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Loosing power/boost after driving after an hour or more
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chuck21401  



Joined: 20 Feb 2005
Posts: 244
Location: Annapolis, MD

PostPosted: Tue Jun 18, 2019 11:17 am    Post subject: Reply with quote

Fasteddie313 wrote:

13 is a little high. 14psi @ 13s AFRs and no intercooler sounds a bit dangerous..

If their is no boost controller on your WasteGate you might have a sticky WG..

Pull the WG line off your upper charge tube and hit that like with like 15-30psi of compresed air a bunch of times to open and close the WG and exercise it. That might loosen it up..


Thanks for that tip. I did that a couple of times...didn't change anything.
I'm not sure, but I don't think the problem is a sticky wastegate....I understand that it was rebuilt at the same time the turbo and engine were overhauled along with a new diaphragm.

Consistently seeing 13psi on the boost gauge. The AFR readings under boost are low 13s but also dipping into the 12s. I brought my 9yr old helper with my and told him to watch the gauges closely. I think I might set up my go pro next. Too difficult to drive at full boost and look down.

Quote:

I would also set your AFR screw with the dwell meter method to about 40-45 on the scale which might get your AFRs down if that is the problem.. Also test your TB microswitches while you are doing that..
You didn't happen to set your AFR screw with your WBO2 gauge did you? That is not a good idea if your lambda system is running..

Other than that a full CIS test and test that your WUR is dropping control pressure when pressure is applied to its port..


Thanks for those suggestions. I'm busy learning so no sure how to do all of that....I'll have to take the car somewhere to someone that knows what they are doing. I do know that that lamda system is not running...so that's another complication. Think I will start with buying a dwell meter.

Quote:

Are all those little vacuum lines from your TB circled in yellow to your WUR and stuff new?


I'd say that most of the vacuum lines are new. I have not yet traced the line back to the wastegate -- maybe it's pinched but I seem to doubt it.

Quote:

Does your WBO2 have any sort of calibration procedure?


I do not know but will look into that as well.
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1981 Porsche 931


Last edited by chuck21401 on Wed Jun 19, 2019 6:28 am; edited 2 times in total
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chuck21401  



Joined: 20 Feb 2005
Posts: 244
Location: Annapolis, MD

PostPosted: Tue Jun 18, 2019 11:38 am    Post subject: Reply with quote

I did manage to get the boost gauge installed so here are some pictures for others that may go down this road.

I went with the VDO Vision boost/vacuum gauge (model 150 121). I found several sources online but with late shipping dates. I found a seller on Ebay with the gauge for just under $62 including shipping and the tubing kit.
Here's the link on the VDO page: https://www.vdo-gauges.com/instruments-displays-and-clusters/by-type/boost-turbo-vacuum/vision-black-30-hg-25-psi-turbo-gauge-12v.html

I considered buying a vintage gauge (see: https://www.ebay.com/itm/VDO-NOS-52mm-Turbo-Boost-Vacuum-Gauge-Porsche-911-930-Turbo-accessory/153448690047?hash=item23ba41317f:g:4DkAAOSwXm9csBjC) but it was just too expensive.

Anyway, I read through the forums and found different routes for the tubing. I decided to go through the heater blower area.

Here's the connection of the tubing to the port after the throttle body. This port was not being used. I bought some crappy connectors from Pep Boys - if anyone has a better solution I would be interested....the tubing kit didn't include the right connector.



I went through the grommet behind the distributor near the battery



The heater blower is held in place by three plastic connectors. I pulled one out and replaced it with a grommet and ran the line through that. Although my car is far from original I didn't want to drill another hole.



I fed the line through that hole and put a flashlight behind it. Once I pulled the glove box it was easy to find the line.

Disassembling the center console to get to the gauges was a bit tricky. The two screws at the top are obvious...in my case the same screws at the bottom were missing...but the gauge pod is also held in with some plastic clips. My advise is just to go slow.



Here is the final result. The dimmer switch works fine; I need to get a green bulb cover to better match the other green gauges...well...except for the AFR meter.


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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1986
Location: Somerset, UK

PostPosted: Tue Jun 18, 2019 5:16 pm    Post subject: Reply with quote

12psi is 0.82bar. This is circa 0.2bar over boosting to stock. I'd expect to see AFR's from a stock set up + WUR circa 10's. 13's is too lean given the boost and no IC. Check the boost line is attached to the WUR so triggering boost enrichment from the WUR. You need to be richer to cool the combustion and avoid det

Do you know if your pistons are the lower compression S1's or higher compression S2's?

At high rpm and above numbers, you may be close to detonation if timing is too advanced. More so if higher compression S2 pistons and ambient and intake air temps are warm.
_________________
1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1999
Location: MI

PostPosted: Tue Jun 18, 2019 11:40 pm    Post subject: Reply with quote

chuck21401 wrote:

Thanks for those suggestions. I'm busy learning so no sure how to do all of that....I'll have to take the car somewhere to someone that knows what they are doing. I do know that that lamda system is not running...so that's another complication.


