Last summer I purchased a high mileage (170K) '91 F150 with a 351 V8. Ever since the purchase I have done some preventive maintenance stuff (plugs, wires, cap, rotor, thermostat, radiator cap). I also replaced the coil and ICM in order to fix a stalling problem.

I have some symptoms that are probably related and can hopefully be traced to a single component. 1-Engine seems to have very little top-end power. Takes off like a rocket to about 3000 RPM, especially during warm-up. Does not have instant throttle response though. 2-After letting off the throttle in a high load situation (low speed acceleration up a hill) the check engine light comes on and stays on for a minute, or so. 3-Sometimes low oil pressure, inconsistently. 4-Temperature guage reads near Cold all the time.

I am thinking: Catalytic converter, Oxygen Sensor, Temperature Sensor, MAP Sensor. Any advice on where to begin? What can be tested/replaced easily and cheaply?

Thanks,
Tim

 

The symptoms you reported sound exactly like my truck (88 F-150 4X4 302V8) except the check engine light, but I thought it was due to a few different things:

Top-end power reduced: I think my exhaust is too restrictive (still stock).
Low oil pressure intermittent: This is directly tied to engine temp and idle speed. When my truck is fully warmed and the idle drops to 750rpm, my oil pressure drops to the "O" in normal.
Temp gauge: My temp gauge never gets to the "N" in normal. I changed the thermostadt and no change. I was told I might have a bad temp sender unit.
Runs like a bat-out-of-hell when cold: that I assume is a rich running condition, which i thought was normal.

If anyone has comments on this, please speak-up. I am listening!!!

Randy

 

in my 85 302 my oil pressure was on H all the time and my temp was at the top of normal..no matter how hard or easy i drove it....i solved my problem a simple way....after putting large dual exhause in it...(sounded like a big block)...nothing changed...i ended up having it smoked and written off..so now i'm gettin a differnt truck.....i just wrote this cause i had no idea about the computer stuff.

 

Tim ,
To start with , retrieve the codes from the computer or have it done if you dont have the means to do it yourself . Cleaning the throttle body / air bypass vavle wouldnt hurt either . Also the quality of the replacement parts is always a consideration ...you get what you pay for . Something else that I dont think is widely known about thermostats ...the newer ones are designed to stick open when they fail ...always make sure you have the proper temp one too ...your engine needs a 192 deg Ford one ...aftermarket I believe is 195 deg . The coolant needs to warm to that temp in order for the coolant temp sensor to send the proper info to the Ecu . It sounds as if you have an enrichment problem ? Verify that all the sensors are operative and within their parameters before you condem them .
Paul

 

Randy,

Last night I removed the air pump intake filter can (in which the elements were totally filled with dirt and bugs). Until I get a suitable replacement I used a rubber band to hold a piece of cloth over the end of the air pump inlet tube. There is a noticeable difference in the top end power and the truck is idling a little lower and smoother now. I found this after using my code reader and begining the troubleshooting methods for the air management system. Now, where to find a reasonably priced replacement for that filter!

Tim

>The symptoms you reported sound exactly
>like my truck (88 F-150
>4X4 302V8) except the check
>engine light, but I thought
>it was due to a
>few different things:
>
>Top-end power reduced: I think my
>exhaust is too restrictive (still
>stock).
>Low oil pressure intermittent: This
>is directly tied to engine
>temp and idle speed.
>When my truck is fully
>warmed and the idle drops
>to 750rpm, my oil pressure
>drops to the "O" in
>normal.
>Temp gauge: My temp gauge never
>gets to the "N" in
>normal. I changed the
>thermostadt and no change.
>I was told I might
>have a bad temp sender
>unit.
>Runs like a bat-out-of-hell when cold:
>that I assume is a
>rich running condition, which i
>thought was normal.
>
>If anyone has comments on this,
>please speak-up. I am
>listening!!!
>
>Randy