Bad gas or jumped timing?....take a guess

[swb85]

Alright everyone, put in your vote. I'm arguing w/myself as I post this, so bear with me.
Yesterday I found a quick shop selling gas 15 cents cheaper than everyone else in town and I was empty so I filled up and drove home. Now today the truck is pinging like crazy under any kind of load. Bad gas right??....Well it's suddenly bucking quite a bit under light throttle at lower rpm in every gear (4 spd). Under normal crusing on the highway it runs normal and I can give ~1/2 throttle without it pinging, but any more and it pings bad. So when I got home for lunch today I shut it off and tried to start it right back up. It didn't turn over smoothly, jumped around a bit but eventually started....made me think waaaaay too much timing....bad gas wouldn't do that. Checked the dizzy and it hasn't jumped, hold down is still secure. Didn't have time to pull the cap. After lunch it started right up smoothly, but idle was jumping around quite a bit. Same symptoms on the way back to work.

The motor is rebuilt 350 (PO did it) and only has 12k miles on it. After hearing the pinging, I was REALLY hoping it was just bad gas....but now I have a sinking feeling the timing jumped internally with the rough turning over when hot and the bucking. The PO was good about replacing everything on the rebuild, so I'd have a hard time believing he didn't replace the timing set (I've never pulled the cover, never had to set the timing). The thing ran flawlessly yesterday....

Thoughts?...Opinions?....Ideas?.....Suggestions?
Thanks guys.

[Oldtruckfanatic]

Sounds like water in the gas. It's almost too much of a coincidence to have it start acting funny right after a fill up. If you pump some from your fuel line into a clear glass you can see the water in it. I have had it happen before.

[rockman20]

Originally Posted by Oldtruckfanatic

Sounds like water in the gas. It's almost too much of a coincidence to have it start acting funny right after a fill up. If you pump some from your fuel line into a clear glass you can see the water in it. I have had it happen before.

This, I would say, sounds a lot more reasonable. There was a station in the area here that you couldn't even get gas out of the pump this past winter. They had to dump HEAT in the hose just to unthaw the pump handle!

[swb85]

Good thoughts.....I actually just changed my fuel filter a few mins ago and poured the gas into a lil paper cup--didn't see any water but it was only a couple tablespoons. I'll dump some HEET in the tank after work and see if that helps. I thought water in the gas would just make it spit/sputter, not ping like I put 87 octane in a 14:1 motor.

[Oldtruckfanatic]

Bad gas or gas that has water in it will cause pinging and spark knock fairly efficiently. Also water doesn't compress like gas does so if there is enough in the system it can make the engine turn over irregularly. The water isn't always easy to see in anything other than glass because it's just a layer of fuel thats kinda cloudy and pale looking.

[swb85]

Alright, stuck some heet in the tank for the ride home....we'll see what happens!

[Oldtruckfanatic]

Hope it works out for ya.

[rockman20]

Let us know. I am curious to see what happens with the HEET and then when you get some fresh gas in it.

[86 GMG]

it seem to be unanimous (sp?) bad \ water fuel heet is a good idea but ithink an bottle of octane boost would help as well atleast for detination purposes. best of luck to you andkeep us informed of the situation

[79BIG10]

Could it have been the new ethanol gas they came out with? I don't know if the same would happen with our engine systems but I'm thinking it could be that causing the lower octane and casuing the pinging.

[swb85]

Update: I'm almost done with this tank of gas, gonna fill up tonight with 91 octane and put another bottle of heet in the tank in case there's any moisture left. It's running a little better....not bucking or hunting for idle, but it's still pinging really bad if you get into the throttle under any kind of load. Keep your foot out of it and it runs great.

79Big10: The station I bought the crappy gas from doesn't have ethanol in it's fuels...yet. I am curious about the effects ethanol will have on our vehicles though.