My Air Fuel Ratio Log

[180bfj20det]

Ok,

This is a stock s13 CA18det (euro version, Im in france at the moment). Only mods are 3" exhaust with screamer. Car runs 12 psi.

I have a feeling that ever since I placed the exhaust on the car that the car behaved differently when i mashed the peddle. My symptom is that from 2500rpm to 3000rpm, the car accelerates well but from 3000rpm there is a big dip in power where then it picks up again slowly. Being scared that this is due to an old tired fuel pump creating a lean-out I logged with my wide band sensor (innovate lm1).

Below is a log in 4th gear from 2500rpm (frist arrow) to 6500rpm (last arrow). Note I would have rpm but I dont know how to hook this up properly and log it (SK help ). If anyone cares to help me hook the rpm sensor up and how to log I would be happy.

During the log, the throttle was fully open.

Luckily I got to do this on a race track because it would be impossible anywhere else apart from a dyno where they charge in france more for just one pull than two hours on a race track....

Now, first of all, those AFRs look to me as very dangerous. I cant hear pinging but that doesnt mean its not occuring and I dont have chasis ears. But can you see that significant lean-out occuring at the beginning of the log?? I bet this is why is dies in the ass at 3000rpm.

I read on the freshalloy forum that stock nissans run towards the 14afr on boost for emission control but I find this hard to beleive

The car cruises/part throttle at 16afr. Idles at 15.5-16.

The car has been driven like this for a long time....i dont know how the engine is hanging together...

I have a new fuel pump on its way and will check out the afrs after its installement.

In the meantime, if anyone could analyse my log and make suggestions/observations (i know now not to drive the car on boost) and also obviously help me make this rpm convertor functional so I can log RPM.

First arrow = 2500rpm Second arrow = 6500rpm WOT during full log.

Edited September 10, 2006 by 180bfj20det

[Adriano]

Just wait until you get a fuel pump. Does the car misfire, if the coils are breaking down, a missfire will show up as leanness on the a/f meter, otherwise it is just lean. Can you do the earth mod as per r33? The other thing that you could do is put a fuel pressure gauge on it and check that under load.

[180bfj20det]

Car does not misfire.

What do you mean by earth mod?

Id like to put a fuel pressure gauge on it, but dont have one here in france but like you im betting its fuel pump. I havent taken out the injectors to see if one injector is playing up, but i doubt that anyway.

Just wait until you get a fuel pump. Does the car misfire, if the coils are breaking down, a missfire will show up as leanness on the a/f meter, otherwise it is just lean. Can you do the earth mod as per r33? The other thing that you could do is put a fuel pressure gauge on it and check that under load.

[Adriano]

Measure the voltage across the pump, and see if it is 12v, but fuel pump is very likely.

[CruiseLiner]

is the second one just before the rev limiter or fuel cut of some sort? my mates engine shows similair results close to redline but sk said its the result of the revlimiter. unsure on the low rpm one though.. sorry thats all i could think of

[paulr33]

if its capable of 12afrs at 6 grand then it should be fine doing it at 3 grand as well. is it remapped stock ecu?

[FATGTS-R]

Traditionally, an a/f plot with a tired fuel pump will show a/f ratios safe or borderline down low and then get leaner and leaner as rpm increases.

Yours is doing the opposite as in it gets richer as rpm increases where the pump has more demand on it. Hence Pauls statement that if it can hold a 12:1 ratio at 6K then one would think it is able to do so at 3k.

[180bfj20det]

Yes, I agree and this is why Im confused and thus posted my log here.

This is a stock ecu, no remap.

One more thing, the fuel pump makes all find of weird noises sometimes when I first prime it.

From what i have seen, stock ecus run very rich on boost, like 10afr, this is no where near this. Im waiting on new fuel pump.....

BUT: shouldnt engine damage be occuring at this afr I logged????

Traditionally, an a/f plot with a tired fuel pump will show a/f ratios safe or borderline down low and then get leaner and leaner as rpm increases.

Yours is doing the opposite as in it gets richer as rpm increases where the pump has more demand on it. Hence Pauls statement that if it can hold a 12:1 ratio at 6K then one would think it is able to do so at 3k.

[carl h]

replace the fuel filter and fit a new pump...or try the filter first.