative low cost of an exchange power stage it seems a lot of work testing it with LEDs. Even if it turns out the PS wasn't the culprit, you have made your car a little bit more reliable again by putting in a new component....

What can I say - I trained as an auto-electrician here in NZ. For a lot of vehicles (especially european) we were 6 weeks and/or several hundred dollars away from replacement parts. We learnt quickly to only replace what was actually necessary...

Also part of the training was that a fault was only truly fixed if you could show what the fault was fault and how it had had been corrected - especially intermittent faults.

I still tend to function that way. Its an old guy thing!