Background: S5 Turbo car with good compression


Original modifications:
Bonez intake
RB REV-II turbo-back exhaust
S-AFC II

Dynoed/tuned Mar 2009: ~220 whp, 205 ft-lbs, AFR ~11:1 (see sheet #1)
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Recent additional modifications:

BNR Stage 1 Turbocharger
RC Engineering 750cc injectors (saturated) in secondary
Supra TT fuel pump
Rtek1.7-chipped, N370 ECU

Dynoed Apr 2010: Halted early due to lean condition
AFR 13.6:1 headed for 14:1 at 4600 rpm. (see sheet #2)
Fuel pressure ~53 psi
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Removed Rtek1.7-chipped ECU. Replaced with un-modified N370 ECU.
Dynoed and tuned May 2010 with S-AFC II:
267 whp, 230 ft-lbs, 11:1 AFR. (see sheet #3)

Question: What is causing the lean condition in the second sheet? Since replacement of the Rtek1.7-chipped ECU allowed tuning to a safe and reasonable AFR with the AFC, the assumption would be that the problem is with the chipped ECU. However, I had Digital Tuning check their installation and they did not find any problem. I also sent the injectors back to RC Eng for testing and they were within spec.

Looking for any ideas on the possible causes of the lean condition.
TIA

 

Which primaries are you running?

 

Stock 550cc injectors.

 

i had one with the same symptom, it turned out to be that the FPR solenoid not being plugged in was causing the ECU not to turn on the secondaries.

so check for codes.

 

Thanks for the idea. It's worth reading any codes so I'll check that out.

However, with the S-AFC tuning and stock ECU, the engine had a gain of 45 hp over the previous setup with stock 550cc secondaries. So there is fuel being added by the secondaries. Just how much is the question as well as why with the maps in the ECU with the Rtek1.7 chip resulted in such a lean mixture.

 

Running lean on the stock primarys is a common problem, i would suggest upgrading to larger (720cc) primarys and getting the rtek 1.8 and trying it again.

Why wouldn't they just tune more fuel in with the AFC and keep the rtek1.7?
An Rtek 1.7 alone doesn't have enough tuning cabablity(IE:no fine adjustment) to keep a stage 1 from going lean, it's foolish to think otherwise, IMHO.

 

good catch, i didnt see that. the car i did, i just plugged the solenoid into the harness, it wasnt hooked up to vacuum at all, and the mixture went from the gradual leaning out after 3k to running 12's across the rev range.

 

The lean condition was above the point where the secondaries stage. The sheet with the lean condition was with the S-AFC tuning maxed out. It was not able to compensate for the lean condition encountered in the rpm range above secondary staging.

 

i have the same problem, but without a safc. at wot im 12.9-13.2 afr. so, i just dont hit boost anymore. waiting for tax returns to get a power fc

 

This doesn't explain why switching the ECU out made the problem go away, but it may still be something worth looking into: http://www.srtforums.com/forums/f187...ectors-421841/. I don't know how credible the source is, but RC would be able to tell you if the injectors you're using are not intended for high fuel pressures. Maybe the secondaries are going a little crazy at random above 43.5 psi?

For what it's worth, I used an Rtek 1.7 with 550cc primaries, Greddy 720cc secondaries, an FD fuel pump and a stock S5 turbo and saw AFRs climb into the low 12s at high RPMs. https://www.rx7club.com/showthread.php?t=903294.

The only reason I can think of that the stock ECU worked versus the Rtek is you instantly increase fuel delivery above the transition point by (~18%) without any SAFC tuning due to the ECU not knowing the secondaries are larger (2600cc / 2200cc = 1.18). Out of curiosity, how much fuel had to be added in with the SAFC on that 3rd run? Maybe that extra 18% on top of whatever the SAFC could add was what you needed.