My 1987 4runner would start and idle for about 10-15 seconds then stutter and die. I replaced the mass airflow sensor and it’s not helping at all. What else could it be?

 

Why would you replace something without testing it?

PS I'm very much ignoring your use of the MAF anagram, but if you really replaced your vafm with a MAF I recommend you get the right part back on there before you start testing anything.. Ok I really didn't ignore it, you caught me..

 

Try unplugging it and start it. I just had an issue where that let it run

 

I thought the 87 4Runner 22RE used the MAF. I thought the later vehicles, 90+ (?) , used the VAfM.

Of course I am NOT a professional Toyota guy. Rank amateur would be closer to the truth. IE: For a mechanic, I make a darn good radar tech, y'know?
Pat☺

 

All 22R-E engines had Volume Air Flow Meters, not Mass Airflow Sensors.

 

Here is how to test the VAFM: http://web.archive.org/web/201209071...33volumeai.pdf

 

Please don't rig your fuel pump safety systems like this! Remember it's not just you you're putting in danger but your passengers, fellow drivers, good Samaritans, and first responders.

 

You need to investigate the fuel supply, most likely there is an issue with the COR circuit. The COR (circuit opening relay) system controls the fuel pump. It's triggered by the ignition switch STA(start) signal initially and then hands of to the VAFM fuel switch.


These are the diagnostics connectors. Located on the left inner-fender.

Plug K


If the vehicle does not change behavior with the fuel pump diagnostic port supplied power, you don't have a fuel problem you have an electrical problem with the ignition system (ignitor, or ignitor wiring)

DO NOT drive the vehicle with the fuel pump hot wired!

 

Ahh, ok. Thanks. I've been calling it the wrong thing. I'll change.
Pat☺

 

Uh I didnt rig anything on my fuel system. I had a vacuum I didnt know about at the time and unplugging the AFM let it run when it would just stall before...

 

You're not getting the point, the fuel pump doesn't turn on unless it's hot wired or it gets the switch closed in the VAFM.

 

Weird.

What should have happened is when the Air Flow Meter is Plugged in, the truck should start and run normally.

When the Air Flow Meter is unplugged, the engine should start and then stall. The Air Flow Meter contains a switch that keeps the fuel pump running once the engine has started. If the Air Flow Meter is unplugged, there is no longer a complete circuit for the fuel pump to keep running, so the engine should stall. If not, the fuel pump circuit safety cut off has been bypassed, either intentionally or unintentionally. When most people bypass the safety circuit, they do so by placing a jumper wire between the +B and Fp Terminals in the diagnostic connector, which allows the fuel pump to run any time the key is in the ON position. That is totally fine for diagnostic purposes, but isn't safe to drive around with.

So, what Co_94_PU is saying is that there is some sort of connection that is keeping the fuel pump running when it isn't supposed to.

 

Well I didn't know that. The truck has always been a hooptie but I never messed with the wiring on anything besides setting up my winch and some gauges. I'm 100% sure none of the terminals are jumpered, I just set ignition timing the other day. I'm guessing someone in the past did something sketchy to it. I think I'll just run a manual kill switch to the fuel pump power circuit. My fuel pump has always stayed on whenever the key is on as long as I've had it, I thought its just how these trucks were. Unfortunately theres no toyota nerds like me around where i live to tell me this was a bad thing lol

 

Do you think you can reach the switch when you're upside down and your arm is broken? Or if you're unconscious?

Yeah, these are extreme examples, but that's exactly why your truck was designed the way it was. As soon as the engine stops sucking air, the fuel pump is supposed to shut down, no matter if the key is on or not. Just keep all that in mind as you go through your modified electrical system.

 

Just so you know, we are not yelling at you.

We are just concerned for your safety. It doesn't matter if this is a show truck, a daily driver, or a beater truck that never leaves the farm.

We are totally willing to help you diagnose the problem to get your fuel system working the way it is designed.

