Failed on highway: Blinking 4LO

Accelerated pretty hard onto the highway and the engine gave out abruptly. It didn't completely stall, but was hovering between 750 and 1500 RPM and not responding to the gas pedal.

4LO was blinking.

I pulled to the shoulder and had no power at all; the engine was running but truck wasn't moving. I turned it off and on again and 4LO was still blinking. It cranked for 4 seconds or so before stopping on its own.

So I got it towed to a local shop, but it'd be great if y'all had any idea what might have happened.

Google shows some people disconnect the battery for a few minutes and it seems to be ok, so I can try that in the morning, but is that a permanent fix? I don't like being stuck on the side of the road.

Google also shows sometimes it's a mass airflow sensor, but in those circumstances it seems like the truck goes into limp mode, and mine wasn't even limping.

 

Sounds like a transmission issue. Disconnecting the battery works for minor things. If your truck lost power and wouldn’t move, something is broke. A battery reset won’t fix that.

 

Thanks for the ideas. Would either of those prevent it from starting?

 

TPS could definitely effect the truck not starting.

 

Without knowing the code it's all guessing. TPS should throw the check engine light.

 

Do you have a check engine light on, and do you have the ability to check for any codes?

 

I'm not sure if the CEL is on because it's always lit until you start it, right? I had it towed to a mechanic so I can't check the codes, but tomorrow is Sunday so maybe I'll sneak over.

 

This is true, I missed the part where it stopped running altogether. Good luck, and let us all know how you make out.

 

Yeah my wife's first thought was a fuel pump. I had 90 miles left in the tank so probably not water in the gas. I never had any warning signs of a bad fuel pump, though.

 

But why would 4Lo be blinking and not a check engine light if it was engine/fuel related?

Sorry I'm not much help here, but this is the first thought that popped into my head.

 

This says only 4 lo flashing is CAI/MAF sensor related. Have you done any work to the truck recently? I remember a thread years ago where a guy was off road and his truck died with the same symptoms. Turns out the tube from his airbox to the intake came loose. I think he just put it back on and tightened the clamp and was good.

A loose intake tube would correlate with it happening when you were accelerating. Maybe the MAF sensed too much air coming in.

 

Thanks for sharing that, I learned something new today!

 

Not my diagram but it’s been floating around here for years. It’s helpful as a first start when you have a dash light.

 

Thanks, I'll check it out.

 

If the intake pipe falls off the throttle body or the MAF has a total failure, the ECU cannot see the air volume flowing to engine and freaks out. This is critical data for running the engine. Try unplugging the MAF sensor. The engine will run without it albeit poorly or in limp mode. If it does run unplugged, there is something going on with the Maf sensor and its output.

 

Thanks for your help, everyone. The correct answer is...

FAILED IGNITION COIL FUSE

Which I definitely could have diagnosed and fixed myself but I didn't want to get it towed to my house if it was going to be too big of a job for me.

Anyway I'm back up and running, $375 lighter.

 

Fuses RARELY "fail." More likely it did its job and was blown from excessive current. Best to see it to confirm that. If the fuse was blown, that is indicative of a downstream problem, likely a short on a failing coil or a wire issue. I fear that your fix was only temporary and likely will see it repeat. Suggest you put an ohm meter on each coil and confirm they are in spec. However, coils are notorious for being fine and dandy when cold and only show their problems when they heat up and often show the issues intermitently. Can't diagnose this in a thread, but IF it was blown, fuse replacement is NOT the fix. Something else caused it to blow and is likely to do it again.

Good luck with this.