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11-18-2013, 09:49 AM
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#1 |
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Registered User
Join Date: Sep 2012
Location: Neeses SC
Posts: 66
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dieseling problem
Ok i have a 1986 chevy k10 with a stock 98 vortec 350with the stock q-jet carb. The engine ran fine on my engine stand but i didnt run it a long period of time because i didnt have a good cooling system on it. But once i got it into my truck and ran it for a while it started dieseling once it ran for a while. So i dont know whats goin on with. Anybody had this problem before?
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11-18-2013, 10:01 AM
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#2 |
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Registered User
Join Date: Jun 2010
Location: Upland Ca
Posts: 4,141
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Re: dieseling problem
Does this mean it runs on after you turn the ignition off? If yes, the most common cause of this condition is to high an idle. What is your idle set at?
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1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703 |
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11-18-2013, 01:33 PM
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#3 |
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Active Member
 
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
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Re: dieseling problem
Overheating and carbon buildup can also cause it to diesel.
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68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... |
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11-18-2013, 03:51 PM
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#4 |
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*** That's interesting ***
Join Date: Oct 2008
Location: Pittsburgh, PA
Posts: 2,772
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Re: dieseling problem
Yep, check idle first. If carb is propped open too far by the idle stop, run-on can easily happen. But if you starve the engine of air/fuel mixture by allowing the butterflies to close all the way, it can't run-on.
If you find that your idle stop is set too high, here are some suggestions to bump your idle without needing to raise the idle stop on the carb: 1) Back off the idle stop screw a turn or two. Set it by eye so it looks like butterflies are closed properly. Make sure truck will idle in park without stalling (shoot for 500 RPM in this step). 2) Use a vacuum gauge, adjust the idle mixture screws to achieve highest vacuum at idle. If you don't have a vac gauge, set it by highest idle RPM, then buy a vac gauge later and use it! 3) Set timing to have a higher initial advance at idle (disconnect and plug vacuum advance). Ideal should be 8-12 degrees advanced base timing at idle. 4) Reconnect vacuum advance to full manifold vacuum. Idle should bump up -- assuming vac advance is working properly! These steps should increase your idle quite a bit without needing to bump up the idle stop screw. In fact, you may have to LOWER your idle stop once you do these steps. Ideal RPM should be 650-800 RPM in park. It may drop as low as 500 in gear, which is fine depending on your setup. You may need to tweak the idle stop one or two more times to get it dialed in after a few test drives. But this will get you going and hopefully stop the run-on. If that doesn't help, then there could be other issues like vacuum leaks, running too hot, or excess carbon as previously suggested.
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Tom  Chevy by day... 1969 Chevy C30 Rollback Tow Truck -- 383 stroker, 4L80E 2011 Chevy Caprice PPV 9C3 6.0L 1995 Chevy Caprice 9C1 1994 Chevy Caprice 9C1 #3 1995 Chevy Caprice Wagon #2 1995 Chevy Impala SS Mopar by night... 1969 Dodge Charger 1972 Chrysler Newport 2dr Hardtop (27K miles) Plus others... Last edited by storm9c1; 11-18-2013 at 04:00 PM. |
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