Hesitating at high speed
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Hesitating at high speed
I have a 99 F150, 4.9L, with 98K miles. The truck runs fine a lower speeds and has normal acceleration but at higher speeds (>55) it hesitates (misses) for a second and then accelerates fine. I have changed out fuel filter and air filter and run fuel injector cleaner with out any change. No engine codes are found.
Any ideas?....on previous vehicles I would replace the rotor and cap but this guy does not seem to have one. The spark plugs are on my list of to do but I thought they would have problems at low speed too as well as changing/flushing the transmission oil/filter
Thanks
Jim
Any ideas?....on previous vehicles I would replace the rotor and cap but this guy does not seem to have one. The spark plugs are on my list of to do but I thought they would have problems at low speed too as well as changing/flushing the transmission oil/filter
Thanks
Jim
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Joined: Sep 2006
Posts: 7,907
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If..... your truck acts as follows;
In overdrive at speeds between 45 and 65 you experience missing at light throttle applications then it goes away, there is a bad coil.
Which one, is a problems to find because it does not set a code.
The problem is a coil with low output and not an outright failure.
Reason it misses at that time of the driving condition, the EGR opens and other things happen to make the air fuel ratio very lean. The low output coil can't fire that peticular cylinder under lean conditions.
As you apply more throttle, the condition changes to a richer mix the coil will fire hence any fault history is cancelled as far as a set code.
Only way is to have a dealer stress test to find which coil is low output.
Note, sometimes changing plugs seems to make the issue go away only to return later because the new plugs are easier to fire until they get some operating time on then the issue returns again.
Good luck.
Other wise trying to chase it with single replacment is a long process unless you change all 8 then hope all the new ones are good.
In overdrive at speeds between 45 and 65 you experience missing at light throttle applications then it goes away, there is a bad coil.
Which one, is a problems to find because it does not set a code.
The problem is a coil with low output and not an outright failure.
Reason it misses at that time of the driving condition, the EGR opens and other things happen to make the air fuel ratio very lean. The low output coil can't fire that peticular cylinder under lean conditions.
As you apply more throttle, the condition changes to a richer mix the coil will fire hence any fault history is cancelled as far as a set code.
Only way is to have a dealer stress test to find which coil is low output.
Note, sometimes changing plugs seems to make the issue go away only to return later because the new plugs are easier to fire until they get some operating time on then the issue returns again.
Good luck.
Other wise trying to chase it with single replacment is a long process unless you change all 8 then hope all the new ones are good.
Lead Driver
Joined: Sep 2006
Posts: 7,907
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I might add something I have never mentioned before.
If a coil fault is just a certain type of fault, it can actually cause a return signal back to the PCM by sort of a reflection signal and cause the PCM to momnetairly 'STOP" processing all activities.
The results of this is felt as a large 'jerk' as if the igntion were shut off for a splt second then on again as the PCM regains abiltity to resume signal processing, then all activities go normal until it happens again.
If a coil fault is just a certain type of fault, it can actually cause a return signal back to the PCM by sort of a reflection signal and cause the PCM to momnetairly 'STOP" processing all activities.
The results of this is felt as a large 'jerk' as if the igntion were shut off for a splt second then on again as the PCM regains abiltity to resume signal processing, then all activities go normal until it happens again.
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I went under the hood to specifically look at the ignition system and found that I have some sort of electronic distributor with plug wires and no COPS. Is there anything in this distributor that can be the source of the problem? Also, how does it work? I looked in my manual and it did not break it down.
Thanks
Jim
Thanks
Jim
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