Still chasing why my truck keeps dying

[Jared Jackson]

A couple of weeks ago, my 97 k1500, 5.7, 4l60e, kept randomly dying. It took a few occurrences to finally start to put together a pattern. It only dies at very low speeds like backing down the driveway or pulling up to a parking lot exit, and it always happens when I have my foot on the brake. Before I put together the pattern of failure, I put on a new MAF sensor (I had a code pop up for this before the truck started dying). I also put on a ignition module and a new coil pack. They appeared to be stock (which means they were old), so I am not mad about replacing them. It was a long shot that I wanted to replace anyway for reliability.

So, when it died this morning, I started putting together the slow speeds and the brake pedal as being a common denominator. I just filled the tank up yesterday, so I knew it wasn't sucking air in the fuel tank... what else related to the brake pedal would cause the truck to die? I just replaced the brake booster, so I know there isn't a vacuum leak there...

Then... I got lucky! I was in the drive-thru for the doughnut shop this morning and I heard a clicking noise start going crazy when I was slowly releasing the brake pedal after putting my truck into park. My first guess is that I am hearing my shift interlock solenoid for the shifter to be pulled out of park. What I wonder is if my brake light switch is bad and causing my Torque Convter lock/unlock to malfunction and stall out the truck when coming to a stop... That's my guess right now. The Delco switch was 9 dollars on Amazon. I am not going to go through the trouble of pulling that switch to test it and not put a new one in for 9 dollars.

 

[Jared Jackson]

Today, something new happened... The truck died coming to a red light trying to make a right turn (brake applied). However, it did not immediately start back up. I had to try about 5 times before it finally fired off and allowed me to drive away. (Motor was turning, but it was not firing off)

This throws a wrench at my brake light switch theory in my mind... That behavior starts to make me wonder if the fuel pump died and the line was sucked dry momentarily. (priming back up as I was desperately cranking while stuck on a busy intersection.)

I know that there is an issue with the switch because of the interlock clicking like crazy when I release the brake pedal. However, that doesn't explain the truck not wanting to fire back up immediately.

 

[Biggershaft96]

hook a voltage gauge to the fuel pump wiring as close to the pump as you can get and try to get it to die. if your converter locking was the issue you would know it because itd be like dumping the clutch in a manual

 

[Jared Jackson]

hook a voltage gauge to the fuel pump wiring as close to the pump as you can get and try to get it to die. if your converter locking was the issue you would know it because itd be like dumping the clutch in a manual

This is right along my other idea... get a fuel pressure gauge connected to the schrader valve (haven't looked for this yet) and see what happens to the fuel pressure when this happens. If it drops to 0... I know the pump gave out (or was turned off)... if it maintains pressure... I know it wasn't a pump failure... Is my logic sound here?

I just need to figure out how to run the line up to the cowl area and zip tie it to a wiper blade or something... I have heard of people doing this, but I haven't had to do it yet.

Found the fuel port... it's actually near the firewall so this idea may work...

 

[jdla140]

This is right along my other idea... get a fuel pressure gauge connected to the schrader valve (haven't looked for this yet) and see what happens to the fuel pressure when this happens. If it drops to 0... I know the pump gave out (or was turned off)... if it maintains pressure... I know it wasn't a pump failure... Is my logic sound here?

I just need to figure out how to run the line up to the cowl area and zip tie it to a wiper blade or something... I have heard of people doing this, but I haven't had to do it yet.

Found the fuel port... it's actually near the firewall so this idea may work...

Pull the "BRAKE" fuse on the inside fuse panel, it will bypass the brake switch for the computer, you won't have abs or TCC lockup but you can use it to verify the issue. Chances are it's a dying fuel pump, or maybe distributor or something like that.

 

[454cid]

Carry a rubber hammer with you. If the fuel pump dies, you might be able to get it going again by whacking the outside of the tank right under the pump.

 

[454cid]

Also, the truck will probably die before the pressure goes to zero. Mine dies at about 10psi.

 

[Jared Jackson]

Pull the "BRAKE" fuse on the inside fuse panel, it will bypass the brake switch for the computer, you won't have abs or TCC lockup but you can use it to verify the issue. Chances are it's a dying fuel pump, or maybe distributor or something like that.

so your theory is to just take the function of the switch out of the equation?

 

[Jared Jackson]

Also, the truck will probably die before the pressure goes to zero. Mine dies at about 10psi.

Right... I basically just wanted to watch the behavior of the fuel pressure when it dies to see if fuel delivery from the pump was an issue.

Noted... I will toss my rubber mallet into the truck.

with 170k on the truck... I don't know if that pump is stock. Might be beneficial to throw a Delphi pump in there anyway as a step and for the warm and fuzzy of knowing I have a new pump in the tank.

 

[454cid]

Noted... I will toss my rubber mallet into the truck.

On my long box with the 32gal tank my pump is very near to the filler, so that's where I hit it. I would assume yours is in a similar spot even though you've got a short box.

with 170k on the truck... I don't know if that pump is stock. Might be beneficial to throw a Delphi pump in there anyway as a step and for the warm and fuzzy of knowing I have a new pump in the tank.

My original pump only last 5 years. The dealer purchased replacement lasted 14. Kind of unpredictable in my experience. I normally don't like throwing parts at something, but in your case, a pump might not be a bad idea if you've got the time and money, and for the reasons you mentioned. If you can spare the truck while you wait for the part, get a look at the pump before ordering. You'll want to get a pump that is compatible with the broadcast code on the pump.... if original/ACdelco it will have it on a sticker. If it's another brand you may need to cross reference the part number. If you can't take the truck apart ahead of time, a dealer should be able to look it up by VIN... of course they'll want to sell you the pump for $$$.