[saab93se123]

Hello folks,
A little history on the problem my car is having. 2000 93 SE. 120K miles.
Car would not start a couple weeks ago - troubleshot to faulty CPS and replaced sensor. Car started, but immediately seemed to have low (base) boost. Boost prior to was all the way to red. Have tried the various troubleshooting methods with the BPC:
1. removed W line, boost goes to red (would have gone beyond, but I backed off).
2. coil (T7) on the BPC is 9 Ohms.
3. I took the BPC apart (compressed air into the top port that goes to intake - this pops the cap). Cleaned it and reassembled.
4. Hooked a 12V battery to it and confirmed that the solenoid energizes and shuttles.
5. I don't believe the BPC is supposed to be energized with the car at a standstill.
6. Still have an issue, even though I know the BPC functions on a bench.
7. Starting to think I have the wrong CPS installed (though I don't know why this would matter, after all, the car runs. If the CPS is the wrong resistance...maybe it is messing with the ECU and the ECU is not energizing the BPC when it should? Maybe I blew a MOSFET in the ECU?
8. Anyone have experience with blown MOSFET's for the BPC...is this common?
thanks!
Jay

 

[jakejm79]

I would start by swapping in a known good (or new) BPC, they are cheap enough for T7 cars ($40), and the diagnosis has pointed to that (or it not receiving a signal) being the problem.

 

[BobSaabit]

A couple thoughts, I'm usually a spectator on these threads...

I don't think a bad CPS would cause the ECU to fail to send aboost signal. A bad CPS causes no start (which you had) or serious run time issues. If the ECU didn't know where the crankshaft was then the problem would be more than just "base boost".

Bad MOSFETs are not unheard of. Google it here. Apparently they eat BPC's when then go. I suppose it's not illogical to assume they might also fail to energize a BPC if they go.

Some folks say that you're not supposed to send 12v direct to the BPC from what I've read. The ECU supposedly sends an intermittent signal of some sort and a pure 12v feed can burn the BPC. Let's note that you had a problem before that, so it may not be an issue.

Do some googling on MOSFETs. You can test them.

 

['97 Saab SE Turbo]

Check to make sure that the actuator rod didn't fall off the waste gate. It's kind of close to the area that you were working in when you changed the CPS... Ron

 

[saab93se123]

thanks for the input...new BPC on order...base boost isn't all bad in the mean time...the mileage is better! (but it's no stinkin' fun either)

 

[saab93se123]

New BPC installed- problem is still there.

Potential issues as I see it:
1. Turbo itself - not likely -no smoking - accel is smooth to base boost...and it will go to red with the wastegate line off.
2. Wastegate checks out (per 1. above)
3. Vacuum lines - need to check these...but I think unlikely
4. BPC - new one could be faulty...but I doubt, and the old one checked out fine with same issue
5. There may be a reason the ECU is limiting the car to base boost (though I run Super all the time...and it's cool here in NY...so I can't see ping/knock restricting it).
6. Wiring...maybe..but I have 12V across the BPC wiring with the car on (but not moving). So I think the wiring is OK.
7. Boost gauge could be wrong - not likely - the seat of the pants is still calibrated and the car is slower.
8. ECU itself...Mosfets...that is the next place I will check. I distinctly recall this issue was not there just before the CPS crapped out. And it was there on the first test drive after the CPS replacement. I am thinking something happened to the Mosfets during the time the CPS was dead...and I tried to crank and crank the car - battery went dead...ECU would have had no power at some point...maybe it got a jolt/surge somehow. What I really need is a chart recorder to tell me what the signal to the BPC is when driving the car...but that might be just a little tricky to set up.

If any ideas (or words of wisdom for MOSFET testing, sourcing and replacement)...I am all ears..!

thanks
Jay

 

[jakejm79]

8. ECU itself...Mosfets...that is the next place I will check. I distinctly recall this issue was not there just before the CPS crapped out. And it was there on the first test drive after the CPS replacement. I am thinking something happened to the Mosfets during the time the CPS was dead...and I tried to crank and crank the car - battery went dead...ECU would have had no power at some point...maybe it got a jolt/surge somehow. What I really need is a chart recorder to tell me what the signal to the BPC is when driving the car...but that might be just a little tricky to set up.

The signal the ECU sends to the BPC is decided by RPM, Throttle Position and Gear (which is calculated by Speed vs. RPM), if any of those items are not reported to the ECU correctly by the sensors that could cause the signal sent to the BPC to be wrong.

 

[BobSaabit]

If any ideas (or words of wisdom for MOSFET testing, sourcing and replacement)...I am all ears..!

thanks
Jay

Search for MOSFET. There are a couple threads with test & repair instructions.

 

[Cm452]

Just wanted to jump in here before you throw more money at it.
1) BPC will rattle and shuttle @ idle.
2) If it does so, it is 90% likely that it's good and thus so are the MOSFET's.
3) Having thrown myself against this same problem over and over and torn hair out, sometimes it's the simplest things.

