2002 Pontiac Montana 3.4L OHV had oxygen sensor code but replaced it and cleared. Head gaskets were leaking as well so replaced (milled heads, pressure tested, valve job, replaced 4 bent intake valves), also replaced plugs, wires, coils and ignition module and O2 sensor, cleaned throttle body. Car cuts out at a specific RPM in relation to how warm the engine is, when cold there is no problem. As it warms, the max RPM goes down, when fully warm max rpm can be as low as 1000, let it cool and max rpm will be higher until it warms again. Feels ignition related and not fuel related.
Condition can be created by driving or by brake torquing in gear (power stalling)or, if warm enough, while in neutral – i know gm’s are limited in free rev rpm to about 3-3500 rpm. Does not throw any misfire codes or any other codes at this time. It is possible to drive car right up to the rpm point where it cuts out but go over that point and it cuts out and tach goes nuts bouncing around – I assume it is losing Tach signal. If you mash throttle, it bucks like it wants to run but only up to a point, cuts out, then re-fires, cuts out , etc. like it had a rev limiter only much harsher. If you then get out of the throttle and let rpm’s drop, it runs again but only up to that specific point – it all seems heat related and ignition related. The warmer it gets, the lower the rpm maximum is.
A couple quick notes before I get to your actual problem. First of all, the heads on the 3.4 V6 engines are NOT capable of being milled. If they were off bad enough to need milling, you should have replaced the heads. This will lead to more problems for sure. And you also say that you replaced 4 bent intake valves? If something catastrophic enough happened to bend valves, which I’ve never personally seen on these engines, that as well would have warranted head replacement, if not the entire engine!
Now, on to your problem. From what you describe, my first thought would be a clogged catalytic converter. If plugged bad enough, as it warms up it chokes off the exhaust flow so badly that maximum rpm comes down further and further until it barely runs. You can attempt to check this by disconnecting the exhaust pipe at the back manifold so it exits before entering the converter. If your problem doesn’t act up after running for a while, you know you need to replace it. If that’s not the cause, I would look into an ignition component or module/sensor failing as it gets hot. This could be anything from an ignition module, to a bad coil or wires, or even a crankshaft sensor or camshaft sensor. A scanner would come in handy to actually watch the live data stream of the sensors and see what is falling off. But I would really check that catalytic converter for sure. Good Luck!
Pontiac 2005 Montana
It developed a miss on acceleration and set error code P0335, crankshaft position sensor circuit ”A”. I found that the wire for #4 cylinder had been rubbing on a hose and was worn about half way through. I replaced all wires and plugs. Miss was gone and ran great but still sets the P0335 code.
1. Which crankshaft position sensor is the ”A” one? Behind the pully or the other one?
2. Have never seen the crank sensor go bad after 3 pontiac vans and 900,000 miles. Could something else set this code. Could the ignition module or coil pack go bad because of the bad plug wire?
It also now only stays running on the 2nd attempt to start. Fails the 1st and always starts on the 2nd try. (Not a fuel related problem)
Crankshaft Sensor A is the one located behind the crank pulley. Arcing ignition wires or other secondary ignition components such as a cracked coil can set the code P0335. You might want to check that area first before replacing a sensor. Also, at times the wiring down to the crank sensor has been known to become chaffed on the block and cause a shorting condition. If all wiring checks out ok, and there are no other ignition failures that you can detect, you will most likely need to replace the crankshaft sensor. Rarely, the vehicles computer is to blame for the code but without proper checks it is really hard to diagnose a bad PCM without knowing you have a good sensor and wiring to it, and no other ignition problems.
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10 Comments on "2002 Pontiac Montana Cuts Off At Higher RPM’s"
Do you mean you can not turn the key or the engine doesn’t turn over when you turn the key?Might want to ckeck your aloetnartr and battery. Should be able to come out of park as long as your foot is on the brake pedal and the battery is charged up enough to operate the park shift lock solenoid.
I have the same problem as 2002 pontiac montana it cuts off at higher rpms.Have you fix the problem and what it turn on to be
Pontiac Montana sputters. What can cause this problem?
Pontiac 2005 Montana
Did you have any thoughts as to why it always starts on the 2nd try other than fuel related?
Check for a leaking fuel pressure regulator or weak fuel pump.
I can pretty much guarantee it isn’t a bad computer, but yes they do need to be programmed and only a dealership can do this. There is no real way to test other than watching data on the scanner. I would still recommend checking fuel pressure, since you haven’t positively eliminated it as a cause. Looks like you may just have a junker on your hands, as that van can’t be worth putting this much money into. You’re just throwing money away while you guess at parts. All that cash could have been saved by having a dealer diagnose the problem.
The engine doesn’t lay over like a fuel starvation problem, it cuts out and I could hear exhaust backfire when I had exhaust disconnected and I mashed throttle, forcing the condition to occur. Is there a way to test the computer? if the computer is the problem, how could it be temperature related as it would have air flowing over it keeping it tempurature stable? are there any other components to the ignition system that I have overlooked? Does a new computer have to be “flashed” for the specific vehicle and how is this done?
The cam sensor is located in the top of the block, right behind the power steering pump/reservoir. You may have to remove it to get enough access to change the cam sensor, if you choose to replace it. I wouldn’t think that is the problem, though, but you never know. I wouldn’t rely on the residual pressure from the fuel line as a good judge of fuel pressure and/or fuel pump functionality. I would recommend an actual fuel pressure check cold and hot. The actual best way to do this would be to put a gauge on it, tape it to the windshield and go for a drive. Watch the pressure as you start to lose rpm and see if that is problem. Since all the ignition components have been replaced, I doubt that’s your trouble either. You might want to look into fuel injectors, delivery, etc. I also doubt you have a bad computer, but it is located inside the airbox if you want to give it a look.
so after several hours I have managed to replace the cam position sensor as well… condition still exists.
update and clarification – heads were “faced” to ensure flat surface, the 4 intake valves were “warped”, not actually bent, have old valves – could just have been poor factory tolerance of concentricity (valves slightly out of round.) replaced both crank position sensors on advice from a reputable shop owner I used to work for, checked fuel filter to see if clogged – wasn’t as far as I could tell (had lots of resitual pressure when I seperated the forward fuel line so pump should be good), unbolted and pulled aside head pipe to confirm catalytic convertor suggestion but problem still exists. almost certain this is an ignition problem of some sort as it cuts out and backfires out exhaust. Tested it first thing this morning when dead cold and it cut out at about 5800 rpm, then as continued to drive it would cut out at 4500, 4000, 3500 etc. Where is the cam position sensor located as I have replaced about everything else – plugs, wires, all 3 coils, ignition module, both crank sensors, forward o2 sensor. what else could it be? could a computer be bad? Aren’t they usually located away from heat like in the passenger kick panel on a GM?