bomhour

I have been doing some work on my 3vze that requires the disconnection of various fuel lines, fuel regulator and diagnostic jumping. My question is, should I hear the fuel pump running when the key is turned to On but engines not running? Some times it will run for minutes while I'm running other tests that require the On position. Brand new fuel regulator just installed. No visible leaks.

Earlier, I started another thread with my other issue requiring some ECM tests and the ignitor...in case you need more info.

thanks for your help?

93toyrunner2

No, you should not, until you start the engine and it sends a signal to the ecm to turn the fuel pump on continuous.

bomhour

Ok that does it. I'm going to do a fuel pressure test. Just waiting for the fitting to come in the mail. If the fuel pump is running continuously then I probably have a leak. I will let you know how the test comes back. thanks 93toyrunner2.

MudHippy

Have you checked the fuel pump switch in the AFM? If the fuel pump is on(w/ the ignition switch ON) without the engine running(or atleast being turned over by the starter), then the fuel pump switch in the AFM is closed(in the ON position) when it shouldn't be. If this weren't the case, there's no way for the fuel pump to run under those conditions. As it would be receiving no electrical power.

That's not how it works. The ONLY control mechanism for the fuel pump is the fuel pump switch. If it's closed(w/ the ignition switch ON), the pump is on. If it's open(w/ or w/o the ignition switch ON), the pump is off.

93toyrunner2

All instructions for testing the fuel pump are in the FSM:
http://www.ncttora.com/FSM/1990-1995...e/fuelpump.pdf

93toyrunner2

And the COR. If the COR is bad, no fuel.

MudHippy

A relay is a relay. Not a control mechanism. Nor is jumping the FP & +B connectors(bypassing the fuel pump switch). Though, it's arguable that the ignition switch is another control mechanism for the fuel pump(among many other things). I'll concede that much. I just wouldn't call it that personally. Since, under any normal circumstances, the fuel pump switch is ultimately what controls whether the fuel pump is on or off.

bomhour

The AFM is pulled from the salvage yard. It has not been tested but the truck does start and will run for 2 seconds or so before it chokes out. so I will look into that fuel pump switch to make sure it's good. I actually started having this problem after I jumped the battery and the FP ports in the diagnostic. I wonder if I caused the ports to short out. I was going to start with a pressure test and work form there. Gathering the right pieces for the pressure test from local sources has been a pain so I'm waiting for parts from ebay. Should be able to do that test by this weekend.

thanks,

bomhour

What are you referring to...COR?

MudHippy

Circuit Opening Relay

The first thing to do, as far as the AFM, would be to check if the measuring plate is fully closing with the engine not running. If it's not fully closed without the engine running(or being turned over by the starter), that will turn the fuel pump switch on(when it shouldn't be). As soon as the engine is turned over by the starter it begins drawing enough air through the AFM to cause the measuring plate to open slightly, closing the fuel pump switch(turning the fuel pump on).

See page EG2-234 from the 93 FSM for more on testing the FC circuit in the AFM.
http://personal.utulsa.edu/~nathan-b...92volumeai.pdf

Punchy

The open circuit relay also controls the fuelpump

TNRabbit

Running for 2 seconds then dying sounds a LOT like a VAFM issue...

bomhour

Thanks everyone for those suggestions. And, thanks MudHippy for providing the link to that spec. I will check that out tomorrow.

MudHippy

You're welcome!
Let me try putting it another way...

1. The fuel pump switch controls the fuel pump via the FC(Fuel Control) circuit, which runs through the circuit opening relay.
2. When the fuel pump switch is closed, this completes the FC(Fuel Control) circuit(if the ignition switch is in the ON position).
3. If the FC(Fuel Control) circuit is complete it energizes the electromagnetically operated switch in circuit opening relay, closing the FP circuit.
4. If the FP circuit is closed, the fuel pump is ON
5. You don't get to 4 without going through steps 2 & 3, OR without jumping the FP & +B connectors in the DLC1(by-passing fuel pump switch/FC(Fuel Control) circuit).
6. So either the fuel pump switch controls the fuel pump, or you do(by jumping the FP & +B connectors in the DLC1). Nothing else does.

bomhour

MudHippy,

That was it. The salvaged MAF I pulled from the junkyard was full of oxidation. The AFM was stuck closed or mostly closed. I tried to clean it a bit but I'm not sure if I can get all the oxidation off for it to operate smoothly.

It drove pretty well tonight. I definitely noticed better power and acceleration. I am still having a bit of lag or stickiness in my throttle. Not sure if I installed the new TPS incorrectly or the AFM is not recoiling freely. If I had to make an uneducated decision, I would say the AFM is sticking. I will have to look into that next. Then I can get back to my original problem which was overheating

Thanks to all you guys for your help. I would not have figured that out on my own.

bomhour

Update. I installed a new $160 dollar radiator and a superturbo catback exhaust $225 installed and the truck is running great. Went for an 1 1/2" highway jaunt over the weekend and there was no more overheating. The catback exhaust has really improved my power and mileage too.

Thanks again for your help everyone.

Looking forward to the ISR Mod next.

scope103

MudHippy -

When you say "fuel pump switch," are you referring to the contacts inside the VAF? You're not referring to an actual (human operable) switch, like the ignition switch, are you?

Where I'm having a little difficulty following you is you talk about that switch as the start of a sequence that runs the fuel pump. Temporally, I believe the ignition switch (in the STArt position) triggers the COR, and then the VAF takes over once there is intake flow.

bomhour

I think MudHippy was trying to get it across to me that my VAF was probably not operating correctly as my symptom was an always on fuel pump with the key in the ON position with the engine off. The actual problem turned out to be that the switch in VAF was stuck open due to corrosion(the switch is the metal flap like regulator that controls the amount of air that is allowed to enter the throttle body). One could conclude, based on this reality, that the switch he was referring to is the one that I found to be corroded in my VAF. If the ignition was in the ON position AND the VAF was operating as it should be, then the fuel pump would would not come ON until the engine turned over.

TNRabbit

Wow! You so CRAZY!! With gas prices so high, I surprised you drove so far....

Gevo

GUYS! I couldn't find this info in the fsm.. probably because it's not useful.. however.. it seems everythign else electronic has a resistance test as one way to see if the item is up to spec.. but there is no resistance given for the fuel pump.

I want to preliminary test it before removing the tank and THEN finding a bad pump and then ordering and waiting. I know what you will say, pressure test, I will be doing that as well, but I have reason to believe the pressure reading may give me a false positive.

Thanks