Fuel pump does not get a run signal. 2004 4X4 regular cab.

Hi. Hope I got this post where it belongs. 2004 4X4 automatic Regular Cab. Only 75,000 on the odometer. Had since new. All OEM.

The problem is bad now. Cut off running for the first time. Had only occurred a few times over the years that it would not start. Troubleshot it till I diagnosed no fuel. I put a small digital voltmeter on the fuel pump wire.

What I know. The fuel pump has no timer like most. When you turn the key on, you see no voltage. Turn it to start and that applies voltage to the fuel pump and starter. When it starts and you come off the start back to on with the key, my added DC meter shows voltage since the ECM now realizes it is running and it supplies voltage.

I am hoping it's not the ECM. Thinking it is the ignition switch but since it cranks, you would think the switch is using the same contact for start and fuel pump. Also, since it died in the running mode, that really worries me. And also afraid to use the truck time I make a stab at a fix.

Need help.

Thank you.

 

As far as I know, that’s exactly how it’s supposed to work. There’s no prime shot on our trucks. Pump runs only when cranking and after startup

 

X2

 

X 3

 

on occasion the connector at the fuel pump sending unit will melt due to a bad ground. unfortunately the only way to verify this is to lift the bed or drop the tank… you just filled the tank too, didnt you.

 

Under what conditions does it just die?

 

The truck just quit now it cranks but no longer starts?

This seems to be intermittent problem your afraid it will leave you sit?

You no longer have voltage at the fuel pump while cranking??

Have you pulled any codes maybe point in the right direction .

Checked the fuses the EFI relay The circuit opening relay

 

When my old ‘84 did that it was the fuel pump relay

 

The 2rz and 3rz do not send power to the pump unless the ECM sees a signal from the crank position sensor.

Do you have a check engine light? Have you checked for stored codes?

 

Totally different system. The pre-taco trucks had an AFM that was also in the system controlling when the fuel pump was triggered. Not just power and a relay.

 

This info is accurate but the fuel pump is triggered based on crank position signal, not just turning the ignition key.


One thing you can try OP is hot wiring the pump.
Tilt your bed to the passenger side to access the pump and all connections and fittings. Run a positive wire to the pump connector and see if it comes on. If it does then try and start the truck. That would determine if you have a fault with the pump directly or not, but still doesn't eliminate a bad crank position sensor\other wiring in between. More troubleshooting would be required depending on the outcome of that test. But at least you would know the pump is 100% functional.

 

There is a reason why your computer is not allowing the fuel pump to run. Take a good flashlight and physically inspect the crank position sensor connection. It wouldn't hurt to check the cam position sensor as well. Check the Engine coolant temperature sensor ECT. My truck has two of those. One on the front and one at the back of the block at the firewall.

 

It might be different but it still has a circuit opening relay.

It seems OP has not been back!

 

The pump is fine. I hot wired it at the beginning. My meter shows no voltage on cranking. The first run cycle comes from ignition switch thru a two pole circuit breaking relay.

Then when key falls back upon starting to just on, ECM gets the signal from crank sensor motor is running and it provides power to the other pole on the fuel pump circuit breaking relay.

I am hoping it's either the ignition switch or the circuit breaking relay.

The ignition switch only provides power to relays, so there is not a lot of load but it wears. Since it has gotten so bad (I don't trust it.. left me sitting at a green light with people blowing horns at the old man)

Since it did it while running, it could be the circuit breaking relay.

I was hoping someone else hat seen it. This system I think is unique to 2004 on. No timer on fuel pump to hear it when you just turn on key. And you sure can't here it cranking. Why I put meter on line to pump.

Sorry, I didn't get back sooner. I checked the option to get email responses on updates and didn't get any, so I did not realize you guys were out there.

PS... No codes.

Thanks for the help
RIPSAW

 

I believe (can’t remember anymore) I had to replace the ignition switch at some point, as well. So, it was one followed soon after by the other. Good luck!

 

Only once. However, it's cold here and that morning, I had to key on three times to get voltage coming to fuel pump when cranking.

And no codes. I have my OB2 reader running now all the time. Battery voltage good (12.7 off, 14 running) and cranks like crazy..

You are correct that when I crank it, with the crank position part of switch controlling fuel pump, it also needs the crank position sensor to fire but not 100% sure at that brief period, it affects fuel pump.

Guess it could. I have all the OEM owners manuals. Back to them.

 

It could be your IAC if you were at idle. It sounds like you're getting voltage to the pump when you should.

 

When it cut off, I pulled it into neutral and started cranking. No voltage to pump. About the 4th on and off on the key and then cranking, go voltage and it started and no problem driving 5 miles hole. Truck was warm when it died. Only has 75K. Idle has never been a problem and it idles up for cold and then you can see it drop back. Only allowing 4th gear when warm. Then even does the fine trim at stop lights. So I it not the IAC.

It has always had a little roll idle when trimmed when hot but I think that is typical of this big four with balance cams driven off oilpump.

 

easiest things first. If she is the 3.4 just in front of the Diagnostic port in the upper intake is the grounding point for the PCM and other circuits. What happens is when techs tighten this nut the eyelets swivel and stress the wire internally and they break, the insulation is still attached so it “looks” OK. You will have to wiggle each eyelet and see if it is still attached. In addition, verify that the ground off of the back of the P/S cylinder head,3.4, is attached to the firewall and the short ground off the negative battery is attached to the inner fender. If these 2 grounds are poor AND the large ground off the battery to the block is poor your only grounding point is the accelerator cable or the TV cable to the transmission if she an automatic.

If she is the 4 cyl, this grounding point is by the throttle body, same story there.

If this is OK you are just going to have to old school this. By this I mean go to an auto parts store and buy some bulb holders for low wattage incandescent bulbs and wire one into power wire that feeds the fuel pump, one into the a wire that feeds the coils and run them into the cab. I will write on masking tape what each bulb does and go for a drive. It is a simple matter of seeing if you are losing power to the pump after the circuit opening relay or power to the coils. If all is good there, move one wire to the signal wire off the PCM to the circuit opening relay and see if that is an issue. For a more professional approach I will use piercing probes for a multi meter.

 

It's a reg cab 4×4 . Auto. Never been worked on other then me and simple maintenance over the years and now at 75K.

My DC voltage meter attached across the fuel line fuse shows voltage when all is good when cranking and then when running down the road.

I had attached a test spark plug by number one cylinder. If it ever will stay broke long enough, I had planned on pulling the coil pack off number one and see if it was sparking. That would eliminate the CPS.

This problem started years ago. Probably at 40k or so. Happened twice only on start. It actually didn't start for a few day. Healed itself.

Now it appears to be often. It will probably start now. But I am a keep it simple, just like you say. My guess is unhook the wire to the starter, hook my meter just before the circuit breaking relay and key to start for a while.

If all looks good, ignition switch is OK. Then meter past the relay and that should check relay. If that looks good, relay is OK.

If the CPS is in effect and in the fuel pump circuit when cranking as it is in running, I am guessing that's not going to work however.