justme

Just started playing with programming and was wondering what to mess with first to get a good idle. Inj constant or Lower VE values. Car idles fair now in open loop but goes lean when it switches to closed. It was rich in closed until I backed down the inj constant.

funstick

i would set the inj constant for the actuall inj size. then i would set VE tables accordingly. you also might want to add a bit of spark.

justme

Another thing is I am getting some knock retard at idle because of the valvetrain noise of the solid roller, any way to compensate for it besides unplugging the KS?

funstick

yes im not sure who but there are a few companie out there making Knock sensors that either mute or ignore valve train noise. or you can try the old standby. try wrapping a bit of teflon tape around the threads of the sensor.itll shut it up but might also make it impossable for the sensor to work so use spraingly.

justme

Isn't there something I could change to make it not retard below a certain RPM? So that at idle it will detect knock but knot retard anyway.

funstick

ill poke around through the code and see what i can find. i dont think so though. i could have missed something but i dont think i would have missed that.

JPrevost

In the 8746 TBI ecm there are knock qualifications that need to be met before timing retarding is done. Default it's set at 10mph and 1000rpm. Anything less and I guess it doesn't retard timing, probably similar in the TPI. Maybe it's because our valvetrain is noisy or maybe it's because at idle you'd have issues with timing retarding down to 0 trying to get rid of false detonation. I really don't know but I'm sure if you did a search in the archives over at www.diy-efi.org you'll find more info.

Craig Moates

Don't forget to service your IAC as a possibility. If you observe hysteresis in the IAC motor steps requested, this could be an issue. I chased around an inconsistent idle for a while, had to get back to actual mechanical work to straighten it out.

justme

Under normal idle and driving situations what are common number so see as far as the IAC goes? Is there a good way to check that the IAC is operating correctly?

JPrevost

The ideal IAC position for a steady idle is 0 on a warm engine. It should idle right at your requested idle speed with just your min-idle screw set to exact spec. In most cases the IAC will be <20 steps on a warm engine which is normal. On a cold motor and depending on your ecm the steps could range all the way up to 50 or more.
I have a theory about the IAC and it goes something like this; it SUCKS!!! The IAC is one of the most annoying things to tune around. Throttle followers get really annoying and why GM thought it was cool to have 64 as the lowest number of steps vs coolant temp is beyond me (ANLU TBI chip). Let's just say that there is no reason for needing more than 10 when the car is warmed up and tuned properly. Even with my BLMs pegged at 108 the car ran smoother with less IAC counts. On a TPI setup it's not so much an issue (dry flow vs wet flow).
I almost forgot....the IAC is a vacuum leak, I just can't get over this fact . This alone should be enough reason for people to start burning their own. Heck, it's enough reason not to buy some mail order eprom.
Anyways, like Craig said, check your IAC and clean it if it's original.
When you've minimized the IAC controls you can then work on the VE for open loop. Don't let the ecm go into closed loop at idle because it'll search for 14.7:1 and you want a slightly rich idle, more like 13:1 depending on temps. You could probably start by getting the light throttle near perfect then locked the BLMs to a 4 window like 126 min 132 max. Once you do that, watch the o2 volts at idle and tune your VE that way. Problem is that the o2 sensor can get "cold" at idle speeds so I recommend driving it steady on the highway to get the o2 sensor nice and hot, then watch the idle o2 volts right away. Either that or get a heated o2 sensor, that's the sure way of keeping the o2 semi-accurate.
There are lots of methods for tuning. Pick one and try it out. Doesn't work so well, drop it and try another. Every car seems to be different and it's an art, not a science. Good luck.