Ok, I have read and read and I think I have the issue narrowed down, however I want to get some expert opinions.

1988 4 Runner 3.0 Ran ok all summer, parked it and now no start. Cranks but not firing. Checked for spark, good to go. Ran a jumper from B+ to FP and nothing, the fuel pump did not turn on. Ran hot wire from battery to fuel pump, fuel pump runs, and it starts and runs until I remove power from the fuel pump. So fuel pump is good to go. Checked the COR by listening for click with starter disconnected and turning key to start, got a click. Listened for click when opening the flap inside the air flow sensor (over the air filter) with key in run position, no click. So my question to the experts is: Does this mean my issue is the air flow sensor or the COR? I want to test the resistance in the air flow sensor (If anyone has a schematic for that handy I would be very appreciative).

I feel like I have it narrowed down to one of these two things, but I am afraid I might be missing something and I'd love your advice on additional diagnostics to make sure I only buy what I need.

Thanks in advance.

 

Somebody jump in and correct me if I'm wrong, but when you jump B+ to FP it bypasses all of that. So if the fuel pump still doesn't run check your B+ terminal for voltage and start looking at wiring diagrams to see where you are either not getting power to B+ or the wiring is broken/shorted/disconnected from FP to the fuel pump.

 

Pretty sure B+ in the diagnostic connector is only hot while the ignition is turned to Run.

It does sound like the issue is either with the COR or the VAFM or its wiring.

 

Yeah I am a little worried about the B+ terminal.... I checked it with key on and got some weird reading like 3.2 volts.... I will check it while having my kid turn it over and see if I get closer to 12 volts. But I did jump from B+ to FP and tried to start and no-go...

 

I am assuming testing the VAFM is only by resistance? Anyone have a guide for doing that or a place to find one? I don't want to replace it if it's not the issue... obviously.

As far as testing the COR.. anything else I can do other than listening for the "click" like I did?

Thanks for the responses already, you guys rock!

 

On my 1986 the system still runs through the COR.

Just because the COR clicks doesn't mean it's functioning properly. Check it with a meter for power out.

I haven't learned how to attach a thread from another post yet, but if you Google search "1988 toyota pickup COR pinout yotatech" it will show you a link to the thread you need to read.

 

https://www.yotatech.com/forums/f116...liable-303166/

Hope this works.

 

Dernation: That does help. Thank you!

I forgot to mention: I removed the COR and jumped from B+ to FP in the actual COR socket under the dash.... nothing happened. Does that change anyone’s opinion?

I feel like I have a wiring issue between the FP and the COR based on jumping B+ to FP in the diagnostic port and in the COR socket nothing happening...

 

Yes, it sounds to me like you have wiring troubles somewhere between the fuel tank, and the front of the truck, where the COR and test block is. As you can see, the test jumper, and the COR connector, are two different circuits, up to a point. If both circuits result in the fuel pump not running, I'd put my money on the hot wire running to the fuel pump.

You can ohm it out pretty easy. 4Runners have that nice, easy to access, hatch for the fuel pump and such. Make sure you pull the battery negative before you do though. It takes very little voltage on a wire to blow up a meter set to ohms. You can make a jumper, and ohm the fuel pump hot wire easily. You can check it to both the test block and the COR socket. Frequently, however, the hot wire, or ground, on the fuel pump hanger assembly develop corrosion right there. A quick look at the connections on the fuel pump hanger can often tell the tale. Remember, check out both the ground AND hot connections. It could be either one.
If it's not the connections on the fuel pump hanger, well, it's time to start tracing wires. You'll need to follow the wire from the hanger up to the front of the truck, and find out where it's open. It could be that the wire rubbed somewhere, and wore through, or a connection just broke. It happens to the best crimp, or solder join.

Good luck, and let us know what you find...
Pat☺

 

So the EFI relay was no good. Replaced that and now I have a start and seconds later a stall, indicating an issue with the AFM.

OHM tested the AFM and I have one bad circuit (E2 to VC).

Do you guys know if a faulty AFM will blow out the EFI relay? It seems weird that both of these things failed at the same time.

I will replace the AFM and update on if it’s a fix or not. Fingers crossed.

 

So now the jump from B+ to FP works. The EFI relay was cutting the power to the diagnostic port(s).

Where would you recommend I purchase a new AFM? I’m having a hard time finding one.

 

I've heard decent things about http://yotayard.com/

 

That sort of thing is more likely connected to the FC pin of the VAF, not VC. You might want to look at it again. Or go through these diagnostic steps: https://www.yotatech.com/forums/f116...-quits-312747/ A VAF is going to be expensive, so you ought to be sure you're looking at the right thing.

 

Found one on Ebay... let's hope it works!

 

Well, for the sake of closure, the new AFM has resolved the issue.

The EFI relay was causing no power to the diagnostic port, that was swapped out for a new one (like $13 at Autozone) it changed from a no start to a brief start to a stall. I figure it was either the second half of the COR or the AFM based on the good start but losing fuel and dying.


Swapped out the AFM, removed the B+ to FP jumper and she purrs like a kitten.

Time to get that top off and enjoy this little pavement princess this summer. Appreciate everyone’s advice and assistance. You guys are a great resource.