xfactor203

Heres the short version: My truck would crank but not fire at all. Got it to start after jumping Fp and B+ in the diagnostic block. Now it runs fine, with or without jumper wire. Worried it will strand me again. Thoughts?

Heres the loooong version: My truck left me stranded four wheeling by myself last weekend. It ran fine all day, until I shut it off for five minutes, started it up and it popped up to ~500rpm for a few seconds, died, and would only crank after that. No fuses blown, no gas on the plugs, distributor cap / rotor looks fine, and I got spark at the plugs. Swearing, handwringing, darkness falling, possible snow (at 8500' in N. Utah a real concern). I got really lucky. Two hunters in a CJ5 pulled me to pavement.

Got the rig wreckered home and poked around at it for a while with no results. Got codes 14 and 21, but I don't know if they are related to problem or not. They don't come back after I clear them and crank the engine again.

I jump Fp and B+ on the diagnostic block to see if I can hear the fuel pump and I can't. However, I am not confident about the connection using a paper clip, so I jump the terminals with a multimeter (it shows 12V) so I can be sure the connection is good. Now I go bang on the gas tank with a 2x4 to see if the pump will come on. No dice. I try to start the truck. IT FIRES RIGHT UP! Whoohoo! I'm all excited, found the problem (the relay behind the glovebox, right?).

Here's where it falls apart: I walk around to the diagnostic block (truck still running), to see if removing the multimeter makes it die. The meter (still plugged-in) now shows 0V. I repeatedly started the truck, drove it a little, and it appears to run fine, no jumping Fp and B+ required.

I'm worried the problem might come back at a similarly inconvenient time and leave me stranded again. Any ideas for a problem consistent with this chain of events? BTW this is a 94 4runner 3VZE.

Kiroshu

Ya know i had a similar situation one time with my truck but my fix results may be diff then the prob you have. Although it sounds to me like your pumps going out if i had to guess. I'd take the pump out and test it with a battery and see how it runs. The pump is under the right rear passanger seat under it through a service hatch held by screws. While your at it toss a fuel filter on there just to eliminate that prob. If its not the fuel pump i sense that relay may be an issue. Test the relay for resistance specifed by toyota and energize it to see if it works.....<Only if you want to. I think its ur pump if i had to guess. The codes i don't remember off the top of my head but yea.

xfactor203

Thanks for the input. I can hear that relay click on when I turn the ignition on, so I'm inclined to think it's working. My real question is with the current between Fp and B+ in the diagnostic block. Does it make sense to have 0V at a jumper wire between these when the truck is running? I'm led to believe jumping these terminals should make the fuel pump run when the ignition is on but the truck is not running, is that correct?

MUCH discussion of that fuel pump hatch in forums (as I'm sure you know), seems like some trucks have it, some don't. Mine affords access to a fuel fitting and connectors, but not the pump itself. Bummer, because I'm guessing you are right and that is the problem.

Kiroshu

Well unlike alot of cars out there, Toyota made their fuel pumps turn on as you crank the motor. Not with key on but with motor crank. Now i have seen a few rigged yotas where the pump was on all the time the key was. Theres really no prob with that. If it reading 0V all the time when the trucks running or does it change.... Sure ur hearing the right relay? ITs the one above the passanger kick panel to the right of the glove box behind the dash. Its called the circut opening relay.

rustypigeon

A possible theory to the 0 volts: When the engine is running, the fuel pump is getting its electric power through the circuit opening relay. When you jump terminals Fp and B+, all you are doing is bypassing the circuit opening relay. It is possible that the volt meter is reading 0 because the electricty is just taking the path of least resisitance through the circuit opening relay instead of the voltmeter. There is no other possible path for the fuel pump to get power. If it is running, then it is getting power through the B+ and Fp through either the circuit opening relay or a jumper.

Jumping Fp and B+ should make the fuel pump run when the ignition is on. If there is a problem with the EFI main relay, that would prevent any electricity from getting to the B+ terminal. A problem with the EFI main relay would prevent the fuel pump from running when you trying to start the engine, as well as when being jumped.

xfactor203

Thanks for the input you guys. I am beginning to be convinced the fuel pump is the issue. *sigh* I had hoped not to drop the tank. Especially irritating because the truck works perfectly right now.

xfactor203

Well, the other shoe finally dropped on this problem. After driving around for a couple weeks w/o so much as a hiccup, the truck left me stranded again (at the carwash this time). I tried jumping Fp an B+ again with exact same results as above re: voltage (btw I am sold on the analysis above: voltage drops to zero upon running / cranking b/c relay has tripped and is sending current to the fuel pump).

More importantly, I had my wife crank the engine while I hammered on the fuel tank with a 2x4 and it started again! So, I'm thinking definitely fuel pump. I've read some other threads that imply this is a pretty good diagnostic for a shot fuel pump. What do ya'll think? Is there a preponderance of evidence here?

I'm going to go start disconnecting stuff now, but won't get the pump until later this week, so if I'm on the wrong track please chime in!

Thanks for the input, I don't post a lot but I sure do read YotaTech a ton. It's a great resource.

CHEEZBURGER

Not to hijack or anything, but what kind of voltage should I have at the fuel pump, with the jumper in I get close to 12 volts, with just cranking it over it gets 7ish, is that normal

bend

iTrader: (1)

Why does banging on the fuel tank make the fuel pump work?

xfactor203

I'm speculating here, but I think moving parts in the fuel pump (which is in the tank) may begin to stick over time as they wear out. Banging on the tank may jar them free, allowing the pump to function again (for a while).

I just went out and did everything but drop the tank (I need to pick-up a gas can to drain gas into). So far so easy. Hosed down the drive-shaft bolts with penetrant just in case, but I'm hoping to not have to screw with that. . .

xfactor203

*bump*

So, any thoughts on the banging / starting as a diagnostic? I ask because I'm planning to go buy a fuel pump in the morning, and it'd be nice to hear that I'm probably not wasting money.

xfactor203

Well, I finally got around to replacing the fuel pump. The truck runs great. As of now I am assuming the problem is fixed. I'll be really bummed if it comes back, tho', the fuel pump was expensive.

Everything was fairly easy (thanks largely to tips I picked up here at YotaTech). I figured I summarize potentially helpful bits with some pictures for the benefit of others:

First off, you don't have to take the tank all the way out. Unbolt the filler from behind the filler door and from inside the fender (behind an access panel inside the wheel well). Also disconnect the fuel fitting using the hatch under the rear seat on the passenger side.

From here you can finagle the tank down using a floor jack (of course you have to take the bolts out. . . ). You don't have to disconnect the driveshaft if you are willing to pry a little. I had to use a small bar to pop the front seam of the tank past the crossmember. Once that is clear, you can drop the front of the tank (the rear comes down some, but the filler tube keeps it from dropping too far). I was able to change the pump from here. The pump assembly was easier to remove after I disconnected the power wires, but I don't know that it was necessary. Some pics are below:

Forcing the front seam past the crossmember with a prybar:

Dropped tank:

From underneath:

The filler neck ends up on the tire:

Fuel pump assembly out of the tank, minimal disconnection:

xfactor203

Guess I don't know how to post pics. I'll remedy later.

CHEEZBURGER

Glad that got her going for you, mine is a little easier to get to, I have an access panel right above the pump

xfactor203

Dude, sorry I ignored your voltage question above. I don't know the answer. I can't believe they got rid of the access panel. Dumb.

CHEEZBURGER

I don't feel ignored, That is dumb to get rid of such a good thing

xfactor203

Okay, finally figured out how to post pics. They are in appropriate places above.