bhcevo

My evo is often delivering AFRs considerably leaner than what im tuning for. Heres
an example of some brief WOT runs in 4th gear.



http://img278.imageshack.us/my.php?image=log1crrx0.jpg

Notice the first two "runs" quickly give AFRs in the low 10s, which is what I tuned for.

The last two WOT events give AFRs of 11.0 or so. These logs were all taken within the same 5 minutes of driving, same gear etc..

This is a big PITA because im trying to detune the car to get rid of knock.

IDCs are below 80%...do I have an intermittent faulty injector? WTF?

Details: 91 octane, 19psi boost, cams, stock injectors, walbro, 03 evo

Mad_SB

iTrader: (8)

do you get knock when the afr's are lower (10.0's) or only when they lean out. Could be hitting diff load cells or could be faulty injector. I would say possible vacume leak near the fpr, but not so sure that would be intermitant, maybee bad connection on the fuel pump or fuel pump going bad.....

bhcevo

The knock is shown in yellow and it definitely is only showing up when afrs are lean.

The load is shown in red and the rpms in blue and you can see that the load
cells traversed over all the runs should be near identical.

I want to know if this sort of variation is normal or am I observing a real problem here.

C6C6CH3vo

iTrader: (9)

Two obvious facts:
1) running out of fuel
2) detonation is resulting - timing retard,

First, make sure your LO octane fuel map is OK (not leaner by a mistake-hell I dont know, but it would do something like this). Then, for shotgun troubleshooting, put a new fuel pump in and please keep thread logged with results

Again I'm going by the first two runs compared to the second two, and if they were done back to back in same conditions.

wrcwannabe

iTrader: (1)

^^ weak pump under extended load is my thought. You might get lucky and have a slightly plugged screen, maybe on the inlet side of the pump. Try logging an extended run in 3-5rd gear to see if the same thing happens. Was this on a Walbro or stock pump.? Lotsa threads about the stocker giving it up, showing as lean conditions on 3rd, 4th runs or extended higher gear runs. I have also come across threads that some Walbros seem to be problematical now.

Keep us posted !

Milburn

bhcevo

Thanks guys. I'll put some time into troubleshooting my fuel system here.

And yes, my fueling is stock except for walbro 255 fuel pump. I still have my
stock fuel pump sitting around ill swap that in.

bhcevo

Here is another back to back log with the same problem. This was from a few days ago where the car had a diff tune (less fuel, more timing) but you see the same problem.

Notice how going from 10.8 to 11.2 afr aggravates the knock significantly.




http://img389.imageshack.us/my.php?image=log2crfk2.jpg

bhcevo

Looks like my fuel pressure gauge won't exceed 52 psi no matter what my boost is. Idle gauge reading is about 38psi. Thats only 14psi of boost compensation, well below whats necessary for even stock boost.

Either my pump is bad, clogged filter or fpr problem. I'll keep ya posted. My walbro is only a year old too. Crap.

mchuang

iTrader: (11)

You know I have the same issue. I tried to tune my rich air fuel to 11.0 to 11.2 and when I get in the 11's the car just doesnt like it. I get as many as 9 knock counts at high rpm range. So I tweak it back down to high 10's and knock is gone. I have no clue what it is.

nj1266

iTrader: (6)

Try pulling back some timing and see what happens. When I leaned my car out to take advantage of the 93 octane gas I had to pull timing to reduce the knocksum.

mchuang

iTrader: (11)

Well I am running around 5 - 6 degrees between 3800 and 5000 and then I added fuel and now I am back in high 10's and no knock.

djd24

I would venture to guess that if your seeing knock at 11.0 : 1, then your timing curve is a little too agressive. You may want to take a look at pulling some timing.