Sentient acceleration/ Engine problems
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Junior User
Joined: Oct 2020
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From: Texas
Sentient acceleration/ Engine problems
I have a 91 f150 with the 5.0 and its having some issues, i fixed a leaking thermostat gasket yesturday and fillde it with coolant today, went well. On the test drive, I knew something funny was happening to the truck. It would accelerate almost by itself and it got to where it was so hard to brake because of the high rpms, i had to throw it in neutral to avoid an accident, when I did the RPM's jumped to about 2,000 randomly so i immediatly shut it off to avoid any damage it could cause. When cold starting, the RPM's are alwasy higher at first then drop down to about 700-800 normally, except when i ran it to bleed the cooling system before the test drive, they never dropped even when it reached operating temperature. Additionally, there is now a significant amount of oil leaking from behind the intake manifold on the china rails. I have no idea what caused this to happen, but I am guessing it is just an engine issue because I belive when in park or drive, the rpms are lower because there is a load on the engine, in neutral there is almost none. If anyone has ever heard of this or encountered it, please tell me how to fix it!
Cargo Master
Joined: Nov 2009
Posts: 2,190
Likes: 620
302's are fairly famous for blowing the rear intake manifold gasket out. The best thing to do is to get a new intake manifold gasket set, and take the china wall gaskets, and toss them right in the garbage. Lay about a 1/4" bead of Black RTV on top of the china wall, let it cure up a bit, then set the manifold back on, and run the bolts down finger tight. Let it sit overnight, and torque them in the morning.
Lead Driver
Joined: Oct 2016
Posts: 6,185
Likes: 633
From: Houston/Sugar Land
I have a 91 f150 with the 5.0 and its having some issues, i fixed a leaking thermostat gasket yesturday and fillde it with coolant today, went well. On the test drive, I knew something funny was happening to the truck. It would accelerate almost by itself and it got to where it was so hard to brake because of the high rpms, i had to throw it in neutral to avoid an accident, when I did the RPM's jumped to about 2,000 randomly so i immediatly shut it off to avoid any damage it could cause. When cold starting, the RPM's are alwasy higher at first then drop down to about 700-800 normally, except when i ran it to bleed the cooling system before the test drive, they never dropped even when it reached operating temperature. Additionally, there is now a significant amount of oil leaking from behind the intake manifold on the china rails. I have no idea what caused this to happen, but I am guessing it is just an engine issue because I belive when in park or drive, the rpms are lower because there is a load on the engine, in neutral there is almost none. If anyone has ever heard of this or encountered it, please tell me how to fix it!
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Junior User
Joined: Oct 2020
Posts: 63
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From: Texas
When you replaced the thermostat gasket, if you removed the thermostat you would not be the first to put it in upside down. To have the intake leak at this time would be a real coincidence. I have never worked on a 5.0 but if you had to or did remove the throttle body make sure the cable is not bound up causing the high RPM's
Thread Starter
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Junior User
Joined: Oct 2020
Posts: 63
Likes: 0
From: Texas
302's are fairly famous for blowing the rear intake manifold gasket out. The best thing to do is to get a new intake manifold gasket set, and take the china wall gaskets, and toss them right in the garbage. Lay about a 1/4" bead of Black RTV on top of the china wall, let it cure up a bit, then set the manifold back on, and run the bolts down finger tight. Let it sit overnight, and torque them in the morning.
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