[Solved] Fuel Pump not Priming or MAF Sensor - broken down and desperate

Currently troubleshooting my Tacoma 96, 3.4L, Auto, 4x4, Ext Cab. 300K+ kilometers.

Was sitting for about 6 months. Wasn't running too good and had a CEL come on and off before parking it due to being too busy to deal with it at the time. But never failed to work. Was just a crabby old bugger most of the time.

Battery died after about 4 months of storage, after charging the battery, it fired up, but still not running really well.

Last week I decided to take it in and get the mechanic to look it over, tune it up and stuff. Fired up first try, again not sounding great, but got it out of the driveway and got about a block down the road and when I depressed the brake pedal, it just died on me completely.

When I crank it turns over but as soon as I stop cranking, it dies. So I pushed it to the side of the road. Went and got another 5 gallons of gas JUST IN CASE the gauge was wrong and fuel was empty. No improvement. Exhaust from cranking smells like gas is bad/old, but I don't live in an area that got more than a couple of degrees below freezing while stored, and it wasn't THAT long.

Anyways I spent a few hours screwing with it and the question I have for now is, is the fuel pump supposed to be working with the key set to ON, or only when set START (and stay on with the engine "running")? May be the relay is fried or the pump. Can't tell without this info I'm thinking.

We have fuel delivery ONLY when cranking (loosened fuel rail bolt to check) and the relay clicks off about 2 seconds after we stop cranking (and engine dead).

Many of the symptoms I'm getting seem to be MAF sensor related but it won't start with or without the MAF plugged in. No codes to pull as I tried cleaning that first and d/c the batt to reset the computer so we're hooped.

 

I'm pretty sure that fuel pump does not work when key is on and engine is not running. When key is set to start (crank) the fuel pump gets the power directly from a the ignition switch, but when the key is in ON, fuel pump gets power only when computer decides to. When computer sees that engine is stopped, it cuts of the power to fuel pump.

 

Toyotas of this era only start the fuel pump after a signal from the crank sensor confirms the engine is cranking over

 

Right. Post 2000 models don't use dual powered relay for fuel pump (Circuit Opening Relay). See on the diagram (this is from 1999 but it is the same for 96):



Black/white wire powers the relay when key is turned to Start (White/black wire is grounded all the time). The when cranking is stopped the relay will be energized only via White/red wire (coming from EFI relay which is energized when key is in ON position) AND Green/Yellow wire is grounded. The Green/Yellow is controlled by ECU, and it will be grounded by ECU only when engine is turning (I don't know what is driving it).

 

thanks for this gang, Do we know if the truck should start with MAF unplugged? Trying to narrow this down...

 

It'll start but it won't want to stay running

 

update: I have spark on #2. Got a code reader, code showed up after a few tries on starting. P1300. Pulled #1 plug and coil out, produced a weak spark on #1. Same weak spark with a new plug, and using the #2 pigtail and new plug. Maybe I had a bad grounding point, but there is current flowing.

Anyone got experience with this? I didn't see any obvious wire problems from visual inspection.

Edit: #1 was gassy, #2 was dry and burn looking will grab pics

 

Is your electrical system up to speed if the voltage drops to low ECM will power down to protect it`s self.

PO1300 means the ECM is not seeing the signal from the igniter so the fuel is shut off to what the ECM thinks is a non running engine.

Loose connection at the igniter??

Evil Rodents come for a visit while it was parked chew on the wiring harness ??

 

Your pump turns on when the key is set to on because your car needs fuel to start, you can even hear the pump work when you set the key to the on position. It probably won't maintain pressure but it definitely pumps some fuel to start combustion. Once the truck cranks up the fuel starts to get delivered constantly.

My advice to you is to have someone set the key to the on position while you're listening to the fuel pump to hear if it works. Near the gas tank. Just take the proper measures and preferably have someone who knows how the car works so he or she doesn't accidentally turn the truck on. The noise is very pecular and will be hard to miss if it the pump does work.

 

Will inspect igniter and wiring to the extent that I can... thanks!

 

As long as that PO1300 code is present it will start and shutoff repeat till it is fixed

 

Wait. Are you saying I have to clear the code before I try again because it won’t truly start with the code present?

 

Following

 

I got it to work! Here's what I did. Inspect igniter wires and connector. Wires looked good, and all in connector firmly. Took igniter out, not that that did anything. Connections looked very good inside but put WD40 on connections and replaced. Pulled #1 coil electric feed line and inspect. Looked ok. WD40'd anyway. Had a few failed starts. Decided to check the reader one more time. No change to code. P1300. About to give up. Cleared the code. Tried again. Started up, thought I was hallucinating, but I held it at 2000 RPM for a whole minute and slowly let it down. Idle's low, just over 500, on startup with no AC, with AC on, it probably idles high. But for now I have driveable vehicle.

Thanks all for the pointers.

Curious now - when it comes to clearing codes, is there anything I need to do? Should I reset the computer? Will the code come back, even if I cleared it? First time doing this.

What I am hoping is that I will continue to GET codes because I know it needs some tinkering.

 

Since that code PO1300 is a critical one as soon as the ECM detects it the fuel will be shut off

If the condition is still present it will trip again when it is cleared

 

glad you got her running. clearing the codes resets the PCM back to factory specs you dont have to do anything but drive it. I dont know that clearing the code is what made it start but I find it curious too.

 

Anybody still on here? I recently replaced my fuel pump because my 98 2.7 was dying randomly on the road and figured 190K on the original was good enough lol

sooo I replaced the old with a Denso one but I’m not hearing the pump come on when I put the key to on. From what I’m understand from a post a bit above, that’s not going to happen until I try to crank and the ECM knows The engine is indeed turning?

i disconnected the fuel line right at the first fitting (where the 3 connections are close to the tank) and no fuel come out at (on) but it definitely spit out when trying to crank.

anybody got any ideas for what to try? The truck was in working condition prior to me doing this fuel pump and I didn’t disconnect anything other than the pump connection above the tank.

 

That is incorrect info posted above about the fuel pump turning on when key is set to on position in ignition.
Before you replaced the fuel pump it started every time but would truck would die randomly while driving? And after replacing fuel pump now it won't start?

 

It was starting every time yes but for a few weeks it was dying randomly and not always starting back on and then what really got me to change it was when when it started and then the shutoff was immediate