Lean running on petrol

[DoubleChevron]

Hi Guys,

I've never noticed before, but in this cold weather than old Rangie runs extremely lean ... to the point where it'll barely run. I almost never run on petrol, but I ran out of gas the night before ...So did the school drop off yesterday on petrol. The motor ran fine when cold, but as soon as it was at running temperature it was running lean as buggery (I'd have had the choke out in a heartbeat if it was one of my old cars). As the kids climbed out the car, I touched the accelerator and it instantly died (like cars running lean will unless you have the choke out). It wouldn't restart. I flicked it to LPG and luckily there was enough lpg there to start it, but it was running super lean as soon as I flicked backed to petrol, so I limped to the local petrol station using lots of revs to keep it alive and filled up with gas.

Anyway, last night I figured I'd better cover the basics first. I whipped the MAP sensor off, pulled off the inlet elbow, whipped the top off the inlet manifold. Pulled the stepper motor... None looked like it was an air leak. The stepper motor was loose and had no seal at the bottom. So I re-assembled with new sealer. It starts up lovely, but as soon as it warms up, starts to lean out and die... and won't restart on petrol if I switch it off ( yes THAT lean ). I have two maf sensors here, so i tried the other one and got identical symptoms.

Does anyone know which wires at the computer to check for the temperature sensor (s) ? The sensor would need to be weirdly out of spec for it to be the issue though. THere is also what looks to be an aftermarket resistor in the wiring beside the computer. Could this be changing the fuel map ?

seeya,
Shane L.

[PhilipA]

Probably the only complaint in history of an RRC running lean!! LOL

I would be looking at the fuel pump or fuel filter first. Also have a look at whether the little hose at the back of the plenum chamber to the fpr is intact, and that the little plate that the stepper fits onto is tight to the plenum.

The temp sensor for the injection should read 300 Ohms across the terminals when warm. It is almost unheard of for it to be lower .The usual problem is high resistance which leads to the ECU thinking the engine is cold.

The resistor is most probably the tune resistor and is what tells the ECU which tune to use eg whether it has cats or not so don't touch it.
regards
Philip A

[DoubleChevron]

Thanks! Perfect, 300ohms. SOmething to aim for :)

I swapped the fuel pump out of the other car into it and it has a new filter in the last few months. I'd imagine the problem would be far worse when cold (when it needs more fueling) if the pressure to the rail is low :confused: I'll see if there is an easy way to get a pressure gauge into the fuel rail to check.

thanks!
Shane.

[DoubleChevron]

How have I never been to this site before ??

Rover 14CUX Hot Wire Mass Flow EFI: Service and Troubleshooting (http://www.britishv8.org/articles/rover-14cux-efi.htm)


bloody brilliant.

https://www.aulro.com/afvb/images/imported/2017/05/551.jpg





"Bottom Row" - pins 1 to 13 (they're numbered from left to right as shown in the photo)


1
Red/Green
Idle bypass valve - circuit 1


2
Brown/Orange
Power feed to the fuel injection main relay


3
Yellow
Throttle position sensor output/reference - see also 20 and 25


4
Black
Oxygen sensors (ground) and to the relay that powers their heater coils


5
Grey/Black
Tune resistor (through VIN LA451517 only)


6
Yellow
Road speed input


7
Green/Blue
Coolant temperature sensor (input) - see also 25


8
Purple/Yellow
Windshield defroster input, if fitted


9
White/Light Green
Diagnostic connector output


10
Black/Yellow
"Check Engine" lamp


11
Yellow/White
Right bank of injectors - cylinders 2, 4, 6 and 8


12
Blue/Red
Main relay "request"


13
Yellow/Blue
Left bank of injectors - cylinders 1, 3, 5 and 7





"Middle Row" - pins 14 to 27 (they're numbered from right to left as shown in the photo)


14
Black
Ground


15
Brown
"Battery" supply


16
Blue/Purple
Fuel pump relay "request"


17
Grey/Yellow
Purge control valve output


18
White/Pink
Diagnostic connector output


19
White/Grey
"Ignition" supply


20
Red
Throttle position sensor (input) - see also 3 and 25


21
Yellow/Black
Air conditioning thermostat input, if fitted


22
Blue/Red
Air flow sensor (input) - see also 25


23
Blue
Signal from the LH oxygen sensor


24
Blue
Signal from the RH oxygen sensor


25
Red/Black
Ground side of coolant, fuel, airflow & throttle-position sensors


26
Green/White
Idle bypass valve - circuit 1


27
Black/Grey
Ground





"Top Row" - pins 28 to 40 (they're numbered from left to right as shown in the photo)


28
Blue/Grey
Idle bypass valve - circuit 2


29
Orange
Idle bypass valve - circuit 2


30
Black
Fault display data


31
Black/Green
Diagnostic connector "request" input


32
Grey/White
Fuel temperature sensor (input) - see also 25


33
Black/Grey
Air conditioning compressor clutch relay, if fitted


34
Orange/Black
Transmission gear switch signal


35
Blue/Green
Air flow sensor (input) - see also 25


36
Black/Green
Air conditioning condenser fan output, if fitted


37
(Not Used)



38
Brown/Black
Fault display data


39
White/Black
Engine speed signal cable (harness includes 6.8k ohm resistor)


40
Black
Ground





So I whipped the plug off and measured the resistance between pin 25 and 7..... Bugger ... within spec ...