I was sure I had the tubing to the BPC hooked up properly, however, after weeks of frustration I ended up fiddling with another part of the car and noticed a subtle "C" on the hose that was plugged into the R. Re routed the hoses to their respective home and voila, full boost.

If the BPC rattles @ idle or after you blip the throttle, then your MOSFETs are prolly good. If it's quiet all the time ( you need to let it warm up a bit before it'll start clicking) then perhaps your MOSFETS are shot. I'd still wager it's something stupidly obvious and near or having to do with your CPS install.

Do a careful once over; you might be surprised at what you find.
Good luck,
-Cm

 

[Cm452]

Jeez, can't even give advice anymore; I drive a T5 car I tuned in T5 suite to use a T7 BPC. This means that a T5 car with a T7 BPC will adhere to what I said above. For a native T7 car/BPC I have no freakin idea.
-Cm

 

[saab93se123]

Thanks for the continued input. One of the things I have been searching for, is "what should the BPC be doing at idle" - I'll have to check what it does with the engine running...but with the key on, it does sit there and buzz...is it supposed to shuttle? I suppose if it's buzzing (PWM signal) you probably can't check to see if the ports change (as it's not "energized" to one side). So, I think based on that, my wiring and MOSFETs are OK. I was giving some thought to some of the other recommendations...RPM and speed inputs to the ECU...of course, I don't know how those are currently being read by the ECU, but the tach works (though that may not be driven out of the ECU). I agree it is probably something simple (though I rule out vac lines to the BPC, since I never touched those until I had an issue). And I know for sure it happened during the time the CPS was replaced....so, what the heck did I disturb when I replaced it? I took the heat shield off today, and the bypass pipe, to have a look. Wastegate opens (by hand) and closes (spring) fine. Maybe I disturbed a connector on the multi-connector mount behind the engine (the one that the CPS plug is held buy)...maybe a sensor was broken or connector dislodged...but which? I believe there is a pressure sensor in the line coming from the intercooler (right below where the bypass pipe and BPV ties in)...if that sensor is faulty, it could be related to the issue. The ECU will energize the BPC valve until it reaches a set pressure (or until it detects knock/ping)..at least I think that is how it works...where does it read that pressure?

thanks again...

Jay

 

[jakejm79]

You say you can move the WG actuator by hand, how easily?

 

[saab93se123]

not too easily...let's say it's 5 times harder than pulling a pinball plunger (to launch the ball)

 

[rawill]

Jeez, can't even give advice anymore; I drive a T5 car I tuned in T5 suite to use a T7 BPC. This means that a T5 car with a T7 BPC will adhere to what I said above. For a native T7 car/BPC I have no freakin idea.
-Cm

Good on you, great mod, and yes they do rattle in our cars (T7 BPC), but maybe not so much in cars they were designed for.

And I think it takes only 1 mosfet to drive the BPC in a T7 car.

 

[saab93se123]

I believe I have confirmed the mosfet(s) are OK. I tried a couple things in the last week (still chasing low boost, after having replaced all vacuum lines, cleaned the MAF and TB, replaced the BPC) - I reset the ECU and forced adaptation. This seemed to have an effect on the level of boost, though still not boosting to red. Then, put in a tank of 87 (I normally run super) - next few full throttle runs, the boost was going lower that half yellow -it seems to vary...sometime is will boost to 25% yellow, other times 75% yellow (it does make sense that lower octane will result in lower boost). What this proves is...base boost is 25% of yellow (on my gauge), as the ECU can control boost that low (the ECU can't control below base boost)...so my mosfets and BPC are good.
My boost gauge could be off - is the gauge (2000 93, T7) controlled electronically? What provides the closed loop feedback for the BPC (other than knock sensors) - where does the ECU get the pressure signal from? Am thinking the pressure transmitter could be on the fritz...giving incorrect boost pressure feedback that the ECU is controlling too.

thanks
Jay

 

[saab93se123]

base boost after CPS replacement

Well, I believe I can close the chapter on this troubleshooting thread. I chalk the issue up to resetting the ECU (battery was disconnected for CPS replacement). The CPU had to adapt. After many adaptation runs and several months of driving the car "hard", the boost is back. :cheesy:

Many thanks for all the help & support.

Jay

 

[rawill]

Great but,

That is very surprising. I mean that it took so long for the ECU to adapt.
I would not have expected it to take that long to adapt, and I can not see why changing the CPS would mean it needed to adapt.

I might ask ablout this on the Ecuproject as it seems odd to me.

/R
But it is good that it works well now, thanks for the post.

And I think that the T7 valve does not do anything when it is on a T7 car.
When we mod a T5 ECU for a T7 we change the idle maps to stop it rattling.
It is so noisy that if it did that in a T7 car, the owners would complain. Hence my reasoning that I think it does not do anything at idle, there will be no power on it at idle.

 

[saab93se123]

base boost after CPS replacement

When I replaced the CPS, I disconnected the battery...this reset the ECU. So, in hindsight, my thread header is misleading...but I originally thought the CPS was the issue and did not take into consideration the Trionic adaptation. I was surprised she was such a "slow learner" as well...but she eventually got the point by me repeatedly mashing the go pedal.

thanks
Jay