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Rough Idle on First Start
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poor-sche  



Joined: 06 Jan 2017
Posts: 73
Location: Los Angeles, CA

PostPosted: Wed May 06, 2020 1:57 am    Post subject: Rough Idle on First Start Reply with quote

Moved this conversation over from the "Wanted/For Sale" section. Figured this should be moved to this forum in case it may help someone in the future; assuming I fix my issue.

Trying to correct some nagging issues to make the car more reliable/"civilized". Ever since I purchased the car a few years back, I've had to modulate the throttle to keep it from dying on first start when the engine is cold. Press the pedal to the floor once, turn the key, modulate the rpms for the next 15-30 seconds. This is the usual routine or sheíll die. Afterwards, the car runs fine.

Performed a test on my cold start valve (CSV) and found it to be dead then moved onto other items based on the suggestion of others.


Quote pulled from "Wanted/For Sale" thread...
Fasteddie313 wrote:
...
Do a good proper CIS test..

The CSV helps it fire up in the first place like a choke and the AAV regulates the RPM up a bit like a throttle so it will idle good while it is warming up..
Thermotime switch tells the CSV what to do and when..
The WUR controls the fuel mixture through and after warmup..

Your problem sounds like the AAV also isn't working quite right..

I suggest just check everything completely, and ofcourse all your vacuum lines, and make it right once and for all..


I don't have my CSV hooked up to anything, don't use it, but sometimes when it is really cold I stick something in my airplate to prop it open a bit and prime the fuel pump up by turning the key on and off untill I hear my injectors spray a bit to give it a little shot of fuel, take the block out of the airplate, and then it will fire right up even if its extremely cold outside..

I don't use an AAV either.. I just modulate my throttle a bit until it idles nicely..
It's not all luxury automatic like, but I don't mind.. Adds to the experience..


I performed a bench test on the AAV by supplying 12v and it appears to be working fine, so I guess the next step would be to make sure power is being supplied to it through the harness.

As for the CSV, maybe I don't need it being I live in southern california, this car is garaged and almost never see temps below 60įF.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1970
Location: Somerset, UK

PostPosted: Wed May 06, 2020 4:47 am    Post subject: Reply with quote

Have you d a cold and warm pressure test? Results?
Have checked idle CO2, adjusted the fuel mixture and idle screw?
Have you freezer tested the AAV?
100% certain there no vacuum leaks
Injectors delivering all the fuel, spray pattern?
Plenty more on here http://www.924board.org/viewtopic.php?t=28790
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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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Then www.924board.org/viewtopic.php?t=31252
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poor-sche  



Joined: 06 Jan 2017
Posts: 73
Location: Los Angeles, CA

PostPosted: Wed May 06, 2020 8:26 am    Post subject: Reply with quote

Have you d a cold and warm pressure test? Results?
No, but will do soon and post results.

Have checked idle CO2, adjusted the fuel mixture and idle screw?
No, but just to be certain, are you only referring to the to mixture control screw on the fuel distributor and not the idle screw on the throttle body?

Have you freezer tested the AAV?
What's the freezer test? How do you perform it?

100% certain there no vacuum leaks?
I can't be 100% certain as I haven't replaced all the vac lines but my boost/vac gauge fluctuates between 18-22 in Hg at idle when warm.

Injectors delivering all the fuel, spray pattern?
I did this sometime last year and they all had what I would say to be a good consistent spray pattern. The car's behavior hasn't changed since then so I assume all is good there.
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poor-sche  



Joined: 06 Jan 2017
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Location: Los Angeles, CA

PostPosted: Fri May 08, 2020 12:36 pm    Post subject: Reply with quote

CIS pressure test results:

Ambient temp | 25C | 78F
System Pressure | 5.8 bar
Cold Pressure | 5.0 bar
Warm Pressure | 5.3 bar
Leak Test @ 10 min. | 2.0 bar
Leak Test @ 20 min. | 1.9 bar

So my cold and warm numbers are very high. Why is that?

My setup...

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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Fri May 08, 2020 1:44 pm    Post subject: Reply with quote

Could be the WUR or a flow restriction somewhere between the FD, WUR, and WUR return line..

You ever run Techron FI cleaner in the tank for a while?

Those high control pressure #s would make you lean, so don't go boosting hard on it like that..

ideola wrote:

Porsche 931 Series 1 (M31.01 & M31.02) Fuel System Specifications
Electric fuel pump Delivery rate: min. 1050cm3/30s
System pressure test value: 5.8...6.5 bar
Adjust, value: 6.0...6.3 bar
Control pressure cold (approx. 20į C): 2.0...2.4 bar
Control pressure warm: 3.45...3.85 bar
Leak test
Min. pressure after 10 min.: 2.0 bar
Min. pressure after 20 min.: 1.7 bar
Opening pressure of injection valves: 2.7...3.8 bar

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poor-sche  



Joined: 06 Jan 2017
Posts: 73
Location: Los Angeles, CA

PostPosted: Fri May 08, 2020 2:17 pm    Post subject: Reply with quote

Fasteddie313 wrote:
Could be the WUR or a flow restriction somewhere between the FD, WUR, and WUR return line..

You ever run Techron FI cleaner in the tank for a while?

Those high control pressure #s would make you lean, so don't go boosting hard on it like that..


