LAracer

Hi all.

I've posted this problem before, but now I have some good info to help visualize what's going on. Basically, my transition is late, and my primary drops off before transition. I thought these were just symptoms of my high altitude (7000ft), but I was told this is not the case.

Here's the "detailed info". It's plots of the pressure/vacuum at each of the valves/actuators during transition:

http://www.geocities.com/laracers_vr_r1/boost_plots

I know this is alot of information, and I realize it may take a while to look at all those plots and help me figure out what's going on, but you guys are my only hope - I'm too far away from any rotary shops.

Any help is appreaciated .

phil

LAracer

ok, I've been looking at those plots for a while, and it seems to me like maybe everything is working normally, just 500-1000rpms late.

Some of the valves (PC, WG) look like they don't open when comparing the pressure it took to open the valves manually to the pressure they see during transition, but I think the valves may require less pressure during actual operation because there is also pressure on the flap of the valve (from the air coming out of the compressors) that I didn't take into consideration (this must be true because I know the PC and WG are working since I see the difference when I play with the needle valves).

Anyone see anything else in these plots?

LAracer

anyone?

rookie7

I've done similar tests with my car, but I only tested the PC and WG. The PC switches at about 4500 rpm's in all gears, by switching I mean it goes from duty control to fully closed(wide open gate). The pressure measured right before the PC solenoid went from about 5 psi during duty control to about 11 psi at 4500 rpm's to redline. I used a defi boost gauge with playback so it was easier to read after I did the run.
The wastegate opens at different rpm's depending on what gear your in. The solenoid starts off full voltage (open solenoid, closed wastegate) and transitions like this:
1st gear wg closed all the way to redline (solenoid full voltage, solenoid open)
2nd gear solenoid duty control at about 5700 rpms
3rd gear solenoid duty control at 5000 rpms
4th gear solenoid duty control at 4500 rpms

I never tested the CCA or TCA, but my transition is pretty much at 4500 rpm although during some of the runs it did seem to me that it was happening late at 5000 rpms by I attributed it to a delay of me reading the tachometer.
I hope this helps and it's not to confusing.
By the way I have a stock 95 BB

LAracer

Great info rookie7. Thanks .

So it lookes like my PC is "switching" at 5500rpm, about 1000rpm late. I would guess that the same is true for the CCV (Primary side), but if anyone has data on that particular valve, please share.

Anyone know what the reason might be for the PC and CCV switching late?

LAracer

Could it be the ecu that causes the solenoids to switch late? Is there any way to adjust this? Would the ecu delay the transition because of the high altitude? I read here that the ecu senses and corrects for altitude - could this be part of it?

something else maybe?

LAracer

Ok, here are some other ideas:

Maybe the drop in boost before transition causes the transition to happen late (I don't really see how, but it's just a thought). Or maybe it's the late transition that makes it look like the boost is dropping, i.e. if transition occurred at 4500rpm, I probably wouldn't even notice the drop in boost before that.

Or maybe the ecu is seeing a different rpm than the tach. I think I asked about this before, but maybe in this context it might make more sense.

What do you guys think about these theories? Don't be shy! give me your $.02 .

13brv3

You seem to be talking to yourself again

Haven't you had a chance by now to get that thing down to sea level to see if altitude has anything to do with your odd transition? I've done a lot of theorizing about altitude effect since the last thread I participated in. I still think it's impossible to say what the ECU will do unless you can decode the programming. Maybe it will shift the transition???

BTW- the plane will be flying in a couple months, and I did install the turbo. I'll know a lot more about altitude effects soon enough, but that still won't help with your FD issues.

Good luck,

LAracer

Hehe, I always seem to talk to myself - can you tell I didn't have many friends in high school .

No, I haven't driven down to sea level yet - the car only has 22k miles, so I'm very reluctant to put an extra 1k on just to solve this problem (I know, I know - it's a car, just drive it, right). Also, after all the thinking I've done on this problem, it's almost cheating to test it at sea level - I have to find the answer!

and...thanks for the bump .

FDjunkie

I'm certainty no expert, but from my reading the FD's ECU controls the transition RPM. What I read in your test results seems to say that your ECU is operating the correctly valves and is controlling of transition; except for RPM. So this has me asking (1) if you've verified the accuracy of your tach, and/or the crankshaft pickup and wiring systems, and (2), have you tried to swap out the ECU with another unit?

One other point. I see one one chart where your primary boost is falling off even before what we call the 'normal' transition RPM. Since the control systems require boost pressure to help achieve quick transition, could the dropp in PSI also be slowing transition switchover timing so much that it appears to be an RPM issue.

LAracer

Good points FDjunkie, and thanks for taking the time to look over those plots .

I don't *think* that the drop off before transition is the sole reason for the late transition, but I don't really know how to make sure of this. If I could keep the boost steady until transition, I would know for sure (maybe an electric boost controller on the PC line - but that's $$$). On the other hand, before I installed the home depot boost controllers, primary boost was 13psi, dropping to 10psi before transition, and the transition was still at 5500rpm. So I think maybe that's enough info to conclude the drop in pressure is not causing the late transition (???).

