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Bracket Talk Bracket Talk Forum Tech Talk - by Abruzzi Q: SBC engine run-on/dieseling, and Top Tier gasolineGo | New | Find | Notify | Tools | Reply | |
| Q: SBC engine run-on/dieseling, and Top Tier gasoline | Login/Join |
DRR Trophy |
I've been working on my old '90 Chevy C3500 tow rig, preparing to tow 350 miles for the NHRA Div. 5 Finals. Last night I had a couple bad episodes where the engine was warm and would not shut completely off, stuttering and stammering. For nearly a minute, before it finally stopped with a big puff of white smoke from the carb. I called a Chevy mechanic buddy of mine and he suggested first to check for a loose timing chain. I put a wrench on the harmonic balancer bolt and found I could get no more than at best 1/2" of free play. Okay, good there I guess. One internet article suggested carbon build up in the cylinders, causing hot spots that can ignite fuel. The recommendation was to de-carbon the cylinders and/or try running Top Tier (TM) gasoline. This morning I removed the cheap 10% ethanol fuel and put in some non-ethanol premium pump gas that I use in my race truck. That fuel is likely not the so-called "Top Tier" gas. After running the truck around town and returning home, it seemed to work okay now, shutting off with the key switch. I do plan to try to de-carbon the cylinders as well, with spraying a bit of water or Sea Foam down the carb while running. And checking and cleaning the plugs. My C3500 tow rig BTW has a HEI distributor, a Holley carb, and a stock, mechanical fuel pump. The truck does have an electric fan, but I hadn't turned it on before the run-on issue. It does use about a quart of oil in 100 miles, mostly I think going out the rear main seal. But some of it does cause baked-on deposits on a couple of the plugs in time. (I am saving for a newer rig) Heck, I'd never heard of "Top Tier" gasoline until now. Remarks, please, anyone? Thanks! | ||
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DRR Pro |
Idle speed is too high? 750-800 rpm hot, in neutral. Idle mixture too rich? Timing retarded, causing excess combustion chamber heat....which leads us to the possible carbon buildup issue, from oil consumption? Get a 160 degree t/stat. "Top tier" is as dumb as "Stage x" cam terminology. Make it run on regular 87, the thing is only 7.x:1 compression. Sure would be better with the O.E. fuel injection.  "Despite the high cost of living, it remains popular." Dave Cook N375 | |||
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DRR Sportsman |
try leaving in gear when you shut it off GM makes a top end cleaner x66p you trickle through the carb to clean out carbon build up Working for the Weekend!!!! Fordyce Motorsports | |||
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DRR S/Pro |
Actually not. Top tier gasoline is guaranteed to have higher and specific detergents in it to combat carbon build up and other deposits. Now you might argue the efficacy of the detergents but being top tier branded does have real meaning. | |||
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| DRR Pro |
LOL, ALL of the motor fuels sold here, with few exceptions, come out of the same tanks at the Whiting refinery, regardless of brand. "Top Tier" simply means they spend a lot on marketing.  "Despite the high cost of living, it remains popular." Dave Cook N375 | |||
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| DRR S/Pro |
No dog in this fight, FYI. Believe what you will. Illegitimi non carborundum | |||
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DRR Pro |
honesty is the best policy,insanity is a better deffense 1.036, 6.16@ 224 | |||
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| DRR Pro |
Many models of Chevrolet [and others] were equipped with anti-diesel solenoids. It would be relatively easy to retrofit such a solenoid. In most cases, idling too fast is the cause of dieseling. [more specifically, the throttle is open too far.] The above post about turning off when in gear, if that solves the problem, then try to idle it slower if possible. The anti-diesel solenoid allows a faster idle speed, but it retracts when the ignition is off, thus closing the throttle. When the throttle is closed, no air goes in, so the engine can't run. Larry Woodfin | |||
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DRR S/Pro |
What engine? Truck was factory with TBI? What distributor are you using? Timing? Have a good temperature gauge? Top tier pumps will have the sticker on the pump. | |||
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| DRR Pro |
Eman, all your questions are answered in his original post. Larry Woodfin | |||
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DRR Top Comp |
Agree idle screw. Old trick when run big cam was to drill small hole in blades. that way you close blades nd not expose the little hole that allow fuel flow. By small talking like .030 to .050 will do it in most cases. America home of free. Brought to you by 2nd amendment. | |||
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DRR Pro |
Agree with above, lower idle speed (the solenoid is a great idea) and shut it off in gear as a bandaid. Mike | |||
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| DRR Trophy |
