1986 4Runner 22RE

Let’s just get this out of the way first: I hooked up a jumper pack backwards after it wouldn’t start. Saw barely a spark and when it didn’t work to start I took the battery in to charge and they said it was bad. So pretty sure I toasted the battery.

My 80 amp fuse in the engine bay blew. I still show connectivity in the fusible link. After replacing the 80mph fuse and new battery, truck turns over strong but won’t start. I have the FSM and ran through some tests.
1. circuit open relay (passenger footwell) passes
2. all fuses inside and out pass (tested connectivity with volt meter)
3. AFM passes

The only FSM test that didn’t pass is shorting the fuel pump test connector on the driver side fender. I got zero noise when shorted and ignition set to on. I’m not clear on if the FSM is showing a pump in the engine bay or if it’s showing the filter as a good place to remove fuel lines. Either way there is no noise from the engine bay or tank area (I did remove the interior access panel for the tank pump).

-could swapping the leads have fried the fuel pump?
-Is it safe to assume the ECU isn’t fried if I’m getting cranking and lights on the dash?
-oil, charge, and brake light are all on when key is ON position, I think this is normal but it’s been 5-6 months since I drove it and can’t remember.

 

If you can't hear the fuel pump running when you jumper Fc to B+ on the diagnostic connector, you have a problem somewhere in your VAF-COR-Fuel pump circuit. Here's everything I know about that: https://www.yotatech.com/forums/f116...-quits-312747/ (yes, you will need a multimeter, but it sounds like you're up on that).

Another test you can do (once you can hear the pump) is to disconnect the return line from the Fuel Pressure regulator. Replace it with a 6mm clear vinyl tube to a suitable container, and run the pump with the jumper. There is no spec, but I get about 1/2 liter / min. (DON'T disconnect anything on the high pressure side, not even to just "crack" a fitting. The crush washers are one-time-use and need to be replaced.)

 

Thanks Scope, I read it and a lot of good info to try.

first thing I tried was shorting the test plug and starting (didn’t do that previously) and no start. Still need to check spark and voltage through the connector. Which terminal is B+? The vertical in the T or the horizontal?

 

I read in a different thread that if the CEL is not on with ignition on, the ECU isn’t getting power.

can anyone confirm?

 

I see you have an '86, which does not have the "later" model diagnostic connector. 4Crawler has an encyclopedic site which covers all the (4runner) Fc connectors I've ever heard of: https://www.4crawler.com/4x4/CheapTr...shtml#FuelPump

I can't tell you which connector is which on an '86, but start with your multimeter. With key-on, B+ will have battery voltage to ground. BUT ... 4Crawler's wiring diagram shows the check connector as grounding the COR coil to close it. (On the later models, the Fc connector goes straight to the pump, so with B+ the pump runs, COR or not.) I believe you have the access panel to the above-the-tank wiring; look for battery voltage there (don't forget to check the ground side of the pump as well).

The CEL is on with key-on, engine not running. But it's a light bulb; there are at least 2-dozen reasons a lamp won't light. Your EFI fuse powers both the ECM and the fuel pump, but you say "all fuses, inside and out" are conducting, so who am I to doubt you checked the EFI circuit?

 

Checked again and EFI fuse is not blown and double checked the other fuses as well.

I do have the access panel and will need to check for battery voltage there. I haven’t found the connector that is supposedly down there though. Based on your other post though, I’m suspecting the fuel pump because I had very high resistance B+ to ground and less than 0.1V with key on. B+ had battery voltage with key off. That information plus not being able to hear anything when shorted makes me doubly think pump, just need to triple confirm at the connector.

 

Well… just going to close this out. I swear I checked the fuses and got a beep through my volt meter on each one. Well I started running ECU tests and they weren’t looking good so I traced the battery wire to the EFI fuse and whaddya know it was blown. Replaced it and started right up. Idk how to test a fuse wrong but I did it!

 

Testing fuses: Remove the fuse from the circuit. Do NOT test a fuse in-circuit. Why? Because you can read back through the circuit, and get a false "good" indication. Once it's out of the circuit completely, set your meter on the lowest ohms scale. NOT continuity test. That's primarily for testing diodes. If you have a 2 ohm scale, great, if not, use the 200 ohm scale. Then simply touch the two blades of the fuse. Since a fuse is just a piece of wire, essentially, polarity is irrelevant. It's a good idea to scratch the fuse's blades, that plug into the block, with the meter's test lead tip. That way you KNOW you're touching bare metal.
Many automotive fuses have test points in the top of the fuse. I never use them, as they can build up a layer of dirt, giving a false "bad" indication.
Never test a fuse in an active circuit. A circuit with live current in it. Meter's ohms scales are VERY sensitive, and it takes very little current through the meter to blow the ohms portion of the meter. Most meter's ohm scales are protected by a fuse, or a circuit breaker in the better meters, which will blow at a very low voltage. It's a good idea to ensure the fuse cannot possibly have ANY current flowing through it when testing the fuse.

Does that help at all?
Pat☺

 

that helps a lot! I didn’t know that about testing a fuse when installed but makes sense why I’d get a reading. Always good to keep learning and glad I found all this out before trying to buy a new fuel pump and ECU.

 

Okay. If you have the need to test a fuse out-of-circuit, you need to use the ohmmeter and millball's descriptions (and warnings) are all correct.

But you usually don't care if the fuse is "good," as much as you care does it "work." For that, connect one end of your voltmeter (multimeter set to about 20 volts full-scale). Then check the recessed metal points on each side of the fuse. If you get battery on one side but not the other, the fuse is blown. If you get no voltage on either side, that fuse isn't powered (yet). If you get voltage on both sides of the fuse the fuse is good. (Sometimes the fuse doesn't make good contact with the fuse holder, so there is a tiny possibility that the fuse is good, it is connecting on the battery side, but not connecting on the load side. Sometimes, ya gotta be paranoid.)

You don't care if dirt on the fuse gives you a "false" blown reading; just pull out the fuse and check the socket tabs. You want to find one with battery voltage (battery side) and one without (load side). If you get no voltage on either, you're back to the fuse is not powered yet.

Can you check a fuse "wrong"? If you were using the ohmmeter in-circuit, as millball points out that shouldn't work. If you were using the voltmeter (or even faster, a test-light), you might have gotten voltage on one side and forget to check the other side.