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It's that pic I posted earlier: Yes, you are correct about the circuit connections. The circuit is fairly common, and I've seen this kit board which should work with a few component changes: http://www.quickar.com/tkit.php The PN is ML-804. I've never tried it though, and I'm just guessing based on the photo.

Last night I drove the car in low 30s F temps and had some surging. It was under ~5 PSI boost, part throttle, and I could see the ECU still trying to close the loop. I have found the ESC1 product which disables the O2 sensor under boost: http://www.splitsec.com/products/conditioner.htm From reading it seems like people use it when they add turbos to a non-turbo engine. The ECU only knows the air mass into the engine. By tweaking the MAF I have fooled it into thinking there is less air, and the ECU is keeping the loop closed under more load. However I have noted the closed loop under boost with even the stock injectors and MAF. The stock ECU seems a little aggressive trying to close the loop. Perhaps the later ECUs didn't do this? Mine is an '88 GL-10. So I think I will try adding a relay to the boost switch. I will wire it to disconnect the O2 sensor under boost. Hopefully that will send the ECU into open loop mode. My guess is that's all the ESC1 does.

That there (NEC C2334-L) looks like a NPN transistor which crosses to a NEC NTE54 (aka ECG54). Your local TV repair shop might have one you can buy. http://www.nteinc.com/specs/10to99/pdf/nte54.pdf

That looks nice, cheap too. I plan on getting one of these soon but they are a lot more expensive. http://wbo2.com/2y/default.htm It has datalogging and you can connect a few inputs to it.

Yeah, you might be right. I thought about that before as my solenoid is clicking away at idle; it's not that loud though. My thought was to connect my circuit to the "Boost" light on the dash, so it is only working under boost, but I haven't got around to that. edit: I attached the ground of my circuit to the boost switch, now the solenoid only acts under boost.

Thanks! I'll keep you guys updated on my progress. I think I'm getting pretty close.

Here is the schematic. It is basically a 555 timer that generates a variable duty cycle PWM signal. The frequency is around 15 Hz. It works pretty good. On shifting (automatic) I get maybe 1 PSI spike. It holds boost to redline; it's way better than the MBC I tried.

20 BTDC w/ green plugs together, it's at stock timing. 91 (R+M)/2 octane gas. So far I've put on a MSD 8222 coil which did help (BTW the stock coil is 0.8 ohm and the MSD is 0.7 ohm) and new NGK BPR6EY-11 plugs which helped too. Gapped plugs to 0.030". Plugs look good, nice even tan color. Compression is from 122 to 126 PSI across all cylinders. Still misses though at high boost. The exhaust note changes notably to an uneven note. I let off for a bit and then get back on it and sometimes it will smooth out and pull away. Waiting for the wires and cap/rotor to arrive.

There is only one O2 sensor on these cars... So you have none at all? Without the O2 sensor it can run very rich, the computer doesn't know the mixture and if your MAF is off it can be bad.

Check your engine grounds too.. My gauge would show overheating when I did things like turn on the headlights, blower fan, etc. I installed a big ground cable right by the thermostat housing and it solved it.

I'll check the brake booster, that's a good idea. Yeah good point, although I plan to use the paddle shifter only on windy roads and for normal driving just use the stock TCU. I'd bet the mileage on windy roads will be the same, except the tranny won't be shifting all over the place. Try 3.80 (premium for the turbo) here in N. CA!

It runs pretty good. I am having a hesitation problem at 10+ PSI boost but not sure why, otherwise it runs fine. I do have bigger injectors and a modified MAF, WRX intercooler. New plugs the other day actually, IAC is good (checked and adjusted it a month ago), doesn't have EGR (CA model Turbo.) The thing is if I don't touch the brakes the RPMs don't come back up. I'd really like to see the TCU diagram, if anyone could scan it for me I'd appreciate it. Anyway I think this tangent of the torque converter locking up and brakes doesn't really matter in the grand scheme of my paddle shifter plan. I really do think just leaving it unlocked will totally be fine. It seems like in the "3" gear selection the torque converter doesn't lock up either, and there is plenty of engine braking.

Sorry, it's really crappy. But here it is: http://presslab.us/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=4822 and another http://presslab.us/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=4825

Well I guess we'll have to disagree. So why does my engine speed raise back up when I let off the brake pedal? I don't touch the throttle. Maybe you can scan them and upload them for me? 88 GL-10 Turbo w/ 4EAT. I only have a '90 Legacy diagram and it has a brake connection. Sure nuff but the old ones didn't lock up the torque converter.

Well, mine does for sure. Lightly touch the brake pedal and the RPMs drop. Let up and the RPMs go up again after a second. I'm sure it uses it sometimes for engine braking, but touch the brake pedal and it unlocks it. It must. Otherwise it'd be pretty much impossible to lock the brakes up without stalling the engine completely. I lock up my brakes all the time, no stalled engine. I'm still looking for a TCU schematic for my 88 GL-10... If I drop the shifter into second, it will shift into second. When cruising at 45MPH my 4EAT is in 4th gear. I'm not sure how that test shows the torque converter locking up... Yeah that's the one I have, the 1st hold switch. It works fine, but it will shift to 2nd, 3rd, etc if I approach redline. Hmm that's interesting. Do you know if the TCU was energizing the right solenoid for 1st gear? In those PDF documents I linked, it shows how the "D" mode can select gear 1, 2, 3, 4 with the solenoid. Should work fine I think.

