My truck is a 1986 F-150 2WD, 302 EFI, dual tanks, auto, with 166M miles.

Normally, I just turn the key to start it up but recently had to depress the accelerator slightly to get the engine to fire - truck then coughed and sputtered like a carb vehicle in which the choke was not working.

Have replaced the air filter, breather element, hi-pressure fuel pump mounted on the frame rail, distributor cap and rotor (tip was corroded), and spark plugs (wires are fairly new and inspected ok).

Removed and cleaned the EGR (replaced the gasket where it mounts to the TB), and removed and cleaned the IAC.

Also inspected the vacuum hoses but found no leaks.

Got a code reader today - no DTC's on the KOEO test but did get a 31 on the Continuous Memory test.

After installing the plugs today, I started the truck and it again mimicked a carb'd vehicle with a choke malfunction (coughing, sputtering, wanting to cut off).

Kept it running by patting the accelerator.

The longer it ran the less it sputtered and finally after about fifteen minutes it would idle without my patting the accelerator (though it still shook slightly).

Drove it around the neighborhood and it shifted very roughly but the engine seemed fairly smooth after the tranny shifted to high gear.

Wondering if maybe the fuel filter has become clogged (it has been changed maybe a year ago) or if the in-tank pump is contributing to this behavior.

Sure appreciate any help.

Thank you.

Tom

 

Almost sounds like the engine temp sensor is at fault. But you would think it would give you a code.

Take it out of a cold engine, and get an ohmmeter and read the resistance of the sensor. Get an idea how cold it is outside and see if it jives with these readings;

50 degrees =58,750 ohms

68 degrees =37,300 ohms

86 degrees =24,270 ohms

104 degrees = 16,150 ohms

 

Dave -
The Haynes manual refers to a "coolant temperature sending unit" which is located near the distributor and sends a signal to the in-dash temperature gauge. Is this the "engine temp sensor" you refer to? If yes, does the sensor have to be removed from the head for checking the resistance and would removal of the sensor require draining the cooling system first? If no, where is the "engine temp sensor" located? Thanks for the help.
Tom

 

Here's a link.
http://www.autozone.com/az/cds/en_us...rInfoPages.htm

They say it's in the intake manifold somewhere. Just be sure you get the sensor with two wires. The single wire sensor is for the gauge. The two wire sensor is for the computer.

If you can guess the temp of the engine, you should be able to unplug the wiring and take a reading with it still in the engine. If the reading says the engine is warm, and it's not, then that would explain why it doesn't run very well when it's cold.

 

Dave -
Found the ECT sensor (just left of the distributor) but am unsure if this is the issue as the analog ohmmeter I have gives the same reading for the ECT sensor presently in the truck as it does for a new ECT sensor I purchased today. Have not yet cranked the truck to heat up the ECT sensor and check for a drop in the sensor's resistance but it seems that would be a non-issue since the resistance of the sensor when cold is what relates to my coughing / sputtering when cold problem (assuming the ECT is correctly transmitting its signal to the PCM).
Separately, it seems I used to hear the fuel pump briefly when I turned on the ignition key - now I don't. Tried to check for a relay that might be faulty but could not locate the fuel pump relay as described in the Haynes manual. Do you know where the fuel pump relay is located and could this be the problem?
Thanks again for your input.
Tom

 

You should have a small row of relays located under the hood located on one of the inner fenders. The fuel pump relay will be one of those.

 

Dave - Haynes manual says the same thing you do but I have yet to find the relays. Still looking. Thanks.

 

Found and replaced the fuel pump relay so have now replaced spark plugs, distributor cap and rotor, hi-pressure fuel pump, fuel filter, air filter, breather element, EGR valve, EVP sensor, idle air control valve, throttle position sensor, and intake air temperature sensor. Do have the coolant temperature sensor but yet to install it per my 5/2/07 post above. I also cleaned behind the butterflies in the throttle body and manifold throat with TB cleaner while I had the TB off to install the TPS. Wondering now if the issue could be a blown head gasket or a small crack in the head (though engine has not been overheated) both of which might get slightly better as the engine warms up. Any further suggestions? Thank you.

 

Still no relief after replacing the engine temp sensor so finally gave in and took truck to mechanic. Problem was bad map sensor. Thanks to those who offered suggestions.
Tom