1G 91-92 CAS in a 90

[Noranuzoki]

Hey guys, I need help figuring out what's going on with my 90 GSX. I've swapped a 91-92 CAS into the car and it seems its the culprit to whats going on. Its a brand new unit and I bought a harness from OHM Racing to have it "plug and play" to my car. I did research on forums here and there to see what was needed or if it was even possible but didn't find a straight answer. I went ahead with it because I figured if they sell harnesses for the swap then it was have been done successfully before.

The car doesn't idle right, the ignition timing is erratic, and as soon as I touch the gas it dies. So at least it runs. The car also goes hay wire as if something isn't grounded right or it thinks the car is on. The fuel pump goes and the injector pulse along with the tach moving. I'm sure its my CAS because I can unplug it and put the key in the ON position and it won't do what its doing in the video.

My only thought is that I would need a 91 coil pack which was lightly mentioned and implied on some other forums here. But no one seems to list it as a requirement so I haven't bought one yet.

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Any information on this swap would help me and it would be appreciated

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[steve]

There isn't a lot to check here assuming the car wasn't doing any of these things before you swapped to a newer CAS.

There is the electrical, the mechanical and the adjustment.

Electrically there are four wires, Power and ground for the CAS and two signal wires from the ECU. Both the 90 wiring and the 91+ wiring are on the site. I'm pretty sure I've posted how the pigtail needs to be wired in the past so I won't here.

Mechanically it's pretty much making sure that the CAS timing marks were lined up and the engine was at TDC when you installed it.

Last part is adjusting the CAS position and locking the ECU in timing adjust mode to sync the CAS pulses to 5* BTDC using a timing light.

It looks like the tach didn't go crazy until after you started cranking, is that correct?

 

[Noranuzoki]

Thanks for the reply Steve!

I swapped to a later CAS out of necessity because the 90 CAS wires were so worn out. I touch them and they fell apart. The CAS is not 180 out. I made sure to align them before installation. As far as your question- the tach and car were going hay wire before any cranking was done. That video only shows it going into the "on" position. The car starts and runs. Just not very well. I've had a timing gun on it and the timing was erratic and jumpy. Im unsure of its exact position on timing but I do know that its BTDC.

However, reading this twice over Mechanically I didn't line up the CAS and the engine at TDC. I just finished rebuilding this car and I'm quite young so I've obviously got more to learn. I'm assuming TDC would be in cylinder 1. Another thing, I'm sure there is a forum about it but how do you lock the ECU in timing adjust mode?

 

[steve]

I thought I heard the starter just before it started acting up. I guess not.

On a '90 the tach signal comes from the tach gate on the coil pack, through the noise filter on the intake manifold stay to the ECU and the Tach. The tack gate takes the coil signals (not sure if it's looking for the back EMF from the firing or the pulses from the PTU) and combines them. Continuing backward the PTU gets signals from the ECU to charge and fire the coils based on the pulses it receives from the CAS. If the engine isn't spinning the CAS shouldn't be producing any pulses. And since it doesn't do this with the CAS disconnected is would seem like it's either bad or the wiring is causing this. You might be able to see if the CAS signals are going crazy with a multimeter.

Pin 1 on the CAS is the Cam Angle and should run to pin 88 (blue/red) on the ECU.
Pin 2 on the CAS is the Crank Position and should go to pin 89 (blue/white) on the ECU.
Pin 3 is the 12v source for the CAS should be a red wire on the CAS.
Pin 4 should have a black wire and is ground.

With the CAS unplugged and the ignition both pin 1 and 2 should have 5v from the ECU on them. With the CAS plugged in they should either be at 5v or 0v depending on the position of the CAS and should toggle as you turn it.

 

[steve]

From the 1G Electrical Manual (you can DL from the resources section)

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[Noranuzoki]

From the 1G Electrical Manual (you can DL from the resources section)

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Thank you so much! Again, for the mechanical timing part. Would the TDC you're taking about be for cylinder 1? I don't want to assume, thats how I got in this mess

 

[Justin DuBois]

#1, closest to the timing belt

 

[steve]

If not specified it's TDC Cylinder 1 end of compression stroke, start of power stroke. The other TDC place is the end of the exhaust stroke, start of the intake stroke but when talking about timing events it's the first that is important.

How do you know which is which? The first one both intake and exhaust valves are closed and for the second one both sets are partially open (during what's called overlap).

You can feel/hear the cylinder trying to compress for the first.

 

[Noranuzoki]

I've determined that the new CAS I bought is bad. I'm going to return the item and buy another one. I'll let you guys know my results when I get another.