Thanks for the info guys. I don't think the torque converter is a problem as the TCU unlocks it whenever the brakes are applied. Gloyale, how did you try to lock it in first? Did you drive the solenoids directly? Below it shows how 1st gear is used even in the "D" mode. Here is a good document on the operation of the 4EAT: http://www.endwrench.com/pdf/feb2004pdf/4EAT.pdf and http://www.northursalia.com/techdocs/pdf/transmission/4eat.pdf

The 4EAT is an electronically controlled transmission. This opens up the door for electronic modifications. I'm toying with the idea of a paddle shifter. Anyone know why this won't work? The transaxle has two solenoids to select 1-4 gear. I'm guessing that reverse is a hydraulic thing that is physically selected by the gear shift lever? I plan on using the stock computer to control the AWD clutch, and of course to keep the stock automatic driving mode. Maybe eventually mod the AWD clutch for adjustable torque bias. How about line pressure control? Should I just modulate that based on the throttle position? Maybe back it off for downshifts? I plan to just leave the torque converter unlocked when in paddle shift mode. Anyway just a hair brained idea, thought I'd throw it out there.

I made up a little circuit to send a PWM signal to the wastegate duty solenoid, for more boost. It has a dummy load resistor so the ECU does not throw a code. The original signal from the ECU is a 20 us pulse at 15 Hz, basically 0% duty. However with this short pulse it can detect if the solenoid is plugged in and throw a code if not. I read somewhere that the ECU will up the boost at high altitude with this signal, but I am at sea level. A 50% duty is giving me about 10 PSI. Unfortunately my engine is missing at high boost + high RPM. The O2 never goes lean but I'm pretty sure one cylinder is fouling out because when it starts missing and I back off the throttle, the engine is lumpy for about 30 seconds and then smooths out again. A flooded cylinder I guess. In trying to figure that out I have played with a variety of MAF adjustments. I can get it to fuel cut at ~9 PSI, or if I adjust it "lean" it can do ~15 PSI easy. The injectors still flow enough to not actually go lean though. I think the MAF adjustment + bigger injectors is going to be fine. I have on order new plugs, wires, cap, and rotor. We'll see if that fixes my engine missing.

Well I do have the wide band sensor itself but I never made the circuit, so no I don't really have one. I am just looking at the voltage of the narrowband O2 sensor. I adjust it until it's basically stoich and then make it a bit richer. A lot of people say the stock injectors are 180cc, but at what pressure? The 280ZXT are 260cc @ 43psi. Someone on here measured the stock XT4T at 210cc @ 43psi, which I think my GL10 has the same injectors.. I mention this because I didn't really have to change the MAF that much with the new injectors.

Put the new o2 sensor in this morning, it's definitely a Titania one. The Titania use a flat strip instead of a cone shape. Attached is a pic of the old sensor, I cut it open. http://www.tomco-inc.com/Tech_Tips/ttt20.pdf I have also installed my brown top 280ZX Turbo injectors I bought from Dr. Injector. I tuned the MAF to offset the additional fuel. So far the car is running great! Next step is a bit more boost.

Ok I found in a catalog on the internet that my sensor is a Titania one. It looks like only the California turbo models had it, which my car is. I found a new sensor on sparkplugs.com for $59 so I ordered it.

Here is the pic of the mod to the MAF. I am using a 100 ohm potentiometer and right now (with stock injectors) it is at 60.5 ohms. You can see the cut trace in the upper right corner.

Mine doesn't do that. I have an O2 sensor "gauge" thing and it still uses the O2 sensor at ~7 PSI boost. (Meaning the "gauge" flickers back and forth.) At full throttle it does not use the O2 sensor. To diagnose this problem I unplugged the O2 sensor and the surging went away too. I think the older turbos did like you said because the service manual mentions something like that. I have an 88 with hot wire MAF and the boost switch only controls the dash "turbo" light. It does not know when it is under boost it only knows the air flowing into the engine and throttle position.

You know I have a wideband sensor in the same spot, on the shelf. I haven't made up the necessary circuit to get it to work though. I wonder what the response speed of the wideband sensor is? I think they are Zirconia too?

The problem is that the MAF will (probably) clip the output signal with more air flow when I turn up the boost. That's why modding internally should have the ideal result. And I didn't have to add an external circuit with all that entails. Just cut one trace and solder a resistor (variable or not) in. I'll try to upload a pic later. I don't really like manual boost controllers... They probably work OK but the boost curve they have is not the best for smooth power at part throttle. If I just apply some duty cycle to the boost solenoid it will just make the wastegate see that average, right? Like at 50% duty cycle the wastegate would see half the boost pressure I think. Is my theory flawed on this?