B230ET stopping.

[rogerthechorister]

A while back I had a woe with my 760T - open the throttle too hard, particularly on a left-hand-bend, and she coughed ominously. That turned out to be an air hose (from memory positive pressure from turbo to intercooler) that was NLA at Volvo - but I got a second-hand one on here.

She has been off the road for several months sorting out an oil gusher on the exhaust side (and no it was not the turbo oil return) but all that is done and I took her out the other day to buy a guitar. Somewhere near Stoke Newington a chav in a Scooby overtook me on the inside and I thought "RUDE" and floored it. There was that cough. And a minute later she stopped pulling well, coughed more, spluttered and died.

I thought "hose", lifted the bonnet and it wasn't that. Sat there for a bit, then turned off the aircon switch (it was a hot day) and tried again. She ran - but finishing the guitar collection and back out into the east end (going to my daughter's, lots of slow traffic) she was plainly unhappy. The following morning she started sweetly, and I ran out on the A13, Dartford tunnel, A2 and home - no problems.

She was due MoT so in she went - there werre a couple of little things, a sidelight, the auto-on for my subwoofer and brakes. So a complete set of discs and pads and £493 later I had MoT. I also asked the garage to trace and cure the cough and die fault. They reported no fault found and plenty of power. But it wasn't as hot.

Over this last weekend, you may have noticed, it was hot. And although she took me to Croydon fine, she coughed spluttered and died several times, but would always re-start if given 20 minutes to cool down, and was OK if I could keep above 40 mph. In light of the symptoms I put off my return home until last night, and she came home like a bird at about midnight - but on my favourite test hill I thought MAYBE a little down on power and a hint but only a hint of a flat spot at one point.

Now these are IDENTICAL to the symptoms that I had on my better SPort Edition, and that turned out to be a crank position sensor - cheap, easy, perfect!. But, and here is the but, Steve at Braydons tells me that my 760T is a Hall Effect car, the bits are (probably) NLA and were always very expensive. This is not encouraging.

Does anybody (a) have a set of the Hall Effect bits (b) have any bright ideas?

I think I might start by removing cleaning and checking all the positive pressure hoses, and by (oh joy) removing the dizzy and cleaning up all of the bits round that where a Hall Effect wire might be cracked or broken - or where oil from the now cured gusher might be contaminating something. Or I could just put a jetwasher on the dizzy and if she will then not go at all at least I will know that that is the area of the problem.

Before anyone else suggests it, it has also occurred to me that a vapour lock in the fuel lines or an issue with the fuel pumps (I think it's two on her) could give similar symptoms.

What does the team think?

[Laird Scooby]

I think i'd be inclined to remove the air cleaner and then the ignition amplifier module, clean the old paste from it and the body work (with a non-abrasive cleaner, use industrial alcohol or similar) then refit it with new heatsink compound paste (try to buy it in a tube rather than a syringe) ensuring an even covering.

When heatsink compound is in the vessel you buy it in, the "juice" inside it has a tendency to "drop out" causing the paste to go very thick, almost solid. That's why it's a good idea to buy it in a tube so the tube can be "massaged" before use to remix it.

If that doesn't cure it, you may have to resort to buying a new ignition amplifier module/ignitor but also check all the connections and in particular, the mounting clamp on the coil as that acts as an earth for the HT side - if it gets hot through increased resistance from corrosion, it will cause problems as it can't produce the spark. Obviously on a hot day it's halfway there already and when you put more load on it then the resistance will cause more heat, more resistance and so on until it gets to the point where the amplifier module switches itself off for self-preservation.

There is a "sweet spot" on all coil circuits whether it's the ignition coil on a car or the crossover in the hi-fi speakers where the circuit is in resonance. This means it is at it's maximum efficiency so will give the best output even with a slightly "off colour" input. Generally for 4-cylinder cars it is between 1500-4000rpm, a bit lower for 6-pots (usually 1000-3000rpm) and lower still for V8s.
This would tie in to you getting the car to run nicely above 40mph as it puts the revs into that range.

