Intermittent lean running

[Alexdaredevilz]

Its happened a few times now, out of the blue it will run to 18:1 or leaner some times and then misfire

Plugged fault code reader in and only came up with stepper fault, but I know that's not been working for over a year

Does go lean some times when at idle and hot, it will only happen every 5 minutes? then some times not at all for 1 hour

Could the fuel pump be on its last legs? im pretty sure the symptoms wouldn't be fuel pressure reg or am I wrong

This has kinda stumped me

Thanks

Alex

[dbv8]

Genuine Bosch 044, Weber Alpha, all new heavier wiring.

Job done

[SILICONEKID340HP]

dbv8 said:

Genuine Bosch 044, Weber Alpha, all new heavier wiring.

Job done

Whats the standard factory fitted pump ?is the o44 one up from the OE factory pump..

Are the 044 a bit of a overkill,it does up to 600hp

Where do the wires go?is it much of a job?
Cheers Derek.

Edited by SILICONEKID340HP on Monday 28th November 19:03

Edited by SILICONEKID340HP on Monday 28th November 19:03

[Alexdaredevilz]

Its all very well replacing it, but what if its not the problem?

What else could it be?

[lestershaw]

mine did that until snibs found an air leak at the back of the hose near the stepper motor, and it helped me get more horses when that was fixed

[Alexdaredevilz]

lestershaw said:

mine did that until snibs found an air leak at the back of the hose near the stepper motor, and it helped me get more horses when that was fixed

Ive checked all hoses and pipes,

And the problem is intermittent one minute it will be 13:1 and the next 18:1+

[blitzracing]

You wont get a fault code as long as the lambda probes switch periodically, its just not that sensitive as the fuel control is quite crude. It would be interesting to look at the lambda switching when it goes lean to see if it corresponds to what the AF ratio gauge is telling you. After all there are two sides to the V8, fuel controlled independently, but you are probably reading an average across all 8. Air leaks have a much bigger effect at idle, and if the pumps starting to fail Id expect lean running under heavy load when fuel demand is greatest. Recently one of the cars on here that was running lean was traced to the AFM, so its output voltage must have been going low. You could strap a test meter to the AFM output and see if it varies significantly at idle when it runs lean. Problem here is the engine is likely to slow down and draw less air when its lean so the AFM output will drop, so you don't know whats cause and whats effect. Generally AFM's and the connectors is always a good place to start with weird fueling issues.

[Alexdaredevilz]

Im running a non cat map

My a/f meter is running on just one side, cylinders 1,3,5,7

'Most' of the time the cars ok under-load, but some times it is not

What 2 wires do I need readings from, and what readings am I looking for?

Thanks

Alex

Edited by Alexdaredevilz on Monday 28th November 20:12

[TV8]

Hi Alex, mine was the one that had the AFM changed. I cant remeber what ones we measured my AFM accross, but it wasnt them!

Hi Mark, did you get the LED unit back ok?

[Alexdaredevilz]

TV8 said:

Hi Alex, mine was the one that had the AFM changed. I cant remeber what ones we measured my AFM accross, but it wasnt them!

Hi Mark, did you get the LED unit back ok?

I think it was the base volt's we measured not the running ones

[Alexdaredevilz]

Bump - need some suggestions asap please

[blitzracing]

Testing is performed in the following manner. Peel back the rubber boot on the airflow meter connector and leave it plugged in to the airflow meter. Set up the digital multimeter to read voltage. Insert the negative probe into the Red/Black wire (sensor ground), and the positive into the Blue/Green wire (Airflow signal).

Turn on the ignition, but do not start the engine. The meter should immediately indicate a reading of approximately 0.3-0.34 Volts after the initial "warm up" spike. Most defective airflow meters will overshoot to 0.8 Volts or higher, and take at least 2 seconds to come down to the correct voltage.

Now start the engine, and the reading should rise to 1.6 Volts (3.5 Litre engine) to 1.75 Volts (5.0 Litre engine).

