OK this is a weird one.

I have a 1985 v-6 camaro (2.8 motor)

The motor has 180,000 miles on it (car has 248,000) Anyways, the motor was partially rebuilt about 15,000 miles ago. (new timing chain, rebuilt heads, new oil pump/pickup, water pump and rod bearings).

The car just passed NJ state inpection and seemed to be running fine....EXCEPT for a vibration at idle 700-900 rpms. The vibration is so bad it will shake the coffee out of your hand. The vibration is not temperature dependent. It happens whenever I am at a light or in park idling.

When i get on the gas, the vibration goes away and it runs fine at highway speeds with no miss or detectable problem.

I did do a compression test: All cylinders were 165-175 psi

I also did a leakdown test. On the driver side bank, the front cylinder leaked about 40% where the other two were about 20-25%

On the passenger side, the middle cylinder leaked about 40% and the other two were 20-25%

I could hear the air coming from the dipstick tube so I am lead to believe the rings are leaking but why a vibration only at idle?

I tried changing the plugs. The old plugs looked fine. no obvious misses or oil coated plugs. After the plug change, no difference.
I checked the Vacuum leak idea....pulls 19 inches at idle while shaking like hell.

I looked from under the car when the motor was running and even though the motor mounts are old, I don't think they are the culprit. The driver side looked worse. I put a jack under the oil pan with a block of wood and raised the motor a little to get the tension off of the motor mounts.....no difference.

The flexplate is not missing any counter weights, nor is it cracked.

Any ideas?

 

If your car has a carb, it could be a bad accelertor pump.

rick

 

Its Fuel Injection. Injectors were replaced 55K miles ago.

Also the coil is an MSD coil. I tried switching back to the stock coil but there was no difference. I run Accel 8.8 wires. Each wire measured around 1000 ohms.

When I tried to short the plug wire to ground on the motor while it was running, there was no arcing sound or white flash.

Could this be a weak spark? If so what can cause this if not the wires or the coil?

 

You've done great detective work.
Only suggestions may be to pull one plug wire at a time to see if....(major tip, try isolating the one problem cylinder).
Could be bad Cat Converter
OR ready for this one
Your Cat Converter may have broken up and become lodged into the beginning of muffler.
I had that happen recently. Yes my CC broke up, became lodged into beginning of my muffler.
This was only diagnoised by removing the muffler to see the effects of the cause. I then replaced muffler and yes car performed better. My car has a cold operation problem, to be solved shortly. Which is teh cause of the CC breaking up (car running too rich, I understand).
Have you cleaned the IAC yet or it's passage?
By your vacuum reading, you SEEM to have conquered any "leaks". YET it could also be your EGR assembly becoming "dead".
YET your passage of the smog check may let you believe otherwise.
Again very good detective work, tho.


Did this "Coffee Mocha Latte Shake" become before or after the smog check?
Why at idle?
Not enough "pressure" to overcome the obstacle, which is "removed" upon greater pedal pressure.

OR IT COULD BE THE "balancer" gone bad, too.
Just some too fun "clues" to help.
Also open hood at night time to see any electrical spark discharge. Which could also assist in the "shake rattle and roll"!

 

Thanks for the detective compliment. This one has really stumped me. I have a 12 sec LS1 car and an 11 sec TPI car in the garage...and the v6 is the one that gives me a problem. geez.

Anyways,

This problem happened about 3 weeks after I passed state inpection with flying colors. I thought about the cat convertor scenario that you mentioned. I haven't unbolted the exhaust to see if the fragments of the cat are scattered but the exhaust note smells sweet and I would think if the blockage was at the exhaust, more velocity of the gases would cause more backpressure resulting in a worse vibration, not removing it.

I have not taken the IAC solenoid out yet. That is a good idea to try. But if that was clogged with dirt either the car would idle low (not enough air getting passed the dirt) or idle high (too much air getting passed because needle valve stuck open) right?

I did check the EGR valve by the crude way of pushing up on the diaphragm from underneath the housing while it is running. The car just about stalls.

I will check the idling in the dark trick tonight. As for checking each wire individually, I should be able to put a plug on the end of a wire and ground it to the block right?

