99 F250 missing under load low rpm
#1
07-10-2010 | 10:38 AM
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99 F250 missing under load low rpm
I,m perplexed. My 99 F250 w/ V10 Triton has been a great motor but recently it started missing @ take off and when under load or pulling a trailer. If you feather the accelerator and don't step into it it accelerates smoothly and does not do this after the truck is moving and at higher speeds and rpm. It is also intermitent. I have changed the egr sensor, fuel filter and plugs. It shows no missfire on a scope and a mechanic swapped the cop's around but did not notice any difference when doing so. Also when you first start it up it dogs really bad, but if you shut it down and retart it several times it seems to help clear this up. I'm clueless at this point, if anyone can give me some insight on this situation I would be extermely grateful
#2
07-10-2010 | 11:35 AM
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Sounds like you have a coil breaking down under load. Just curious,,,,,,,if you swap positions with a questionable coil what do you accomplish? I suspect you have a bad coil and the only way to swap and isolate it is to start with one new coil. Wouldn't you agree? Did you scope check the coils under load? Also, a questionable crank sensor can give the same symptoms you describe.
hanky
hanky
#4
07-10-2010 | 07:59 PM
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Before you go getting into a lot of unecessary expense, You repeated you tried the coil swap. What I'm trying to say is; if you move a defective coil from one place to another , it's still defective!!! They have had a lot of problems with those coils. I know they are not cheap, but if you get a new one and substitute it for each coil one at a time , its a pain in the butt, but you will find the the defective coil that is breaking down under load. Did you do this? hanky
#5
07-10-2010 | 08:10 PM
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Some of the early model tritons had a problem with intermitent coolant leak dripping down on the back coil pack on the right side of the engine, might want to check for this, and or change this coil pack just incase it has been damaged
#6
07-11-2010 | 07:30 AM
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Here is one of those off the wall shots that theoretically should work.
If you can get the engine to misfire long enough the ECA/ECM should pick up which cylinder(s) are msfiring. You should be able to get this info from the ECA/ECM with the proper scan tool or code reader. In the process you may or may not get a check engine lite to come on. This should help isolate the cylinders that are causing you problems. It should save you some time and work. If you decide to try it , let me know if it helped you. Thanks,,,,,,,,,hanky
If you can get the engine to misfire long enough the ECA/ECM should pick up which cylinder(s) are msfiring. You should be able to get this info from the ECA/ECM with the proper scan tool or code reader. In the process you may or may not get a check engine lite to come on. This should help isolate the cylinders that are causing you problems. It should save you some time and work. If you decide to try it , let me know if it helped you. Thanks,,,,,,,,,hanky
#7
07-11-2010 | 08:07 AM
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Thanks for the input. I ended up leaving the first new coil in the back right position,understandably. I bought a second new coil and did the swap out again. No noticable change, but, after each test drive the problem lessened, truck had more power. I know that coils don't normally fail systemically, but the truck has 170k miles on it and my thought is that they are weakening w/ age. Make any sense?
#8
07-11-2010 | 09:17 AM
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Considering the problems they have had with these coils, it makes a lot of sense and you could have more than one giving you heartburn! It is possible after you exchange a coil,the plug cleans up and fires more efficiently. Glad you 're having some success in your efforts. 
Thanks for the update. hanky
Thanks for the update. hanky
#9
08-02-2010 | 07:00 AM
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99 F250 Still running bad
Since my initial post I have replaced all coils, sparks, egr sensor, fuel pump, filter,and pressure regulator. I have replaced TPS, pcv and hose as well as air filter and swapped out my mas air w/ a good one and it still bogs down under load. I had a Ford dealership put it on a scope and they couldn't tell me anything either. Says it shows a mas air sensor butI have allready checked that. If you lightly put your foot into the gas it will sputter but then accelerate smoothly. If you step into the pedal from a stop it will miss/ bog but will accelerate slowly until you hit 2500-3000 rpm or so and then smooth out and accelerate normally. Once you are running on the road it runs fine, can kick in passing gear normally. When you brake torque it , it misses poorly and only reaches 1000-1200 rpm then cuts out and sometimes dies. If you gun it in park it cuts out but accelerates slowly up to about 2000-3000 rpm the smooths out and continues to accelerate normally. I have noticed that sometimes you can hear a loud whirring/soft howl from the air body, throttle body. Also, when I changed the plugs they were all white indicating that it is running lean. I am ready to pull out what's left of my hair. Anybody got any thoughts? Thanks
#10
08-03-2010 | 02:13 PM
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Does this make any sense to you? If it was a carburetor fed engine what would you look for suspecting a lean condition from looking at the plugs? Insufficient fuel sound good to you? You have from the plugs appearance been led to suspect a lean condition correct. If just about all the fuel system has been changed , whats left? Air getting in after the air flow sensor, and how could that happen, Maybe a vacuum leak that the ECM cannot compensate for immediately, but when it gets the signal from the o2 sensor on acceleration it corrects but you are now at a higher RPM and somewhat reduced load. Maybe this is a lot of hot air ,but Do a thorough check of the entire intake system , hoses , vacuum canister all that stuff. Don't overlook any thing at this stage of the game. If this keeps up, I'm gonna go bald with you!,,,,,,,,,,,,hanky