2013 4.0 Throttle Dies Under Hard Acceleration

2013 4.0 auto

Was doing a lot of highway driving yesterday, hard acceleration to pass etc. between 75-85mph. Truck ran fine until at one point going up a hill around 65, the truck tried to downshift as I gave it more gas, and then felt like it went into a limp mode. Tac dropped even though my foot was on the gas. I pulled over and the truck would go through gears fine going up to speed again. Hard acceleration would replicate the problem. Limped the rest of the way home at 60 with light throttle. No issues shifting after coming to stops as long as I was not in a hurry.

Today I went to start the truck and it wouldn't ignite. I think this is a separate rabbit hole that I've been down before (had the fuel pump replaced a year ago), and think it's related to the after market security system some dealers put in with the immobilizer control. I did manage to get the truck to start and went and filled up with 91 and some sea foam. Before the drive home yesterday I had filled 3/4 of my tank at a dodgy gas station, so bad gas may be a factor here.

Truck ran fine to and from the gas station today as long as I kept the throttle light. However, even at lower gears, if I try to hard accelerate, it will have the problem (so not just high gear uphill like yesterday).

It will also do this in park, see the video below. My foot is completely to the floor and does not let off the gas pedal. Around 3k it's like I let off the pedal entirely, but my foot is still down. It will kick up again as you see. None of that is done from my foot. If driving this basically feels like I slam on the brakes and then floor it again before slamming on the brakes. It will do this until I lay off the throttle and let it gain speed smoothly. It sometimes also backfires while doing this.

https://youtu.be/naicuV5UCC0

 

Sound like the fuel pump.
These trucks run on 2 speeds.

Low speed, Low engine loads = Low speed ( through the fuel pump resistor )
High Speed, High Engine Load = High speed (No fuel pump resistor)

 

This is a resistor within the fuel pump itself?

 

When is the last time your truck had a tune up. I mean a thorough professional tune up?

 

No, it's located behind driver side headlight.

 

I haven't. Just have performed the scheduled maintenance (mostly, need to do the trans flush and change spark plugs) pretty on point since I got the truck at 19k miles. Just under 62k now.

 

Looks like this:

 

The fuel pump relay could possibly be bad, at higher RPMs and loads it bypasses the Fuel Pump Resistor to run the pump at high speed.
You could test it by putting a test light from battery ground to the Black/Red wire at the Fuel Pump Resistor (mounted in front of the battery) and see if it stays lit when the truck want's to stall, if it doesn't either the relay is bad or the wire from the relay has an open circuit.

 

Resistor is here

 

So that’s what that does.

 

When you say "to the Black/Red wire at the Fuel Pump Resistor". I see the wire, just curious how I would get a test light/meter on it, as it goes into the plug.

thanks, found it and took a look. Nothing obvious as far as corrosion or torn wires or anything.

 

Either backprobe the wire with a needle or other suitable tool or unplug the resistor, jump the terminals together, and put your light on the jumper.
You could also poke a hole in the wire but make sure you seal it up with some liquid tape.

 

ask in the hp tuner thread. lots of great knowledgeable people there if you havent found the culprit.

 

Thanks, I'll give this a shot tomorrow

 

No problem, I would also say if there's another non critical relay in the fuse box that is the same as the fuel pump relay you could simply swap it and see if it fixes it.

 

Thought about that, I think the STOP LP CTRL is the same, but wasn't sure if swapping would be an issue while driving. Looks like that is for skid control, so probably won't hurt to temporarily swap?

 

May set an ABS code but shouldn't hurt anything, also won't have any stop lights with that relay pulled.

 

Dimmer relay looks like a good match?
What do you think @Dm93

The Stop lamp is different from the fuel pump.

One looks normal open, the other closed?

 

Pinouts look to be the same but whether they are physically the same or not is the question, I'm not near my truck right now or I would go look.

 

Backfire makes it sound like it's running fuel rich at load. Maybe check/clean the MAF?