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Help tracking down rough idle / whacky tachometer issue (video)


xylicon
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Pathinder is hard to start and runs rough at idle and the tachometer is very sensitive, no codes are being thrown except for code 55 - no malfunction found

​Sometimes it'll start and idle fine, but then it'll turn itself off after about 10 seconds, other times I experience whats in the video below.

​This leads me to believe its some sort of loose connection somewhere, I've checked/wiggled all connectors I could see and didn't notice any improvement.

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If it came on without warning, or after moving the distributor (or if you check the dizzy and it's loose) then it could be timing. Wouldn't hurt to check the distributor bearings as well, especially with the tach acting up. Anything about how the issue started that might help diagnose it?

 

55 means the ECU doesn't know there's anything wrong. IIRC if it knows there's a problem with a sensor it'll throw a code and fudge that sensor's output from stored values--you might try unplugging the usual suspects (MAF, O2, coolant temp maybe) one at a time to see if it runs better guessing than it does reading them.

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The problem started as I was pulling into a parking space, I put the truck into park and as I was reaching for they keys to turn it off, the truck turned off for me. Ever since then it's been acting like this, sometimes it'll startup and run just fine then die a few seconds later. The distributor is tight, no indication that this is timing related as far as I know. I will take your advice and tinker with some sensors.

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How many miles? Have you ever had the timing belt changed, or are there receipts showing it was?

 

If not, check the timing with a light, if it is off at all, probably the belt skipped.

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Jumped timing I bet - check the T Belt

 

 

 

How many miles? Have you ever had the timing belt changed, or are there receipts showing it was?

 

If not, check the timing with a light, if it is off at all, probably the belt skipped.

 

I am having a hard time believing that this is timing related as the truck will start and idle perfectly fine sometimes and other times do whats shown in the above video. The distributor is tight and has not changed position. I did a timing belt job last July of 2014 using all Nissan OEM parts, and following advice in this forum and by using the Nissan repair manual extensively, I am confident it was done properly. I have put about 4000 miles on the vehicle since the timing job. (I posted a thread about the timing belt/fuel injector job back when I completed it here).

 

So far I've ruled out the fuel pump, fuel injectors, and all fluids are at the proper levels.

 

I havn't had any additional time to diagnose since posting this thread, but as soon as I do, and if and when I find out what the problem is I'll be sure to report the findings.

 

Thank you all for your suggestions.

Edited by xylicon
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My tach has been doing the exact same thing for months now but my '93 Pathfinder runs great. I suspect it's a short somewhere in the wiring harness or a bad ground connection? Sometime when I adjust the electric mirror, it affects the tach and it jumps back to normal. It's on my "to do" list to take the dash apart and find the culprit.

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The tachometer in these are usually not functioning. Mine doesn't work, my brothers does. Mine jumps around sometimes.

I can feel it in the throttle pedal so I don't worry about the tach.

 

Check the idle air control valve. There is a controller for it. There is a procedure for checking it in the manual. Could be a faulty injector. I have one in my rig that acts up at times. It sometimes will run bad, most of the time is runs great.

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Had some time to tinker with the truck today, I checked multiple relays and isolated several different sensors with no changes. I also didn't have any luck in tinkering with the fusible link.

 

Checking the timing was not possible, as the timing marks were jumping all over the place.

 

As always the ECU is still indicating code 55 (no malfunction found)

 

I did notice a connector under the driver's seat, it looks like it goes into a box labeled "Impact Sensitivity Selector" and then it goes off to somewhere else. I disconnected this on a hunch and the truck would not attempt to start. I re-connected it and the truck started up just fine, idled nice and smooth. I left it running for about ten minutes, shut it off and it started right back up no problem.

 

Not sure if this disconnect/re-connect fixed my issue or if its just a coincidence. I will continue with experimentation.

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Hey I recognize those crazy shenanigans! I had this happen not once but twice to me! For me it turned out to be a bad hall effect sensor in the distributor, best fix is a whole new one. Also before you install the new one check the useless ground on the front. I replace my distributor and it fixed this issue but the lead for the ground was weak and snapped off and the sensor burned out again 2 months down the road. This can have some pretty odd side effects if you continue to drive it for a while(dies while doing 50 on the way home from work for instance.)

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  • 3 weeks later...

Hey I recognize those crazy shenanigans! I had this happen not once but twice to me! For me it turned out to be a bad hall effect sensor in the distributor, best fix is a whole new one. Also before you install the new one check the useless ground on the front. I replace my distributor and it fixed this issue but the lead for the ground was weak and snapped off and the sensor burned out again 2 months down the road. This can have some pretty odd side effects if you continue to drive it for a while(dies while doing 50 on the way home from work for instance.)

 

Right on sir! Replaced the distributor and the issue has been resolved, runs like champ now.

 

Although now it looks I will be doing a head gasket job, its spewing white smoke all of a sudden, :pullhair:

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Although you repaired this problem by replacing the distributor, I would like to share a little story with you and the others in this forum.

I just went round and round with a family members 91. It would idle but would pop back and stumble under load. It got worse and worse until you could not drive it. They replaced the mass air flow sensor under the direction of the dealer and the cap and rotor to no avail. They brought it over to my house and we started digging. We were looking at the knock other wires the readings were good. The cylinder balance was in-consistent sensor causing the spark timing to be off. When I hooked my induction tech leed to one of the plug wires, I noticed the reading were all messed up. Onfrom hole to hole as well. The compression seemed even and the plugs, although a little sooty, were firing ok. I took the cap off again to look for carbon tracks even though the cap and rotor were recently replaced. There were no signs of tracks or any reason for the spark to be jumping around. I took the cover off that is under the rotor. This cover protests a thin 360 hole degree wheel. Not sure what it is for but a light passes through it to send a signal to something. The area under the sealed cover under the rotor was contaminated with a fine red dust. Probably from bushing wear. I gently blew the dust away with compressed air, put it back together and, low and behold, it ran great. So after $200 plus and lots of looking and exploring, a little cleaning off was the repair. Now it may come back and start missing some day and I might have to take five minutes and blow it off again, but it won’t cost them anything, and with over 200K miles on it, little repairs are good. For as deep as the knock sensor in on a 91 pathfinder, I'm glad it wasn’t that. As we were cleaning up the job, I noticed the power steering pressure hose had a pin hole leak in the top of the bend on the pump side, so we got to replace that this weekend.

 

Good luck with the head gasket. I have had good luck with a product called Water Glass to seal up a leaking head gasket. I was not wanting to put a lot of labor and money into the pickup as it was on it’s way out any way. But the leakage stopped.

 

Good Luck

Steve B.

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  • 1 year later...

Yes, an erratic tach reading coinciding with a misfire/stumble is usually due to the dizzy - the sensor that drives the primary ignition system is inside there and can give erratic signals if dust and/or debris contaminate it. In turn, dust (usually red) or debris there is usually caused by bushing/bearing failure in the dizzy. Replace the whole unit sensor and all. A word of caution about merely cleaning the junk out and putting it back... When the dizzy starts to fail it also tends to try to jam up. I had this happen to mine. It will destroy the timing belt. Fortunately I caught mine before the belt broke. Put a new dizzy in and it fixed my misfire issue but I heard a knocking sound coming from the new dizzy (old one did it too, I thought it would go away with a replacement). Did some research and apparently a knocking sound from the dizzy on a VG series engine is a tell-tale sign of imminent timing belt failure. Took the upper timing cover off and the teeth were almost completely ripped off and rubber dust was everywhere.

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