No, I havenít run Techron cleaner in the tank. Before I do that, would disconnecting the lines and blow compressed air through them help?
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Fri May 08, 2020 11:37 pm    Post subject: Reply with quote

Maybe, but a stiff shot of techron is highly recommended for these CIS fuel systems.. Like a whole bottle to only a 1/4 tank of fuel..

Could jump the pump and let that circulate for a while and then drive on it easy for a while..

Then try your CIS test again..

When the tank gets really low it's a good time to pull the intank fuel pump and check it's screen for gunk, and changing the fuel filter is also a good idea..

To make sure everything is perfect you will eventually need a dwell meter and a timing light so keep an eye out for those if you don't have them already..
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poor-sche  



Joined: 06 Jan 2017
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Location: Los Angeles, CA

PostPosted: Sat May 09, 2020 12:42 am    Post subject: Reply with quote

I suppose it won't hurt to do both. I just happen to be at about a 1/4 tank so I'll go ahead and the techron. How long would you suggest running the "jumped" pump?

I'll be sure to check the in-tank pump screen.

I've got both a dwell meter and timing light but admittedly, I haven't used the dwell meter before.
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Sat May 09, 2020 2:10 am    Post subject: Reply with quote

Awesome.. You will be in great shape..

You could put a battery charger on it on low and run the jumped pump for a few hours, drive it a bit.. Let it sit for a day, jump it for another couple hours, drive it a bit..

If that doesn't clear up the fuel system then it's probably time for some parts or rebuilding parts.. Like the WUR..

With just the pump jumped fuel will constantly flow through the WUR path and go back to the tank..
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poor-sche  



Joined: 06 Jan 2017
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Location: Los Angeles, CA

PostPosted: Tue May 12, 2020 12:17 am    Post subject: Reply with quote

Here are my results after adding the Techron. I also drained the gas tank and cleaned the screen on the in-tank pump. Verified the injectors where shooting a good spray pattern with similar volumes between the 4.

CIS pressure test results (Round 2):

Ambient temp | 20įC | 69įF
System Pressure | 6.0 bar
Cold Pressure | 5.7 bar
Warm Pressure | 5.8 bar
Leak Test @ 10 min. | 2.1 bar
Leak Test @ 20 min. | 2.0 bar

So, it would appear to have not really helped. One additional thing of note is that I was measuring 9.4 v at both pumps while they're running. Is that correct?
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Tue May 12, 2020 1:52 am    Post subject: Reply with quote

Well, if you are sure you have you valve on your tester wide open for the control pressure test, it would seem that then next thing to do would be to remove the WUR and either replace it, or try taking it apart for a good cleaning the best you can and see if you can fix it that way..

Seems the electronic portion of your WUR is working but the valve and/or screen in it are likely plugged up with gunk or rusted or something..

They can be sent our for 'rebuilding" but who knows right now...

I'd try cleaning it myself if I was you, and if that doesn't work, I'll sell you my old WUR for less than a rebuild costs, if you want..

They are a little bit of a pain to remove but not too bad if you are good at doing things by feel..
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poor-sche  



Joined: 06 Jan 2017
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PostPosted: Tue May 12, 2020 2:46 am    Post subject: Reply with quote

Fasteddie313 wrote:
Well, if you are sure you have you valve on your tester wide open for the control pressure test, it would seem that then next thing to do would be to remove the WUR and either replace it, or try taking it apart for a good cleaning the best you can and see if you can fix it that way..

Seems the electronic portion of your WUR is working but the valve and/or screen in it are likely plugged up with gunk or rusted or something..

They can be sent our for 'rebuilding" but who knows right now...

I'd try cleaning it myself if I was you, and if that doesn't work, I'll sell you my old WUR for less than a rebuild costs, if you want..

They are a little bit of a pain to remove but not too bad if you are good at doing things by feel..


Unless my tester is faulty, not likely but you never know, the valve is definitely wide open. I'll remove the WUR then take and post photos. Thanks for the offer, I'll take it if cleaning mine doesn't work.

Any thoughts on the voltage readings at the pump?
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Fasteddie313  



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PostPosted: Tue May 12, 2020 3:22 am    Post subject: Reply with quote

The fuel pumps ground by the inside of the left rear taillight.. Could clean all those ground contacts, the contacts on the pumps, the fuse contacts, check your chassis battery grounds, positive battery wires to the starter and alternator and stuff are often degraded..

I have my fuel pumps powered and grounded straight to my battery (which is in the rear) through a dual/parallel relay circuit back there, switched from my MS..
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poor-sche  



Joined: 06 Jan 2017
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Location: Los Angeles, CA

PostPosted: Tue May 12, 2020 12:57 pm    Post subject: Reply with quote

Got it out and honestly didnít look too bad at first glance except there was only a screen inside one of the ports, is that correct? Tried removing the screen and f#@%ed it. I thought the screens should come out easily? Guess not. After damaging it, I figured what the hell and just went for it with a pair of locking forceps. Still canít get it out completely. Itís just tearing into small pieces.

Before


After


Guess Iím gonna need that WUR afterall.
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Wed May 13, 2020 1:09 am    Post subject: Reply with quote

You ever get into the round part from the backside?
Them metal shim looking diaphragm thing in there covering the fuel passage holes is where it would probably gunk up..

The screen is only on the in flow side..
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