The next test is full load, and as with the fuel pressure test it will require use of a rolling road or a steep hill in the same manner. Under full load the voltage should rise to 4.45 Volts (3.5 Litre engine) to 4.95 Volts (5.0 Litre engine).

On non catalyst systems, the idle CO mixture adjuster is provided on the airflow meter. It is located in a boss on the top of the airflow meter, pointing towards the engine. Leaving the multimeter negative probe in the Red/Black wire, move the positive probe to the Blue/Red wire.

Now turn on the ignition but do not start the engine. Observe the voltage. The normal adjustment range is between 0.0 and 3.6 Volts, with the higher Voltages producing higher idle CO values. There are approximately 20 turns of the adjuster screw to cover the entire range.

Annoyingly, the adjustment may be clockwise or anticlockwise to increase the value, and this varies from meter to meter! For this reason it is always preferable to have the multimeter connected in this manner when adjusting idle CO, so that you see can something is actually happening.

Typical Voltages that would be found at this point are between 0.9 to 1.4 Volts for non-catalyst cars. This Voltage is always factory pre-set to 1.8 Volts for catalyst vehicles. A value near to 3.5 Volts will generally produce an idle CO value of 9-10%. These Voltages may be used as safe initial values particularly if no CO measuring equipment is available

And yes I have the LED unit back- thanks.

[blitzracing]

Just an additional thought, as you are running the non cat map, double check the CO trim connection wire and Ground wiring to the AFM, if this is intermittent it will throw the mixture all over the place.

[biper]

Can I ask what a non cat map is?
I don't understand.......You can take the pre cats out and there is not a problem,
the lam sensors are before the main cat, so why should taking the main cat out affect the readings.
Barrie

Edited by biper on Tuesday 29th November 14:52

[Alexdaredevilz]

Thanks Blitz

I owe you a beer for your wealth of info!

I had 35 psi fuel pressure on idle clamped the return till it hit 38 psi

And problem sorted! so orderd new adjustable fuel reg and rail adapter thinking that will be the end of that

On the way home the a/f was much better (fixed it's self?) abit rich if any thing, so might need to tweek the c0 screw to get it perfect, is it lower or higher voltage to set a/f higher?

[blitzracing]

You should only have 38 psi with no vacuum in the plenum, ie wide open throttle. Anything less than this and the regulator drops the fuel pressure to stop extra fuel being pulled from the injector nozzle when the vacuum is greatest (over run and idle.) To do a basic check remove the small black pipe that joins the regulator to the plenum and block any air from entering the plenum from the pipe. The pressure should lift to 38 psi from whatever the idle setting is and the car should run horribly rich.

Edited by blitzracing on Tuesday 29th November 18:52

[blitzracing]

biper said:

Can I ask what a non cat map is?
I don't understand.......You can take the pre cats out and there is not a problem,
the lam sensors are before the main cat, so why should taking the main cat out affect the readings.
Barrie

Edited by biper on Tuesday 29th November 14:52

It does not matter if you ran a catalyst fuel map with or without physical catalyst, as what it does is keep the fuel/ air ratio in a very tight band using lambda feedback to keep the emissions as low as possible. This is not best for power or economy and can be the part of the reason for the engines to shunt at low speed. So if we did not have catalysts fitted, the engine will run better on the non cat map (where correctly chipped that is) as you set the fuel to the engines best requirements not the environment. This is way outside the narrow band lambdas probes ability to measure the mixture, so they are not used. If you try and run a catalyst without this tight fuel control they overheat and melt! As you dont have the lambda probes working, you have to set the low speed mixture by hand using the CO trim on the side of the AFM. This controls the mixture up to around 2500 rpm.

The different fuel maps are all part of the fuel chip that has a total of 5 different maps in it as standard (yes even in the late 80's ecu) that you simply change a resistor in the loom to access. You can even make them switchable with a rotary or inline switch and various resistors.

As for the CO settings, a higher voltage is richer. On mine that's clockwise, but you really need to measure the voltage as you go to check its working.

Edited by blitzracing on Tuesday 29th November 18:41

Edited by blitzracing on Tuesday 29th November 18:56

Edited by blitzracing on Tuesday 29th November 19:01