Toyota 4runner 2004 V6 no acceleration RPM jumping

The car in question is 3rd gen Toyota 4runner MY 2004 4WD V6 with automatic transmission and 373.000 km. We have it for 1,5 years and have done roughly 35.000 km with it driving around south america. 

Last few weeks we're in Peru and a problem occurred. We have done a journey of 1100 km in four days and had no problems on the first day. But on a second day after few hours of driving when going uphill it started. At that time we were at around 3500m above sea level. Driving some 60km/h the car did not accelerate above 1500 RPMs but just kind of got stucked around there and kept falling on its nose. Which of course meant it also did not change gear from 3rd to 4th. After some more driving uphill we had more steep hills with more curves where you had to take some speed off. Which meant our speed dropped to some 30-40km/h and so eventually it did the same thing and we were stuck in 2nd gear as it wouldn't shift up.  Finally we had to stop as we would get stuck in 1st gear and it was impossible to drive on. So we waited for 20 minutes for the car to cool down and continued the drive. And for some 10 minutes it would all be fine but than started to act in same way. It was like that all the way to the top of the hill. Going downwards it all became normal after few minutes the RPMs and the shifting part. 

Because we were descending from some 4000+ meters above sea level to some 2400 we were not driving uphill for some hours. Later on the levelled road the car behaved normally but in the evening when going uphill – same thing as before.

As we were in the middle of nowhere we had to drive on the next day. And more or less it was the same story. The difference was that it was more or less all flat road so everything was normal for the first 3-4 hours until of course we came upon hill climb. And struggled for the ascent again.
 
We finally got to a decent town and visited a mechanic. He hooked the car to a scanner but did not find any codes. As he was a transmission specialist he suggested we should change automatic transmission fluid which we did. Previously we have been in Bolivia which is known to have a really poor gasoline quality (some say less than 70 OCT) so we also changed gasoline filter. With these two changes done the next day we moved on. And yes same story after few hours. It was slightly better as we had an ascent from 2500 to 4700m the problem did not appear so soon as days before and it might be that RPMs were getting stuck around 1700 but struggled again with turning the car off and waiting to drive on.

 So to summarise: the problem seems to appear after the car has been driven for a while after it gets heated up. It starts with the drive uphill but can continue when driving on flat road. The problem might disappear when driving downhill if the drive downhill takes some time. It just doesn't accelerate over 1500 RPMs but gets stuck there with kind of falling on its nose« feeling. This eventually means it doesn't shift and if the drive uphill is long or we get stuck behind a truck results in getting stuck in 1st gear. After cooling the car down we can continue driving for some 10 minutes with no problems. There is no check engine light and no codes to read.
 
We are planning on having this car for few more months visiting Ecuador and Colombia and on one hand we will be on the road and we want to be safe while driving on the other hand we don't want to spend money on parts we don't necessarily need. So what do you guys think, where should we start to look to solve this problem?

My initial thought is that you're experiencing a catalytic converter that has failed, and is becoming more and more of a restriction as it heats up. Letting it cool a bit eases the restriction, and the cycle repeats.

The easiest place to start would probably be a vacuum gauge on the intake. There are several good videos on YouTube showing how this method works. ScannerDanner hasn't used this method in a video that I'm aware of. Your 4Runner doesn't have an EGR system, so none of those quick methods will work.





Using this method, it's important to take readings when the engine is cold AND while it's falling on its face. I suspect the problem will be more apparent that way. This is also a perfectly good opportunity to get to know the vacuum gauge, which is EASILY one of the most useful diagnostic tools out there.

If you suspect an exhaust problem, you can attempt to remove the upstream oxygen sensors to ease the restriction and give the exhaust somewhere to go. I don't recommend doing this casually, as the sensors are expensive and can be labor intensive to remove/reinstall.

Thank you Tyler for your answer.

UPDATE: Yesterday we visited a local mechanic and explained our problem. He suspects fuel pump failure and advised us to change it simply by saying it's not that expensive and testing fuel pump would mean taking it out (it's inside the tank in our 4runner and you have to remove the tank to change it) which would cost almost as much as buying new one.

Now, we're a little scepctial about it. Can't we test it's functionalitty without removing it (with vacuum pump) so we troubleshoot the problem correctly and not by just changing it. Would a bad fuel pump act like this – starting to act funny after few hours and working poorly under more load (driving uphill and needing to send more fuel)?

But if we are looking at a fuel pump how much labour hours are we looking at approx.? Mecanic said it would take two days but but we didn't talk specifics.

When mentioned if the problem could be the catalityic converter he said no without any proper explanation. Same with our question about cleaning fuel injector or MAP sensor.

So we are having doubts about this mechanic and thinking about visiting another one. Maybe a little paranoid but as a foreighner you are sometimes beeing looked at as a walking wallet

We also called the mechanic which changed transmission fluid and fuel filter and explained it did not help. His suspicion is on catalitic converter or fuel pump failure.

What do you guys think?

As Tyler earlier suggested check for a plugged cat he outlined how to do it in an earlier post . You can check fuel pressure without dropping the tank , I assume your engine has no Schrader valve so what you will need to do is disconnect the fuel line wherever easily accessible (normally either at fuel filter or at fuel rail ) and connect a fuel pressure gauge straight to the fuel line but this should be done during the time it runs bad or it will likely test fine.

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Yeah, I'm with Ben, replacing the fuel pump seems premature at this point.

I don't believe your 4Runner has a MAP sensor, either. I suppose a MAF sensor issue is possible, but I've never seen one fail this way. The local fuel has me more concerned than anything, really. Less than 70 is not fantastic, and that deficiency may show up worse when gaining altitude. Any chance of getting your hands on some octane booster?

Is there a way to check timing pull for each cylinder? I used to be able to do this with vcds on VW and Audi.

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Found the culprit - failure of fuel pump.

We came to a garage in Lima and the mechanic checked the car and suspected the fuel pump failure.
So he tested it and the readings pointed to the pump. So we took it out of a tank and the inner filter was also all dirty from soil and i don't know what. Bought new one and went back on the road.

We were a little worried at first but after 2000 km and driving from sea level to 4000m we are now in Ecuador confident it is now solved.

Thank you all for your help!

That's great news!

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