My 2003 5.4 suddenly has an issue.

At greater than 35mph, suddenly and randomly my trucks transmission will back down, the truck engine will stall losing power steering and the odometer reads all dashes (hyphens). The tach and speedometer go to 0, and the oil light, check engine light, and battery light come on. While coasting to a stop, after 2-3 seconds the tach and speedometer will begin to read again, the warning lights still stay on and I must park the truck. Upon parking, I can immediately restart the engine and the truck starts fine. I can then drive away fine until I get back up to speed. I only get about 3 miles at those speeds before it will stall again.

I cannot get this to replicate under around 35mph. I cannot get it to replicate parked doing rev tests or moving various wires around to find a short. Battery seems connected well enough in my opinion.

While diagnosing on a country road, I could not get it to respond to me driving it hard or babying it. It was completely random when it would choose to fail.

Sometimes it will seem like it's about to fail, the battery light will flicker for a near instant (not enough enough to light the bulb fully inside), and I'll regain power. I'd say it's a 30% chance I can recover and continue to drive.

I ordered an OBD2 sensor but it wont arrive until Friday.

Other info: I have no aftermarket parts installed that I know of except a new COP on one of the spark plugs. That plug was causing misfires, which have been fixed since I put the new plug and COP in.

So, any ideas?

 

The dashes is a voltage issue, it will do that if you slowly turn the key back, loose engine power, but still in the "on" position

I'd be looking at either battery, cables, main grounds, or ignition switch type of major electrical failure points

 

Alright, I had more time to work on it. I took the advice and found the battery terminals were in pretty bad shape after all, so I cleaned those up to new, and that's fixed some issues but revealed some new ones.

The problem is still happening, but now instead of the vehicle shutting down, the transmission is only slipping into neutral and then going back to drive after 1-3 seconds (unlike before where it would slip out and then the truck would stall).

With a lot more testing, now I've been able to tell that it's not just a random speed. It seems to be 3rd or 4th gear causing issues. Oddly enough I don't think it's doing it while actually shifting, because it will do it in cruise on a flat straightaway at 50mph. The cruise will high rpm it when it slips and then recatch and continue driving fine. When it slips, the check fuel cap light will sometimes semi-flicker and come on for a split second alone.

Transmission fluid is at acceptable levels. It is pink as it should be.

edit: Sorry, I'm sure this is now in the wrong subforum due to the nature of the problem shifting around.

 

The dashes in the odometer window indicates that the cluster has lost communication with the PCM. Usually, this is seen when the PCM looses its operating power, most commonly at vehicle start-up.

I'd be suspicious of the following, including their mechanical socket connections:

PCM Power Relay, fuses F2 F18 & F23, & PCM Diode under the hood and F30 under the dash
Worn ignition switch


The OBDII adapter will be useless, all it will do is drop communication when the failure occurs.

 

I checked all the fuses and cleaned the PCM relay ports and swapped them around. Still doing the same thing =/

So unless it's in the actual wiring to the relay connectors that's mysteriously only shorting out in 3rd+ gear, I'm sad to report it's not relay related.

At this point, there isn't a whole lot left I can do myself at my knowledge level and google has been utterly useless. While I'm still hoping it's a fluke on the electrical side or a sensor gone bad for the transmission, I'm worrying it's the transmission itself

I'll check codes tomorrow just in case, and then decide who I'll send it to with what I've already troubleshot.

 

Go back and check those fuses I listed. A loose fuse SOCKET can do some awful strange things...

 

If you don't find a bad fuse, take your battery and have it load tested. I suspect that it's been damaged by being consistently undercharged because of the bad connection.

 

He hasn't yet found a bad connection, but that's my suspicion.

If the battery was bad, he'd be reporting issues with cranking/starting and none of those symptoms were reported.

 

He said "Alright, I had more time to work on it. I took the advice and found the battery terminals were in pretty bad shape after all,".

That says bad connection to me, particularly when charging. A heavy current draw like starting will often burn through a dirty connection but the battery won't get enough charge and will slowly drain and if left with a low state of charge long enough it will damage the battery. The low state of charge is also what causes the hard starting problems and that's usually when people first realize that there's a problem.

In my experience, a weak battery USED TO show as cranking/starting problems but in the last 5 or 6 years most of the battery and/or electrical problems that I have seen have shown up as just random, intermittent, total electrical power losses. The battery frequently starts working again a short time later but the problem of random failures always gets worse and worse until I replace the battery. I've seen the same thing over and over and on many makes of cars. The one thing that seems to be consistent is that the batteries almost always came from Discount Auto Parts!

The clue as to whether it's a PCM power problem or a battery (or battery terminal) problem is whether or not he loses ALL electrical power at the same time. If the head lights, dome lights, brake lights, etc keep working then the problem is in the PCM circuits but if the problem is related to the battery, he'll lose all electrical functions.

But the short version is that it simple and easy to get a battery tested (many parts houses will do it for FREE) and then he'll know for certain one way or another.

OP. You said "So unless it's in the actual wiring to the relay connectors "

THAT is a very real possibility! In the past I've found a lot of bad fuse and relay sockets. Look at the sockets very carefully when you pull the fuse and connectors and particularly look for any signs of heating or melting. If you seen ANY sign of that from the top, well, you'll find a lot worse on the bottom! The manufacturers are really skimping on material, especially copper wire and they make the wires as SHORT as possible. The result is that sometimes they're too short and will pull loose or they're so tight that they rub against other wires or the body and short out. After you check the easier to access areas, if you still haven't found the problem, unbolt the relay and fuse blocks and take a good look at the back of the sockets and the wires leading to them. (Disconnect the battery first!)

Also check all grounds thoroughly. Electrical devices require power and GROUND to work. It seems too obvious but many people just assume that everything is well grounded and sometimes that's not true.