Yota Engines Woes, Any Suggestions??

59Willys

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1989 4Runner with 3.0 V6

Runs fine when its cold, the warmer the engine gets, the worse it runs. (Runs about as good as putting regular unleaded in a sports car!) No power, shakes and won't idle, and exhaust smells like raw gasoline. We have tried a new ignitor, new knock sensor, and new coil with no luck.

Local Toyota dealer has had it for a week with no idea of whats wrong with it, this was a daily driver and we really need it back!!

142K, it should have plenty of life left in it....

Any suggestions greatly appreciated.
 
Injectors dumping fuel? Possible PCM issue missfiring the injectors at the wrong time.Can be an issue between cam sensor/crank sensor, wiring, giving misleading info to the PCM.
 
I had a Runner, and the TSB was done on the heads, the heads are also prone to pitting( according to the internal paperwork at toyota), I just don't think that the raw fuel issue would come from the heads.They typicaly burn oil and overheat when the heads leak on them.
 
Here's a clue to why it runs OK cold but not warm: in general, CPU controlled engines of that OBD era run in an open loop mode when cold. The CPU generally disregards the sensor inputs altogether below a certain temp, adding them to the mix as the temp increases, and runs on pre-programmed parameters until temps get up into the normal ops range. Bad temp sensor(s), manifold absolute pressure sensors, and O2 sensors are notorious for ganging up and producing this set of symptoms, but they aren't the only combo that can cause this. A puking EGR valve can add its middle finger to the mix and confound the diagnosis, too. Bad air flow sensors added to that mix will skew the diagnosis because their input only becomes 100% influential at mid to normal ops temps. They'll check good at cooler temps and bad at higher temps. Doesn't necessarily have to be broken to be bad either. It could just be normal at low temps (relatively) and way off in its output to the CPU as it gets warmer. Same goes for any sensor on the vehicle that's not totally kaput.

Computer codes don't always point a finger at the real culprit. Any combo of two or more sensors can produce codes that have nothing to do with what's really wrong. Example: personal experience says a bad road speed reading in relation to the engine's RPM reading and throttle position sensor reading will throw a hard O2 sensor code on some Mitsubishis and Toyotas. Go figure.
 
radioman said:
Here's a clue to why it runs OK cold but not warm: in general, CPU controlled engines of that OBD era run in an open loop mode when cold. The CPU generally disregards the sensor inputs altogether below a certain temp, adding them to the mix as the temp increases, and runs on pre-programmed parameters until temps get up into the normal ops range. Bad temp sensor(s), manifold absolute pressure sensors, and O2 sensors are notorious for ganging up and producing this set of symptoms, but they aren't the only combo that can cause this. A puking EGR valve can add its middle finger to the mix and confound the diagnosis, too. Bad air flow sensors added to that mix will skew the diagnosis because their input only becomes 100% influential at mid to normal ops temps. They'll check good at cooler temps and bad at higher temps. Doesn't necessarily have to be broken to be bad either. It could just be normal at low temps (relatively) and way off in its output to the CPU as it gets warmer. Same goes for any sensor on the vehicle that's not totally kaput.

Computer codes don't always point a finger at the real culprit. Any combo of two or more sensors can produce codes that have nothing to do with what's really wrong. Example: personal experience says a bad road speed reading in relation to the engine's RPM reading and throttle position sensor reading will throw a hard O2 sensor code on some Mitsubishis and Toyotas. Go figure.
Click to expand...


Ahhhh. sensors, computers, etc. Oh, how they harmonize. Beauty is created when they work, devestation is the result when they do not.

Good luck man. :)
 
Compression check is fine.

I really think its a combination of bad sensors etc, its going to be just a matter of finding the right combo. The only thing that shows on the diagnostics is a bad knock sensor, but the Yota master mechanic says thats just an indicator of another problem - not the problem itself.

Doesn't run hot, or burn oil either.
 
Coolant temp sensor?
Master mechanic man is prolly right as far the knock sensor being a reprocution of something else.
What about injector heating up and staying stuck open....dumping fuel.I am tryin to take all your symptoms into account.
Running rich dumping fuel, possible o2 not switching.
Injectors.
Has the pcm been pined out? If I could see it on a scope or at least a scanner, might be able to give you better info.
Egr? Egr solonoid?
See if you can get some more specs.
 
They seem to have traced it to the wiring that connects to the knock sensor. Lookin like a $45 part and $700 labor...blah!
 
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