I haven't verified the accuracy of the tach, it certainly feels like 5500rpm when the tach says 5500, but I don't know for sure. How would I go about checking the tach?

I would *love* to install another ecu just to see what happens, but I don't have access to one. I could buy one (or just an afermarket one), but as you've probably guessed, I'm trying not to spend too much money diagnosing this problem (If I new for sure the ecu was messed up I would drop the cash no problem). Anyone have an old stock ecu that they want to part with for cheap?

LAracer

NEW INFORMATION!!!

I pulled the engine codes (check engine light was not on, but I figured, what the hell). I got:

13 - pressure sensor
16 - EGR valve (California only)

Now, these may be from old problems and just the service codes weren't cleared, but that #13 sure does look suspicious. I think I actually tested the pressure sensor. The voltages were slightly off, but I figured it's just the altitude so I didn't worry too much. I need to check it again. Meanwhile, does anyone know what the results of the pressure sensor test should be at 7000ft?

Not sure about #16. The car was originally bought in CA, so it might be relevent. I'll do a search, but if anyone knows anything about it, feel free to chime in.

LAracer

Well, looks like I'm talking to myself again . No problem.

Results of pressure sensor test:

Correct voltage when vacuum applied
Voltage about 15% low when pressure is applied - numbers below

pressure(psi)........voltage(V)
17...........................4.22
15...........................3.95
14...........................3.85
12............................3.6
11............................3.5
10............................3.4

The shop manual says I'm supposed to get 4.35-4.65V at 14.3psi (98.7kPa)

Anyone care to do the same test and compare?

Also, if the ECU says the pressure sensor is bad, what is it using to make this decision? How does it know?

Engberg

Wow, still working it out. I'm impressed by your determination and scientific method of solving this problem. If it matters at all, I tried pulling ECU codes as well and got nothing. So I think our problems are a bit different. But an aftermarket boost controller like the Apex'i AVC R comes with a new pressure sensor no one likes spending money without justification. I did not get mine installed like I had planned...go figure. I got offered an internship in the auto industry out in California and am scrabbling to get my butt out of boulder. I will have the car at sea level in July, will come back and get then, and if you are still having the problem I'll let you know if the boost pattern changed.

cymrex

iTrader: (2)

I live at 8111 feet and have the same late transition. I bought my car in Miami at sea level and it had a 12-10-12 pattern with transition at 4500 rpm. When I got home it had a 15-6-15 pattern with transition at ~5000. These are both according to the boost gauge and the tach. This is also with the same pills in the line. When I asked around I was told that this was normal at altitude. I looked up pressure at alititude and on a reference day like 70F 29.92 inHg, 14.7 psi, my pressure at 8111 ft at the same temp should be 22.18638897875615 inHg, 10.89704763200203831041257367387 psi. So since the MAP sensor is Manifold Absolute Pressure it is giving me the same absolute pressure eventhough I am at altitude. The map sensor is trying for 12 (my sea level boost) + 14.7 (atmospheric pressure at sea level) = 26.7 absolute. The boost gauge at sea level is showing 26.7 (MAP sensor target) - 14.7 (Atmospheric pressure at altitude) = 12.0. The boost gauge at alititude is showing 26.7 (MAP sensor target) - 10.89704763200203831041257367387(Atmospheric pressure at altitude) = 15.8= ~15 I observe. This is working the turbos much harder at altitude since the pressure ratio is higher 26.7/10.9 = 2.44 at altitude where it was 26.7/14.7 = 1.82 at sea level. So it is good you lowered your boost.

Remember, your pressure guage you are using to apply the pressure to the MAP is probably also referenced to atmopheric pressure so that would explain your 15% difference.

LAracer

Engberg: Congrats on getting such a cool internship - is it engineering? Mechanical?. I'd be very interested to hear how your boost pattern changes when you get down to sea level.

cymrex: Wow! I knew if I talked to myself long enough someone would eventually answer . If your transition is late then I think I don't have anything to worry about (woohoo!). I'm so glad. My car may actually be normal (what a shame it's in my garage in about 100 pieces ). Thanks so much for your input - in case you hadn't noticed, I've been trying to get to the bottom of this for a long time.

If anyone else has any boost-at-altitude experiences to share, please speak up.

Thanks everyone that helped.

Now, all I have to do is figure out that EGR valve...

13brv3

Glad to hear this is "normal" at altitude. Of course it's too bad you still can't explain WHY the transition is late. Go ahead and quit though. You don't really NEED to know. Just because you're an engineer, it doesn't mean you HAVE to obsess over this. Just forget about it

LAracer

Obsess? Me?

Well, it would be nice to know why, but there are enough things that I don't understand about this car that I can just add this to the list and forget about it. Maybe.

Thanks for all the help guys .

LAracer

Just adding a data point to this thread - I talked to someone in Boulder (5800ft) and he also experiences late transition ("after 5k rpm").

I'm still always happy to hear from anyone at altitude .