Hi all. Have a few questions. I have a 1999 full size Montero and keep getting random codes. Po130 & po135 are the most common. Also getting po125 when I drive down the highway. Today I got po510. Truck is federal emissions and I have changed the front o2 twice with no luck. I only have 2 o2's on the truck is this correct? Any suggestions would help. Thanks.
O2 question and codes
- Thread starter tlr
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jeep-N-montero
Expedition Leader
Should be an upstream and a downstream sensor, are you running cheap gas in it or do you buy from Chevron, Shell or Texaco 100% of the time? And how old is the catalytic converter?
JohnnyBfromPeoria
I'm Getting Around To It
Are you running 91 octane because you have a "Premium Fuel Recommended" sticker in the gas filler door? I'm not as familiar with the SOHC 3.5 since my newest Montero is a 95 with the DOHC 3.5 that does have that sticker and the ability to take advantage of the higher octane, so that's why I'm asking. If you don't see that suggestion, STOP using premium fuel, as it does you absolutely no good and may in fact be fouling your emission system due to incomplete combustion and byproducts thereof. Higher octane fuel resists combustion more than a lower octane rating and requires different parameters to combust fully, namely, a higher compression ratio and a more aggressive timing curve.
Additionally, a "high flow catalytic converter" isn't necessary on a vehicle that can barely hit 6000 rpm and only displaces 3.5 liters. The best one is a stock one. That may be one reason for the codes, which I admit, I didn't look up in the Google-izer.
Are you using Denso (original equipment) oxygen sensors as replacements or something else?
John B.
Additionally, a "high flow catalytic converter" isn't necessary on a vehicle that can barely hit 6000 rpm and only displaces 3.5 liters. The best one is a stock one. That may be one reason for the codes, which I admit, I didn't look up in the Google-izer.
Are you using Denso (original equipment) oxygen sensors as replacements or something else?
John B.
JohnnyBfromPeoria
I'm Getting Around To It
Again, "seems happier with it" doesn't mean it's doing you any good. ANY. It may be doing your engine harm, to some degree.
The 3.5 DOHC "listens" for engine knock and will retard the timing so you can use regular if you want, with a resulting slight hit in mileage and power. Not many engines do this. Again, not sure on yours. Consult your owner's manual, and if it says to use 89 octane, or 87 octane, DO IT.
John B.
The 3.5 DOHC "listens" for engine knock and will retard the timing so you can use regular if you want, with a resulting slight hit in mileage and power. Not many engines do this. Again, not sure on yours. Consult your owner's manual, and if it says to use 89 octane, or 87 octane, DO IT.
John B.
JohnnyBfromPeoria
I'm Getting Around To It
And, wait, what elevation are you at in Cottonwood? Just saw that you live there; the guy I bought my 95 from lives in and works for the city of Clarkdale. In addition to what I've already posted, the higher elevation means lower atmospheric pressure and an even lower effective overall cylinder pressure, meaning an even LESS need for premium fuel.
Just sayin'.
Just sayin'.
Swank Force One
Adventurer
Running higher octane than called for will not ever harm an engine. It might not give any benefits but it wont hurt anything and it won't kill a cat either.
Relying on a decade or two old knock sensor to save your motor going the other way on the other hand...
Rear o2 should be cheap. Normally i hate diagnosing by throwing parts around but for $20 give it a shot.
Any random misfire or lean codes?
Relying on a decade or two old knock sensor to save your motor going the other way on the other hand...
Rear o2 should be cheap. Normally i hate diagnosing by throwing parts around but for $20 give it a shot.
Any random misfire or lean codes?
jeep-N-montero
Expedition Leader
Stop pulling random ASSumptions and misinformation out of your pocket, there is ZERO side effect from running premium in an engine that doesn't require it, when in fact they do run better and get better mpg because of it. Every vehicle my parents before me and now myself have ever owned gets filled with nothing but premium and it hasn't been uncommon to get over 200k miles out of our cars on the ORIGINAL SENSORS. I even fill our boat up with premium ethanol-free that runs 30 cents more per gallon than the ethanol crap, all 80 gallons of its tank. Most of us really don't give a second thought to filling up with premium in relation to price, if someone is so strapped financially that they have to debate between regular or premium with a 10-12 cent difference per gallon then they likely do not own multiple vehicles like most of us do on here, in my case owning 5 vehicles and 2 boats.
Just sayin....
JohnnyBfromPeoria
I'm Getting Around To It
Again, your "mileage" may vary, but your (and your parents?) experiences do not lend any more explanation to 'why' things work the way they do. You simply state that's the way it works and decry my explanation of the way things are constructed on a chemical level.
http://www.edmunds.com/fuel-economy/to-save-money-on-gas-stop-buying-premium.html
http://www.caranddriver.com/features/regular-or-premium-test-results-page-2
The above articles don't support my claim on fouling but it does mention the behavior of premium formulation versus regular, so you can see that my *** is a part of me that paid attention in chemistry class.
Original poster, have you tried running in an intake cleaner (like old school Seafoam) through the brake booster line until the smoke screen starts, shutting down for an hour or so, then driving the cr@p out of it until it clears up? This can have the effect of clearing out a lot of build-up, a non-technical term. I'd change the oil after that, too, in case of blow-by.
John B.
http://www.edmunds.com/fuel-economy/to-save-money-on-gas-stop-buying-premium.html
http://www.caranddriver.com/features/regular-or-premium-test-results-page-2
The above articles don't support my claim on fouling but it does mention the behavior of premium formulation versus regular, so you can see that my *** is a part of me that paid attention in chemistry class.
Original poster, have you tried running in an intake cleaner (like old school Seafoam) through the brake booster line until the smoke screen starts, shutting down for an hour or so, then driving the cr@p out of it until it clears up? This can have the effect of clearing out a lot of build-up, a non-technical term. I'd change the oil after that, too, in case of blow-by.
John B.
JohnnyBfromPeoria
I'm Getting Around To It
The difference currently between regular and premium here is at least $.27/gallon and is as high as $.34.
Not sure it's important, but I currently only own four vehicles myself, and I installed that supercharger system listed in my signature, not a high school Harry add-on P.O.S., by my self about 15,000 trouble-free miles ago.
John B.
Not sure it's important, but I currently only own four vehicles myself, and I installed that supercharger system listed in my signature, not a high school Harry add-on P.O.S., by my self about 15,000 trouble-free miles ago.
John B.
Swank Force One
Adventurer
I own a 25 year old Mazda on original motor and transmission huffing 25-30psi out of a 60-1 turbo myself, but it's not a Montero. 
(Yanking your chain.)
(Yanking your chain.)
jeep-N-montero
Expedition Leader
You would actually get more fouling on a lower grade fuel due to retarded engine timing that can result in an incomplete burn of the fuel, if the system fails to retard timing then you will have a pre-ignition or lean cycle as a result and can kill an engine. I have actually built a few high HP cars and designed dozens of turbo setups for customers in a previous life, so most people would say I do have some idea of what I'm talking about.
Most modern premium fuels have a fuel conditioner/cleaner formulated into them that lessens the need to run a top end cleaner such as seafoam, but they do help to a degree if you live in a dusty environment and want to clean up the intake tract, even more so if someone is unintelligent enough to use a k&n filter that does not filter very well.
jeep-N-montero
Expedition Leader
I own a 25 year old Mazda on original motor and transmission huffing 25-30psi out of a 60-1 turbo myself, but it's not a Montero.
An old 323 GTX by chance, or an FC? I'm trying to recall what Mazda has from 25 years ago that will spool a 60 series turbo without a lot of lag.