Diagnosing 85T Base Boost?

[Hans]

Got a 2-day TSD starting tomorrow. Meanwhile, we're trying to solve a base-boost problem on the 85T we'll be driving.

Have confirmed that the knock sensor works (solenoid chatters when KS is hit); have confirmed pressure transducer works (solenoid chatter at 1/2 bar). There is no brake switch or cruise control stuff on the 85, so that's not an issue. Only thing left is the signal from the coil to the APC.

We're measuring just shy of 12V at Pin 7. When the multimeter is on duty cycle, we're getting about 85% at idle, then it duty cycle _drops_ with more revs.

So what is this signal supposed to look like? Do we have a short here? What kind of V should we be seeing? Duty cycle? Everything else checks out. We just don't know what to look for at this circuit.

Yes, we know the 85T wiring is sh!t.

Given that a 69 Sonett won The Thunderbird Rally a few months ago, it's safe to say we don't REALLY need the boost. But we really WANT the boost anyway...

Here's the ride:

[Crazyswede]

just out of curiosity, how does the rest of the wiring harness in the car look? it it suffering from fallapartitis? I have heard of some people having boost troubles on the 85's due to interference from the coil....its a long shot.

[Hans]

Saab gods have smiled upon us: *most* of the 85 wiring was replaced at some point (still need to do the fan wiring, but they work, for now).

Dan (owner of the car in question and newly-registered here) just picked up a $200 86 -- it's got some bad wiring, too, and we've seen a couple more 86Ts in the junkyard with "soy-based" insulation.

Anyway, would love to know what we need to look for at this wire from coil to APC, as I am an electronics reetarddd.

[Fieldsc]

Why are you so sure it is the electrical instead of a vacuum problem? Can you see exposed wires, or is there just alot of patch work. Goto step 3, taking out the W hose kills the bpc's ability to control the turbo. In the 85 I fixed it turned out to be the hooter valve. Follow this 4 step diagnosis.

1) I would also check every vacuum line, or even just replace them. Cracks develop that are really hard to find, sometimes only opening under full boost. An alternate way of testing the lines is while the car is idling get a map gas canister and without lighting it let the gas out over the lines. If the engine rev's jump up, there is a leak in that area.

2) Locate the bov (hooter valve) and disconnect the 3.5mm vac hose going to it. And connect a clean 2-3 foot hose to it. Suck on it. You shouldnt be able to get any air out of it. If its not restrictive then the bov is shot. This will severely limit your boost. Any bov off any saab will work. So just goto a junkyard and do this test until you find a good one.

3) Next if you still are not getting good boost, disconnect the hose on the bpc labeled W. It will disable the waste gate so it will boost until fuel cut. And drive it. If you get lots of boost, then a shudder than the bpc is shot. What happens is the disc inside the bpc gets clogged and wont flutter up and down. Sometimes u can spray wd-40/electric parts cleaner inside and flush with compressed air. I havent had luck with that although.

If you dont get boost, then you still have a big vac leak or the turbo is shot.

4) Check waste gate. Sometimes the clip that connects the lever to the arm rusts out and the arm falls off. Or somebody monkeyed with the arm and it is not adjusted properly.

I hope this helps.

[SaabsBreakDown]

I have heard that 85's were the only year for the bio degradeable harness.

I think you should just get rid of APC altogether. If you know what your doing you don't need it, anyways. What works really nice for me is wiring the APC selenoid on, and putting a valve on the drivers left port on the selenoid to regulate boost.

I have also seen people getting rid of the APC selenoid totally and using a tee with a restrictor plate, or going honda racer style with a MBC and only one line from the compressor to the wastegate.

The way I do it if you ever want to sell the car or try to troubleshoot apc, you can just open the valve all the way up and plug the selenoid back in.

[DeLorean]

I have heard that 85's were the only year for the bio degradeable harness.

yeah, 85's are the only ones I have ever seen that not only have the ends fall apart, but if you take an original 85 harness apart, all the lightly colored wires will have the insulation crack and fall right off of them. on one of my friends cars (an 85 turbo) before we "rebuilt" the wire harness, it was having the strangest faults... running the starter at random, idle control valve just going to full open, airflow meter wire glowing red at all times :lol:

[Geoff]

late response here (sorry, I was at the festival in Sweden!).

Most of the boost problems I had on '85 turbos (three of them) were ignition related. Replacing the coil and wires helped. I've also had a lot of trouble with the distributors and the Hall sensor wiring to them. I finally fixed the problems by replacing the distributor with a later one (better plug) and replacing the wiring to the plug in its entirety (you don't want to cut the wire harness to the hall sensor because you'll mess with the insulation/shielding which will give you more ignition problems).

[Hans]

We ran the event without boost. We got a bunch of 0s and 1s, but the navigator (hmmm, that'd be me) blew it on the Timewise, so we got some, erm, 3s and 4s, too (though, on one leg, Satch Carlson got a 3 & 4 vs. our 4 & 4, so we didn't feel so bad...).

We've found recently that the boots is intermittent. We'll put some Bougicords on and maybe swap out the coil. Everything else appears functional.

Thanks for the responses...


+100 *F in Eastern Washington:

[Crazyswede]

3's and 4's? wow you guys really suck.

[Hans]

3's and 4's? wow you guys really suck.

Not sure if you're kidding.

We're running Equipped class with a thousand dollar computer: we're *supposed* to be getting 0s & 1s with that kind of technology. The trouble is, the Timewise usability is, well, it ain't real usable, so I'm still struggling to do stuff like, not accidentally Park the odo in the middle of a regularity.

Also, on gravel, figuring out a good Factor with an undriven wheel when all courses are usually set with AWD is tough, especially when the noob navigator (moi) introduces too much of a fudge factor and things get all sorts of out of whack pretty quickly...

We did a short "Friday Nighter" last week and zeroed 3 of 4 regs (on one, I messed up a Pause and added 3 not 30 seconds), so I'm slowly getting the hang of it. Driver Dan's got the hang of this thing way more than I do.

This is all in preparation to run Alcan 5000 in February. Brrrrrrr...

[Crazyswede]

I was kidding. We usually run class "C" which is no computer, no odometer, no GPS or any other distance measuring device...its entirely speedometer and stopwatch. We usualy get a few scores down in the sub 5 area but several hundred points in a rally is typical.

[Geoff]

Yeah, Seth and I love the NER "C" class. We ran this way in the last Buffum rally and totally spanked on Travis Pastrama who was running "S" (stock odo) :lol:

A few hundred points is typical for us in a Buffum rally. But we've ran more tame events and run around 100 points total (with generally an average of 12 checkpoints in the event). People in the "A" (unlimited) and "B" (limited) classes always gasp when the event organizer reads our points off, "34, 15, 0, 1, 0, 6, 18, 12, 3, 2, ..." Of course there are some events that get all messed up or we get beat by the guy with the TSD program on his Palm Pilot. We just use a $5 calculator and stopwatches that we tend to leave at checkpoints.

All this in a POS beat up old 900 with a speedo that isn't too accurate anyway

[DanComden]

Boost is mostly back. Who knows why? Most likely the dodgy wiring on the side of the car we haven't transplanted yet has decided to "fix itself" (one of the more amusing things one can say about car problems).

Thanks, all, for the hints. And Hans shouldn't sell himself short, he's picking up the navvie stuff quite handily. It's the dang driver having too much fun sliding around corners causing just as many problems.

[SaabsBreakDown]

Me and pops took 1st in vintage class at the rain drop rally a few years ago in a sonett III, I don't recall the score but I'm sure it was over 100