I need some advice with 2 unrelated turbo problems on a c900

[happyandy]

My car is a '88 c900 16v turbo w/ 5spd. As far as I know it all stock at this time, but its not going to stay that way much longer!
The first problem is this; the apc soleniod chatters almost constantly, even when the engine is not running. The solenoid is good and it does stop when the brakes are applied.
The second problem is that the orriginal T3 turbo is starting to smoke on a regular basis. I would like to upgrade to a more capable turbo anyway because I have plans for power adding mods in the near future. Is there a turbo that I could easily swap in from annother saab or some other common (low cost) source? Are the mitsubishi turbos a signifigant improvement?

[Raul]

My car is a '88 c900 16v turbo w/ 5spd. As far as I know it all stock at this time, but its not going to stay that way much longer!
The first problem is this; the apc soleniod chatters almost constantly, even when the engine is not running. The solenoid is good and it does stop when the brakes are applied.
The second problem is that the orriginal T3 turbo is starting to smoke on a regular basis. I would like to upgrade to a more capable turbo anyway because I have plans for power adding mods in the near future. Is there a turbo that I could easily swap in from annother saab or some other common (low cost) source? Are the mitsubishi turbos a signifigant improvement?

This forum is strictly off road saab rally and preparation and maybe some saab performance discution.
The questions you are asking should be posted in bigger forums that deal with drivebility issues on stock cars. Like saabnet and saabcentral.

I once had a problem with apc chatter and I replaced the boost sensor and the chatter went away.
The cheapest way for turbo is to replace it with the same turbo. Any other turbo will need modification to fit. Mitsu unit is smaller than garret.

[Crazyswede]

Watch out....Raul is the self imposed traffic cop around here.....give him a donut and he will quiet down.

Your chatter problem could be from something as simple as interference from the coil wire. But if it chatters when the engine is not running then something must be wrong in the wiring. You might have a bad ground or some corrosion thats causing problems. I'd start by checking the condition of your battery cables and connections. Next I'd clean all the grounds and do a wire wiggle test to see if you can get it to stop. You might check out the overboost switch too.

[Geoff]

It sounds like there is something living in your engine, hammering on the knock sensor. nasty trolls...

Anyway, check the wires to the solenoid, you may need to trim back the sheath that they go through. If the insulation has fallen off and the wires are crossing the solenoid will chatter like that. A cracked coil or cheap plug wires will do that too but as Mongo said, it shouldn't chatter when the engine is off if the cause is the coil or wires (I think...).

I'm not sure about the turbo swap because I've always just let them smoke a little. They last for a long time like that

[Jordan]

Don't listen to Raul, he just likes to get in peoples faces. Actually Raul, this forum is specifically for on road. As for the turbo... the t3 is a little larger, with a bit more bang to it, but the mitsubishi is smoother with less surging. For stock power levels the mitsu is fine, but anything more than 18psi it's efficiency goes down hill. If you are going to upgrade... go with something similar in size to the t3 but with a more modern design. Newer turbos, in general, are far more efficient even at the same pressure levels. As for the APC, its been a while since I had similar problems, but I'd agree to triple check all the wiring and connectors.

[Raul]

I'm sorry you are correct.

[ric]

The APC problem, if I remember right so if you lose the connection with the pressure transmitter(no 180 on the wiring diagram pin 23 and 10 on the APC unit) or if it´s broken the valve will start to shutter.
The transmitter should be located on the left side under the dashboard.
At 0 pressure it should be 10 Ohm +3 - -5 then increase the pressure to 1 bar and lower it to 0.60 bar and it should measure 88 Ohm +-5.

[Jordan]

If you do the DIY APC mod, it takes out input from the pressure transducer (which ric is talking about I believe) and it might solve you problem.

[happyandy]

I am interested in the diy apc mod. aren't there a couple of different ways to do it? What is the best one? and where can I find good (prooven) instuctions? I've seen this topic discussed on several saab related web sites, but I don't know any one who has done it them selves. Also I repaired damaged wires going to the apc solenoid when I first got the car and that didn't help. The wires were melted, and I grafted in new wires. Is it likely that if there was a short in the melted wires that the coil driver inside the apc control box was damaged?

[Jordan]

It's possible that if there was a short that melted the wires, the circuit board could have been damaged. The units are pretty robust however. I've had good luck with the SAABWORKS modification instructions:

http://saabworks.com/projects/apc.html

[Crazyswede]

I did a simple apc installation in my old 86 2 door. When i installed the pressure transducer I left the vacuum hose off but I did plug in the terminals. This made a significant improvement in the way the boost ramped up...no more surging.

[Sean Tennis]

Chattering is most likely faulty pressure transducer under the dash, sometimes it is a loose main electrical harness connection at the APC control box.

Most modified APC units I've seen eventually failed and took the engine with them...

IMHO,
Sean Tennis

[DeLorean]

Most modified APC units I've seen eventually failed and took the engine with them...

uuh..... what? How and how?

[Jordan]

I was wondering the same thing.. usually when the APC fails , the car just get stuck at base boost. Unless you get some dumb-asses that disable the knock sensor some how (k pot?) or take the safety measures off in general. The pressure transducers always are going bad...so I would mod the box and not touch to potentiometers to keep boost at stock level but bypass the bad transducer.

[paulh]

yeah the APC's aren't the issue, usually its a problem with people running way too much boost on stock, or near stock fuel injectors. Theres basically no way you can safely make over 225whp or so on the stock fuel injection, anything past there is pretty much a crapshoot as far as reliability is concerned.

Paul