If you can find the Bosch part number on the module (should start 0 227 or similar) or if it's been replaced with another make, the part number from that there's a good chance it can be cross-referenced. However the usual sources i use to find parts don't list one for the B230ET so it's not possible to find one easily.

[rogerthechorister]

Thanks. Expect reply when I am sober.

[Laird Scooby]

Yesh, ok, hic!

[aardvarkash10]

Originally Posted by rogerthechorister

... There was that cough. And a minute later she stopped pulling well, coughed more, spluttered and died...

Over this last weekend, you may have noticed, it was hot. And although she took me to Croydon fine, she coughed spluttered and died several times, but would always re-start if given 20 minutes to cool down, and was OK if I could keep above 40 mph...

Does anybody (a) have a set of the Hall Effect bits (b) have any bright ideas?

With Dave (sorta) here. Temperature sensitivity points to ignition amp. My usual caveats about diagnostic process apply.

The 40mph thing? Think airflow... This isn't a sweet spot issue, its an air moving through the engine bay and cooling stuff issue.

The resonance stuff Dave talks about was true bitd, but low impedance, high current coils and electronics put an end to that nonsense. The coil rise time and discharge resonance is so short it could keep producing excellent results from stall to 15,000rpm if the engine would hold together...

HE sensors are criminally reliable. That said, everything gets old, tired and grumpy at some point. They are easy to test and so generic that you could probably adapt the sensor into the dizzy from a stock industrial item (automation position sensors are often HE).

[Joe of Loath]

Yes, I expect you can pull apart the hall effect sensor, find the part number, and solder in a new one if required. However it's more likely the connector on the hall effect sensor than the sensor itself - they're solid state after all.

[rogerthechorister]

To Laird Scooby

I might get thermal paste from some computer people - it's a very critical item for CPUs so should be good.

I'm not quite sure I buy your theory on the resonant frequency in resonant circuits. When I was doing my A levels decades ago I almost understood AC circuits.

[Laird Scooby]

Originally Posted by aardvarkash10

The 40mph thing? Think airflow... This isn't a sweet spot issue, its an air moving through the engine bay and cooling stuff issue.

The resonance stuff Dave talks about was true bitd, but low impedance, high current coils and electronics put an end to that nonsense. The coil rise time and discharge resonance is so short it could keep producing excellent results from stall to 15,000rpm if the engine would hold together...

Airflow??? On a component buried under the air cleaner box behind the headlamp in a place where airflow is probably at a minimum?

All coils will have a resonant frequency regardless of whether they are electronically switched or not. What i was referring to is this :

https://en.wikipedia.org/wiki/Resona...ctive_coupling

This still enhances the efficiency of the coil to produce a better spark. If the module is weakened due to being close to an overheat condition, the spark intensity will be reduced. A much higher spark voltage is needed to ignite a weak mixture so at a cruising speed where the revs coincide with the resonant frequency of the coil, the output will be that much better even with a weak input. Hence above 40mph where the coil is in it's most efficient band the misfiring is minimised.

While i agree electronic control mitigates this effect and in perfect conditions would happily give (near) full coil output up to 15000rpm (or 7500rpm for 8 cylinder engines) all day and every day, it would appear here that we have less than perfect conditions due to a suspect module. As such these clues need looking at and interpreting.
I'm not saying mine is the definitive answer and wholly agree with your normal caveats about proper, methodical fault finding but even proper methodical diagnosis needs a starting point. In this case all the evidence is pointing towards the module being the most likely cause making it a good place to start.
There could be a split hose somewhere, possibly even a MAF problem but the heat-related conditions point more towards ignition related faults than the MAF, bearing in mind the MAF works on the "hot wire" principle and as such is obviously more efficient when it's hotter - to a certain point obviously!

[James_N]

Originally Posted by rogerthechorister

To Laird Scooby

I might get thermal paste from some computer people - it's a very critical item for CPUs so should be good.

I'm not quite sure I buy your theory on the resonant frequency in resonant circuits. When I was doing my A levels decades ago I almost understood AC circuits.

Ive just bought some from eBay to install my ignition module. 99p

[rogerthechorister]

She is dumb Motronic, so has an air flow meter (spring loaded flap) rather than an air mass meter.