What can cause lean afr?

[Jay_Kay]

Had the car on the dyno today and it made poor power.
AFR's were lean at around 13.7.
What shall I check first? Fuel pressure?

 

[mark smith87]

Possibly the fuel pump pressure is low. My 172 was struggling to increase fuelling last week at RS tuning. They reckoned the fuel pump was getting a bit weak. Hardly surprising as its 12 years old and done 124,000 miles

 

[Jaff.]

Blocked injector? Poor fuel pressure, blocked fuel filter? When was it last changed? That's the easiest thing to sort

 

[Jay_Kay]

Would the car being mapped on a walbor 255 fuel pump and then being run on the standard pump make a difference?

 

[Jaff.]

Yes it's possible

 

[Russ_16v]

As said, a few things can cause it, but First we need to know the specification of the car

 

[Jay_Kay]

Williams 2.0ltr F7R
AP Development stage 2 Headwork
Piper 285 Cams
Piper adjustable pulleys
Supersprint Manifold
Magnex exhaust system with decat
Group A Scuttle induction kit
Bosch 802 injectors
Rs tuning live remap

 

[Russ_16v]

Nice spec!

Where was it rolling roaded mate? Just ruling out any equipment malfunction on the RR?

 

[Jay_Kay]

South wales tuning. Only went to this place because they have a dyno dynamics rolling road.
Made 161hp and just under 140lb/ft.
AFR was around 13.5-7 when it should be around 12.7 ish.

Only difference i can see from the previous dyno (180hp and 155lb/ft) run is the fuel pump being standard this time.

 

[Russ_16v]

The standard pump is fine for that power, how come it had an uprated pump mate?

Bear in mind the rollers could still be different to Pauls rollers.

 

[Jay_Kay]

The shell it was in before kept on having problems with it running lean and an uprated fuel pump solved this. Most fuel pumps in mk1 dont get 12volts these days or are dying as they are 15years old now.
Im going to buy an AEM UEGO wire it up and then see how i go from there on.

 

[Jay_Kay]

I've been battling against lean afr and now its starting to missfire now.

I've changed fuel filter, fuel pump, fuel lines.
Checked the fuel regulator.

It was running quite good top end. 12.8 odd. But sudden yesterday and today its been running 13.7 odd top end and high 14 midrange.
The misfire happens at around 2k and clears up by 3.5k. When the misfire occurs the afr gauge is blipping from lean to no fuel at all.

Im going to get the injectors cleaned but could it be anything electrical?

 

[Dan519]

new lambda sensor