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No power under full throttle


Fordmonsta

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I've got a 99 extended cab 4x4 auto with the ohv 4.0. It runs good under normal driving conditions, when you floor it, it just gives up. I mean it gains speed but real slow, it runs better at half throttle than on the floor. When I bought the truck it wouldn't rev even in neutral. So I pulled the 2 rear cats off and they were all busted up so I gutted those. At the same time I replaced all 3 02 sensors along with to and crank sensor. I heard some rattling from under the truck today so I gutted the other 2 cats on the y pipe.it still runs the same, no check engine light. Any help is appreciated
 


Rock Auto 5% Discount Code: 70D65189E6D8FF: January 5th, 2022

Fordmonsta

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So I hooked up a fuel gauge this morning and found pressure dropped from 60psi at idle to about 45 wide open. Also hooked up our big scanner at work to view live data. It showed a tps update rate way out of range first off. Secondly I looked at ignition timing. It started out 27-28 degrees at idle and as you ease into it itll ramp to about 32 at half throttle, after half throttle it drops to about 12 degrees. Are these 2 things related?
 

RonD

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I would certainly put on a new fuel filter if you haven't already

The 45psi is a concern
In 1999 both the fuel pump and the fuel pressure regulator are on the same assembly in the gas tank, if either is failing then you will get the pressure drop on high demand(full throttle)

At wide open throttle computer doesn't use O2 sensors at all, just opens injectors for max power

Spark advance is less when fuel mix is richer, accelerating, but 12deg sound like too little advance, that would be a PCM(computer) issue in a 1999 Ranger

On OBD2 live data you should see TPS at 16-19% throttle closed
Then 90-93% throttle wide open
TPS is a 5volt sensor, expected voltage throttle closed is just under 1volt, so not quite 20% of 5volts
Wide open voltage is 4.5v or more, so 90%+, but never 100% that would mean something is wrong

I would use a vacuum gauge to test engine
18-20" is expected at idle
Raise RPMs up to 2,500(approx.) and hold, should drop then climb back up and stay steady, it is slowly dropping the longer you hold it, then you STILL have exhaust blockage(muffler?)

Check your air delivery system, i.e. air filter and box

Also there is an RPM limiter on all fuel injection computers, not a Ford thing
Usually its set for 3,000rpms
So try run in say 2nd gear up passed 3,000rpm to se if you have the same issue, so not a "throttle" issue its an RPM issue
Limiters are engage when trans is in Neutral or Speed is below 5mph
 

Fordmonsta

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1999
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Transmission
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I've installed new air filter fuel filter and maf assembly. Also installed a new muffler, tps, crank sensor and cam sync. Didnt replace all at once just one at a time to see if there was any change. I also put new 02 sensors on but they were some cheapo ones off rock auto. I'm kinda baffled
 


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