mad-mic, high idle, running rich

[steve1ph]

still need help with two problems im having. just got thru putting on the super ram intake 58mm tb and 36# injectors. now the car will idle normally for a few or untill it gets warm i guess then the idle will jump to 3k and stay there. also now the car is running very very rich. i replaced the o2 sensor and the pvc valve. still the same. also while the car is running iv sprayed ( carb cleaner) around all the intake, vacume lines, tb any where there could be a leak and did not get the car to rev up, hence no leaks. as well there is no check engine light on at the dash. puzzeling. all advice will be tryed. also want to let every body who reads this that iv done some business with another forum member by the name of MAD-MIC and want to let everybody know that he is trustworthy as well as myself. hey mad-mic handshake to you, that wasnt possible in person..........thanks

 

[Mad-Mic]

hey steve thank you bro! i pulled a 13.7 tonight at 102.5 mph. i need some DR's now cause i can't hook worth a crap. best 60' was a 2.11 :eek last week was a 1.96. the track was terrible tonight.

since your running larger injectors try lowering the fuel pressure to around 38-40 psi. i'm thinking since your running rich the ecm is idling alot higher trying to lean it out with more air. there is an idle screw on the TB but i'm not real sure where it is. did you go with a new TB? if so it might need some adjusting. i know this one might be alittle obvious but is the TB closing all the way? i'm sure it is.

larger injectors = less fuel pressure. worse comes to worse throw your stock injectors in set the fuel pressure to 46 psi and see what happens. from what i hear this is a good setup and the vettes stock fuel system is good till 450 hp.

maybe 69myway can give you some more ideas on this. i know you checked the vacuum lines but sounds like there is one off somewhere. i know on my 82 Z with crossfire injection if one came off the back of the TB it would do the same thing.

hope we can get your vette worked out!

good luck bro!

 

[rrubel]

The idle set screw on the throttle body is at the very top front of the throttle assembly. It's adjustable through the back, where there's a little push-in plastic cap (if it hasn't been taken off and lost). I think the procedures for adjusting it were posted on here maybe two weeks ago along with the IAC valve adjustment (you did do that after replacing the throttle body, right?) and TPS adjustment (you did THAT too, right?).

[RICHR]

 

[Mad-Mic]

also what is your cam specs? i still think the ecm is geeking out and trying to pull more air to help the richness factor. if you are using stronger cam (ZZ9 specs and higher) the ecm is trying to over correct for the bigger cam. you may need to speak with -=Jeff=- as he can give you some insight about prom burning since he does this for us members here

 

[steve1ph]

iac adjustment

no, i didnt know there was an adjustment for the iac valve. as for the other the idle screw yes i did move that but all it does is open the butter flies. where can i read up on the adjustment for the iac?. the specs for may cam are: its a bullet racing cam out of olive branch, ms. 224/230 duration -- 503/510 lift. thanks

 

[vader86]

2 Things: you need to adjust that IAC and idle screw, and what voltage is your TPS reading at idle?

Plus i think #36s are big for that combination, you should turn that FP down some more.

It would be nice if you had a scanner to see what your O2 sensor is reading, or get her on a dyno for a better tuneup so you can monitor that A/F ratio on the wideband sensor.

 

[rrubel]

You need this post:
<http://www.corvetteactioncenter.com/forums/showthread.php?s=&threadid=36358>

It details the TPS and the idle adjustment. I believe during the idle adjustment the IAC is recalibrated.
[RICHR]

 

[WhalePirot]

Check this link for injector sizing

http://www.jimsperformance.com/tech.html

Also, your ECM may be reading low vacuum and judging a lot more throttle opening than is actually the case, thereby, adding fuel, regardless of other inputs. I expect that any adjustments to TPS or IAC will do little or nothing to help you, but are fine for tuning an engine that has components matched.

I agree that those injectors are likely too large, but you don't give power numbers for your engine. My 406 puts out over 500hp & /lb.ft. each with 30pph injectors, set to the standard Corvete fuel pressure of 45, I believe. A 52mm BBK feeds it nicely, all the way to the 6200 rpm shutoff. A larger opening may decrease air velocity and intake charge, hurting power, if the engine doesn't need all of it.

You will want to size the injectors properly, given the above equation's guidance before doing any chip burning. Lowering fuel pressure MAY fix the richness, but approaches among pros I have talked to vary, and some are concerned about adequate spray patterns at lower pressures.

It comes down to metering the proper amount of fuel. The larger injectors squirt more fuel at any given pressure. The ECM has limited bands of adjustment to pulse width, to control how much open time for those little nozzles, based upon inputs from all those sensors.

A new chip can modify the starting point in the fuel tables, allowing the ECM to make the normal, rather minor changes required to deliver an optimum fuel/air ratio, measured by the voltage output from the oxygen sensor.