Finally finished my 3vze full rebuild at the end of 2019, and I'm psyched to have my 4runner back on the road. However, I couldn't get the thing to stay running for a long time, until my shop manager walked over and unplugged the AFM at which point the motor ran like it was brand new... well it is brand new, but it idled and revved perfectly where before i had to hold the throttle open and it sounded terrible. Now I don't care too much about this, the truck is just a wheeling rig and never sees daily driving or any critical use, as long as it runs I don't care much, but any idea why it wouldn't run with it plugged in? The current spec of the truck is: Machined block, new pistons and bearings, new heads, all valves lashed, basically a new long block, timing verified, TPS adjusted. The truck has straight pipes, not my idea but it actually sounds pretty gutsy and I don't feel like buying mufflers. The 02 sensor isn't hooked up and hasn't been for 3 years, i drove it for a year without it with no apparent issues. The 02 wiring was ripped out and when I reconnected it it blew out the EFI fuse over and over so I said to hell with that. I tested the AFM for resistance, no faults, but swapped it out for one in my parts pile, same exact issue. The only engine-related change during the rebuild was an LCE EGR delete but I feel like that wouldn't affect it. Just curious is maybe someone has seen this before. The truck runs pretty dang good and is a total blast to ride around in again with no exhaust, no doors, no problems. I'll get pics up soon hopefully.

 

It sounds like your 4runner has been pretty hacked up, at least electrically.

With the Air Flow Meter disconnected, the engine should just start, run for a few seconds, then stall out. Inside the Air Flow Meter, there is a switch that turns on the Circuit Opening Relay, which keeps the fuel pump running after the engine has started. You can bypass this switch by jumping the FP and +B terminals in the diagnostic connector, but since the jumper bypasses the factory safety feature of shutting off the fuel pump if the engine dies (for instance, in a crash), the jumper method should be used for diagnostic purposes only.

With the oxygen sensor removed, the engine is always running in open loop, which is not optimal for the engine.

Have you tried doing the resistance and continuity test on the Air Flow Meter?

With the amount of work you did to the engine, I would get everything sorted out electrically.

 

thanks for the info, I did test resistance and continuity on both AFMs. I'll work on extracted the severely rusted 02 sensor and rectifying that whole cluster. The truck definitely had some "electrical work" done before i got it, its got well over 300k and has been a wheeling rig for a while, I'll see if i can undo the butchery. I know its a hooptie but thanks for the advice, it wouldve been scrapped a long time ago if it wasnt for me and In trying to get it decent.

 

Vacuum leak maybe? When in doubt Toyotas run rich/retarded timing so if it's running better when it can't see how much air is coming in my first thought would be that you're getting air in where it shouldn't be, when AFM is hooked up and it thinks it knows what the mix should be. No O2 also richens mix, as was said. But yea, 95% chance it's a mix issue one way or the other, rich or lean.

 

Just wanted to update this with the fix. I was a dumdum. When I did the EGR delete I took off the mounting bracket for the little 3 way vacuum pod thing on the front of the intake and tossed the bolt in a drawer, I thought the bolt just went into a thick part of the casting, nope, it went straight into the main intake chamber. I plugged the whole, hooked up the AFM, and it runs better than it has in years. Thanks for yall's advice, once I finish the suspension (I was halfway through lifting the front when this happened) Im gonna set about fixing up the wiring. Thanks again guys!

 

1988 3vze---trying test AFM, I see you had some luck when doing so. Can you provide or direct me to the correct process (testing the ohms at the correct pins)

I could only fond one online but was for a 1990, not sure if the same....I dont think it is since the 88 is a oddball

Thanks!