QuestionQUESTION: Symptoms: when pulling a grade and activating the Transmission Power feature the truck bucks or stutters. It's as if it can't decide on a lower gear or is getting only intermittent spurts of fuel.
This now occurs almost every time these conditions prevail, though of course when I took to my mechanic it didn't (in the A.M.)
In the heat of the day (not necessarily when the vehicle is warmed up) the bucking or stuttering occurs even without the Power activated. That is, when trying to accelerate (and therefore downshift) it happens. So, when my mechanic tested in the P.M. during 90 ambient temps it happened.
Sometimes if I can take a grade gradually without accelerating and forcing a gear shift, the truck runs smoothly up the hill.
Someone suggested this is a Throttle Control Sensor failure.
Advise appreciated.
ANSWER: Cliff,
It could be the throttle position sensor or the map sensor that is causing the problem or even a vacuum line that is leaking due to rot or coming off. Check these first and if all checks find then the computer or the valve body itself need looking into.
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QUESTION: I changed the tps and found a A.B.Valve hose cracked so changed that. Problem persists.
What is a map sensor? I don't see one on my sensor schematic.
I've determined that the issue is really ambient temperature specific. We had some cooler weather and the symptoms disappears, only to reappear when the mercury rose again.
So, I'm inviting you to test drive my truck with me. We'll drive it when the ambient temp is under 85, when it is over 95, on the flat and on a grade.
Hop in:
http://thecriticalcrab.net/postits/nissan_testdrive.html
Let me know what you think
Thank you
Cliff
ANSWER: Cliff,
Awesome video you have! I would be looking at temperature related things like the fuel pressure. Get a gauge and install it on the fuel rail and drape the hose under the hood and tape it to the windshield, so you can see the reading when things start happening. If the fuel pressure drops off you will know if the fuel pressure is dropping off. Second, if it is not then it is ignition based. And, if that is the case it is probably the coil or the distributor. With the age of the vehicle the distributor shaft seal could be blown allowing oil onto the optics. If that is the case replace the distributor with a rebuilt unit. High temperature, excessive oil blowby and it could cause the problem with higher revs like in the video.
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QUESTION: Thanks for the response.
"on the fuel rail"? What's a fuel rail?
Do I need a special pressure gauge?
Sorry to be ignorant.
If fuel pressure drops, what needs changing?
Distributor is interesting option.
Thank you
Cliff
AnswerCliff,
On top of the engine there is a fuel rail that feeds the engine. There is a schrader valve like the one on your tire. Get a fuel pressure gauge from the local parts store, screw it on to the valve and drape the line to where the gauge can be taped to the windshield. Or, put it under a wiper arm so it will not flop around. Use a rag since some fuel will probably leak out while installing it. Now, drive it and see if the pressure drops off when you experience bucking. If so, check the pressure regulator. Get a Haynes Manual for the procedure. If the regulator is defective replace it. My thought is the fuel pump if pressure drops and not the regulator or it would do it all the time. If the pressure drops probably replace the fuel pump. The distributor has a shaft weal and after ten years or more they usually fail and contaminate the triggering mechanism under the cover. This is under the cap, rotor and rotor post. There is an optical shutter wheel like your computer mouse. If oil gets on it you will get the sputtering and bucking you experience.
