Hello,

I have a 1996 F-150, long bed, standard cab, 4x2, with AC, 4.9L inline 6, auto trans. The truck starts and runs great when started while cold. However, intermittently when starting after engine is warmed up, the engine stumbles and idles very rough. Sometimes when I give it plenty of gas pedal it gets over it—most of the time I turn it off and try again—sometimes with success, sometimes not. The scan tool shows no pending or any other codes.

Does anyone have ideas as to what this could be?

Thanks,

Dennis

 

When was the last tune up performed on your engine?

I am going to say wires...

 

I'd check the ECT resistance.

 

Tec-doc,

Thanks for the reply to my post--I know its been 10 days since-- but commuting is great.

I recently did a full tune up including plugs, wires, rotor, distributor cap, air filter, fuel filter.

--how do you check the fuel pressure?

I think I've located the schrader valve on the fuel lines coming up on the backside of the engine closest to the firewall--it is not real easy to get to of course. is it just like checking the air pressure in a tire--with a gauge of some sort?

One more piece of info...I have a two tank system and when switched to the rear tank there is no trouble at all ever. However, when switched to the front tank and the engine is warmed up it does the start/rough idle dance (intermittently).


Thanks,

Dennis

 

PKRWUD,

ECT = Engine Coolant Temperature?

How would I go about checking the resistance?

Thanks,

Dennis

 

Unplug the electrical connector (the sensor is by the t-stat), and connect your DMM across the pins on the sensor, with your DMM set to measure K ohms. Start up the engine and read the resistance as it warms up. When the t-stat opens, it should be right around 2.8 K ohms. If it doesn't test good, remove it and test it in a pot of water on the stove with a known good thermometer. It should read as follows:

104 degrees F = 16.15 K ohms
122 = 10.97
140 = 7.70
158 = 5.37
176 = 3.84
194 = 2.80
212 = 2.07
230 = 1.55

If it does not match any of those measurements, replace it.

 

Hello all,



After checking the front tank fuel pressure at the schrader valve and seeing a low reading of 42 psi key on engine off (KOEO)(initially it showed 24 psi)--the tech manual CD stated the pressure should be 50-60 psi KOEO and 28-45 engine running.

Long story short, I replaced the in-tank fuel pump in the front tank...no issues since replacement.



Thanks for all the advice/help.



Dennis