So far we know something is wrong, but we just don't know where the problem is yet.

 

Don't most cars run the fuel pump with just the key on? I work in a shop and I feel like we've drained fuel tanks before by just doing that, from what I've read Toyota's COR design is fairly unique. I'm totally down to try and fix it I just dont know much about it. From what I've read there's two coils in the circuit opening, one gets power from the key on, and one is powered from the AFM. So I'm guessing someone either hardwired the AFM side or bypassed the relay completely? Is the "switch" built into the AFM?

 

Of course.

I don't work in a shop, and I don't know the fuel system of all cars. I can tell you that on Hondas the fuel pump starts with key-on, then shuts off after about 5 seconds. I've emptied a Honda fuel tank with the pump, but I had to keep switching the key on and off every 5 seconds.

Emptying a Toyota fuel tank with the pump, on the other hand, is easy as pie. You just jumper FP to B+ in the diagnostic connector, and the fuel pump will run (with key on) until the battery dies. If you search this forum, almost every time you see reference to that diagnostic, the poster reminds you to not drive around that way. For the safety reasons already mentioned.

 

Well I got up under the dash tonight, it's a cluster for sure. The COR and it's immediate harness doesn't seem to have been touched, but on the drivers side it's a mess. multiple cut and spliced wires, some with no connection.
COR looks to be unmolested

got 2 wires fouled up coming out of the speed controller, anyone know if that thing is for idle speed or what? It's a manual truck and the speedometer is mechanical, Cruise Control maybe?



Then some genius hardwired this connector that normally goes to a pigtail that goes up to the far driver side of the dash, I think it's for the security light

this 2 prong plug on the main fuse block has some splices


No idea what the hell they were thinking here

And then we reach total madness under the steering wheel.

Honestly I might just see if I can track down a body harness and just swap the whole thing. I'm not great with factory wiring. I can solder alright and running wire for stuff I'm installing is fine, but factory wiring diagrams make my head hurt. I'm also fairly certain that if I wire all this back up like it was (doubt I'd be able to do it right) I would then run into whatever original problem caused someone to butcher this in the first place. For now I'm just going to try and repair the fuel pump circuit.

From what I can tell the circuit goes like this Chassis ground------------FUEL PUMP-----blue-wire-------------COR_----EFI RELAY(engine bay)-------EFI-FUSE(under dash)
I-----VAFM

So they probably ran power directly from the EFI relay in the engine bay to the fuel pump? I don't think they hardwired the AFM circuit itself because I've had the engine harness out on a table when I built the motor and the ECU-AFM wiring seemed untouched. I'll try and check the continuity there with the key on tomorrow. Hopefully it's that and not some other random key-on power source. Wish me luck, holler if I've made some massive error in my logic

 

I was a radar electronics tech my entire working life. Just so you know, when following a schematic you normally go from power to operational item, not ground back.
So that should read Battery-->Main FL-->AM2-->EFI Fuse-->EFI Relay switching contacts-->COR B+ pin -->COR Latching Coil and COR FP pin -->Fuel pump. The COR Latching coil gets it's ground through the VAFM FP Switch. When you go to start, the COR main coil is energized through the Start Relay. It's only energized while cranking, so once you let go of the key, IF there is air flow through the VAFM holding the FP switch closed, the COR's Latching coil takes over, allowing power to continue to the FP. If the engine stops, no more airflow through the VAFM, the Latching coil looses it's ground, opening the COR contacts that allow power to the FP.

I attached a PDF with a schematic of this system. I hope it helps some...

If the PO wire power direct to the FP, IMO, it should be corrected as soon as possible, as it means you're driving a potential fire-trap.

Good Luck!
Pat☺

 

Yes schematics read left to right and too to bottom, but in this case it makes since to start checking at the tank, there might be a new wire run and it will be obvious here, this doesn't mean you might not have to work your way thru the harness junction points to find whatever fault they were tryi g to bypass.