The Forever Car: 1989 Honda Prelude 2.0 Si 4ws

Yikes, it has been entirely too long since I've posted updates.  Admittedly in part that's because I haven't been working on the car as much as I should, but I haven't totally stood still on it.

I finished up the cylinder head and got it bolted back on.  Unfortunately I didn't take any pictures of that process. But I think we've all seen a Honda cylinder head before. :)

I sent my fuel injectors off to be cleaned.  273k miles with no cleaning (so far as I know) and the results seem pretty worth it.  I'll have to add the before/after results from the sheet in a bit.

I do find the fuel injector cleaning services a bit frightening.  I basically toss $500 worth of parts in a box with a letter that says "please clean these" and my credit card number and I hope I get it back.  But it's worked every time so far! 

And I redid the valve cover paint.  I spent a lot of time on prep getting it as clean and ready as I could.

I was pretty happy with how it turned out.  The unevenness shows up in the pictures, but hardly at all in person. And I'm guessing once it's in an engine bay it won't be noticeable at all...

Gotta do valve adjustments, but the engine is about back together! Then just some clean up on the transmission and ATTS, and it should be ready to go back in!

The engine is pretty well set, so now it's time to focus on some of the auxiliaries.

First up is the ATTS (Active Torque Trasfer System) system. The ATTS system is primarily what makes the Prelude Type SH a 'Type SH'. It's an active differential that biases the engine power to the outside wheel in turns. Honda still has a very nice write up on it here:

Honda Global ATTS Explanation

And here's another thread where someone took theirs apart.  Mine still seems to work just fine mechanically, so I will NOT be doing this! :)

ATTS Disassembly

It is, essentially, just a tiny automatic transmission bolted onto the back of the block and in the output path of the manual transmission. It works using the same principle of locking up clutches in order to drive planetary gears to change a gear ratio. Somewhat interestingly, but totally unnoticeable because it's at like the 3rd decimal place: the over-driving ratios are slightly different from left to right because of the different path the gearing takes: The left overdrive ratio is 1:1.1538 while the right is 1:1.1555.

Mine is out and on the work bench.  It has 270+ thousand miles worth of grime on it.

To start with, I'm cleaning it up. Lots of paper towels getting used for this!

Mine was throwing a code about the oil pressure sensors before I did all this.  The oil pressure sensors are a known weak point, although they're no longer available. Supposedly the connector part of the sensors normally breaks (physically), but mine appear to be in ok condition.  I'll be doing a bit deeper dive on them once I finish cleaning it up all the way.

Ok...a couple things....

One: The mid engine Prelude is freaking awesome, Looking forward to seeing you resume progress on that

Two: Am i reading this right...the Red Prelude essentially has a manual transmission with a secondary AT on it that is dedicated to the Diff??

Thanks!

For point 2, yes, it has a manual transmission, but it might be more accurate to say that it has a tiny secondary automatic transmission that IS the differential.

BA5 said:

Thanks!

For point 2, yes, it has a manual transmission, but it might be more accurate to say that it has a tiny secondary automatic transmission that IS the differential.

That seems confusing as hell...im just gonna try to run this through in my head... So essentially where the manual trans would have its differential this mini AT is in its place, So what normally would be the pinion in the MT is a coupler or similar input into the AT in place of what would normally be the Torque converter on a full size AT. What would be the reason for this added complexity?

I'm getting close, so the speed is picking up a bit.

A much better look for the ATTS unit:

Now, it was throwing a code for the unit before all this happened and the ATTS wasn't really working. I mention it above that I had checked the code it was throwing and it indicated an oil pressure sensor problem.

So I put the multimeter to the sensors:

Yay!

Boo!

Now, the factory sensors are long since discontinued.  But according to a random post I found on the internet (that at least lines up with some of the limited factory information I have), they're 100 psi pressure transducers. The ones I've found online only have 1/8 npt threads, but otherwise match up.  So I ordered a transducer and adapter from the company we all buy our cheap chinesium crap from and we'll hope for the best.

I also replaced a seal since it was one of the few parts that was still available from the factory (although according to one of the site I visited, the whole unit is still available for like $3500).

Just for fun, I bolted it up the backside of the engine.  It's pretty chunky on there, but It's interesting the see how it fits:

Lastly, the lower engine cover was in bad shape, but luckily they're still available from Honda.  So I bought a replacement:

So a bit of a dive into the oil pressure transducer wiring.

They're 3 wire oil pressure transducers.  They have a supply voltage, a ground, and the signal voltage.  Here they are in the factory manual:

Specifically my left one is dead. I bought a replacement, that looks like this:

I need to match up the wire leads on the above to the wires already on the car. They're on separate pages, but I can follow where the wires from the transducers go:

Since 1 and 2 on the transducers are tied together, I can presume that they're the supply voltage and ground.  Can't tie the signal wire to anything else because then you wouldn't be able to get an individual signal.

If I follow pin 1 from the transducer through the schematic (blue), I can eventually find my way to a ground symbol.  So pin 1 is ground.

If I follow pin 2 from the transducer through the schematic (fuchsia?), I eventually get to a VCC label.  A label like that is usually indicative of a voltage source or fixed voltage of some sort. So pin 2 is voltage supply.

Pin 3 from each transducer just goes straight into it's own pin on the computer, so pin 3 is the signal.

So I'll connect:

New transducer wire color -> Old wire harness color

Black -> Green/Black

Red -> Yellow/Blue

Green ->  Blue

Also luckily this is the easier sensor to get at once the engine is back in the car, so even if I have to trouble shoot it won't be buried too badly.