Hi all, longtime reader decided to finally register and post. Great forum here!

I've got a '85 F-150 XL (Explorer trim) with the 300 under the hood, 4WD, and NP-435 manual. A couple weeks ago, I filled both tanks with non-ethanol premium from a small town gas station 10 miles from my house. This is the first time I've used this particular gas in the truck. It always idled a little rough, but otherwise ran fine--just on the rich side. Since this new gas, it will start OK when cold, but as soon as the truck warms up at all or I try to drive it, it seems like the engine is flooding. It bogs down under any kind of load, and starts bucking around 35-40 mph in 4th gear. Lifting off the gas and coasting in any gear smooths things out, but touch the go pedal and the problems start immediately. Stop for any reason, and the truck idles very slowly and wants to die, which it will do it I don't give it some gas to keep going, but the exhaust smells very strongly of gas. I haven't converted to DSII (yet) so it still has the feedback carb. I did solve a rough idle last spring by cleaning out my EGR valve, but I've since replaced it anyway. But this is way worse... the truck barely runs after it's warm. Could this all be bad gas? Any suggestions?

 

Welcome to FTE.

First thing to do when questioning the behavior of any computer-controlled engine is to ask the computer what it thinks is happening. IOW pull the codes, parts stores will often do it for free using a code reader (assuming they know how to pull OBD-I codes).

 

Does the problem go away as the truck warms up completely, or does it always run poorly?

 

It actually gets worse as the truck warms up. When cold, it idles rough and drives rough, but it doesn't try to bog down or die.

I do need to get the codes pulled. Guess I'm wondering if this could really all be bad fuel? For what it's worth, I've put the same gas in my car (Audi) and my wife's (Acura) with no issues. I can't imagine they're more tolerant of bad gas than my trusty 300!

 

Yes, it could be bad fuel. I had something similar happen a few years ago - 1970 to be exact. Filled up and it started running badly almost immediately. Flooding at idle and the gas gauge dropped very rapidly. Ran two cans of carb cleaner in that tank and that didn't do it. Ran that tank out, which didn't take long, put a full tank of good gas and two more cans of cleaner in and that still didn't do it. Had to pull the carb apart and wipe the needles down to get whatever the stuff was off them. After I did that it ran perfectly.

 

All good advice by the above intelligent gentlemen! Let me add a couple of thoughts.

First, why premium? Yes, I know premium has a better detergent package in some brands, but is not needed with the 4.9L low compression engine and is actually counter productive to performance and emissions.

Second, has the weather turned considerably cooler where you live during the past couple of weeks? If so, your choke may need a seasonal adjustment.

Since your truck still has the computer controlled carburetor and ignition system, if anything is out of whack, the computer will revert to the "limp home" or "safe" mode and the fuel mixture will be very rich along with your timing being locked, so performance will suffer and fuel mileage will be horrible [~8-11 mpg; ask me how I know?]

Have you tuned the engine recently and checked for vacuum leaks?

Welcome to the forum!

 

The premium at that station is non-ethanol. Thought I'd give it a try since the truck isn't a daily driver and I don't want ethanol corrosion/water in my fuel if it sits in the tank for a while.

This past week, the weather went from mid-60s during the day to 30s and a winter weather advisory! I haven't done a choke adjustment... suppose I can do a forum search for the procedure.

I checked for leaks, everything seems OK. I haven't done anything to the engine recently except for an oil change and EGR replacement.

I hate the thought of siphoning $100+ of gas out and replacing it, but hunting season's here and maybe I hate the idea of being truckless even more!

 

See if this will help?

https://www.ford-trucks.com/forums/1...ent-101-a.html

 

For about 5 minutes, that is... Here's the update:

I pulled the plugs. #3 was basically wet with gas, so I'm missing. Pulled the wires off the dizzy cap... Wow, I'm surprised those contacts didn't crumble instantly as badly corroded as they were. So, I replace the plugs, wires, and dizzy cap. The truck runs better, but not great. Check the oil level... it's really high and smells like gas. Replace the mechanical fuel pump. Still same problems. Figure the O2 sensor has to be caked with carbon at this point, maybe it's reading wrong and throwing the comp into limp mode. While I'm over there, decide to check on the throttle position sensor. It reads way out I spec, so I replace it too. Reconnect everything, fire the truck up and WOW does it run. I drove around the block in 3rd gear at 20 mph without touching the gas. So now I have a new problem, the truck is idling too high. I get nervous, shut it down, pull off the air cleaner and touch something on the back of the carb (fast idle cam, I don't know) that springs to a different position. Cr@p!!! I go back, turn the truck on and... We're back to square one. Gassy, flooding, stumbles under throttle, wants to die. I pulled the negative battery cable off and called it a day. This morning, I'm hopeful that if it threw it into limp yesterday having the battery disconnected all night will have cleared the codes and it will run right again, but no such luck. What did I do? I had this thing fixed and messed it up all over again?

 

Go back to the 2nd post and follow what ctubutis suggested. In the long run, doing this will save you time, frustration and money!