B230ET stopping.

[rogerthechorister]

Hoping to further the possibility of it being an overheating ignition amp later this week. I have used her for some local runs in cooler wevva and it's situation NFF so far!

[rogerthechorister]

Well, following the info on page 1 above, this week Tim the Mecco removed the air filter box and found underneath - no ignition amplifier! Where else might the thing be?

[rogerthechorister]

Hmm. A careful reading of Mr Haynes (for the 740/60 series) and Son (for the 940/60 series) suggests a theory. Neither mentions an "ignition amplifier" and only the 9 series book mentions a "power stage" which I thought was a synonym for "ignition amplifier".

This would imply that on the dumb Motronic cars (and she is definitely one of them, having an air-flow meter rather than an air-mass-meter) the ECU directly controls the LT to the coil, much as in the old days the points used to do.

This in turn would lead to the theory that if the issue is overheating, it is overheating in the coil or the ECU. Or I suppose a rise in resistance in wire between the ECU and the coil. Now the ECU is inside the car (near the driver's right foot) so the fact that she runs OK over about 40 mph would tend to indicate that it is not the ECU overheating, and also if the fault tends to go away when the aircon is turned off (so making the area near the driver's feet warmer) that points in the same direction. And, I've never had an ECU out of a Motronic car but I have taken them in and out of a 2.4 car many times and I have seen no suggestion of thermal paste on the mounting strap.

But I have had overheating coils in the past (on a Mk1b Cortina, a Mini, and a Morris Minor) and they symptoms were always the same - a gradual loss of power until the engine faded away altogether until the coil cooled down again.

So, first question, is anybody ABSOLUTELY sure that a B230ET (760T) in fact has a "power stage" or "ignition amplifier", and if so where is it?

Second question, can anyone absolutely confirm or deny that on a B230ET (760T) the ECU provides (and interrupts, it's the interruption that produces the HT voltage) the low tension signal?

Third question, if it is the ECU that is the source of the problem, who can test/rebuild/supply one, and should there be any form of heat sinking for it?

[rogerthechorister]

This thread appears to confirm that in dumb motronic there is a power transistor inside the ECU that provides and switches low tension current -

https://www.volvoforums.org.uk/showthread.php?t=30859


The FAQ say that there is an ignition amplifier on the LEFT inner front wing panel, but I suspect this is for US 760Ts and so would be B230FT not B230ET, and therefore LH2.2 not Motronic.

[aardvarkash10]

If its motronic, then yes that looks to be the case. The ignition is switched directly from the control unit, not via an external amplifier.

Before pulling the ECU out I'd do a soak test on the system. Voltmeter and ammeter on the coil circuit and just leave it idling for a while. Coils TEND to fail short circuit as the insulation in them breaks down so you should see an increase in coil current over time (say, 20 - 30 minutes). If the current drops over time, I'd suspect and earth fault or the power transistor in the ECU

[rogerthechorister]

Coil ordered (new Bosch, only 40 squid) and second-hand ECU only 45 squid. If it's not them then it HAS to be the impulse sensor(s) NLA from Volvo but I believe the same as some Porsche ones pattern variants of which are on ebay for under a tenner each.

[Chesh740R]

On the 740 and 760 turbos with motronic, the powerstage located above the battery (weather they moved its location on the later 760T's i cant recall) , its a black or silver box with fins is susceptible to heat and eventually dies.

It is number 289 in the pictures below.

I take it you have also replaced or reflowed the solder connections on the Motronic relay number 135, again it was in main fuseboard/relay behind ashtray on early 740/760's, could be different location on a late 760T.

[aardvarkash10]

Originally Posted by Chesh740R

On the 740 and 760 turbos with motronic, the powerstage located above the battery (weather they moved its location on the later 760T's i cant recall) , its a black or silver box with fins is susceptible to heat and eventually dies.

That is indeed the power amplifier stage, but for the injectors, not ignition.

[rogerthechorister]

Well, on the 760T the fuses are in the right hand side of the dash, accessible only when you open the driver's door. You describe the power stage location for (AFAIK) a US spec B230FT 760T perfectly but I cannot inspect my left inner wing panel until it's light. So it might be there on mine. OTOH, Braydons said I hadn't got a separate power stage or ignition amplifier either! I have not reflowed anything yet - and if it's in the back of the fuseboard getting at it is going to be a real ar5e, and from memory the relays are soldered in on my fuseboard! This is getting like a Sherlock Holmes.

[Chesh740R]

Originally Posted by aardvarkash10

That is indeed the power amplifier stage, but for the injectors, not ignition.

yes indeed, if the ignition is fine which is usually very reliable on the motronic cars, then i would look to the fuel side