Thank you for all the great remarks, guys. Much appreciated. So far, I've only had engine dieseling on this one occasion, and I've been running it for 13 years. It seems to work fine now, especially after doing a little mitigation. I get a little spooked you know when something like this pops up at the last minute, while preparing for a very long, 350-mile tow. I paid $2,000 for this truck 13 years ago, and have pretty much gotten my money's worth out of it. I normally only need to tow 38 miles, one-way, on secondary oil. The previous owner had put in that engine with the HEI, Holley carb and mechanical fuel pump. I did like all that at the time, as there was not a whole lot that this shade-tree mechanic could not fix by the side of the road. I was looking for a 3/4-ton pickup at the time, but this came up and was cheap enough. I do like the very stable platform of a one-ton dually, and I do not worry about tongue weight!  I did have to limp home one time when the plastic gear in the TH400 transmission governor wore out, and would not shift out of 1st gear. I carry spares of that part now.... The cam is mild or stock. Idle speed appears to be normal. The engine may in fact already have a cooler thermostat in it, as I never see the temperature get very warm. I read up on that solenoid that Larry described. I'd heard of it before but had no idea what it was for. The timing I'm not sure of; I must get a new timing light. Lol, the engine ran fine so I didn't give it any thought. For me, best not to futz with something that's not broken. I have elected to switch to 'Top Tier' gas whenever possible. It seems to cost no more than the 'ordinary' gas I was filling at the corner Kum & Go station. That was an interesting YouTube video, Canted Valve; thank you. Have a great weekend, all! Good luck racin'! | |||
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| DRR S/Pro |
Ah, the good old day when mechanics dealt with mechanical things. Don't know why but that made me thing of vacuum choke pull-offs (today's IAC). I guess because it too was a carb add-on. Illegitimi non carborundum | |||
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| DRR Pro |
Your post doesn't mention if you are running vacuum advance (or not) on your HEI distributor. If you have vacuum advance hooked up, and connected to a full manifold vacuum source (i.e. not a ported vacuum source) this will RAISE idle speed, allowing you to screw the curb idle adjustment back OUT to LOWER you idle speed back to where you want it. You'll then be idling with a smaller throttle opening, The smaller your throttle blade opening at idle, the less likely you are to experience dieseling, as noted in one of the first posts. This might be easier/cheaper than the anti-dieseling solenoid, if you don't already have vacuum advance at a full manifold vacuum source. Mike | |||
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| DRR Pro |
Canted, since I am old [78] and worked with cars most of my life, I know all about choke pulls, vacuum advance, mechanical fuel pumps, socks in gas tanks, R12, squealing blower motors under fenders, trans modulator vacuum hoses, squeaking u-joints, whew, what a ride! And that only touches the tip of the preverbal ice berg. Just carrying on, smiles to all from an old man who is still learning and still trying Larry Woodfin | |||
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| DRR Trophy |
Thanks, Mike; sounds like some good tips. I am in fact running with vacuum advance, being it's a street-driven vehicle. And thanks for the reminder to check if it's connected to the right vacuum port. Remember too; I only had the dieseling on one occasion, and I get a little nervous about malfunctions right before a very long haul. It hasn't happened again since that evening about 3 nights ago. I must have corrected whatever had caused it. Thx again, T. | |||
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| DRR Trophy |
Larry, you just described my tow rig! | |||
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| DRR S/Pro |
I too am 78 and been an enthusiast car guy most of my life. While I'm not near as talented as you, I'm more of a water seeks it's own level kind of mechanic. Oh, and I've got some R12 on the shelf! Oh, and don't forget the road draft tubes. Speaking of Freon, for those that might be as uninformed as myself, I just bought a new set of A/C gauges and thought I'd get some R134a with my Amazon order. Well Amazon doesn't sell R134a, only R134a "replacement"! Can't just add it to the system, you have to evacuate it and recharge from 0. So, I went down to my local clearance store and bought a reserve of 134a (<$10ea). I hope some of the sweeping changes in the EPA will curb some of this Freon turnstile BS. Illegitimi non carborundum | |||
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| DRR Pro |
One thing, most pump fuels are not "gasoline" at all. Apparently there are thousands of way to formulate "motor fuels", but gasoline is a formulary. Originally produced and sold by pharmacists. IF the pump says "gasoline", it's real, if not, it could be anything. VP race fuels are mostly labelled simply "hydrocarbons". "Despite the high cost of living, it remains popular." Dave Cook N375 | |||
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Bracket Talk Bracket Talk Forum Tech Talk - by Abruzzi Q: SBC engine run-on/dieseling, and Top Tier gasoline
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