Loss of Engine response to throttle application

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colpic101
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Joined: Mon Jul 03, 2017 6:14 am

Loss of Engine response to throttle application

Postby colpic101 » Wed Aug 02, 2017 2:03 pm

2004 Pathfinder 3.5L
I have recently been hit one minute to the other with the vehicle loosing response to throttle application.
The vehicle gives a jump when I first press the accelerator and then dies off to idle again. I can repeat this process a few times before it stops responding and returns to idle (700 rpm, down to 500rpm but rougher idle) and I will coast only with the power of idle speed (automatic)

I have recently replaced the battery to a 100 amp, rebuilt the alternator and replaced the fuel filter.

a mechanic hooked up a computer to read the codes, there was 'low battery' and a 'high voltage' code. I understand the low battery, it was put in discharged for a day but the high voltage? He hooked up a tester voltage tester to the battery (after it had been charged), read 17.5 v, that was at idle speed with the engine. this was when the vehicle was not responding well with the throttle. The tester the guy had was digital.

The next day the truck starts and responds perfectly to the pedal, I go to another mechanic with all needle testers (analogue), this tester read right at ideal, 14v idle. we reved the engine to a constant 3000 rpm and the needle didn't jump much higher than about 15.5-16v but would normalize.

Could this be a problem with the voltage regulator in the alternator? This was replaced with the alternator rebuild to a new one. The alternator tested at about 14.6v just after the rebuild, I wish I could tell you was it was beforehand...

Any suggestions would be great, thanks!



The throttle body on my vehicle is electrical, with a sensor at the pedal and throttle b. I opened up the thottle and there was a but of oil gunk but nothing serious. The throttle control motor is sealed in a plastic cover on the side of the throttle body chamber.
Might the problem be with either of these pieces (pedal/TB), and how could I diagnose which one it may be?

If there is any info which I am may be missing, please ask


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smj999smj
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Postby smj999smj » Thu Aug 03, 2017 12:40 am

The charging voltage should never go above 15.5v. Overcharging is just as much of a problem as undercharging as both will play havoc with electronic controllers, among other things. Most late model Nissans will charge right around 14.7 volts under most conditions. It sounds like the rebuilt alternator is faulty, by your description. Years ago I worked on an Altima that had a similar problem. It would idle fine and the charging voltage was fine, but once you drove it down the road, the voltage would increase to over 17 volts and the vehicle would start surging and jerking until it stalled out. I usually recommend using genuine Nissan reman alternators as the aftermarket rebuilds tend to have a poor quality control issues.

colpic101
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Joined: Mon Jul 03, 2017 6:14 am

Postby colpic101 » Sun Aug 06, 2017 3:08 pm

Thanks smj999smj for your quick reply.

Well, I took the alternator out and found it to be burnt out. I am still not exactly sure what happened as the prediction is different with every electro mechanic I see. The alternator started to squeel quite loud one day driving, the transmission oil temp light and battery low lights on the dash came on. the truck still ran alright but I believe I was running on just battery, when I hooked up a tester the battery read 13.3v. The alternator was difficult to take out as it was burning f*%$ing hot.

The alternator might have been making a short circuit between the copper coils and the housing. This would have happened because the little connections that go from the copper coil to the voltage controller were touching (says mechanic 1). The varnish on the copper coil is all black on the inside with some parts of the varnish coating on the wire peeling off. How touchy is the copper coil in respect to the varnish? should I expect a short service life or another catastrophic failure if I reinstall this copper coil into an alternator with new components? Another mechanic tested the copper coil, it tested good between all of the phases and the ring (which the copper is wound through) was isolates from the copper.

The copper coil wasn't soldered properly to the voltage controller not all of the four wires that come off of the coil were connected to the controller.
This is also an obvious faliure but I am not sure if it was soldered well originally and melted during the overheating of the alternator.

In the end I have not Idea if the problem originates in improper assembly or in a faulty voltage controller, failing to control the high v's.

Also, the alternator was squeeling because the bearings heated up and expanded, creating the squeeling noise. These bearings are not bad quality, but how good are bearings to withstanding overheating as such. Are these still usable?

I will be buying a new alternator (the short solution), but would like to salvage what I can from the old one. Any responses to would be appreciated.

If I could learn something from this, never trust a rebuild, unless it is an oem rebuild as smj999smj explained or a trust able rebuild brand. Expect at least some sort of a guarantee as well, I got screwed.

Every time I use a mechanic I realize why I do my own work to my own vehicles.....

colpic101
Posts: 12
Joined: Mon Jul 03, 2017 6:14 am

Postby colpic101 » Thu Sep 07, 2017 9:23 am

To keep this post running a bit;

The alternator was investigated and it was found to be a faulty voltage regulator. I guess the regulator was a cheap one and the controller inside burnt out. This in turn created the spikes in the voltage and burnt the varnish on the copper coil and melted the bearings.

Is it possible that an alternator running at a high voltage can damage something else within the vehicle that would in turn make the alternator more susceptible to damage in the future? Seems like a dumb question, but if there are any ideas...
I mean there are sensors and other controllers that can affect things, could one be burnt out more easily if it hasn't burnt out already?

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disallow
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Postby disallow » Thu Sep 07, 2017 9:45 am

Yes it is possible. But most stuff is good to 25v or so for short periods. Maybe even up to 32v.


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