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

these intermittent problems are a real pain to find. you cant fix what isn’t broke.

 

Some more updates. Sadly too cold in garage to work on vehicle.

Manuals are 7" thick and like trying to learn chest. Even if you know how, your only so good if you can't see 10 moves in front.

But.

The hard 7.5 ignition fuse receives power from ignition switch when cranking. It drives a EFI relay that drives the fuel pump circuit opening relay. The ground for the circuit opening relay is a W/L colored wire goes to ECM for ground control. Not sure what else it needs.

There is a another 20 amp fuse for EFI driving injectors and the other pole on fuel pump circuit breaking relay that also goes to ECM for ground control. This works both on on and start but is controlled by what the ECM sees from the crank sensor. So if it just key on, fuel pump won't run.

I can check relays and ignition switch. Not sure exactly how to check crank sensor.

The OEM parts are a little pricey to just start throwing parts at it. Was hoping someone had had this problem to see what goes first.

 

Honestly it sounds like a crank sensor. Since it is happening intermittently, no starting and cuts off while driving. I doubt your teeth are messed up causing a bad signal.

first thing I did when I bought my 99 used was replaced all sensors. These trucks are so old and most of the time running on the stock sensors. Even with yours being such low mileage, sensors do get old and begin to deteriorate.

If I were you I would start investing into replacing all the sensors and if you haven’t done so give her a good coolant flush. Some things you can’t go by mileage and have to go by age deterioration.

edit* I noticed you live in Florida, I’m sure that deterioration is accelerated based off where you live. I remember Tyndall afb real well and that humidity is something else.

 

You may be right. All the relays are fine. Tomorrow, going to check CPS. Checking should be no problem. Sure hope it's way off.


Getting it out requires removing skid plate, alternator and mount bracket.

It's that or the ECM ground control for the pump relay I guess.

This problem actually occurred couple times at 30K.

I sure miss points and a fuel pump on the side of the block.

PS.. Brake fluid has been flushed couple times. Has original brakes but close on front.
Radiator, PS and transmission fluid has been changed out at 50K with OEM . Truck looks new even underneath. Garage kept.

Only problem other then this was a heater went on the front oxygen sensor. Thru a code. Read it, replace it and all good again.

If it actually is the ECM just for the fuel pump, I can bypass it with a simple hard ground for the wire coming off relay. Would loose some safety features of that.

However, that would only help if the EFI part on the ECM is still functional.

Is a replacement ECM plug and play?

 

as far as I know there is no programming for a replacement PCM.

points and an eccentric driven fuel pump… yeah those were the days when things could be actually fixed and not HAVE to be replaced. Unfortunately things like a dwell meter and distributor wrenches are display pieces now.

 

Keep in mind the coils in relays can sometimes do strange things when warm.

Your ECM is plug and play

 

Well the CPS checked out at 1999 ohm. Easley in tolerance.

Got a sneaky filling it just may be ECM.

It probably when it was not getting fuel, probably wasn't getting spark or injection of at least a drip .

I did check ignition and it appeared a little erratic. But really hard to check. So I have pulled it.

Another day to figure it out.

 

Have you tried swapping your efi relay with another similar relay in the fuse box? I would hope it’s anything but the ECM.

 

That what I first checked. Pulled them and visually checked and then ohm checked them with battery voltage across coil pulling in contacts. Fuel pump, EFI, taillights and cab power ports for 12 volt are all the same.

After I get ignition switch out and checked, going to pull ECM and check it's ground points behind glove box.

 

there arent any ground points for the PCM in the glove box area

 

Thank you. Yes, I went through my 2004 and have all the ground point triangles down. Got those you show here. Also a few others. From the other components. Just going to check them all. But will focus for sure on these. There two on both the left and right behind the lower kick panels.

Appears you have the wiring diagram manual like me. Look at the ones on the 3RZ 4 cyl. Note the ground marked IE. It's on the right kick panel. Appears lot of the ECM goes first to the Data Link Connection and then to that one. Not sure what that data link connection is. Is it the OB2 port?

I have left one off but they must be hidden by the fuse box.

Think is has already been mentioned here about the air flow sensor but my granddaughters boyfriend is a mechanic. He said the first thing he would have done was clean it. He said they can read resistance fine but if they are a little dirty, at cranking air flow, they will sometimes not signal the ECM. I have not studied this in manual if this signal is required for fuel pump like the crank sensor is.

 

Well it's running now. But that doesn't mean it's fixed. Couldn't find the two grounds on the motor. The one ground strap on back to the firewall is fine. The two behind left kick are impossible to get to without major disassemble. Fuse box needs to come out.

Right side is the same with the heater box blocking checking it.

Only way to check them is remove ECM and go from the plugs pin numbers.

Could see right kick ones and they are clean and look new.

Cleaned the MAFS . Going to leave all the plastic off for a while. First chance I will discount the MAF SENSOR and see if I don't see a fuel pump power voltage when cranking. It goes straight to ECM and directly feeds the fuel injectors. I assume it's the on timer for them.

 

With the engine idling use the handle of a screwdriver and lightly tap the mass airflow sensor if the idle fluctuates the mass airflow sensor is bad or so I hear. I could be wrong but good luck

 

Hey I need help. I have a 04 Tacoma 3.4. Stopped at store the other evening truck was running great. Went out to leave truck would not start. Check outlet side of fuel filter no fuel. Checked inlet side had pressure thought filter was stopped up. Replaced filter still nothing. Figured with filter stopped up must have burnt pump out. Replaced pump still nothing. Just don't seem to be fueling. The truck will hit as if about to start. Maybe make two or three rotations but that's it. I've read everything under the sun. But it seems all the things I've seen not really relevant. My thoughts is cps. No ecm signal for pump to operate ? Any ideas on where to start? I'm lost.

 

Have you pulled any Codes?

Have you done any trouble shooting or just changed parts?

Having the schematics for your year truck is a very very big help.

Time to break out the Meter start at the EFI fuse. Efi Relay .Circuit opening relay

Keep in mind the fuel pump circuit is only energized while cranking or when the engine is running.

 

Checked fuses and relays all good. No codes. Only thing I don't understand is why my reader says catalyst and EVAP not ready. But don't see that having any effect on running. Or no fuel pump signal.