There you go, that's why you are lean, one good reason atleast..

The lambda system NOT running at all is full lean via minimum differential chamber pressure..

Fasteddie313 wrote:
The results are in..

All of these numbers are with the airplate at 100% travel and full flow, per injector..

103 psi system pressure

Frequency valve full closed/unplugged
76.5 grams in 30 sec

Frequency valve plugged in and running as default (can measure actual duty cycle later)
102.53 grams in 30 sec

Frequency valve full open, +12v constant
163.97 grams in 30 sec

Frequency valve full open, +12v constant @ 89 psi system pressure (removed my bump shim)
159.53 grams in 30 sec


Makes for a big difference.. You are missing like 25% of your fuel at a given airplate position..

You need to fix your lambda system or control it otherwise somehow..
I or others have all lambda system parts so you can get them if you want to fix it..
Or you can control it with Megasquirt, but with a lot of wiring and stuff..

That frequency valve needs to be running though, aleast in WOT mode (WOT swich) or failsafe mode (O2 unplugged), both give around 50% or something..

Max lean on the diff pressure ain't gonna cut it..


I don't know about your overboosting.. Maybe your WG is modified somehow or something..
It would be fine with an IC or meth kit, and proper AFRs..

What is your goal for the car?
Better get those AFRs under control before ya blow it up though..



chuck21401 wrote:
I'll have to take the car somewhere to someone that knows what they are doing.

I'm not sure if this is a realistic solution to be honest..
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bureau13  



Joined: 07 Sep 2017
Posts: 281
Location: South Florida

PostPosted: Wed Jun 19, 2019 12:56 am    Post subject: Reply with quote

Interesting, I didn't realize the lambda system did anything but run closed loop for better mileage during cruise.

If I unplug my O2 and run in failsafe mode, does that give me all the fuel under boost that I should have? You said something about 50% but I wasn't sure what that meant...
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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morghen  



Joined: 21 Jan 2005
Posts: 8180
Location: Romania

PostPosted: Wed Jun 19, 2019 1:25 am    Post subject: Reply with quote

bureau13 wrote:
Interesting, I didn't realize the lambda system did anything but run closed loop for better mileage during cruise.



haha, how do you think it does that?
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bureau13  



Joined: 07 Sep 2017
Posts: 281
Location: South Florida

PostPosted: Wed Jun 19, 2019 1:35 am    Post subject: Reply with quote

On this car, I have no idea, really. CIS is pretty much magic to me. But that's mainly what it does on my 928, and you can unplug the sensor there and I don't think it will do anything to WOT operation. Completely different animal, with the electronics in that car, of course...

morghen wrote:
bureau13 wrote:
Interesting, I didn't realize the lambda system did anything but run closed loop for better mileage during cruise.



haha, how do you think it does that?

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1986
Location: Somerset, UK

PostPosted: Wed Jun 19, 2019 1:40 am    Post subject: Reply with quote

bureau13 wrote:
On this car, I have no idea, really. CIS is pretty much magic to me. But that's mainly what it does on my 928, and you can unplug the sensor there and I don't think it will do anything to WOT operation. Completely different animal, with the electronics in that car, of course...

morghen wrote:
bureau13 wrote:
Interesting, I didn't realize the lambda system did anything but run closed loop for better mileage during cruise.



haha, how do you think it does that?


And no on boost enrichment required on a 928
_________________
1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252
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bureau13  



Joined: 07 Sep 2017
Posts: 281
Location: South Florida

PostPosted: Wed Jun 19, 2019 1:43 am    Post subject: Reply with quote

That's true. I guess I was thinking the flow of air was being metered and wasn't expecting the lambda system to have anything to do with that.

Is there a good writeup somewhere that details this? Apparently I need more learnin'

Carrera RSR wrote:

And no on boost enrichment required on a 928

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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bureau13  



Joined: 07 Sep 2017
Posts: 281
Location: South Florida

PostPosted: Wed Jun 19, 2019 1:50 am    Post subject: Reply with quote

OK I apologize for derailing the OP's thread here a bit, but unless this is wrong, I don't see how the lambda sensor has anything to do with fuel mixture under boost:

"Lambda only operates at idle (after warm-up) and at steady part-throttle. At all other times, it comes out of that "closed-loop" control and the mix is controlled mechanically by the fuel distributor and WUR. In addition to the temperature-dependent control that all WURs exert, the 931 WUR has full throttle enrichment that enriches the mix when manifold pressure is high (while under boost by the turbo)."

bureau13 wrote:
That's true. I guess I was thinking the flow of air was being metered and wasn't expecting the lambda system to have anything to do with that.

