Lean condition related to RPM/gear?

[Maverick3169]

Hey guys, I tried searching, but with no sucess.

I'm having a problem with running very lean after about 6000 rpm. No matter how much fuel I add or take away, the A/F ratio remains the same... lean. This problem also seems to be different in each gear.

Usually, you would think that it would be leaner in the higher gears due to the increased load, right? Well, this isn't the case for some reason. 1st gear is by far the leanest. Usually reading as bad as 13.6, which totally scares me. In the remainder of the gears, it usually reads between 12.2-12.8 after 6000 rpm.
I am totally clueless when it comes to this problem, and I can't think of why this is happening.

I can feel it pulling timing, so it must be knocking. I'm starting to wish that I had invested in a datalogger long ago... too bad I don't have the money right now.

Hopefully someone here has some sort of an idea, because I don't.

Here are some of the things I've tried...
Checked the base timing, it's set at 5* before TDC.
Checked for boost leaks. There seems to be a small leak at the TB... maybe the seals. Will fix it when I have some extra cash
Plugs/wires are good... not thinking it would cause a lean condition anyways.

 

[andymoraitis]

When you throw more fuel at the problem and it doesn't go away, this leads me to believe you have a fuel volume issue related to insufficient supply from the fuel pump. I looked at your mod list, but didn't see a pump listed. If you have a 190, I'd step up to a 255 with an AFPR. If you already have a 255 and an AFPR, I'd check voltage to the pump to make sure it's working properly.

Aside of that, I'd pull the plugs and see if there are any substantial variances between them since this can point to issues with the injectors.

As an FYI, unless you have a Keydiver chip installed and can read knock, a logger is a must with an AFC to check for physical knock, IDC and IPW.

Hope that helps,

Andy

 

[Maverick3169]

When you throw more fuel at the problem and it doesn't go away, this leads me to believe you have a fuel volume issue related to insufficient supply from the fuel pump. I looked at your mod list, but didn't see a pump listed. If you have a 190, I'd step up to a 255 with an AFPR. If you already have a 255 and an AFPR, I'd check voltage to the pump to make sure it's working properly.

Aside of that, I'd pull the plugs and see if there are any substantial variances between them since this can point to issues with the injectors.

Hope that helps,

Andy

Thanks for the quick response Andy!
I have a Supra TT pump.
When I checked the plugs, they all looked exactly the same. I was actually suprised that there was no signs of detonation.
When I add fuel, it changes nothing, when I take fuel away, it still changes nothing. Keep in mind that this problem only occures at 6000 rpm and beyond.
Thanks again Andy.

 

[andymoraitis]

The Supra pump flows more than enough for your power needs, but it may be getting up there in age. I'd check the voltage to make sure it's constant and not below 12v. Also, if you haven't reqired the pump, I'd do so to get a bit more flow from it. If you find that the pump is on it's way out, replacing it is an inexpensive solution.

You are running an AFPR right? If so, what's your base fuel pressure set to with the vacuum line off?

 

[Maverick3169]

The pump is rewired, so that shouldn't be an issue.

Any idea on why it's leaner in 1st as opposed to a gear with more load? Or why this problem is linked to rpm?

About the voltage... this may be a problem.
My SAFC-2 reads as low as 11.6 V at times, while the alternator and battery always read about 1 volt higher. The SAFC reads about 13.1 volts when I first start the car, then within 3 minutes it's down to 12.5 volts, then it continues to drop. Eventually it makes it's way down to between 11.8-11.6 volts after driving the car for an extended period of time. So that means there is a voltage drop occuring somewhere, but I have no idea where.

Oh, and I don't have an AFPR... my part throttle is fine.

 

[fourreGsixty3]

Get a AFPR the pump is over running the stock one. That maybe a big part of the problem. You need an AFPR if you go higher then a wally 190 FP. Also when you get it set the psi to 43 off vaccum.

Dustin

 

[Maverick3169]

Get a AFPR the pump is over running the stock one. That maybe a big part of the problem. You need an AFPR if you go higher then a wally 190 FP. Also when you get it set the psi to 43 off vaccum.

Dustin

Can you please explain to me how this is causing me to lean out?
This problem just started happening... and I've had these mods for quite some time now.
Thanks.

 

[fourreGsixty3]

Oh that wouldn't cause the leaning out, I was just mentioning that because it will cause problems down the road. http://www.roadraceengineering.com/fuelpumptechtip.htm, Check that out, it shows how much voltage is related to flow rates. You may want to rewire the pump with a thicker guage wire, because the lowest you should be is 12V @ 43psi.

Dustin

 

[andymoraitis]

I would look into the voltage issue and test the alternator to be sure. Also, I'd get an AFPR installed since you're not at a true 1:1 rising rate with FPR overrun. Make sure that when you install the AFPR you set base pressure to 37 psi (not 43 as indicated above).

Keep me posted,

Andy

 

[Maverick3169]

Thanks a lot guys. I'm going to try to check the voltage going to the fuel pump.

Would you think that the alternator is bad if I'm seeing some sort of voltage drop?
I bought the alternator from autozone about 8 months ago, and I just replaced the battery 3 months ago as well.


I'm still not sure about the AFPR... I thought that the only reason I should use one would be if I was having part-throttle issues. But if this is something that could really cause a great deal of problems, maybe it is something I should look into.

Thanks again everyone.

Also, is it normal for the voltage to drop this much between the alternator/battery and the interior of the car? It's been like this ever since I installed the SAFC (which was before the newer battery/alternator install).