I am new to this forum but I have owned Fords all my life. I have never had this problem. I have a 1990 F150 inline 6 4x4 with a 5 speed manual. When I bought it I was getting about 15-17 MPG. About 2 months ago my engine started to spudder in first and second gear but I did not notice any MPG changes or power change. I thought it was probably the spark plugs or wires so I changed the wires, plugs, distributor cap and rotor. This did not change anything. About a month ago I took off my muffler for the fun of it and to see how it sounds. It didnt sound the best but I left it off anyway. about 2 weeks later the catalytic converter fell off because the weld broke from the pipe. I got great gas mileage (18-19 MPG) for about 2 weeks (2 tanks of gas). it was also very loud. Heres the problem: These past 3 tanks I have been getting about 10 MPG and the spuddering is worse. When I begin driving the first 2 minutes are smooth without any studdering. There is only a noticed spudder in first and second gear. It idles as if it were about to die then it catches itself, although the idle is not that noticeable unless you are paying attention. The check engine light is not on and I really have not noticed a decrease or increase in power. The worst part is my gas mileage. I have not had time to check it out, because of work. But if anybody could give me a clue as what to look for, it would be great.

 

My knowledge of later engines is limited, but if it's EFI I'd cheque the Injectors or Carb'd cheque the Jets.

 

yeah its EFI, Thanks for the advise, I will check them out.

 

Wish I could be of more help.

 

well have you checked fuel pressure? the regulator could be going bad and fluxuating causeing these spurts. you may also check for vacum leaks and intake manifold leaks by spraying wd40 or somthing of the like on the seal and if it revs up you found a leak. you may also check for slack in timing and adjust the timeing.

 

Oxygen sensor? Without the cats and muffler, and with the age, maybe it's out of whack. That could have the engine running in a default mode like "cold start" and using tons of gas.

 

oh and does it come into the operating "normal" range completely?

 

The stumble in first and second gear is commonly caused by a throttle body gasket that has been sucked in to the intake causing a big vacuum leak.

Have you ever changed the fuel filter? Sounds like it might be getting too lean.

 

Chrono4: what do you mean by "operating 'normal' range completely"? after I am in third gear or higher I dont seem to notice a problem with the way the truck runs unless I pay close attention. If I listen closely I can hear and feel a small studder but nothing too big. I do not know if that is the answer to your question though.

85e150six4mtod: I originally thought it was the oxygen sensor also but after reading on this forum, it sounds like the check engine light would come on if it was bad. I have no idea though, I just figured that it would come on. How can I go about checking the o2 sensor without buying a new one? is there a way?

Silver Streak: I have not yet changed the fuel filter. I will most likely do that since it is the cheapest and considering the truck has 190,000 miles on it, it should be changed since I dont know how old this filter is.

Thanks for all the quick response, I really appreciate it. I will take a look at the truck on Sunday since I dont have to work.

 

sorry about that, i meant to say tempurature range

 

The temperature range is normal, actually since it is so cold it is running cool.

 

well if the computer doesnt sense that the engine has completly heated up then it wont come out of the cold loop cycle and will dump excess fuell into the engine to try to heat it up. this could be the cause of the gas mileage, and the spuddering.

 

hmmmm... thats a good point, it has been running pretty cold lately, I just figured it was the cold weather but even after driving for a while the engine does not heat up to normal. Would that be the computers fault that it is not reading how hot the engine is or is it something else. I would guess it would not be the computer since the computer does not tell the engine how hot to run, but what would it be?

 

well it could be that the thermostat is stuck open, and not restricting flow enough to heat up.

 

I finally found some time and checked my codes. I got a 32 and 67. 32 is EVP circuit below minimum voltage of 0.24 volts. 67 is just about the neutral safety switch. I think that since my check engine light is not on, my EVP circuit is still good but since my catalytic converter fell off, the EVP is getting bad signals from not having much backpressure. I am going to get my exhaust fixed and see what happens.