I had thought that possibly the one cylinder that leaked 60% of the air passed the rings might cause the vibration (dead cylinder) but why would it come back to life off idle?

Thanks again for all the help so far!

 

The pulling plug wire means that
IF ya pull a good plug/cylinder, the problem becomes worse.
IF ya pull "that cylinder" plug wire the engine reacts "no difference".
Meaning ya isolated the problem to a "cylinder" not electrical or the exhaust.

IAC is "a guess".

Exhaust mission... that part stinks (figurativly).
Lotta work to see "if". Mine, Wife complained of exhasust fumes into car with window down. I went to muffler shop (I had aged, used muffler installed previoulsy-cheap fix), cut off muffler and to my surprise....

Good to know it happened after emissions testing.
Atleast ya got car on road for detective work!

Open hood at night to see "if any funky electrical storm" is occuring. Easy test. Do in area without lights.

Lucky ya got some cars to play with (I assume) Atco or Englishtown or backstreets of Long Island.

And EGR is a $30-ish guess, also. BUT ya never know on that one. IF ya remove it and see lots of carbon build up, well that could be the problem, too.
10mm pipe wrench is the solution before ya break off those old aged EGR nuts.

Outta curosity...
Is water level in system remaining same or ya adding water?

 

Englishtown is the track of choice in these parts.

water level is remaining constant. When I did the leak down test, the instruction booklet described where to look and listen if a cylinder was passing air (bubble in radiator would be head gasket, out of exhaust would be exhaust gasket etc.)

There is no exhaust smell in the car at all and as I said before, the exhaust has a sweet smell to it. Not like tis running on Cam2, but the smell you get when a car is running good.

When I rebuilt the motor about 10K miles ago, I changed the EGR bolts to brass studs...much easier to get on and off now. Is there another way to check the EGR besides pushing the diaphragm up?

What would cause a weak spark when grounding the plug wires to block? The wires checked good, 2 separate coils did the same thing. Its my understanding that the ignition control module either works or it don't.....?

 

IF you have an original EGR or a replacement of not your doing, swap out the EGR & see what happens.
Ya can always return it.
There could be a slight tear in diaphram that "seals/leaks" upon its on wishes.
I replaced mine as a just in case, cause prior, I only "cleaned" out the carbon.
But replace the aged rubber?
New.
Plug wires again, ya just trying to isolate the "bad cylinder", not doing the spark plug grounding test. Accomplish that by pulling a plug wire (even at cap is ok for this test) to see if engine idles worse or "stays same". If stays same, pass on mechanical, move to next test.
Electrical or "vacuum".
Yep ICM works or not!
Oh other idea MAY BE TO CHECK ALTERNATOR!
Weak power out put can do "nasty things".

I have pics from my first attendance at Englishtown, 1972 Summernationals. I drove there in my 1966 Corvette. Recently saw a car that raced there, Dyno Don Nicholasons 1971 Maverick Grabber at a drag reunion at Fomosa, Bakersfield, CA several years back.
May you never redlight.
Thanks for the memories.
And people wonder why I have (now) no hearing! I stood on right side, at the starting line, all day.
WORTH IT!!!!!!!!!
Bill Grumpy Jenkins
Dyno Don
Sox & Martin
Dandy Dick Landy
The final Pro Stock race was "Grumpy" Against Sox & Martin.
I believe Sox & Martin won.

 

? and the Mysterions

 

.

 

I agree with altenator doing funky things. My car had NEVER pulled a code, and I got one one night a while ago I checked it and it said Low Voltage MAF Sensor. the car ran like crap. THe stereo started being really screwy too. Next day it died on the way to school. I got a junkyard altenator that day and the car was back to normal

 

I checked the voltage to the alternator while it was idling... 13.70

I like to see voltages over 14. Will a 13.70 really do anything? Could this explain the weak spark condition at idle?

 

no, anything betweewn 12-15 is normal.

 

Are you sure? Because the base voltage of the car battery should be around at least 12,5 - 13 V . Now if the idle voltage of the alternator is around this or lower, the battery will not charge/it will discharge. And I have always heard from other sources that the alternator output should be around 14v at all times.

