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Maybe buy a second ecu. Maybe get for $100. Take it apart for practise.
The ecu will be expecting the charge control solenoid to be functional and will be adjusting running dynamics accordingly.
Interestingly, although my shop switched my turbos over to parrallel arrangement, by fixing (welding) the valve to the second turbo open, they left the change over valve operational. The reason: to leave a wee bit of sequential effect in place. They have eliminated the solenoid however, the actuator just operates off the vacuum (or air pressure) continually.
Based on the table below, the charge control valve is opening under acceleration and heavy load. If it is not opening, it seems to me you will have a bigger drop off of boost when the second turbo valve opens, than what the ecu might be expecting. Would this mean that the ecu is dumping more fuel in in expectation of more boost than is actually happening? What is the processing delay time from what the MAP sensor is telling the ECU and its reaction to that reality? Is there a negative feedback loop, where the ecu is continually getting info from the MAP sensor that it does not expect?
Note: "Off" means "open" in the case of the Charge Control Valve. This can be confusing. (I suppose "off" means the vacuum line from the solenoid is shut off, allowing the actuator to be moved by the manifold pressure/vacuum. alone)
I may be getting the pre-control valve and the charge control valve mixed up. Seems if the charge control is not opening when the secondary turbo kicks in, you'd be starving boost, compared to what the ecu expects.
In any event it seems you should make sure the charge control valve is working.
Looks like the charge control solenoid is buried pretty deep in the rat's nest. Disturbing an old rats nest can cause lots of headaches, nipple breaking off solenoids being a big one.
But you have a rat box instead. Nevermind. Is the charge control in the rat box?
According to the Version 5 ('99) parts catalogue the reference part number is 18-741D. 18-741D corresponds to two types of solenoid: "B6AT-18-741" and "FEGC-18-741".
The Version 4 parts catalogue breaks these out into two reference numbers and the one that corresponds to the position "4" in the diagram is "B6AT-18-741".
I picked this one up off Yahoo Japan (through Buyee) pretty cheaply. The box contains three of the B6AT-18-741 and four of the FEGC-18-741, so I can likely use it for parts, if the box in its entirety does not work. I have picked four others from various sources at well below the C$600.
Thank you!
Having given it some thought, it seems like starting out with the combined box is cheaper in the long run, so I'll order one of those, along with a used ECU.
Thank you!
Having given it some thought, it seems like starting out with the combined box is cheaper in the long run, so I'll order one of those, along with a used ECU.
When you receive it, please keep us posted with the retrofit. A Series 6 to Series 7/8 Solenoid Rack Retrofit guide would be a great addition to the 3rd Gen FAQ
Got quite a bit to unpack, but for starters, she lives, at least somewhat!
What we ended up doing was a straight swap of the original S8 solenoid rack to a "new" one, another N3F1-20-4B0, and ditched the idea of replacing the individual solenoid completely, especially since the others were likely on borrowed time.
We then changed all of the rack's remaining vacuum lines to silicone, which was a minor nightmare, but something that definitely needed doing all the same.
Now, I didn't think it did anything to start with, as the idle is still all over the place when cold, popping and backfiring at every opportune moment.
Noticeably though, one of the turbos spooled for a second when it first started, which it has never done before, not that I even know if that's a good thing, but it is something.
However, we figured we'd give it a run around the building once it had warmed up, just to see if it had improved at least a little bit.
Thankfully, it absolutely has, as it now comes completely alive when given some revs, fully using the turbos, which we concluded couldn't have been even slightly present previously.
There's no hesitation or massive backfires to speak of, and we even managed a climb to redline with no complaints or smoke in sight.
It should be noted there's still very minor crackles every now and then when warm, but at this point I'd wager it's the exhaust's lack of a proper silencer (only non-stock part), unless of course there's something I've missed again.
So in regards to the hesitation, it was very likely a culmination of the twin solenoids, the charge control solenoid, the incredibly crusty lines surrounding them, and possibly the O2 sensor.
Unfortunately I can't say which with absolute certainty, as we rarely did one single thing at a time.
The remaining pain point is now the cold behaviour, as that hasn't changed one bit.
The replacement/trial ECU I bought hasn't shown quite yet, but as soon as it does, we'll try switching them, and if that doesn't work, we'll open them for a checkup.
The auto-adjusting for the idle you showed could easily be the culprit for that, so I'll give an update as soon as I've tried it out.
Should that not work, we're completely lost, yet again, so any other ideas on that now (thankfully!) specific problem would as usual be greatly appreciated!
Duty Cycle for the IAC Valve is usually around 45-50% at Idle IIRC. Can't recall the exact numbers offhand, but this is something where it might be worth grabbing the Oscilloscope and seeing what comes up on it. Signal is a regular Ground PWM signal, just like the Injectors.
To know if your ecu is thinking straight, during idle, you could turn on some of those load items, such as the A/C and listen if the ECU changes the idle.
The 1999 parts catalogue (s8 Version 5) shows the ISC valve:
Valve P/N: N3A1-20--660
Gasket P/N: N3A1-20-661
The existing gasket might be reusable in a pinch.
Those Pin numbers look like they might be Miata parts numbers.
No, it's a regular FD part with the N3A1 prefix used for mechanical or electrical parts. Miata would be B0xx or something else. This is likely a paper gasket that's been in place since 1999. I'd bet money that will crumble if you look at it wrong. Fel-Pro #3137 or #3157 is what I use when the original gasket is not available or is otherwise unsuitable for one or more reasons. Not too hard to make a gasket, just impress the shape into the material with a hammer, then cut with scissors. An xacto knife works well for cutting out bolt holes if you poke it through twice to make an "X".
01-02-22, 12:44 AM