The Coolant Temperature Sensor should change resistance with heat, per the following specs.


10C
(14°F)
9100-9300 Ohms


0C
(32°F)
5700-5900 Ohms


20C
(68°F)
2400-2600 Ohms


40C
(104°F)
1100-1300 Ohms


60C
(140°F)
500-700 Ohms


80C
(176°F)
300-400 Ohms


100C
(212°F)
150-200 Ohms








So I let the car warm upto 70degrees (there is a proper temperature gauge in the radiator ... the fans were not yet running, so the entire cooling system should be at about 70degrees.... And I think it was 2300ohms I still had. So the coolant sensor is quite a bit out of range .. but it should be RICHER not leaner.... bugger.

The petrol tempe sensor ( pins 32 and 25 ) measured much the same as the coolant sensor when cool ( at about 20degrees)... I didn't check again when it had warmed up.

You know, with it about 15 degrees outside rather than 5degrees.... It's drivable on petrol. It's all but un-usable when cold though.

I also checked the fuel map resistor.

http://www.g33.co.uk/images/fuel_i10.jpg

mine is almost like this... For a few seconds I was dumb enough to think "crap I can't make out the colours well enough to decode the resistance" ........... then my snail like brain thought .... Oh, you actually have a multi-meter in your hand right now... so I chucked the ohm-meter over the resister ... 178ohms. So bloody close to 180ohms it doesn't matter .... Aussie spec fuel map. so leave alone.

Onto the fuel rail I guess, I'll see if I can figure out how get a pressure gauge into it.

seeya,
Shane L.

[DoubleChevron]

OK ... so has anyone figured out an easy way of fitting up a fuel pressure gauge to a 3.9 litre serpentine belt V8. The rail is metal, the lines running forward are metal, there is two lengths of flexible line front and back where the tank and motor connect. I do NOT want cut into them!

seeya,
Shane L.

[DoubleChevron]

Oh gee's ... when will I ever learn to put 2 and 2 together and get four.... :( I was just looking at the prices of fuel pumps on ebay (yes all the cheaper ones don't have the wiring harness on them required for htis car. I wonder if you can just wire the old plug on). Anyway, I'm looking at the pumps and thought .............................. Crap, there is another issue that my problems match. I head out to the shed and unscrew the filler cap ... It was hard to unscrew. The Oring was half way down the threads. With this off the car is running perfectly.

I'll take it for a drive on petrol later tonight and get it nice and hot and verify it's ok (with the cap on loosely).... but it looks like my problem the entire time has been the tank isn't vented. So yes, I sure did get it sealed up well when I was trying to stop the petrol smells last year!

seeeya,
Shane L.

[Davo]

That IS funny!

Shouldn't the tank be vented to the charcoal canister so that it can't be sealed up anyway?

[PhilipA]

Yes it should be vented to the charcoal canister which has a valve that is supposed to open at part throttle to vent into the inlet manifold. check that the connector is actually connected. I cannot remember whether it is 5v or 12v so be careful if you want to test it.
regards Philip A

[Pedro_The_Swift]

the 4L has a schrader valve, next to the firewall behind the right? bank,,

maybe?

[DoubleChevron]

Thanks Guys,

this car had horrendous fuel smells when I first got it ... really, really bad. It looks to have been fiddled iwth many times to try and fix this. It has a small 38'ish litre tank in the rear wheel arch. This leaked at every join (and the hacked down filler neck). I managed to get it all air tight. The lines run forward to where the charcoal box is under the bonnet.... but it's been removed. I'll need to refit a charcoal canister and get it all working under the bonnet again. The back of the car I've fixed, but I haven't messed with the front (because I've never had a problem until now).

seeya,
Shane L.

[PhilipA]

If you want to be an environmental vandal, just run a breather from the tank , up the D pillar to the outside of the car. You only need a pinhole size opening.
The vent has to be far enough above the top of the tank so that it cannot siphon, if say you are stopped on an extreme angle. I had an auxiliary tank inside the RH side of the rear load area in a 77 , and I recall being on a trip stopped on a hill and watching the fuel siphon out.

You can add an inline filter as a small reservoir which will cut down vapours.

BTW the earlier model RRCs had a small square tank high up in the RH mudguard to act as a buffer reservoir to account for angles.
Regards Philip A