81 surging issue
Thread Starter
Racer
Joined: Mar 2018
Posts: 390
Likes: 50
From: wilmington Ma
81 surging issue
81 corvette surge driving steady speed , code 45 rich exaust , mc dwell 55ish if I open a large vacuum hose the mc starts to go down close to single numbers o2 goes to 1000, I dont feel like its a computer related issue ... before I go crazy any thoughts on a metering rod issue in the carb ? Only surges at steady speed not idle and it does smell a little rich ...
Racer
Joined: May 2018
Posts: 297
Likes: 43
the 81 uses both the tps and iac sensors to control mix but the cpu only controls this at idle position, if the tps is reporting the throttle is at idle when your actually past idle then the computer will try to take over mix, the o2 sensor can also be sending bad info. past that and assuming its not ignition coil or module it could be a leaky vac line somewhere most especially in the dizzy advance.
Thread Starter
Racer
Joined: Mar 2018
Posts: 390
Likes: 50
From: wilmington Ma
Thanks for the replie , maybe I should have mentioned all sensors are in range , I dont beleive the o2 is giving bad reading I can smell a little rich odor and the readings indicate a rich mixture , tps,baro,map,o2, mc, all in range doing tests . Only other thing I thought of besides a metering rod I should check the evap purge to make thats not an issue. This carb does not have an iac thats for fuel injection.
Thread Starter
Racer
Joined: Mar 2018
Posts: 390
Likes: 50
From: wilmington Ma
Racer
Joined: May 2018
Posts: 297
Likes: 43
81 uses a e4me carb, Idle Mixture Control Solenoid not iac, thanks for the correction said one thing was thinking of another. heres a couple links on the e4me but you stated all sensors in range so I dont know if any of these will help, because if you know the range and have checked them you know about the carb. if all the electronics are good only other thing it can be is dizzy related because issue is not constant but rather sounds rpm based.
http://www.early3rdgen.com/forum/viewtopic.php?t=25
the second link user also has rich problem, maybe worth reading.
https://cliffshighperformance.com/si...p?topic=1814.0
http://www.early3rdgen.com/forum/viewtopic.php?t=25
the second link user also has rich problem, maybe worth reading.
https://cliffshighperformance.com/si...p?topic=1814.0
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Racer
Joined: May 2018
Posts: 297
Likes: 43
diagram says to test from mc soloniod, however the 81 has diagnostic link that does the same thing no need to fart making an adapter to fit the mc plug. the diagnostic link is the single orphan wire coming out of the harness alongside the passenger side valve cover, just slightly forward of carb and towards the overflow bottle. its usually green.
Thread Starter
Racer
Joined: Mar 2018
Posts: 390
Likes: 50
From: wilmington Ma
damm car ran so good forgot thats going to happen today
Race Director
Joined: Jul 2004
Posts: 12,686
Likes: 329
From: Scottsdale Arizona
it was quite advanced when the surging occurred. You’re kind of stuck on the stock 81s with measuring advance at idle with the plug disconnected, but I recall having issues above 12 degrees advance. Other than the surging, it ran great.
Last edited by CA-Legal-Vette; Aug 11, 2018 at 12:09 PM.