1999 Ford Explorer 4.0 SOHC hesitates, bucks backfires

[Ranxeroxlubna]

This is a repost.

Initially, the hesitation began just at the start up. Wait a second and it would smooth out and no problems.

2 days ago the following happened.

• Motor died on the road.
• Repeated attempts to start it resulted in a stuttering idle, bucking, and the motor stopped running.
• After restarting the motor, if you work the throttle and let the engine spool up, it would accelerate up smoothly to wide-open throttle.
• If you open the throttle all they way suddenly, you get backfires in the manifold and the hesitation and stuttering really go nuts.
• I drove it home after clearing out whatever was involved, it stuttered and hesitated all the way home, but it got there. I put it in neutral at the lights and revved it up to keep it going.

What I have done.

• I sprayed starter fluid on all the vacuum connections with no change to the idle.
• I pulled the spark plug cable off the coils, one at a time; the front row caused major changes to idle, the back row did not seem to have as much of an effect, less as moved from 3-2-1.
• I disconnected the MAF connector and it did have a very subtle effect.
• I disconnected the intake hose at the throttle body and it ran a bit better, although moving the throttle manually repeated the aforementioned problems.
• When I reconnected the intake hose to the throttle body, it just died.
• I get no codes.
• The computer seems to struggle to connect with the diagnostic device.
• I cleaned the MAF in late summer.
• Before I changed the fuel filter, I checked the Fuel Pressure, which is at 24 PSI, dropping down to 21 PSI if you accelerate.
• I changed the tank, the fuel pump and the gas lines in February of 2014.
• Fuel filter replaced - Gas clear - EFI pressure still at 24 PSI, but doesn't dip.

What I did after fuel filter replacement.

• Poured 2 cans of Sea Foam into a full tank and left it running for 30 minutes. Took it out on the highway and it ran okay at the start, ran better as it cruise home.

What it does now.

• Stutters and staggers with cold start
• Idles smoother, no stalls as it warms up
• Will spool up to 3k RPM, then catches a bit, then spools up to 5500 RPM.
  
• Accelerates fine.
• Will run smoothly at highway speeds
  
• Pressure still at 24-25 PSI when I checked upon return home.

Could it be the fuel pressure regulator?

Here is the information from the diagnostic tool:

Fuels sys 1 - CL
Calc LOAD% - 28.6
ECT F - 188 DEGREES
STFT B1% - 10.1
LTFT B1% - 25.0
STFT B2% - 13.2
LTFT B2% - 25.0
ENG RPM - 675
Veh Speed - 0
IAT F - 69 DEGREES
MAF lb/mn - 0.474
TPS % - 17.6
02S B1 S1 V - 0.425
STFT B1 S1 % -8.5
02S B1 S2 V - 0.670
STFT B1 S2 % -NA
02S B2 S1 V - 0.730
STFT B2 S1 % - 12.5
02S B2 S2 V - 0.770
STFT B2 S2 % - NA
OBDSup - OBD2

This is an average out of 5 frames in memory.

 

[Ranxeroxlubna]

ANYONE?

 

[fordapprentice96]

have you found a fix? my truck has similar symptoms but mine pings and missfires when i rev it up. it has been sitting for 4 months though i think my problem is bad gas because it only missfired before i let it sit

 

[RandomNerd2000]

Your fuel trims seem really high, suggesting low fuel pressure, if memory serves, your pressure should be somewhere around 35. My 01 runs at a higher pressure, but almost did exactly what you're describing