cormel

Hi all, just wanted to ask this question. I bought a 91 4runner 22re this past fall. the previous owner had an issue with the power going to the the fuel pump so he hooked it up so the power to the pump works off the ignition switch. Will this cause any issues? would this cause the AFM to not fucntion properly? Currently I am getting a CEL code 2 with points to the ARM. I swaped the AFM still having issues with the truck actually running properly once it is warmed up. Any thoughts?

abecedarian

it all depends on what the issue was with the fuel pump in the first place.
here's the "nut shell" of what happens when you turn the key (for simplicity, cold start's not included):
key turns to 'crank'
power is applied to the ECU, igniter, Circuit Opening Relay (COR) and Starter
the COR applies power to the fuel pump
engine cranks over and distributor spins, signalling to the ignitor when to fire plugs and to the ECU when to fire injectors
ASSUMING everything is working, the engine begins running and sucking air in
once sufficient air is sucked through the AFM (not MAF), the AFM applies a signal to the COR, turning it on (remember, it's already on by the ignition switch)
so now the engine's running, you let the key go and the afm keeps the COR on (and consequently the fuel pump) and thus the engine running.

If the PO had wired the fuel pump in some wierd way or went about it "hit and miss" looking for the right wire, the wiring to or from AFM or even ECU may have been damaged.

thook

I know I posted in a different thread with this same question last night. Were you, Cormel, the same author?

If so, what Abe said is correct. What I'd stated about having wiring to the ignition did not exclude or bypass any function of the AFM circuit. All I'd done was bend the relay contact over in the COR so that it remained closed all the time. The AFM, in this case, never loses signal contact with the ECU, but then the COR operation is no longer dependent on AFM functioning.

Like Abe said, if the original wiring was pooched by the PO, you could be getting the consistent code from that. However, I still don't see how it could cause running problems particularly related to temperatures.

The AFM circuit is, if I understand correctly, just a voltage supply.....a switch that is regulated by operation of the AFM's internal door movement. Then, you have the COR switch......which alternates the power source from initial start up and the IG switch to AFM operation requiring a constant running condition. In other words, it's not temperature specific. Your vehicle runs fine when cold yet not once it's warmed up. That's a temperature specific problem.

Abe.....care to comment? Am I missing something here?

abecedarian

There are 3 'electrical' components within the AFM of which two are operated by the 'vane' or flapper in the unit. There is an air temperature sensor and the switch contacts for the COR/fuel pump / variable resistance component to let the ECU know how much air is entering the engine.
If the air-temp sensor were reading out of range, the ECU would throw a code 8. But now we know two things- the air-temp sensor is working and there is voltage getting to the AFM from the ECU. And to clarify- the voltage from the ECU to the AFM is only used by the air-temp sensor and the air-flow sensor. The switch contacts within the AFM only ground the COR to turn it on, which consequently turns the fuel pump on.

I would start with figuring out what the PO did to get the pump working and then undo it. Then start troubleshooting what's really wrong. You might find that the PO's wiring is causing the problem.

cormel

I know how the fuel pump is actually wired now. He just ran a new hot wire from the switch to the fuel pump with a fuse on that wire, so really it bypasses everything. Would this potentially cause the issues? With the Fuel pump running would this cause the code 2 AFM issue do you think?