850 primary tuning
 

I know this has been beat to death, but I'm having a problem I can't figure out.

My idle and light-load are very rich (10.8 at light-load and 11.3 at idle). I have tried going with negative lag, and the AFR will initially go up, say to about 11.7, but then it will go back down and settle at where it was to start with. Sometimes it will settle at 11.4 at idle, but that's about it.

Is there a limit to how much negative lag I can give it?

Also is there some setting that I'm missing or anything else anyone can think of that I might be missing?

Thanks a bunch.

What did you put in the settings 5 page for them?

64.7 with a lag of -0.04

Ok, so I went out and played with it again. I managed to get it to idle around 12.8 with -.40 lag.

Does anyone have any ideas why my injectors need so much negative lag when other peoples' are idling fine with much less?

have you capped off the injector atomization port on the LIM? If you did, it's certainly not helping.

Or do you still have O2 FB tuned on?

What is that?

O2 feedback is turned off

Anybody? I searched for it, but I couldn't find anything about injector atomization ports.

...there is a small vacuum hose on the LIM, located near the front injectors. Some single kits include vacuum caps that blocks the port. Actually, i have connected it to a vacuum port on the UIM. Hadn't really noticed any difference...

...i actually have the same config: 4x 850cc injectors. try to get my single (garrett GT3584R) running fine. Idle and low boost runs fine, i have problems with high load (which i actually cant test because of too high afr's) i have used the PowerFC manual to tune the injectors....so like you, 67,5% and 0.04 lag....

Ok, I'll try looking for that, but I don't think I capped off anything on the LIM. I have 850's and 1300's.

I think you misread my lag, I have -.40 not -.04. That's why I'm wondering why mine is so much greater than anyone else's.

I have the same setup, I also use -.40 and have a good idle.

Any change from the -.40 Just does not seem right since it calls for .04?? anyone know why

should be '0.04' as per the math in the PFC manual.

That is due to you having it connected wrong!
If you had checked the stock setup in the manual, you would have seen that the hose should be connected directly to the turbo/s outlet. This forces a small amount of air directly to the base of the primary injectors and this flow is not affected by throttle position and usually it will cause your idle rpms to increase which then allows you to close down the TB a little.

I have not seen it make any difference in idle quality but use it anyway since it allows another path for posible more air flow into the engine.

That makes complete sense,,,you the man

So no one has any ideas why the two of us have so much more negative lag than other people?

Sorry, I don't get on here much anymore ...

I've run that neg lag before. Every car is different, the amount of negative lag needed can vary depending on other settings that affect inj duty cycle or fuel delivery. If you have the fuel map set so low that making them lower will not affect AFR, meaning you are at the min inj duty cycle that the ECU can support, and then you use negative lag to get the idle lean you might have less negative lag than someone else. But, once you set it up this way you can no longer make fine adjustments to further lean out the idle with the commander cause the duty cycle is already at it's lowest output.

Or, if your fuel pressure is higher than some one else you may need more neg lag to get the same AFR.

Think about it and it should make more sense later, gl.

I went back and reset my powerfc and did what cewrx7r1 said to do. I am now running lag of .04 and it works good. I can now continue my tuning. Thanks

I'm having the same issue with 750 pri/1300 sec. Again the issue is with the idle, reading mine at 11.4-11.8. but the other than that the rest of the readings are good. My concern is that, using -.4 negative log, I have to re-tune my maps all over again.

I had to run about the same to lean it out, but I set it back to 0.04 and just deal with the rich idle because I don't feel like retuning the whole map.

I have to run -.40 as well on my half bridge single. I cant even get some of the partial throttle leaned out. Some of the high vacuum cruising areas sit at 11:1. I also had a bucking problem in those areas, it took me a while to figure it out because the A/F was rich, but any feathering of the throttle revealed that those cells would not put out any fuel if the TPS requested it so I had to richen those cells back up until they made a visible difference in the log.

Chuck, do you think if I hook up that LIM nipple up to the turbo inlet it just might lean out some of my rich high vacuum cruising areas? This is the first time I've even heard of it.

Edit: wow, just looked at the diagram. I feel like an idiot. I've always been just applying that as a vacuum source in both of my cars. It is the one that is right below the front secondary injector, right? Is there any bias on where that air will go or does it flood the LIM equally?

If you ever looked at the LIM when off the engine and how it mates up to the engine, and follow the air flow from that nipple, you will see that the air flows into both primary intakes through special ports. See the two small holes in the small slot above the ports.

You can learn so much more by rebuilding an engine.

yeah I've rebuilt several, just never looked at it close enough to care. I bridgeported my most recent engine, you think someone who can do that would pay attention to some holes in the engine, lol.

I have 850 primaries and 1600 secondaries. Instead of running negative lag, I am thinking of ditching the 850cc primaries for a set of 660cc Greddy Type ND topfeed. What do you guys think of using 660cc primaries and does Greddy make good injectors?

Greddy just rebadges OEM stuff.

The 660cc's are, believe it or not, the OEM injectors off the 6 port 12A engines in the early 80s Cosmo. Those engines were equipped with only two of those injectors to run the whole engine.

I have had very good luck with Denso low impedence top feed injectors. I am using the Greddy/Denso 720's and have not had any problems with a rich idle. I don't even use negative lag. Any kind of low impedence top feed injector is much more responsive than the FD 850's. The FD 850's were not designed to be in the primary position, people just put them there because they think it's cheaper/easier.