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4.6 DOHC with hesitation and LTFT high

01-13-2009, 01:35 PM
I have a 1998 lincoln with 100K 4.6DOHC.( I figure this is the same engine as the cobras and might have a better respone here) I am getting severe hesitation /Jerking /Surge on light acceleration. I have replaced

fuel pump and all filters (old pump was running at 22 lbs)
coils been rotated and checked using a new coil ( changed 1 at a time and test drove)
Throttle bottle cleaned with new gasket / EGR as well ( will make a popping sound with vacuum applied)
cleaned injectors and rebuilt with new kit
New Pressure sensor / regulator

car has good gasmileage with no PIDS.

My STFT are between 4 and -4 for both banks
MY LTFT is now about 20 ( disconnected battery and reset)

If I should punch it out (WOT), the LTFT goes to 0 and my STFT goes to 20 so it basically reverses. Does this indicate a massive air leak? At idle, I am getting a steady reading of about 20 .

My I/M monitors shows the following system as INC ( 2 days after battery reset)

EGR , EVAP and CAT MON.INCOMPLETE Are these related to my issue?

car is still driveable but the hesitation sucks. ... Any Thoughts

01-13-2009, 06:40 PM
After installing the new pump did you recheck the fuel pressure to be sure the pressure regulator is working properly.
Pull the vacuum hose for the regulator and if it has gas in it replace it with a new one.
Put a vacuum hose on the solenoid for the egr and make sure it isn't leaking vacuum. Check the EGR and make sure it isn't leaking.
Use a can of carburator cleaner and check for vacuum leaks around the intake. If you hit a leak with spray the engine will smooth out. Use a bolt and plug the vacuum booster hose and see if this smooths out the engine.
People have been installing aftermarket EGR's without reading directions and the flow is wrong causing these type of problems.

01-13-2009, 07:05 PM
Hello and thanks for replying.

The fuel pressure was not checked due to my guage line breaking. I can say the car is alot more repsonsive after the fuel pump replacement. I bought the car 6 months ago from a 80 year old guy. It ran great until a few months ago. The fuel pump sending unit was clean as a whistle but that dont mean anything. I have a pressure sensor and not a regulator but the sensor does have a good steady vacuum (I can put my finger over it and it will leave a mark on my finger) Can I use my vacuum guage and check the egr valve? If so, I will check it tomorrow and would like to know how I should do this but I read in many forums these things are bullet proof and the egr was removed and clean and I did this twice to make sure but nver tested in circuit. I Also used a propane tank to check for leaks at idle and nothing was found. I also have a smmoth idle and it doesn't fluctuate more than 20 rpms. 620-640 in drive with the brakes pressed. Do you have anything else??

01-13-2009, 08:58 PM
I'm outdated on this engine but the moderator in the Crown Vic forum is up on these engines.
My truck a Chevy has an electrically operated EGR but my 1997 Ford manual shows a solenoid. These solenoid's are electrically operated and supply vacuum to the EGR normally you tap the vacuum line to the EGR and with a fully warmed up engine gun it to appx. 2000 rpm the vacuum should come to the valve. Then hooked up feel the diaphram under the valve and make sure it opens.
On your system the computer pulses the ground to the pump so fast it effectively changes the voltage like the blower resister does for the fan motor this changes pump speed and flow and pressure.
If it was my vehicle I would repair my connection and recheck the fuel pressure. The sensor could be out of calibration for this pump.
Any way try posting on the Crown Vic forum.

01-14-2009, 11:24 AM
On my 3rd day after resetting the battery /ECU, My EGR I/M is now complete and OK. Iwas also informed that the EGR valve doesn't really kic in until the higher rpm range. The egr valve does have the DPFE sensor and solenoid pump. My hesitation is basically between 1600- 2000 Rpms at it's worst and may have a surge issue at cruising speeds under light acceleration. I can alsways throw another 50 bucks at it and replace the EGR valve. its been a 2 month troubleshooting process


01-14-2009, 03:58 PM
Ask in the Crown Vic forum. The moderator is a supervisor of a county police car repair shop. He is real familiar with these engines.

01-14-2009, 05:09 PM
Say no more, If I ever find out,I will posted the fix here. Thanks

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