1994 Pickup, parked and will not start, would almost catch then die, now won't catch.

I checked out some threads here, especially one listed at bottom, good info but didn't specify action when there is no continuity between the B+ and FP wiring to the Circuit Open Relay. I'm getting 12.6V when B+ is grounded to chassis, but 0 when it's connected to FP, regardless of key position. Just want to make sure I'm chasing the right thing before proceeding: does this mean there's a break in a wire to the fuel pump, or a break inside the fuel pump, or something else?

I get the same results at the Diagnostics port.

Thank you


.

https://www.yotatech.com/forums/f116...-quits-312747/

 

B+ is, uh, B+ (~12v) with key-on. (This is through the EFI fuse and relay and doesn't involve the COR.)

FP is direct to the fuel pump. It should be 0v (to ground) with key-on or key-off. Remember, the COR doesn't close until the key is to STArt, or the FC pin in the VAF connects to ground, so there is no B+ connection to FP with just key-on.

Given that, checking your situation is trivial: jumper B+ to FP. Can you hear the fuel pump running? (In my garage, I have no trouble hearing it standing at the diagnostic connector. Outdoors by the road you might need an assistant.) If not, did the EFI fuse blow? A blown fuse means FP is shorted to ground somewhere between the diagnostic connector and the pump. "Nothing" means an open in the pump (bad pump) or in the wiring.

If your last photo is with key-on, you're getting no continuity to ground through FP so the pump is bad or a wire is broken.

(Why are you using the BAT range, instead of the DCV range? I don't know your meter, but I expect that BAT puts a certain load on the circuit to look for voltage drop. Doesn't make much difference with a big-ass car battery, but why?)

Good luck!

 

Thank you.
Jumping B+ to FP doesn't start the fuel pump, that's why I:
-tested B+ to ground to make sure there was current coming to fuel pump
-tested B+ to FP to see if there was continuity to the fuel pump

Just to be clear: when jumping B+ to FP the pump will activate when the key is at 'ON' (as I doubt I would hear it over the engine starting). I read somewhere that these engine don't 'pre-pressurize' the fuel system before starting like some others, and unclear if jumping these connections changes that.

It seems we are on the same page with something wrong with the fuel pump or wiring to it.

Using BAT as I don't have much experience using these and was familiar with that.

Thanks again!

 

All you need to do is check for continuity between Fp and the fuel pump hot lead. The FP pin in the diagnostic port goes straight to it.
You do not, NOT, want to check for continuity between B+ and FP. Chances are the meter will blow it's fuse instantly. If you do with the negative lead off the battery, it's safe, but will read open.

Remember, avoid using the meter in OHM reading ranges, with voltage in the system being tested. It will blow the meter. Good idea to pull the negative lead off the battery. Better idea is to pull both battery leads off before ohming any system out. Always verify the meter is fully functional before using to measure OHMs by touching the leads together. The meter should go to 0 (zero). Many meters have a fuse in the OHM circuitry to protect against such events. You may need to open the case to find it. Check the paperwork that came with the meter for more information.

B+ is directly connected to the battery, through the keyswitch's ON contacts. All you should see on it is the battery voltage reading to ground. You can check it by reading across the battery terminals, then moving the meter's + lead to the B+ pin in the diagnostic port.
If you jump B+ to Fp, and turn the key to ON, you should hear the fuel pump running. Don't turn the key to start, just to on.
A way to check 1/2 of the COR is to turn the key to STArt, but do NOT press the clutch, or clutch start cancel switch. Again, you should hear the fuel pump running while the key is held to start, but not cranking the engine. The tone of the pump will change as the fuel system pressurizes.

Hope this is some help...
Pat☺

 

Sorta. Some cars (e.g,, the Hondas I've worked on) run the fuel pump for about 2 seconds with just key-on. Your Toyota doesn't run the fuel pump until the key is all the way to STArt. Jumpering FP to B+ bypasses all of that; the fuel pump will run continuously with just key-on. Which is why you don't drive around like that (think: accident that breaks a fuel line).
Sounds that way to me.

Not quite. As I said, B+ is powered through the EFI relay and EFI fuse. The keyswitch only closes the EFI relay.

 

if jumpering b+ and Fp without the key on, nothing should happen. if the pump turns on when the key moves to on (as you appear to claim) with the jumper in place, your pump and the wiring to it are working.

 

Thanks for all the advice.
In case it wasn't clear: the fuel pump does NOT go on when I jump B+ to FP, key position ON.
Currently dropping the tank to remove the fuel pump. Thanks.

 

those of us with 1st gen 4runners have it easier than pickups and later 4runners as far as the pump goes; there's an access hatch under the rear seats. no tank dropping required.

 

A bit more information:
-bench tested the pump and it's good
-tested for power at the pump connection (wire in truck) with both the relay jumped and the relay in and power is good

Since the truck was almost starting and immediately dying I suspect something amiss in the 'run' fuel system (as opposed to the 'start' fuel system) so will check more around that. Just giving update in case anyone has any other suggestions.

Thanks.

 

This doesn't add up.

If you have voltage to ground AT the fuel pump, and the pump is good, then the pump runs.

You don't mention the conditions of "relay in and power is good ..." With relay (COR) in and open there should be no voltage at the pump. The COR closes with either a) key to STArt or b) key-on and FC switch in VAF closed. You either did a or b, or your COR is shorted. But with all three of these the fuel pump has to run.

The only "electrical" possibility with the results quoted above is a break in the FP wire between the diagnostic connector and where it flies past the COR on the way to the fuel pump. That wouldn't affect start and run.

 

Thanks Scope. I'll retest Key On and B+ to FP jumped. In bench testing the pump I noticed that it is very quite. In my old Mustang fuel pump was very loud, so that was my reference for hearing a pump. I definitely wouldn't be able to hear the pump with the engine turning over but I should be able to with Key On.

 

A loud pump is pretty much always bad. What happened to the old Mustang? ....

It is always possible that in your tuggin' and pullin' to get to the pump, you've re-made an open connection. Take things step-by-step, rechecking with your multimeter at each point. For instance, check resistance to ground at FP (key-off). If you do something and the resistance changes from low to infinity, you know that "something" broke a connection.

 

I connected the pump to the truck wiring, stuck it in a bucket of water, jumped the relay, and with Key On the pump pumps. So looks like I completely misdiagnosed the problem based on how quiet the fuel pump is.

I'll start back at square one checking spark and fuel pressure at the engine (although there doesn't seem to be an easy way to do that on these engines).

The old Mustang was actually Fox body drivetrain that went into a FFR Cobra that I built.

 

Both spark and fuel pressure are very easy to check.
Spark can be checked by hooking the inductive pickup of your timing light to the spark plug wire in question. If the light flashes, there is spark in the wire. Easy check.

Fuel pressure: Just attach a pressure gauge to the cold start injector's fuel supply connector. It's right out in the open, easy to get to.
Just remember, you MUST replace the crush washers ANY time the fitting is loosened/opened. That means one set when you install the fuel gauge, and another set when you remove it. At least two sets. Make sure you only torque them to the FSM specification. You can snug them a little above that, but not too much, or the crush washers will deform and not seal correctly.

Make sure you have at least one more set of crush washers than you think you'll need. Chances are, you'll need at least one of them. They are readily available from any dealership, for a very reasonable price.

Good luck!
Pat☺

 

Just wanted to follow up. Everything tested good so I reinstalled and it fired right up.

That might indicate that some wiring was loose, but all of the connectors were solid, so not sure what it was.

Thanks for the help.