Well tonight I installed a Z32 MAF along with 370cc injectors. Install went pretty smooth, the MAF is straight up/down, and the car seems to run decent, but there are a few issues that concern me. For the record, with the cutout open I hit about 11psi of boost.

First, I am still reaching about 90psi of fuel pressure at full boost. To me, that seems really high for having 370's... has anyone else experienced this? The AFR at this setting is around 11.4-5:1. I lowered the pressure rise a little bit, and the AFR did not change too much for as much as I turned the screw, I think the fuel pressure was somewhere around 80-85psi at full boost, with an average AFR of 11.7:1. Is it possible that this fuel pressure is doing nothing, and I would be able to lower it safely, or has someone else had to keep the fuel pressure this high?

Second, after being into the throttle for a bit, the car will run very lean while cruising. I was seeing AFR's around 17:1, and as high as 20. The AFR would eventually go back to normal, sometimes I would have to rev the engine in neutral. With the cutout closed, there was less of a problem with this, however having the cutout open never caused my engine to run lean as it did with this new setup.

Does anyone have any insight into these issues? I have driven about 35 miles with the injectors and MAF in.... would driving more allow the ECU to adjust better? I do not have an SAFC or anything, and my timing is pulled back 2 degrees. Any help is appreciated.

 

From what you describe your using a Cartech. What is the base fuel pressure at?

When using 370's with a Z32 MAF you will still need a decent amount more fuel to bring AFR's down that low. You added a MAF that meters much more air than what your new injectors flow more fuel. Running 550's and a Z32 MAF put me at a low 10:1 AFR with no other fuel added. I could see that you would need to run quite a bit more fuel pressure to bring AFR's down that low. If I could remeber the formula I could calculate what cc/min your 370's are flowing at 90psi. I bet it is somewhere around 450-500 cc's. I wouldn't worry about it too much. 85psi is fairly safe to run the injectors at.

I don't see how you would think the fuel pressue is doing nothing. I would leave it where you get the correct AFR and leave it at that.

 

I dug up the formula





Did you have these 370's flow tested? That would only be the way to know for sure. But if they flowed 370cc at 43psi base fuel pressure then at 90psi it is like having 535cc injectors. So that is not too far off. I would bet these 370's probably just flow a little less than 370.

But the #'s are not too far off so I would not be concerned.


Edit: I forgot that I also run a very high base fuel pressure of 50psi, so my 550's probably flow more like 600cc's. So you needing to run 85-90 psi of fuel pressue to get an 11.5:1 AFR is very probable.

 

And one more thing.....from my expierence, uisng a Z32 MAF with larger injectors (w/o a ROM tune) does not give a flat AFR curve since the z32 MAF and A32 MAF are not linear to each other. I had some peaks and valleys when data logging the AFR's. When just watching a WB it seemed to be flat but data logging told me different. That is why an SAFC is good to use since you can just add or subtract fuel in certian rpm ranges instead of a FMU that just add's fuel accross the board.

 

Great info Mike, thanks! My base fuel pressure is set at 37psi. The A/F while cruising is usually perfect, barring the situation I described in problem 2. I didn't have the new injectors flow tested, but I'll probably be getting 550's eventually once I figure out some sort of engine management. Do you have any idea why the car wants to run lean while cruising after getting into the throttle?

You said you run a base fp of 50psi, what kind of a/f does that give you?

 

It goes lean after you in the throttle then you let off. That is no big deal. Cruising AFR at 0 or very little throttle doesn't really matter.

50psi gave me a very low 10:1 AFR but got up to 10.5:1 at higher rpm's.

I talked to by brother this morning and I asked him a few things about this. He said every set of 370's he has ever flow tested flowed 410cc at 43.5 psi. He aslo said that that equation I posted is only really accurate at moderate fuel pressure changes. Using it to go from 40-90 psi will give higher results than real world will give

 

Well the A/F while cruising after running the car hard was reaching like 18-20 last night, the car started to buck a little because of that. The wierd part is that after revving the car, the a/f will go back down to normal. I'll try rasing my base fp a little and see if that helps anything.

 

Your base fuel pressure is fine

 

hey guys any idea when a supercharger is coming out for 2004 and up for maximas

 

Brad, your just running a stock computer with rich afr and -2deg timing?

~Alex

 

Yeah, the ECU is stock, I'm only tuning with my FMU and a wideband.