93 V6 fuel pressure release.

[sgould]

The level sensor feeds were the first thing I checked with the Tech2.  They arrive at the ECU separately, but Tech2 only sees the combined value. Actually it only reports the lowest of the two, which is why the gauge falls to zero when one goes open circuit.

It may be warm enough today to work on the electrics without dropping anything.  I’ll try.

[sgould]

One stage further. and the two issues.

The P0089 fuel pressure code and engine light gets more odd each time.  Last night, as reported, the light was off when my wife drove to her concert.  When she went to come home the light was off in the car park and on leaving the event, but came on soon afterwards.   This morning I went out for fuel and, as expected, the engine light was on because I hadn't cleared it.  Then a quarter of a mile up the road it went off of its own accord.  So who knows what is going on.


The second issue with the fuel levels is a bit further on towards a solution, but has got a bit more confusing.  I disconnected the ECU and measured the resistance to each of the two level sensors at the ECU connector.  The WIS says they should be 40 Ω on full and 250 Ω on empty.

I measured with the gauge showing about ⅓ full and the resistances were...

Level on fuel pump sensor: 158 Ω
Level on second separate sensor: 121Ω

Which seems about right.


After I filled the tank, I checked the resistance again and they were...

Level on fuel pump sensor: around 23 Ω (It was wandering about from 21 Ω to 25 Ω, not steady)
Level on second separate sensor: 42.4 Ω which is about right for a full tank.

So the fault seems to lie with the sensor attached to the pump.  It can't be a broken wire in the resistance strip on the sensor as the reading is not zero, and it can't be a corroded connector in the line because that would give a higher resistance.  But it's reading below 40 Ω, so presumably the ECU is seeing this as out of range.  It implies that the float is going higher than expected, relative to the resistance winding.  All I can think of is that the sensor has become detached and is loose and moving about a bit.  But at least it's likely to have identified the sensor that's at fault, I think

It looks like a garage job to fix it.  To get to the tank, it's: 

Anti-roll bar off
Exhaust off
Propshaft off
Heat shield off
Rear diff unbolted and hung on a strap to lower it a few inches
Detach fuel filler
Remove fuel pipes
Undo main electrical connector
Unbolt tank and fiddle it out

That's too much for me these days.  I might even leave it as it is for a while.  Oh! for a hole in the floor like the 9-5.

[carrera]

Funny.... having seen the agricultural engineering approaches to ripping open a hole in the 9-3 floor to get access to change the pump, I was wondering "what about getting a 9-5 cover plate (perhaps with part of the 9-5 floor) and spending the money on doing what Saab should have done in the first place".

Or you could just put a 20 ohm resistor in series   

[sgould]

Both of those thoughts have crossed my mind!!

[sgould]

Two days on and the engine light is still off.  Fingers crossed...

Forte engine cleaner has arrived.  Two days late due to Royal Mail delays.  I might as well use it!

[carrera]

Now you will never know what solved the problem....

[sgould]

I'm sure it will happen again.  The last two occasions the light stayed off for a few months.  But if I put some Forte in every 6 months or so, It might confir it's a restricted fuel line or injector.

Short of running 100% of the time with the fuel pressure recorder, there's not much else I can do.  Unfortunately I would have to keep an eye out as the scanner doesn't doesn't record.

[sgould]

Engine light was still off this morning, but came on again on the second journey back home.

The only small positive is that, if it is the fuel pump, if that is replaced, the level sensor will be replaced too.