I've got a 1990 Ford F150 3.9 that was running great until this afternoon. I drove about a mile, the CEL came on, and if I press over about 10% on the throttle, the engine bogs down like it's getting no air.

So far I've done the following:
-Checked for obvious things like loose wires, corrosion, etc.
-Checked for vacuum leaks
-Checked the intake for debris
-Replaced the MAP sensor

No change. Any ideas what I should do next? Your help is much appreciated.

 

If you can't pull the codes, the first place I'd check is the throttle position sensor, and then put a gauge on and check your fuel pressure as the fuel pump may be going bad

 

Thanks. Checked the throttle position sensor and its voltage reads between 3.5v and 4v no matter where the throttle is, with a steady 5v supply voltage. Seems like that might be the issue. Now begins the challenge of whether I can get those screws off without stripping them

 

Finally found the problem. Two of the capacitors on ECC had their posts burnt off.

It finally hit me to check there when I noticed the fuel pump would stay running when the key was in the on position. If I remember properly, it wasn't doing that when I first posted. Checked the rail and fuel pressure read 55psi, so that wasn't it. Turns out it was a capacitor in the ECC set up as a timer for the fuel pump. Since it didn't work, the fuel pump remained on and the engine wouldn't spark.

I'm not sure yet what the other blown capacitor was for, but replacing those got everything working fine again.

Thanks for the help!

 

What is ECC?

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