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Installed AFPR. Lean down low rich up top.

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forcefed86

15+ Year Contributor
1,007
12
May 23, 2006
wichita, Kansas
Installed new AFPR. If I set it at 42psi base, it will idle around 14.5 to 15.5. But WOT is 9.9. If I crank down base to around 32. I get low 11's WOT and 20's at idle.(idles is obviously ruff) Anyway to fine tune this a bit more? When I was running the OEM FPR I idled around 14-15 and wot was in the high 11's.

I am only running 14lbs or so. I suppose I could just set it back to 32 and up the boost to lean it out.

Thanks
 
Last edited:
Yes, it is rising rate. Would resetting the ECU help at all? I'm sure while in closed loop idle the ECU can only remove or add a small percentage of fuel. I'm assuming I'm beyond this? Anyone know how much control the ecu has?
 
It's an OEM ecu, non chipped. I wanted to go to an AFPR so I could bump up my base FP and run a little more boost. I don't really have a "tuning" device, just watching my AF ratio's and playing with base fuel pressure.

Have my "MOD" list in my profile.
 
Update your profile so that others can see what kind of mods you have on the car... you can't just increase or decrease your fuel pressure and expect to see different a/f on different RPM ranges..;)
 
You should be setting it to 36.3 psi base (with the reference hose off the FPR and pinched).
The car should go into closed loop at idle and cycle around 14.7:1 and run about 9.3:1 at WOT.

The stock 450cc injectors will start to hit 100% IDC around 14 psi and the car will begin to lean out because the injectors can't keep up with the demand. That might explain your WOT reading before.
Otherwise (if your injectors were up to it) the ECU would have kept the rich factory tune as you raised the boost. Lowering the base makes the injectors smaller that the ECU thinks and leans the AFR out but also means you'll still run out of injector. What you want to do is get something to really tune with and some bigger injectors so you can max out the current turbo and then get a bigger one.
 
Update your profile so that others can see what kind of mods you have on the car... you can't just increase or decrease your fuel pressure and expect to see different a/f on different RPM ranges..;)

Sorry about that. I think my info was lost in the "update". I'll fill it back in again.

I thought at WOT the ECU went into open loop and didn't rely on the 02 sensor for fuel correction anymore? So if it's just reading fuel maps based on the MAF output why wouldn't raising the pressure raise the AFR across the board?



You should be setting it to 36.3 psi base (with the reference hose off the FPR and pinched).
The car should go into closed loop at idle and cycle around 14.7:1 and run about 9.3:1 at WOT.

The stock 450cc injectors will start to hit 100% IDC around 14 psi and the car will begin to lean out because the injectors can't keep up with the demand. That might explain your WOT reading before.
Otherwise (if your injectors were up to it) the ECU would have kept the rich factory tune as you raised the boost. Lowering the base makes the injectors smaller that the ECU thinks and leans the AFR out but also means you'll still run out of injector. What you want to do is get something to really tune with and some bigger injectors so you can max out the current turbo and then get a bigger one.

Wow, I didn't know the factory AFR at wot was that rich!

I actually am waiting on my 750cc injectors and socketed/chipped ECU from dsmchips.com at the moment. I had just installed the WB at the same time as I added the AFPR. The AFR's seemed excessively rich to me, but I suppose it's normal. Thanks for clarifying that.

:hellyeah:
 

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Thats insane! You'd think that would cause all kinds of knock and power loss, cyl washing?. Bet I'd pick up 20whp just leaning this pig out a bit.

New chips setup for 11.4 @ WOT can't wait! :sneaky:
 
I've still got a few weeks before all my new parts arrive. I'd like to figure this out.

I have the base Fuel Pressure at 45psi vac line off. Drops to about 40psi with vac line on. I have to have the pressure this high to even idle. Even with the base pressure at 40 @ idle the AFR's are in the low 20 high 19's.

Is this because the lower MAF screen is removed? What could be causing this lean idle? I've done no other changes.

Car ran great with factory FPR. I'm assuming this is because the factory FPR mixed with the 255 walbro fuel pump was giving me very high Fuel pressure at idle from the tiny return line in the OEM FPR. Then as the fuel system was supplying the injectors under a load my FP would bleed off all that additional pressure.

And another thing....
\
Not sure if that is related or not. When the car is cold and I first start it it will read 9.5 or so AFR (as it should). But within 5 seconds or so it goes very lean (back in the 20's). Shouldn't the car run rich until the coolant temp gets up? Think my coolant temp sensor could be part of my problem? Or does the ECU use the temp sensor in the MAF?

Thanks!
 
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