Topic: Bouncing Tachometer and Truck Vibrations on Acceleration

[bigyotad]

On my drive home today my 85 4runner started vibrating in a way it has never done before, only while accelerating. Trying to figure out why it was shaking I noticed the tachometer was jumping up and down about 1000 rpm from 2000 up to 3000 and 2500 up to 3500 just back and forth and back and forth. So I let off the gas the tach stops jumping and the vibration goes away. I got out and checked the driveline just to see and the was no real slop or play there. No mater what i did, i checked all gears and it does the same thing but only while accelerating, let off the gas and it feels like it always did. When i got home I crawled underneath to take a look and I could her a "ting, ting, ting, ting" sound that cant be good. I went inside to see if anyone was home and came back outside and the truck was still "tinging" softly until it eventually stopped. I have plenty of oil and coolant and I'm not sure exactly what is going on. Motor was just rebuilt at most 200 miles on the motor. Anybody have any ideas?

[Snowtoy]

Can you duplicate the vibrations and tach bounce while just revving the engine?

[bigyotad [OP]]

No only while in gear and moving. In neutral it acts normal.

[redneckcustoms13]

Check u joints, then check rear pinion flange make sure your pinion nut hasn't backed off. If it's ext cab make sire your center bearing isn't bad. Does it act like it could possibly be a fuel supply problem? That could explain whey you'd be surging under load.

[bigyotad [OP]]

Check u joints, then check rear pinion flange make sure your pinion nut hasn't backed off. If it's ext cab make sire your center bearing isn't bad. Does it act like it could possibly be a fuel supply problem? That could explain whey you'd be surging under load.

U joints are all good. It doesn't act like its a fuel supply issue but im not ready to rule it out. It feels more mechanical and very consistent. It didn't seem to get much better or worse trying different driving techniques however it is less noticeable at lower rpm. Just for shits and giggles I shifted into low 4.7 high 2.28 in 2wd and its still noticeable with the t case in low range no foot on the gas but not nearly as bad as when im driving down the street. Need to check the pinion nut tomorrow.
When it first happened I was driving and everything was fine, stopped at a light and when i took off I noticed the problem which existed entire drive home and hasn't stopped so it feels like something has broken or became loose. Trans needs a rebuild it would be nice if that would fix the problem. 

[brainlessfool]

my 83 has a MSD ing. box on it. when the ing needs work the tach jumps. under load. not saying that's your issue, butt keep it in mind if all the rest looks good. not sure if a stock ing. box would do this or not.

[Snowtoy]

When it first happened I was driving and everything was fine, stopped at a light and when i took off I noticed the problem which existed entire drive home and hasn't stopped so it feels like something has broken or became loose. Trans needs a rebuild it would be nice if that would fix the problem.

Check the trans mount. 

Might also see what the trans sounds feels like w/o a load on it.  If not familiar with testing the trans this way, you put the transfer case in neutral, and shift through the gears with the engine running, revving and shifting as if you are driving.

[bigyotad [OP]]

Check the trans mount. 

Might also see what the trans sounds feels like w/o a load on it.  If not familiar with testing the trans this way, you put the transfer case in neutral, and shift through the gears with the engine running, revving and shifting as if you are driving.

I will try that tomorrow. I've also been told twice it could be a misfire. I didn't believe it because it seems fine with tans in neutral but second guy said I might not be able to feel it until there is a load on the drive-train. Will do some tests tomorrow. 

[bigyotad [OP]]

Problem solved and I am an idiot. Checked my plugs and wires today and a plug wire had backed off the distributor. What i was experiencing was a cylinder misfire. Tach is no longer jumping and truck no longer vibrates. Glad to be back to normal. Thanks for all the insight and info I can't believe it was that simple!

[brainlessfool]

Problem solved and I am an idiot. Checked my plugs and wires today and a plug wire had backed off the distributor. What i was experiencing was a cylinder misfire. Tach is no longer jumping and truck no longer vibrates. Glad to be back to normal. Thanks for all the insight and info I can't believe it was that simple!

just something to keep in mind. the tack can let you know of ing trouble. strange butt true. had a coil wire going bad one year, started just a little bounce and then moved on to jumping.
could not "feel" anything wrong when it was just a little bounce.

[bigyotad [OP]]

just something to keep in mind. the tack can let you know of ing trouble. strange butt true. had a coil wire going bad one year, started just a little bounce and then moved on to jumping.
could not "feel" anything wrong when it was just a little bounce.

Will keep that in mind thanks
.

[Mudder]

I had my tach bouncing on me just a few weeks ago, turned out the alternator took a dump on me.

[bigyotad [OP]]

So this issue is re-occuring without the cylinder misfire. Tachometer bounces and motor feels in tune with bouncing, alternator is brand new. Need to test the coil, want to test the throttle position sensor and make sure there are no vacuum leaks. Any other insight is helpful. 

[bigyotad [OP]]

Check u joints, then check rear pinion flange make sure your pinion nut hasn't backed off. If it's ext cab make sire your center bearing isn't bad. Does it act like it could possibly be a fuel supply problem? That could explain whey you'd be surging under load.

Think you might be correct on the fuel supply issue. After a lot of testing I think i have it narrowed down to either a faulty fuel injector or wiring issue leading up to the injector on the 1st cylinder. The injector works at times and does not work other times. Not sure if it is the injector or the wiring its very hard to diagnose because it does not act up all the time. So when it starts acting up I'm trying to test everything I can think of before it stops acting up. Previous owner cut damn near every wire coming off the motor then ass connected them all back together. All injector wires were cut I thought I had everything soldered back together correctly but I might have missed something.

[redneckcustoms13]

Do you have anyone to borrow a set of injectors from? Pop another set in and see how it does. That could help narrow I to the harness.