Is there a good writeup somewhere that details this? Apparently I need more learnin'

Carrera RSR wrote:

And no on boost enrichment required on a 928

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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chuck21401  



Joined: 20 Feb 2005
Posts: 244
Location: Annapolis, MD

PostPosted: Wed Jun 19, 2019 2:08 am    Post subject: Reply with quote

Fasteddie313 wrote:

There you go, that's why you are lean, one good reason atleast..
The lambda system NOT running at all is full lean via minimum differential chamber pressure..
Makes for a big difference.. You are missing like 25% of your fuel at a given airplate position..

You need to fix your lambda system or control it otherwise somehow..
I or others have all lambda system parts so you can get them if you want to fix it..
Or you can control it with Megasquirt, but with a lot of wiring and stuff..

That frequency valve needs to be running though, aleast in WOT mode (WOT swich) or failsafe mode (O2 unplugged), both give around 50% or something..

Max lean on the diff pressure ain't gonna cut it..


I did read about the lambda system in a number of threads. As I was under the dashboard last weekend I found the control box; need to check to see if the wiring is in tact.

Quote:

I don't know about your overboosting.. Maybe your WG is modified somehow or something..
It would be fine with an IC or meth kit, and proper AFRs..


Intercooler could be an option; I've been reading about various installation options. I'd prefer not to run a hood scoop, I like the NACA duct.

Quote:
What is your goal for the car?


Goal is to have a fun car to drive on the back roads and occasionally autocross for fun. Also wanted something interesting...I've owned a 944, 944 turbo and a 968. The driving experience in the 931 feels a lot more "engaged" if that makes any sense.

Maybe another option is to dial back the boost?

Quote:
Better get those AFRs under control before ya blow it up though..

Good point and appreciate everyone's feedback.

Quote:
I'm not sure if this is a realistic solution to be honest..

Well with a project car I'm not in a huge rush....will have to continue my research and learning. What is the best resource on the lambda system? The factory workshop manuals?
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chuck21401  



Joined: 20 Feb 2005
Posts: 244
Location: Annapolis, MD

PostPosted: Wed Jun 19, 2019 2:18 am    Post subject: Reply with quote

Carrera RSR wrote:
12psi is 0.82bar. This is circa 0.2bar over boosting to stock. I'd expect to see AFR's from a stock set up + WUR circa 10's. 13's is too lean given the boost and no IC. Check the boost line is attached to the WUR so triggering boost enrichment from the WUR. You need to be richer to cool the combustion and avoid det

Do you know if your pistons are the lower compression S1's or higher compression S2's?

At high rpm and above numbers, you may be close to detonation if timing is too advanced. More so if higher compression S2 pistons and ambient and intake air temps are warm.


I believe that the pistons are s1 (1980 engine) but don't know for certain. Will check out the WUR connection...though as noted above...having the lambda system disconnected is another factor.
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1999
Location: MI

PostPosted: Wed Jun 19, 2019 6:22 pm    Post subject: Reply with quote

It's complicated...


The lambda system has control of the lower chamber pressure in the fuel distributor. 5

When pressure is reduced in the lower chambers it created a larger gap for fuel to flow up the injector outlets. 10

The lambda system by default runs the frequency valve at about 50% or something.
The throttle body has 2 switches on it of the lambda system.. An idle switch and a WOT switch.. At idle the system tries to adjust the fuel mixture to get the O2 sensor to read stioch. At WOT it drives the frequency valve at like 65% duty cycle..

Without it running at all, the frequency valve is at 0% so it is closed giving high lower chamber pressure and therefore less fuel at the same airplate position compared to as if the frequency valve was running in any working state lowering the lower chamber pressure to let more fuel flow out the injector outlets..
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1986
Location: Somerset, UK

PostPosted: Wed Jun 19, 2019 9:43 pm    Post subject: Reply with quote

Glad we don't have this added complication on RoW cars.......and we get more power!
_________________
1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
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bureau13  



Joined: 07 Sep 2017
Posts: 281
Location: South Florida

PostPosted: Wed Jun 19, 2019 10:56 pm    Post subject: Reply with quote

That is very helpful! Thanks for posting that.

I stand by my claims that it's all magic

Fasteddie313 wrote:
It's complicated...


The lambda system has control of the lower chamber pressure in the fuel distributor. 5

When pressure is reduced in the lower chambers it created a larger gap for fuel to flow up the injector outlets. 10

The lambda system by default runs the frequency valve at about 50% or something.
The throttle body has 2 switches on it of the lambda system.. An idle switch and a WOT switch.. At idle the system tries to adjust the fuel mixture to get the O2 sensor to read stioch. At WOT it drives the frequency valve at like 65% duty cycle..

Without it running at all, the frequency valve is at 0% so it is closed giving high lower chamber pressure and therefore less fuel at the same airplate position compared to as if the frequency valve was running in any working state lowering the lower chamber pressure to let more fuel flow out the injector outlets..

_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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