1990 Ford F-150 truck hard to start when cold

Tiny
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.
Wednesday, September 23rd, 2009 AT 7:19 PM

3 Replies

Tiny
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
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Wednesday, September 23rd, 2009 AT 7:47 PM
Tiny
HOTROD351
  • MEMBER
  • 2 POSTS
The haynes manual calls for, on 4.9 EFI, 50-60 psi engine off and 45-60 psi running with vacuum hoses connected. I dont know why but the 4.9 calls for more. All others say 35-45 engine off and 30-45 running. And my engine doesnt have a MAF.
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Wednesday, September 23rd, 2009 AT 8:20 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Mit1 .com specs below:

KOEO 50-60psi KOER 45-60psi

Your fuel pressure is okay lets start checking the items I've mentioned earlier also inspect and test the fuel pump relay and the PCM power relay


https://www.2carpros.com/forum/automotive_pictures/12900_f510_2.jpg

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Wednesday, September 23rd, 2009 AT 8:34 PM

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