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Corvette
C3 Forum
1970 C3 LS5 ... Question about fuel
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<blockquote data-quote="Roger Ramjet" data-source="post: 226561" data-attributes="member: 6682"><p>Just bought the car about two months ago and I’ve been filling up with mostly Ultramar 91 octane, which as I understand contains ethanol.</p><p></p><p>This week is storage time, I'll be storing the car where it can also be looked at mechanically throughout the winter months. The car is in great shape, the only known issue (up until a couple of days ago) is that the steering needs attention. It gives me a hard time when trying to turn while at a dead stop and this will be addressed while in storage.</p><p></p><p>Anyway ....</p><p></p><p>Since I bought the car, I have been experiencing some “dieseling” (engine continues to run, cough and sputter when turned off) on a few occasions. This has happened a total of maybe five times in the relatively short time I've driven the car and this lasts about 5 seconds each time. After doing a bit of research, I decided to start using Shell 91 V-Power two days ago. So I pull into my local Shell and top-off a good half-tank worth of Shell 91 V-power. So now the gas tank is completely full (half Ultramar 91 and half Shell 91).</p><p></p><p>Took the car for a long drive and after turning the car off the engine keeps going, this time the dieseling is more intense, white smoke, some backfiring. This lasts a good 15 seconds (maybe more). So while this is going on, I turn the ignition on again. The engines resumes but at higher RPM. Can’t get the RPMs to come down. Stopped the engine in ‘drive' gear .... more dieseling.</p><p></p><p>After letting the car sit for a good 45 minutes, I re-start the car. Normal RPM by the sound of it. The tach is not hooked up because the previous owner had changed (upgraded) the ignition system and the stock tach cannot be hooked-up to the new distributor. This will be addressed during winter storage because it will require the removal of the dash.</p><p></p><p>My question is are the two issues related (the "dieseling" and the high RPM)?</p><p>Is (was) the use of the Ultramar gas the problem? Now that I've changed over to Shell VP 91 will the problem go away next spring?</p><p>Or, given the engine is of a higher compression, will this dieseling issue continue no matter what fuel I use (ethanol-free or not) and would octane booster be required going forward? </p><p></p><p>Could the problem be the ignition system itself? My neighbour tells me it may be too advanced (he drives a '68 Mustang). My mechanic tells me he checked the ignition and made sure it's where it's supposed to be, but he'll consider it again during the winter months while the car is in his care.</p><p></p><p>Thanks.</p></blockquote><p></p>
[QUOTE="Roger Ramjet, post: 226561, member: 6682"] Just bought the car about two months ago and I’ve been filling up with mostly Ultramar 91 octane, which as I understand contains ethanol. This week is storage time, I'll be storing the car where it can also be looked at mechanically throughout the winter months. The car is in great shape, the only known issue (up until a couple of days ago) is that the steering needs attention. It gives me a hard time when trying to turn while at a dead stop and this will be addressed while in storage. Anyway .... Since I bought the car, I have been experiencing some “dieseling” (engine continues to run, cough and sputter when turned off) on a few occasions. This has happened a total of maybe five times in the relatively short time I've driven the car and this lasts about 5 seconds each time. After doing a bit of research, I decided to start using Shell 91 V-Power two days ago. So I pull into my local Shell and top-off a good half-tank worth of Shell 91 V-power. So now the gas tank is completely full (half Ultramar 91 and half Shell 91). Took the car for a long drive and after turning the car off the engine keeps going, this time the dieseling is more intense, white smoke, some backfiring. This lasts a good 15 seconds (maybe more). So while this is going on, I turn the ignition on again. The engines resumes but at higher RPM. Can’t get the RPMs to come down. Stopped the engine in ‘drive' gear .... more dieseling. After letting the car sit for a good 45 minutes, I re-start the car. Normal RPM by the sound of it. The tach is not hooked up because the previous owner had changed (upgraded) the ignition system and the stock tach cannot be hooked-up to the new distributor. This will be addressed during winter storage because it will require the removal of the dash. My question is are the two issues related (the "dieseling" and the high RPM)? Is (was) the use of the Ultramar gas the problem? Now that I've changed over to Shell VP 91 will the problem go away next spring? Or, given the engine is of a higher compression, will this dieseling issue continue no matter what fuel I use (ethanol-free or not) and would octane booster be required going forward? Could the problem be the ignition system itself? My neighbour tells me it may be too advanced (he drives a '68 Mustang). My mechanic tells me he checked the ignition and made sure it's where it's supposed to be, but he'll consider it again during the winter months while the car is in his care. Thanks. [/QUOTE]
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C3 Forum
1970 C3 LS5 ... Question about fuel
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