1990 Ford F-150 truck hard to start when cold

HOTROD351

MEMBER
1990 FORD F-150
6 CYL
4WD
AUTOMATIC
160,000 MILES

I have a 1990 ford 150 with a 4.9 and EFI. Its getting harder and harder to start in the mornings. I checked for vacuum leaks and found none. I checked fuel pressure, key on and engine running, and it holds 50 psi with key on and a little higher when running. I replaced the MAP, IAC and coolant sensor. I but a new EGR valve on it a week ago but it was getting hard to start before that. The plugs are good and the cap and rotor plus the plug wires are pretty new. It also feels like it is surging a little at highway speeds. It idles perfect when warm and starts up great when warm. The surging and hard cold starts are what im trying to figure out. I also did a wiggle test with the code reader and nothing wrong there. Any ideas on where next to look.

3 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Hi there hotrod351 and TY for the donation

the surging and hard cold starts are what im trying to figure out.

You got a fuel pressure of 50psi the book says it should be 41-47psi-hook up a fuel pressure gauge and monitor the pressure with and without the fuel pressure regulator. Hence: when you disconnect and plug the vac hose to the FPR the pressure should rise 8-10psi also blow thru the fuel return line to make sure its not clogged-up and run fuel injection cleaner thru the system injector/s could be sticking

Below could also caused your problem

Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires