3.0L Megasquirt w/ EDIS: Headers running at different temps?

[jangell]

There should also be a throttle stop screw on the throttle body that you can adjust.

At the moment the throttle are completely closed at idle. I need to look for that screw; I'm sure it's somewhere, but I keep forgetting to look for it. At the moment I seem to have too much air, though, rather than not enough air.

-- Joe

[opethmike]

You don't have too much air; you have too little fuel. Here's what I would do:

Take the IAC 100% out of the equation. You don't NEED it for it to idle correctly; just for it to idle consistently across engine temps. With that out of the way, adjust the throttle stop screw so you're at, say 1,000 RPM or so when stone cold. Play with the warm-up table, adding fuel as necessary to keep it around 12.5 AFR while stone cold, mid 13s until 120 or so, then mid 14s from there until ~185 degrees.

The RPMs will increase as the car gets warmer. That's fine, don't worry about that for now. Wait until the car is fully up to temp (185). Then adjust the throttle stop screw until the car idles around 750-800, depending on your preference.

At this point, there should be NO influence on the fueling from the warm-up table; fueling should be 100% determined by the VE table. All the cells that the car is idling in should be just about the same number. Keep playing with that until you reach a low to mid 14 AFR at idle. You may also have to play a little bit with the throttle stop screw to return the idle speed to desired target.

The whole purpose of this is to get your warmed up idle correct. This accomplishes a few things:

1. You can set the IAC to be closed at fully warmed up idle. You really shouldn't need it at that point.
2. Having the fully warmed up idle sorted out for both idle speed and AFR will allow you to tune the warm-up fueling and the warm-up IAC without chasing your tail.

Basically, don't worry about getting other things sorted out until you have your full warm idle sorted and locked in.

[FABombjoy]

I remember the wiring in the MS documentation to be wrong for two things: The IAC and the coil pack firing order.

That would explain why so many folks seem to have trouble with the stepper IACs.

If need be I can check my own wiring, too.

[opethmike]

I HATE stepper IACs with a passion. Pulse width modulation is just so much more pleasant to deal with.

[FABombjoy]

Ask Mike about his flyin' pintles.

[jangell]

You don't have too much air; you have too little fuel. Here's what I would do:

Take the IAC 100% out of the equation. You don't NEED it for it to idle correctly; just for it to idle consistently across engine temps. With that out of the way, adjust the throttle stop screw so you're at, say 1,000 RPM or so when stone cold. Play with the warm-up table, adding fuel as necessary to keep it around 12.5 AFR while stone cold, mid 13s until 120 or so, then mid 14s from there until ~185 degrees.

The RPMs will increase as the car gets warmer. That's fine, don't worry about that for now. Wait until the car is fully up to temp (185). Then adjust the throttle stop screw until the car idles around 750-800, depending on your preference.

At this point, there should be NO influence on the fueling from the warm-up table; fueling should be 100% determined by the VE table. All the cells that the car is idling in should be just about the same number. Keep playing with that until you reach a low to mid 14 AFR at idle. You may also have to play a little bit with the throttle stop screw to return the idle speed to desired target.

The whole purpose of this is to get your warmed up idle correct. This accomplishes a few things:

1. You can set the IAC to be closed at fully warmed up idle. You really shouldn't need it at that point.
2. Having the fully warmed up idle sorted out for both idle speed and AFR will allow you to tune the warm-up fueling and the warm-up IAC without chasing your tail.

Basically, don't worry about getting other things sorted out until you have your full warm idle sorted and locked in.

I'd been so focused on not having the cats glow, that I forgot that the whole point was getting the system up to temperature so that I can tune the idle when warm. Having this as a guide will help a lot -- a process to follow is definitely what I need. The MS startup guide one is great, but it covers so many possible configurations that it can be easy to get lost (I probably should have made a new doc out of the relevant parts or something).

Also, I'm pretty sure my IAC is wide open, given how loud the "whooshing" sound into the slot above the throttle plate is, and thus where all the extra air is coming from, since I'm fairly sure my throttles are completely closed right now. I'll fix that wiring and the LC2 ground first thing this weekend, then boost the fuel, get everything warmed up, and tune the idle.

Thanks!

-- Joe

[opethmike]

Don't forget to also hug the car.

[Josh]

Don't forget to also hug the car.

Follow Mike's directions carefully.

He taught me how to tune a several years ago, got me through some tough binds. We tuned my car from hobbling around town to cross country travel in a week.

[jangell]

Back at the garage today.

I checked the LC2, and apparently my wiring diagram is wrong, and the ground wire goes through the bulkhead connector to the engine ground bundle. So it is properly grounded, and not connected to the signal return wire.

This led me to trace the ground and signal return wires back to the DB37 connector. I seem to have taken... liberties with the ground pins. Sensor return isn’t on the right pin, and the pins I did connect to aren’t the ones labeled “power grounds” in the manual. So I’ll be resoldering those now. I’m not sure how much it matters, but I’m betting the ground traces on the power ground pins are more robust than the other pins.

I have no excuse for sensor ground being on the wrong pin.



Also, now that I’m looking at the MS grounds, I could have saved myself some trouble by connecting them to the parcel shelf ground post instead of running it through the bulkhead to the engine, but it’s already wired up so I’m just going to leave it.


I’m just starting on the IAC, but I found that one of the wires had pulled out at the bulkhead connector. I’m not sure if this just happened (most likely) or if it has been broken for a while. I still need to pull the IAC from the engine and run a test on it, which is what I’m going to start doing one I fix the MS grounds.

Thanks again!

— Joe

[jangell]

I lied — sensor return is wired correctly. I just wired four of the other grounds to adjacent ground pins instead of the power ground pins for good reason. So I’ll just move those to the right pins. I’m guessing that’s where all the noise is coming from.

— Joe