Massive Lean Out...

[Granthem]

Hi Guys,

There was abit of a carshow in Rocky on the weekend, with a dyno set up. So I put mine on for a run to check air fuel ratios, and here are the results.

As you can see, run 1 made 341rwhp, a/f's were all fine.

Ran it up a second time, car was following pretty much the exact same line, went 337rwhp... but the a/f's went haywire. The operator wasn't keen to run it up again. His first thoughts were the lambda had fallen out of the exhaust. Apparently tho, this was not the case.

I'm pretty much wondering what you guys think. If it really leaned out that hard, surely it would start making more power (considering its on the rich side of things) before it leaned out wayyyyyy too much and started to detonate and lose power. The fact it follows the exact power of the first run kinda says to me its an error with the lambda, and not a problem with fuel delivery in my car.

Car has a walbro pump (i know i know), nismo 550's and a nismo FPR.

Surely a dying fuel pump would be more 'progressive' then the almost verticle climb of the a/f's on the second run? blocked injector?

Any ideas or comments would be great!

Edited June 20, 2010 by Granthem

[paulr33]

your idea seems reasonable, such a drastic change in AFR

given its a dyno day and the sensor is moved around a lot, it might be a bit whacko or something

for such a dramatic change in AFR, i would have expected wonky power curve, detonation

[R31Nismoid]

Walbro pump.

Exactly what mine did around 260rwkw.

[JonnoHR31]

wont always knock from that but i'd expect a decent loss in power at least. +1 for incorrect reading, only way to be sure tho is to check it a few times with another sensor

Edited June 21, 2010 by JonnoHR31

[Granthem]

your idea seems reasonable, such a drastic change in AFR

given its a dyno day and the sensor is moved around a lot, it might be a bit whacko or something

for such a dramatic change in AFR, i would have expected wonky power curve, detonation

That's what I was expecting aswell.

Walbro pump.

Exactly what mine did around 260rwkw.

Was yours a "Mt Everest" like mine. I always pictured a more progressive leaning out when a pump slowly starts karking it?

wont always knock from that but i'd expect a decent loss in power at least. +1 for incorrect reading, only way to be sure tho is to check it a few times with another sensor

Hmmm yeh. There is another dyno in town, might be worth throwing it on theirs for a check up. They have always been ridicuously safe. I thought a pump would show on both runs, not just rear its ugly head on the second run... at least I'm hoping!

[R31Nismoid]

Mine played up some dyno runs, others it was fine - but overall it was just lean at the least.

250rwkw is about their limit for flow.

If you've upped the rail pressure above factory, even more so.

[STATUS]

Check it on another dyno to make sure it is the car, if the A/F sensor is on its way out they default to 14.5:1 so it could be a failing A/F sensor, that curve is also very common in such a scenario.

[Granthem]

Check it on another dyno to make sure it is the car, if the A/F sensor is on its way out they default to 14.5:1 so it could be a failing A/F sensor, that curve is also very common in such a scenario.

Very interesting Trent. Thank you very much! I'll look into another run on a different dyno

[Granthem]

PS - assuming it was a lambda fault, would you guys take some fuel out of those a/f's and sneak abit more power out? Surely there is more left in it with those ratios

[l0WRB]

get some boost into it ! atleast 18-20psi

[Granthem]

Haha yeh, I'll upload the graph with the boost curve tomorrow. Its on 14psi

Another question - Ramp Rate - how much does it affect things?

On the 3 times its been on a dyno, every operator has chosen a different ramp rate.

Godzilla - 100@150 = 337.1rwhp

Prodyno (first comp) - 100@140 = 337.7rwhp

Prodyno (most recent graph) - 100@200 = 341.1rwhp

[KiwiRS4T]

Well its not going to be your O2 sensor because that has stuff all to do with the afrs at the top end. Have you at least got your Walbro wired for full voltage? Stick a fuel pressure guage in after the fpr and see what it reads at high revs next time you're on a dyno. (My tuner uses two O2 sensors - one in an extra boss on the downpipe and one in the tail pipe).

[Adriano]

PS - assuming it was a lambda fault, would you guys take some fuel out of those a/f's and sneak abit more power out? Surely there is more left in it with those ratios

Unless its a track car, i would be leaning those out for sure

[PM-R33]

Out of curiousity could you post up the boost graph on the 14psi? Would be interested to see how it looks as mine really has trouble holding lower boost levels. Is yours just setup to 14psi from the adjustable actuator?

Edited June 21, 2010 by PM-R33

[JonnoHR31]

Well its not going to be your O2 sensor because that has stuff all to do with the afrs at the top end

+1 for a leaner tune if all is good atm. 10.5:1 is a little rich

[Guilt-Toy]

I think it was the sensor, it just dicked out for a bit. chuck it on another dyno to confirm.

[JiN_MaN]

For it to have almost exactly the same power curve and the AFM to be all over the place, surely its the dyno not the car.

The power doesnt even change and seeing at A/F ratios have a HUGE impact on power the curve should have changed is some way.

[Granthem]

Out of curiousity could you post up the boost graph on the 14psi? Would be interested to see how it looks as mine really has trouble holding lower boost levels. Is yours just setup to 14psi from the adjustable actuator?

Sure mate. I will post up the dyno with the boost graph. I have one from Godzilla and one from the other day. They didnt start the boost graph until it was already on boost so its just a flat-ish line.

Mine no longer uses the HKS actuator. It uses a garrett 14psi actuator, so it hold fairly nicely.

[Granthem]

Well its not going to be your O2 sensor because that has stuff all to do with the afrs at the top end. Have you at least got your Walbro wired for full voltage? Stick a fuel pressure guage in after the fpr and see what it reads at high revs next time you're on a dyno. (My tuner uses two O2 sensors - one in an extra boss on the downpipe and one in the tail pipe).

I have a Greddy Fuel Pressure Gauge, reads around 3.5-3.6 bar at full noise (2 bar idle).

Unless its a track car, i would be leaning those out for sure

Its a street car... I wouldnt mind getting abit more HP out of it, and some more fuel economy

[PM-R33]

Mine no longer uses the HKS actuator. It uses a garrett 14psi actuator, so it hold fairly nicely.

Interesting. So the garret one holds lower boost better?