Fuel cut just doesn't come in

[soldave]

For the first time since getting this once non-working S5 Tii FC I got it onto the roads and finally got it into boost. Have a very old HKS EVC boost controller and set it up to use normal stock boost. Put my foot down and watched my boost gauge (aftermarket, not the stock one). Quickly headed up and hit over 9psi before I got off the gas. Was expecting the fuel cut or boost controller to come in but it just didn't.

Now the boost controlling problem is a separate issue, and could be down to a duff controller or a sticking actuator or something. But I was really surprised the much talked about fuel cut didn't hit. I don't have a visible FCD in my engine bay or anywhere else, so I was wondering if it's possible the previous owner has ghetto-rigged something by cutting a wire. Very curious as to how the boost was going so high without a cut coming in. If it doesn't fuel cut then that's potentially great, but I'd really like to know why.

[LunchboxCritter]

Have you opened the ecu to see if it has an aftermarket chip installed?

[soldave]

I haven't, but will try that in the next day or 2.

[soldave]

Just a thought, but can anyone confirm that the N374 ECU does have a fuel cut? Might seem like a silly question, but just through past experience with DSM ECUs in the States compared to early Mitsubishi Evos here in Japan. The ECUs were almost identical but a couple of things like fuel cut were not in the Japanese cods.

[junito1]

Dude. DO you even know where a FCD goes?

[soldave]

2 options really. It connects to the boost pressure sensor which usually has a vacuum line going into the upper intake manifold, or alternatively the nipple just below that. When it does that it then reconnects up to the main harness which goes through the firewall and to the ECU. The pressure sensor is bolted onto the front driver's side strut tower on the front side of it, close to the headlight. I'm saying this from a Japanese point of view though; you'd probably see it on the passenger side.

Alternatively, (and I think in the case of some HKS models and maybe an RE Ameniya one) it connects much closer to the ECU, or even next to it, and splices into the wire from said boost sensor.

Why, are there other places it will connect? Maybe you can enlighten me.

EDIT: Reading your post again, maybe you're asking me if I know where the pins from the FCD (and therefore boost sensor) go. If so then one I believe is to ground, one will go to a constant voltage (5V sticks in my mind), and the other pin will give a varying voltage depending on the pressure detected. Is that what you're wanting to know?

[junito1]

HAve you looked at the ecu yet?

All the ones i have seen are the one on the strut tower. Or ecu related.

[junito1]

HAve you looked at the ecu yet?

All the ones i have seen are the one on the strut tower. Or ecu related.

[soldave]

Not yet as last night there were storms and flash floods in my area. Hope that answer about the location of the FCD cleared things up for you.

[soldave]

Will finally get to do some multimeter testing on my ECU tomorrow or Monday as I've got a long weekend due to a national holiday.

Was on the expressway though and floored it in 5th. As soon as it got spooling is was heading way up to 1bar/15psi and I had to get out of it. Could be a sticky actuator or duff boost controller but I'll find that out in time. No fuel cut though. One thing I did notice was that the stock boost gauge only starts to show any movement at all once I'm already in boost. What I mean is that the needle is nowhere near 0 on the stock boost gauge until I'm at least at 3-4psi. Is this normal for the stock boost gauge or should it be a little more accurate than that?

Will test voltages tomorrow and see what results I get.

[soldave]

OK, voltage tests finished and it doesn't help me a huge amount. 2.35V is detected at the sensor, and when 100mm of vacuum is applied it drops to 2.05V which is right within spec as checked by page F2-82 of the FSM. Checked pin 2H at the ECU and got exactly the same voltages, which would suggest that there is are no breaks or resistors in the line between sensor and ECU.

However, I think the FSM is throwing out some false spec values on page F2-78. It states that the voltage at the ECU from pressure sensor should be 2.8-3.2V. But that value is higher than the original signal voltage coming from the pressure sensor (spec is 1.9-2.1V). Now I'm no electrical expert, but voltage shouldn't increase along a stretch of wire). Do you get what I mean?

Doesn't help with the lack of fuel cut but thought I'd let you know the results.

[NoDOHC]

With a FCD doesn't the Factory boost gauge stop at 8 psi or so, even if the boost goes higher? I think I remember that as the big reason to do the upgrade chip instead. Please correct it I am wrong, it has been a while.