Hi Frank,
Now that you have some time on this now, do you have any issues with hot starts? You have the IAT sensor in a pretty thick piece of aluminum and this has given some people fits in the past.

It takes the same time to start when hot as when cold - not very quickly - maybe 3 revolutions to fire. I noticed there is a 2 msec prime pulse set for starting (I think - need to check closer) and I remember you said it's best to defeat that function. As it begins to fire, it sounds like it's backfiring through the blower, but I can't really tell - tried leaner and richer with no change - maybe the prime pulse is the cause.

Sometimes, the idle speed is high on hot starts, but that may be an IAC control issue.

I don't think I have any issues with the IAT sensor. I counter-bored the side of the discharge plenum to get a socket on the sensor, plus the probe is set well into the airstream. Also, I'm using the fast reading open element sensor - not the solid probe style.

Interestingly, I haven't seen really hot discharge temperatures..... nothing noted over 175*F yet - even with sustained boost. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Fuel economy continues to improve, with the change to 29" tires adding maybe 1 mpg on today's trip to Atlanta - even at 75-80 mph. I'll try to check it at 65mph on the way home this weekend.

Frank

I'm used to it. I drive like that all the time. <img src="/forums/images/graemlins/evil.gif" alt="" />

Frank, see if you have any real tootsie rolls in the tire pile, like some of those 275/60-15's I used to have on the D50 pickup. I could outcorner Beemers on those tires. And they'd leave more impressive donuts...

On today's drive from Atlanta to Columbia between 65-72 mph (trying to maintain 67 mph) - 201 miles traveled - consumed 10.06 gal for a very good average of 19.98 mpg..... I'll call it 20 mpg. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Frank

A bit of difference in rolling resistance would you say! <img src="/forums/images/graemlins/cheers.gif" alt="" />

More like wind resistance - I got 17mpg on the street tires on the first trip, driving 75mph. I noticed long ago that the Gen1 sweet spot is around 65mph... might be better at lower speeds, though.... I just can't seem to drive any slower than 65 on an interstate highway and maintain my sanity. <img src="/forums/images/graemlins/lol.gif" alt="" />

Frank

I've found one quirk with the change to MegaSquirt.... the A/C compressor no longer works.

In checking the FSM wiring schematic, it looks like the A/C engine temperature switch leg runs through the OE ECU before the A/C relay can be powered. I don't yet know if the circuit is a pass-through in the ECU, but it might be possible to jumper the ECU in/out legs in the now unused OE ECU connector.

Charlie, did you run into this on any of your MS installations? If so, how'd you work around it?

Frank

that's what appears from the schematic...but somewhere inside that black box the idle speed is bumped up.


The classy thing to do is re-wire it all to an on/off switch

Yes, that's why it runs to the ECU - for idle speed control.

I'm guessing that the connection in the ECU is a pass-through with a tap that feeds a signal to the IAC stepper motor.

When I get some time to play with it, I'll jumper GR-#1 on C-39 to BW on C-40 and see if it works.



The ON/OFF switch is already there and wired - it's on the dash where the little button says "A/C". <img src="/forums/images/graemlins/lol.gif" alt="" /> All I "think" I need to do is repair the now open circuit.

Frank

The AC power goes through the ECU so the compressor can be cut off at high power and abnormal temperatures.