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maxiblu
Joined: 31 Oct 2005
Posts: 23
Location: Hobart, In
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 Posted: Mon Dec 17, 2007 12:28 am Post subject: 1980 931 idle mixture problem |
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I have a 1980 931 that runs great when cold, has a hot start problem, runs rich after arting hot, and the idle mixture (CO) changes while on my exhaust gas analyzer. I can set the idle mixture to the range specified in the manual (.5 to 1.0 CO) and let the car idle for a few minutes, rev it a few times, and when the car comes back to idle, the idle mixture will read much higher CO (5.0 to 8.5). I don't have CIS guages but suspect the problem is control pressure. My question is: (1) - could this be a fuel accumulator problem, (2) - a control pressure regulator problem, (3) - a fuel pump problem, (4) or something else to cause me to lose sleep over? I searched thru previous posts but didn't see anything that covered this. Thanks
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1980 931
1984 944
1975 MGB
1973 MG Midget H Prod |
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maxiblu
Joined: 31 Oct 2005
Posts: 23
Location: Hobart, In
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| Posted: Mon Dec 17, 2007 7:18 am Post subject: idle mixture |
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Sorry, forgot to say the oxygen sensor, computer and frequesncy valve have all be disconnected in trying to isolate this problem. thanks
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1980 931
1984 944
1975 MGB
1973 MG Midget H Prod |
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RonDwyer82-931
Joined: 10 Sep 2007
Posts: 35
Location: San Leandro, Ca.
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| Posted: Sun Dec 30, 2007 9:59 am Post subject: |
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I discovered a lot of things bringing my basket case back to life. The sensor plate assembly in the fuel metering housing can stick if there is any corrosion or varnishing on any of the surfaces. A bit of steel wool and carb cleaner. Another area was disconnected hoses, like the one that vents the crank case to the air housing was not yet connected. Valves were out of adjustment too. It takes time, but focusing first on the basics like verifying all of the components are functional is necessary. You may even need a warm-up regulator. It too is connected to the intake with a vacuum line. I believe it has a dual function to alter the mixture under load when cold. Replace all vacuum elbows, hoses and boots. Even the one on the crankcase vent. ALL HOSES. By this time you will run out of things to fix. Save the regulator for last.
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82 931 mostly new |
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RonDwyer82-931
Joined: 10 Sep 2007
Posts: 35
Location: San Leandro, Ca.
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| Posted: Sun Dec 30, 2007 10:01 am Post subject: |
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And I put in a new frequency valve. They can be bought quite inexpensively, but you will need to put the old fitting ans new plastic hose on the new one. Takes a special CIS tool.
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82 931 mostly new |
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Rasta Monsta
Joined: 12 Jul 2006
Posts: 11733
Location: PacNW
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| Posted: Tue Jan 01, 2008 3:34 am Post subject: |
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Ron, selling your baby, eh?
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Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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John Brown
Joined: 07 Nov 2002
Posts: 903
Location: Leesburg VA
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| Posted: Thu Jan 03, 2008 2:32 am Post subject: Re: idle mixture |
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| maxiblu wrote: | | Sorry, forgot to say the oxygen sensor, computer and frequesncy valve have all be disconnected in trying to isolate this problem. thanks |
The O2 sensor can be disconnect. But you need to have the frequency valve working. That fuel distributor is designed to have at least the fixed bleed provided by the frequency valve. Without it the mixture adjustment must be cranked way off 'center' and then will not be correct through the range. Also the frequency valve provides enrichment at WOT and acceleration.
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John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82 |
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John Brown
Joined: 07 Nov 2002
Posts: 903
Location: Leesburg VA
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| Posted: Thu Jan 03, 2008 2:35 am Post subject: Re: 1980 931 idle mixture problem |
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| maxiblu wrote: | | I have a 1980 931 that runs great when cold, has a hot start problem, runs rich after arting hot, and the idle mixture (CO) changes while on my exhaust gas analyzer. I can set the idle mixture to the range specified in the manual (.5 to 1.0 CO) and let the car idle for a few minutes, rev it a few times, and when the car comes back to idle, the idle mixture will read much higher CO (5.0 to 8.5). I don't have CIS guages but suspect the problem is control pressure. My question is: (1) - could this be a fuel accumulator problem, (2) - a control pressure regulator problem, (3) - a fuel pump problem, (4) or something else to cause me to lose sleep over? I searched thru previous posts but didn't see anything that covered this. Thanks |
1) no
2) absoutely
3) unlikely
4) yes
One more time with feeling: There is NO WAY to diagnose a CIS without investing $100 bucks in a fuel pressure gage.
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John
80 931 - #931 44Cup
99 Escalade - tows track cars
gone but not forgotten: original 924.org car - 82 |
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GP924
Joined: 16 Jan 2006
Posts: 34
Location: Grants Pass, OR
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| Posted: Mon Jan 07, 2008 8:34 am Post subject: Similar experience |
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I had a similar experience just before the diaphragm in my fuel distributor went bad. Could not get the idle correct but got it pretty close. Then over a matter of days the diaphragm disintregrated.
Took me several months and a lot of help from members of the board to determine it was the diaphragm. One of the members sent me material (see old posts) and I was able to rebuild mine.
It may not be your diaphragm going bad but it is possible and you can rebuild this yourself if you wish or spend several hundred having it rebuilt. |
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