Hi! So I recently ran my fuel tank really low on my 1991 f150 4.9l XLT Lariat. I was doing it on purpose to drop the tank and clean it out but something came up and I ended up not doing it, so I threw in some cleaner in the tank and filled it all the way up with premo gas, which I always use at least mid grade. When I drove it around after this the engine sputters if any load is on it at all, I have to get RPMS high to get any power at all. If I try to start off in second which I can usually do no problem, albeit slower, it won't do it. It bucks and engine dies. On Highway speeds it does fine, 70-75. The check engine light came on, I am going to read it using the flashing method I saw on YouTube this week. I am also replacing fuel filter, since maybe some gunk got in it. Also it is idling a lot higher than normal. I'm checking for vacuum leaks, I know of one small one, but I have had it before this issue and I'm still waiting on my package to come to fix it. I also stopped it up, nothing changed. When I let out the clutch going higher speeds, the engine will stay high idle, then drop to 400-500 for a second then return to high idle. Any ideas what I can check? I'll update with engine code once I figure out how to do the flashing code self test on my truck.


Edit: cleaned air filter and fuel filter, solved problem!

 

What was wrong that made you want to clean out the tank?

What was the cleaner?

 

Well I have two tanks fuel pump on one is out, I was planning on dropping both, cleaning, replacing both pumps, just do general overhaul on them. I noticed the truck running a little rougher when getting to 1/4 tank so I figured I had some gunk or bad gas on the bottom. I used injector cleaner stuff you get from autozone since I ran it so low.