james1767
New CEG'er
Hello all,
Wondering if anyone has any thoughts on this: I installed the replacement Motorcraft updated fuel pump a few months ago - no problems with the install - removed the locking ring from the bottom of the tank as required. Ever since, or at least what I think is ever since, the car has a slight shake or stumble under part throttle just after the shifts into 2nd and 3rd, most pronounced just after a shift into 3rd as the engine climbs from say 2,200 rpm to 3,000 rpm. It feels like it's more pronounced when under load, up hills, around corners - almost like it could not be getting proper fuel pressure. The stumble does not occur if accelerating hard from a stop and does not occur at all after the secondaries open. This only occurs under part throttle. I've checked for vacuum leaks related to me pulling off the air intake duct when I relieved the fuel pressure for the fuel pump install, nothing found. Also....car runs FINE when stone cold - nice smooth acceleration through all gears, the stumble/hesitation starts appearing within 1-2 minutes after car has been running from a cold start, or anytime engine is warm/partly warm (like after the engine enters closed loop from open loop). No check-engine lights or misfire codes. Spark plugs and wires recently replaced and done 1 month prior to fuel pump install, car ran fine for that month.
I researched that old lengthy "my very own misfire/hestitation" thread and found this from brapple:
Wondering if anyone has any thoughts on this: I installed the replacement Motorcraft updated fuel pump a few months ago - no problems with the install - removed the locking ring from the bottom of the tank as required. Ever since, or at least what I think is ever since, the car has a slight shake or stumble under part throttle just after the shifts into 2nd and 3rd, most pronounced just after a shift into 3rd as the engine climbs from say 2,200 rpm to 3,000 rpm. It feels like it's more pronounced when under load, up hills, around corners - almost like it could not be getting proper fuel pressure. The stumble does not occur if accelerating hard from a stop and does not occur at all after the secondaries open. This only occurs under part throttle. I've checked for vacuum leaks related to me pulling off the air intake duct when I relieved the fuel pressure for the fuel pump install, nothing found. Also....car runs FINE when stone cold - nice smooth acceleration through all gears, the stumble/hesitation starts appearing within 1-2 minutes after car has been running from a cold start, or anytime engine is warm/partly warm (like after the engine enters closed loop from open loop). No check-engine lights or misfire codes. Spark plugs and wires recently replaced and done 1 month prior to fuel pump install, car ran fine for that month.
I researched that old lengthy "my very own misfire/hestitation" thread and found this from brapple:
ok I looked at and drive the car last night.
this is not a miss fire because of plugs or wires.
this is not an intake or maf issue. we installed a stock SVT airbox w/mesh screen and the maf from my 99 SE and it didn't make a difference.
watched the O2 sensors and maf air flow rate and all seems correct.
watch the fuel pump pulse width and fuel flow rate via livelink. the flow rate was smooth and increased/decreased with engine rpm. the pulse width did also.
however I believe there was a quick drop out in the fuel pump pulse width when the car bucked. I am pretty sure it was as the same time anyway.
So I am leaning towards a fuel issue as it seems similar to the hessitation/bucking I get in my SVT when near a full tank of gas (it has the classic hesitation/bucking when below 1/4 tank of gas)
I have the log file from driving around that I will post for someone to look at. The one weird think that I noted was the spark advance at time spiked to a very, very large number then came back to normal. never seen that when data logging.
Also brent test the egr valve as I suggested just to rule it out.
this is not a miss fire because of plugs or wires.
this is not an intake or maf issue. we installed a stock SVT airbox w/mesh screen and the maf from my 99 SE and it didn't make a difference.
watched the O2 sensors and maf air flow rate and all seems correct.
watch the fuel pump pulse width and fuel flow rate via livelink. the flow rate was smooth and increased/decreased with engine rpm. the pulse width did also.
however I believe there was a quick drop out in the fuel pump pulse width when the car bucked. I am pretty sure it was as the same time anyway.
So I am leaning towards a fuel issue as it seems similar to the hessitation/bucking I get in my SVT when near a full tank of gas (it has the classic hesitation/bucking when below 1/4 tank of gas)
I have the log file from driving around that I will post for someone to look at. The one weird think that I noted was the spark advance at time spiked to a very, very large number then came back to normal. never seen that when data logging.
Also brent test the egr valve as I suggested just to rule it out.
Last edited by BrApple; 08-01-2008 at 10:13 AM.
I am wondering if I have a faulty fuel pump that could be causing this, or did something else happen around the time I replaced the pump? What I am wondering: what is the best way to test and observe the operation of the fuel pump - mine is the returnless system, and my understanding is that the fuel pump driver module regulates fuel flow by regulating the pump itself - so I would think if the pump is not responding properly to the driver module under all operating conditions, the potential exists that the pump is not providing proper fuel pressure under all conditions.
Other things I've checked - roll restrictors look fine, ignition wires look fine (they are NGK wires).
Any thoughts especially on equipment/software to "watch" the operation of the fuel pump would be appreciated.
Thanks,
I am wondering if I have a faulty fuel pump that could be causing this, or did something else happen around the time I replaced the pump? What I am wondering: what is the best way to test and observe the operation of the fuel pump - mine is the returnless system, and my understanding is that the fuel pump driver module regulates fuel flow by regulating the pump itself - so I would think if the pump is not responding properly to the driver module under all operating conditions, the potential exists that the pump is not providing proper fuel pressure under all conditions.
Other things I've checked - roll restrictors look fine, ignition wires look fine (they are NGK wires).
Any thoughts especially on equipment/software to "watch" the operation of the fuel pump would be appreciated.
Thanks,