94 4runner 3vze missing under load
#1
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94 4runner 3vze missing under load
Have been fighting this for months now and am out of ideas. Truck has been stumbling under load for over a year now. Started as an occaisional minor annoyance, now will barely get to 50 mph on flat ground. Starts up and idles smooth, but the slightest load and it bucks and sometimes even backfires through intake. No engine codes. Fuel system seems fine w/ good pressure at all rpm's, all injectors firing. Have recently replaced tps, maf sensor, distributor, cap, rotor, wires, coil, timing belt less than 1 year old, egr tested ok, checked for vacuum leaks, vacuum at steady 20 inches at idle, intake and throttle cleaned, compression at ~160 within 10 pounds for all cylinders. Tired of throwing parts at it and am running out of things to test. Any ideas?
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Dang! Something is wrong.... but I guess you knew that.
Can you get it to stumble when you blip the accelerator from under the hood?
The '94 has no maf, so when you say you replaced it, I assume you meant the AFM, right? That is an expensive part. But it has no "sensor", only a pickup which detects the angle of the air gate.
The TPS is easy to get in incorrectly, as you know. I'm assuming you are sure its in correctly.
I'm still thinking the timing may not be correct under load. Don't know of a way to check that.
Just thinking out loud here.
Can you get it to stumble when you blip the accelerator from under the hood?
The '94 has no maf, so when you say you replaced it, I assume you meant the AFM, right? That is an expensive part. But it has no "sensor", only a pickup which detects the angle of the air gate.
The TPS is easy to get in incorrectly, as you know. I'm assuming you are sure its in correctly.
I'm still thinking the timing may not be correct under load. Don't know of a way to check that.
Just thinking out loud here.
#6
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have you checked the timing of the timing belt....it could have jumped a tooth. Might also want to have a look at your fuel filter and the gas tank's fuel pump's sock... something is clogged.
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Can't get it to stumble from under the hood. The toyota dealer took a shot at diagnostics on it and said that the AFM was bad and they could replace it for _only_ $1000. I found a remanufactured afm for $180 and replaced it myself. Later I found some info on how to test it with a voltmeter and the old one was just slightly out of range but imho probably not enough to cause any issues.
It's certainly possible that I screwed up on the tps adjustment. I'll pull the throttle this time and check it again.
Also had the timing belt off and reinstalled checking both the marks on the gears and the paint spots from the original install. But may as well pull the cover and check that again anyway.
The fuel system has been pretty much vetted end to end. Pulled the gas tank and cleaned it out, replaced the pump, sock, fuel filter and pulsation damper. Pressure (steady at 40 psi and never drops below 35 when reving the engine) and delivery is good, tested from under the hood.
It's certainly possible that I screwed up on the tps adjustment. I'll pull the throttle this time and check it again.
Also had the timing belt off and reinstalled checking both the marks on the gears and the paint spots from the original install. But may as well pull the cover and check that again anyway.
The fuel system has been pretty much vetted end to end. Pulled the gas tank and cleaned it out, replaced the pump, sock, fuel filter and pulsation damper. Pressure (steady at 40 psi and never drops below 35 when reving the engine) and delivery is good, tested from under the hood.
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#9
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I'll vote for the TPS.
And if you set it while in the truck, that's even a bigger vote.
that thing's a pain in the backside to set on a bench, about impossible to do it in the truck
It may even be bad...they do wear out.
And if you set it while in the truck, that's even a bigger vote.
that thing's a pain in the backside to set on a bench, about impossible to do it in the truck
It may even be bad...they do wear out.
Last edited by MonsterMaxx; 12-11-2006 at 05:15 AM.
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Possible plugged Cat convertor. Try removing your O2 sensor from the exhaust and see if it drives better. Other things to check: Intake hose from AFM to Throttle could be cracked and seperating under load, bad/missing ground wire. Probably best to find a local shop that has a good driveability Technician and let him figure it out. (not talking about the dealer)
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Thanks all.
#12
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Is the TPS a throttle position sensor? and where is it? I just bought my 4runner and I'd like to know how to adjust it, because it seems that it is slugglish when I lay on the gas. It has delay, and acts retarded sometimes.
Thanks
Thanks
#13
Missing under load come usually from 2 areas, either leaking secondary ignition (all high voltage stuff) or plugged injectors giving you a lean missfire. It wont set a code in your case either. Have the injectors cleaned or flushed on the rig. If you flush them on the rig, only use a Motorvac? system. I havent seen anything else that works "on the rig" like the Motorvac does. (Motorvac is the same as the Snap On system cleaner)
#14
Have been fighting this for months now and am out of ideas. Truck has been stumbling under load for over a year now. Started as an occaisional minor annoyance, now will barely get to 50 mph on flat ground. Starts up and idles smooth, but the slightest load and it bucks and sometimes even backfires through intake. No engine codes. Fuel system seems fine w/ good pressure at all rpm's, all injectors firing. Have recently replaced tps, maf sensor, distributor, cap, rotor, wires, coil, timing belt less than 1 year old, egr tested ok, checked for vacuum leaks, vacuum at steady 20 inches at idle, intake and throttle cleaned, compression at ~160 within 10 pounds for all cylinders. Tired of throwing parts at it and am running out of things to test. Any ideas?
#15
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displacedAlaskan -- download it, bookmark it, reference it: http://personal.utulsa.edu/~nathan-buchanan/93fsm/
Makes working on your vehicle so much easier.
Makes working on your vehicle so much easier.
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