1990 F150 runs in park and neutral, dies in gear

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Yesterday | 04:32 PM

Canthelpmyself

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2nd Gear

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1990 F150 runs in park and neutral, dies in gear

I have a 1990 f-150 XLT Lariat 302 with the E4od. The motor starts and run fine in park, shift into gear fine, but as soon as I touch the gas it dies. Will rev fine in neutral, cannot take any load. Pulled the code 99 for Electronic Pressure Control Circuit, pulled the harness back to the engine bay and checked for continuity. Tested the solenoid and had no resistance where I should so I dropped the pan and replaced the solenoid pack. Just checked codes again and still getting 99. I assumed that if the transmission was defaulting to maximum line pressure that would kill the engine much like dumping a clutch at idle on a manual transmission. Any ideas? The overdrive light is still on the dash as well.

Yesterday | 06:54 PM

Prototypemech

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From: Mojave, Ca

Disconnect your throttle position sensor and test your truck again.

Yesterday | 07:17 PM

Canthelpmyself

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Quote:

Originally Posted by Prototypemech

Disconnect your throttle position sensor and test your truck again.

Thank you, that was my next guess. I have a replacement TPS, PCM, and IACV ready to go in, I was just stumped by the solenoid replacement and still pulling the 99 code. I bought the truck from my neighbour who said it started doing this while parked on his property, he just towed it into his garage and never got around to figuring out what the problem was. I ordered the likely suspects before I found that code thinking I would just throw cheaper parts at it before going down a transmission rabbit hole. I’ll get to the TPS this week and update the results.

Today | 04:58 AM

Prototypemech

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From: Mojave, Ca

99 is an odd code to throw. Remove your ecu, open it up, and look for leaking capacitors and corroded traces on the main board. Its very common for our generation trucks to have leaking capacitors and it causes weird problems.