My Monty went puughhhh..

[Silverwulf]

Last night I went to drive my 99 montero and it started fine, but when I pressed the gas pedal, it kinda bogged down and didnt go anywhere. This lasted for 30-40 seconds, then it ran like normal??? Any ideas anyone?

 

[off-roader]

Was it in drive or were you revving the engine?

 

[Silverwulf]

It was in drive. When I ressed the pedal it seemed as the rpm dropped had no power. It did this for less than a minut. I heard kind of a poof sound from the engine bay. Then It ran normal again :/

 

[off-roader]

Is it still happening or has it disappeared?

does it also happen when in park/neutral?

Trying to isolate if it's in the engine or drivetrain...

 

[RttH]

Mine has done that in the past too. I don't know what it is. Sometimes when I am taking off from a stop light and other times while cruising at about 35-40mph. It has happened probably 5 times in the last 3 years and I had it looked over at the dealer. Nothing to be found? Its been 6 months since last time it happened. It seems fuel related, but I am not sure. Dealer said to run premium, but I never do. It is very random! Good luck...I'll be listening to see what you find out.

 

[Silverwulf]

It seems to have only happened when it is cold outside and I re-start the car.
Also seems to be fuel related.
Cold start valve?, TPS? o2 sensor? egr ? I'll figure it out....

 

[tdesanto]

Gents, I have a 2001, but don't these late model gen 2.5s and early gen 3s both have the same 3.5L SOHC engine?

If so, I've experienced this exact same thing when I used regular fuel for several weeks in a row. The last time that happened was over four years ago and it stopped within 48 hours of my filling the tank with premium and never looking back. I don't know why the premium makes that much difference, but it did in my truck. It hasn't happened since.

I can't say that this is your cause, but it's worth a try. Fill the next few tanks with premium and see if that helps.

 

[Silverwulf]

Funny you mention the grade of fuel. I always run supreme in my e38. I was trying to see how the montero ran on different grade fuels. I put regular on the last time I got gas. Ill put supreme in next and see what happens.

 

[off-roader]

That's interesting about the fuel. My dohc 3.5 only requires regular unleaded. If the sohc 3.5 is the same then perhaps something else is wrong requiring premium fuel...

 

[datrupr]

In my build thread we have a brief discussion about this. The fuel door says to use 91 or higher but the manual says to use 87 octane fuel. I found I get better mileage using 87 and it costs less. I have had no issues with my Monty doing this (yet). I have 111K trouble free miles.

 

[Silverwulf]

I just filled up the montero with 91 octane. Used 87 last time. Only got 16 mpg. I will say that I noticed a big difference in throttle response and power getting on the freeway! Kind of surprised me!

 

[Silverwulf]

So, I got gas this morning. I put 91 in it again. I did not have the hesitation proplem last tank of 91 and my MPG went from 16 mpg to 17.5mpg:wings:

 

[off-roader]

Iirc folks have said if a vehicle isn't tuned for a higher octane fuel, then there is no power or mileage advantage to the higher octane gas. That said, I wonder if the difference was due to the driving conditions?

 

[speedtre]

Iirc folks have said if a vehicle isn't tuned for a higher octane fuel, then there is no power or mileage advantage to the higher octane gas. That said, I wonder if the difference was due to the driving conditions?

This is true. I wonder if the original owner was someone who was very easy on the gas or the Monty was mostly a town vehicle or even they used 91 octane when it wasn't needed? The resulting carbon buildup from a motor that spends it's life loafing can cause an increase in the compression ratio in the cylinders. That would explain why it's running better with the higher octane. The increased compression could be causing some mild detonation issues with the lower octane fuel so the higher octane fuel is running better.

Some info.

http://www.bearriverconverters.com/data/BearRiverNewsletter5.pdf

Read the part where it says Octane Requirements

http://books.google.com/books?id=tp...snum=10&ved=0CEEQ6AEwCTgK#v=onepage&q&f=false

 

[tdesanto]

So, I got gas this morning. I put 91 in it again. I did not have the hesitation proplem last tank of 91 and my MPG went from 16 mpg to 17.5mpg:wings:

So, I'm curious if you've had the problem again or if it looks like the higher octane fuel is helping. It might be too early to tell as it's only been a few days. Are you still on this first tank of 91?