220 tyres and cutting out

[white exec]

Yep, it's correct - one of the relays is a double switching relay (one set of simple open/close contacts, but the other is a two position contact set) according to the diagram.

That's interesting, and quite different to other models.
Could you post that part of the circuit diagram, Iain?

[wurlycorner]

Sure - attached.
nb sorry, I wrote the post above from memory. There aren't two sets of contacts in one of the relays, it's simply a two position contacter)



Components are;
634 - Engine Cooling fan (RH)
635 - Engine Cooling fan (LH)
733 - Cooling fan relay (air conditioning)
772 - Cooling fan high speed relay
773 - Cooling fan series/parallel relay
850 - Engine cooling fan thermoswitch

So basically, in first phase, 850 L/H contact closes. This runs the fans in series through the 'normal' position of 773.
In the second phase, 850 R/H contact closes. This energises 772 coil, which routes fan 635 directly to earth via the contacts of 772. It also feeds the coil on 773, which energises and changes over the contacts in 773, to route an alternative feed onto 634.

733 is independent - coil energised by the A/C control unit (60) which closes the contacts and runs both fans directly. Operation of this relay doesn't affect the operation of the cooling fans (even is 733 was energised/closed, when 850 L/H contact closed, it would effectively bypass 733).

[white exec]

My error, too, Iain.

Cars with the two-stage thermo-switch are fitted with just two relays (one operatng as a simple Make, the other as a Changeover), because the slow speed (series) running is switched by the thermo-switch itself. An additional relay (733) is actuated by AC coming on, and also triggers show-speed running.
The two relays (772 & 773) cut in together to trigger high speed (parallel) running.
All as shown in your diagram and description.

Cars with ECU controlled cooling fans (eg XM) have no heavy-duty thermo-switch, so use 3 separate relays to control fast and slow speeds. One of these switches on slow speed, the other two come on together (as before) to trigger fast (parallel) running. AC is sensed by the ECU as well, so bringing on slow speed.

So, it's 2+1 for the CX (and BX...), and 3+0 for the XM !

[marc61]

It’s a 2 bar MAP sensor, a standard GM part that’s fitted to GTi Turbos. I replaced mine a few weeks ago and it stopped the cutting out under load. The AEI needs to know the pressure to ensure the right ignition timing is applied, it’s a turbocharged car that’s why a MAP sensor is fitted, to measure the manifold pressure. The LE Jetronic just looks after the fuelling not the ignition timing; the MAP sensor provides a signal to the AEI not the LE Jetronic box.

It has a MAP not a MAF sensor.

[Bilkob]

MAP sensor???
What?
Where?

[wurlycorner]

It’s a 2 bar MAP sensor, a standard GM part that’s fitted to GTi Turbos. I replaced mine a few weeks ago and it stopped the cutting out under load. The AEI needs to know the pressure to ensure the right ignition timing is applied, it’s a turbocharged car that’s why a MAP sensor is fitted, to measure the manifold pressure. The LE Jetronic just looks after the fuelling not the ignition timing; the MAP sensor provides a signal to the AEI not the LE Jetronic box.

It has a MAP not a MAF sensor.

Marc I'm not trying to pick holes/score points, but you did say it uses the MAP to adjust the fuel/air mixture;

Yes the CX uses a MAP sensor (manifold air pressure) to work out engine load and the fuel/air ratio that’s needed - it’s located near the header tank and bulkhead.

...which could only be done via the injection ECU - which is why I then outlined that it doesn't go near the Injection system and isn't used by it.

And as I also explained, yes it does use the MAP to adjust ignition advance/retard - so we are agreeing there. But that isn't air/fuel mixture.

And yep, again, we're agreeing it's not a MAF. I just added the statement about MAP/MAF and whether part of the L-series jetronic systems or not, as a wrap up bit of info.

[marc61]

My understanding is the map sensor measures the manifold pressure, signals it to the AEI box which then adjusts the ignition timing as to whether it’s under boost or not and simultaneously the LE Jetrinic adjusts the fuel/air mixture. Maybe I could have expressed that better, but I don’t see why the problem is. It must have a map sensor else the ignition won’t get retarded under boost and the engine will detonate. I replaced mine and it helped and it stopped the engine dropping out that’s the only message I’m trying to communicate here. If you don’t believe that or don’t believe it’s got a map sensor tucked up under the bulkhead then that’s your choice!

[Bilkob]

Gentlemen...............

[wurlycorner]

Well I'm lost how something has got so lost in translation.

[Bilkob]

Right, back on target. Today I let the car run to cutting out, took a good 10 minutes, but just before it cut, the throttle became increasingly unresponsive and the car sounded like it was missing if held at say 1500 rpm......
Then it cut out. I quickly cracked the fuel union after the pressure regulator and............... there was fuel!
But not at any great pressure. Any thoughts?