V6 wont go past 2800 RPMs

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For all you motorheads out there, here is a question that has left me and many mechanics absolutely baffled...

I own an '88 Pathfinder, V6 (throttle body injection), with 110K miles. I drive it daily, and it runs fine. Overnight, the following problem surfaced - the engine sputters at 2800 RPMs and wont go past that mark! It idles real nice runs absolutely fine before it reaches that mark. It doesnt matter what gear I'm in, what kind of load its under, the position of the throttle (which rules out the throttle position sensor, right?), the engine runs fine exactly until it reaches 2800 RPMs, and then begins to sputter and jerk until I lay off the throttle. (Although it seems to have a little less power and might miss while going up steep hills)

There are no vacuum leaks I've found, no obstructions in the exhaust (I temporarily disconnected the cat, and the problem doesnt go away) From a visual inspection, the injectors are getting plently of fuel at the point of sputtering. I changed plugs, wires, and cap, without solving the problem. What could the problem be?

Although, by use of the throttle, the engine wont go past 2800 RPMs, I was able to get it past that mark by downshifting while going down a steep hill. Here's what happens: the engine still runs above 2800 PRMs, though pressing on the gas pedal has no effect, save a slightly different sound from the engine. As the engine slows to 2800 RPMs, pressing on the gas will cause the violent, on-again off-again jerking, until it goes below the mark and runs fine.

I am at my wits end! If anyone knows a quick fix, or if this is a common problem with the old Nissan V6s, please let me know. Thanks!

Scott Roney

posted by  scott14450

Are there any service codes stored? Does the MIL work? Have you done the simple things like replacing the fuel filter and checking fuel pressure?

Some more info would be useful here...

posted by  cpprioli

My brothers ford Focus was having the exact same problem. It turned out to be a clogged catalytic converter. You could do what we did and see if it works, Just remove the cat take out all the innards and put it back on. Or you could replace it with a new cat or just a stright pipe. If you take out all the ceramic interior or replace with a straight pipes you wont pass emmissions though. But before doing anything, take out the cat and see if its clogged.

posted by  Zalight

The fuel system or catalytic converter arent clogged, but get this:
I put a timing light to it. And here is what is happening: at low RPMs, the timing is fine. As the RPMs increase, the timing naturally advances, but it keeps on advancing until it is way out of range (of the tickmarks) and the engine sputters at 2800 RPMs. So, it seems I have a timing advance problem, and I would assume the problem is either with the mechanical advance in the distributor or the ECU. How do I find what exactly is the cause? And if this is the case, what is the best (and cheapest) way to fix? Can I just replace the whole ECU with another Ive found in a junkyard?

posted by  scott14450

I have a 1997 Pathfinder SE with about 102,000 miles. It was fine until last week when accelerating on a highway, the RPMs seem to get stuck between 2500 - 2800 and the car just jerks violently until I gun the gas and it jumps to 3000 - 4000 RPMs but then settles back down to 2500 and starts jerking again. It seems to get worse after driving for a while and then this morning, started doing it on back roads too. I will take it in to the Nissan shop but I'd like to get a sense of what I am going to be dealing with here. It's very scary to be driving it when it's happening. It sounds as if it's shifting OK but just jerking when the RPMs go higher. It's an automatic transmission. Thank you!

posted by  Gillianjcf

Well the cheapest way is definately not by changing random scrapyard parts (duh). I think ur best bet is to have ur truck connected to an osciloscope and check the readings. It will tell u exactly what is going on at all rpm's.
:thumbs:

posted by  Carcass

I have seen a similar problem with a nissan pulsar. The engine timing was off by one tooth and the engine cound not "breathe" properly.
Make sure your crankshaft and camchaft sprokets are properly timed.

posted by  rj_allan

Sounds like the same problem I have. The cause of mine - and it seems the cause of yours as well - is that your computer is in failsafe mode. Something has made it trip the switch. Have a servicemen pull the code to see what the problem is.

posted by  scott14450

Yep sounds like limp mode. If you can't pull the fault codes, try disconnecting you negative of the battery for 30 seconds to reset the ecu. Sometimes the MIL lamp won't indicate a particular fault.

posted by  Wally

it had the same problem. check ur mass air flow sensor.mine had been coroded and i replaced it and it ran great after that.

posted by  huffman_nissan

its been more than 2 years I think hes figured it out already

posted by  newyorker

Hahahahhahahah

Way To Revive A Thread!! Nice Job!!

Ahahhahaha

posted by  MgsJester

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