Full throttle bog out
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4th Gear
Joined: Aug 2025
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Full throttle bog out
At a roadblock I’ve got a 1994 f150 5.0 5spd that starts runs great but bogs under full throttle or at any rpm driving unless eased to rpm. I’ve done new tps new fuel filter new coil new plugs wires new fuel regulator gutted the cat the truck has headers from when I bought it so smog isn’t hooked up or egr I’ve tested fuel pressure and it’s good but the truck runs rich or doesn’t burn the fuel well and will bog and almost hold whatever rpm it was at and backfire through exhaust and intake but all 8 plugs foul evenly the truck puffs black smoke but the only time I’ve got it to run great and even spin wheels under throttle is after I forgot I had the eec jumped to check engine codes and it ran perfect under load and full throttle so are we thinking computer or what?
Hotshot
Joined: Jun 2015
Posts: 12,830
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Is there an oxygen sensor and is it plugged in? Have you or did you ever check for Key On Engine Off (KOEO) fault codes or did you keep throwing your wallet at it? I have a fuel pressure gauge and there is no “good” mark anywhere on it so what pressures do you have with and without the vacuum line attached?
Cargo Master
Joined: Mar 2007
Posts: 2,822
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I know with the Tweecer program that at some point, once the EEC-IV sees a certain throttle opening, it should ignore the O2 sensor signal. If it is indeed bogging at full throttle, it's probably not the O2 sensor. On the other hand, it's too easy to just to unplug it and see what happens.
Great point on the test spec 'Good'. It's used all too often and when I was the Shop Foreman and the tech told me it was 'Good' I instantly knew the test was not done. I once had a tech tell me the coil was bad. I asked him how did he know that. 'I just know'. I had him hold the coil wire and I was going to crank over the engine. He jumped back and yelled 'No! It might just come back to life!'. The guys around me all laughed. I don't recall what the real problem was, but the car left with the same ignition coil.
Great point on the test spec 'Good'. It's used all too often and when I was the Shop Foreman and the tech told me it was 'Good' I instantly knew the test was not done. I once had a tech tell me the coil was bad. I asked him how did he know that. 'I just know'. I had him hold the coil wire and I was going to crank over the engine. He jumped back and yelled 'No! It might just come back to life!'. The guys around me all laughed. I don't recall what the real problem was, but the car left with the same ignition coil.
Hotshot
Joined: Jun 2015
Posts: 12,830
Likes: 2,436
See… I was wondering if there was a sensor installed with the new exhaust system and you know that there is. If there is no sensor then it could definitely be a problem with overfueling.
Logistics Pro
Joined: Aug 2010
Posts: 3,716
Likes: 583
From: Chillicothe
the way I'm reading the op post is that the cat us gutted. Which makes me thing that is has shorties to the original y pipe and cat. So it SHOULD have the O2 sensor unless it was removed or not hooles up. But on the other hand, he says it has no Smog equipment.
Tuned
Joined: Jul 2023
Posts: 461
Likes: 51
I guess with the 302 you may need a square head plug fitting with some thread tape (similar to what is pictured at this hyperlink) to cap off where the EGR pipe threads into the intake manifold, but the plug itself would have to be the same thread pitch as the EGR pipe threads at that point.
Smith Cooper 150# Black Malleable Iron 1/2 in. Square Head Plug Pipe Fittings - Threaded - John M. Ellsworth Company
Smith Cooper 150# Black Malleable Iron 1/2 in. Square Head Plug Pipe Fittings - Threaded - John M. Ellsworth Company
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Thread Starter
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4th Gear
Joined: Aug 2025
Posts: 4
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I know with the Tweecer program that at some point, once the EEC-IV sees a certain throttle opening, it should ignore the O2 sensor signal. If it is indeed bogging at full throttle, it's probably not the O2 sensor. On the other hand, it's too easy to just to unplug it and see what happens.
Great point on the test spec 'Good'. It's used all too often and when I was the Shop Foreman and the tech told me it was 'Good' I instantly knew the test was not done. I once had a tech tell me the coil was bad. I asked him how did he know that. 'I just know'. I had him hold the coil wire and I was going to crank over the engine. He jumped back and yelled 'No! It might just come back to life!'. The guys around me all laughed. I don't recall what the real problem was, but the car left with the same ignition coil.
Great point on the test spec 'Good'. It's used all too often and when I was the Shop Foreman and the tech told me it was 'Good' I instantly knew the test was not done. I once had a tech tell me the coil was bad. I asked him how did he know that. 'I just know'. I had him hold the coil wire and I was going to crank over the engine. He jumped back and yelled 'No! It might just come back to life!'. The guys around me all laughed. I don't recall what the real problem was, but the car left with the same ignition coil.
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Logistics Pro
Joined: Aug 2014
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At idle and WOT, the computer is in closed loop.
At part throttle, its open loop and uses the O2 sensor as feed back.
Why did you change all this: new tps new fuel filter new coil new plugs wires new fuel regulator gutted the cat ?
Did you replace with motorcraft parts?
Is the TPS adjusted correctly, or did you just put it on?
Was the problem there before, or after you changed parts?
Did the problem happen suddenly or slowly?
To me, sounds like timing, running rich is fuel.
Is your fuel regulator working? What is the pressure at idle, and when driving?
Do you have any exhaust leaks?
If the cat is gutted, does it leak?
Probably crap aftermarket coil and plug wires, bad spark, and or cross fire/incorrect firing order on the plugs.
You don't notice at idle, but as soon as you put your foot into it major misfire coming out exhaust and intake.
Or you engine timing chain is completely stretched or jumped a tooth.
Doesn't spin the tires anymore, you probably have worn out the engine.
Thread Starter
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4th Gear
Joined: Aug 2025
Posts: 4
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Thread Starter
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4th Gear
Joined: Aug 2025
Posts: 4
Likes: 0
Is there any way to test the eec to figure that out or is it just a toss up