 

IF ya can, try to score an alternator (for comparison testing on your car). Ask ahead of time if it is returnable.
OR bring yours in for bench testing & see what they say.
Could this be cause of the idle problem,
I certainly don't doubt it.
I do know these cars need peak electrical output for "perfect" operation.

 

OK I think I have some headway on this problem. When I pulled the plug wires one at a time to isolate which cylinder was not firing, I identified the middle driver side cylinder as the culprit.

When I put another known good wire on that terminal of the cap and shorted the end to see if there was any spark...there was none.

I pulled that plug and it was a white as a baby's bottom.

Now with a good wire in place, a new cap, and a new rotor, how could this happen? Bad distributor?

 

Maybe the fuel low to that cylinder is bad.
Maybe the plug is bad.
Glad ya found that trick to be helpful, atleast ya know where to go for trouble spot.
Rebuilding distburator is very simple, but detailed. And returns on performance is great, too.
It could be weak parts nthe distb shaft, that coil down there. It's only atleast 20 years old now!

 

Well it wasn;t the plug or the fuel that was not there. The wire itself was not getting current. I tested this by have a current probe (wraps around the wire to tell when firing) and also by shorting the metallic end of the wire basket out on the block and saw no spark.

If the distributor is bad, I am trying to grasp how.

The star spins inside the cage. When the points of the star line up with the legs of cage, it signals the coil to fire. When it does it send the voltage over to the cap and it travels to whatever cylinder the rotor is telling it to. How would it preferentially not send voltage to the middle driver side cylinder?

Again with a new cap and rotor, I can rule out the prong being bent or the rotor edge being worn. How would the distributor not fire on just that cylinder? We already established that the Ignition Control Module either works or it doesn't.

How would the star/cage relationship in the distributor miss only 1 out of every 6 firings and what would make that problem go away at higher RPMs?

 

Well stated response & so true.

My ONLY GUESS COULD BE
The pick up coil at base of distb.

IF original, it's aged. The jump from none to some at "speed" may be the electrical signal sent that overcomes the "resistance" at idle.
IF this is the original distb. set up, it's time for a rebuid with electrical fresh stuff in there (not the ICM, tho ya may want to add a new ICM to the mix, anyway).
Why exactly only that one spark plug/cylinder, is any ones guess, but electrial gremlins come to mind.....

 

Instead of rebuilding the distributor (which has 249,000 miles on it) I was planning on buying a new one.

I assume you re-use the distributor when converting to a 3.4 right? This swap is planned for the summer based on 2 of the cylinders showing leak past the rings and a cam and lifters with 180,000 miles on them.

Thanks for all your help. I will post results when I get a new distributor in there. As for price, I have a way of getting an AC Delco with warranty for about $100.

 

Instead of rebuilding the distributor (which has 249,000 miles on it) I was planning on buying a new one.

I assume you re-use the distributor when converting to a 3.4 right? This swap is planned for the summer based on 2 of the cylinders showing leak past the rings and a cam and lifters with 180,000 miles on them.

Thanks for all your help. I will post results when I get a new distributor in there. As for price, I have a way of getting an AC Delco with warranty for about $100.

 

1,000,000 correct on
REUSING MANY OF THE ORIGINAL 2.8 parts.
That short list includes
Re-use
ORIGINAL VEHICLE MOTOR
Induction
Ignition system
hook 3.4 motor exhaust manifolds right back up to the 2.8 pipes left under car!
From 2.8 also reuse the OIL FILTER HOUSING
From 3.4 passemger side head
remove the recessed block plug for insertion of the original vehicle cooling fan switch.
For this swap also plan on new sensors (cooling system, cooling fan switch).
In all honesty, that's about all ya "need do".
Fine details include removing original vehicle motor oil pan & matching timing cover and all orig vehicle engine front accessory moutning bracketry.
I have a thread for the swap.
It's so simple yet very detailed.
Super effective way to have a great car, faster, stronger, for dirt cheap!

 

well the saga continues.....

Instead of buying a distributor I took a shot and bought a cheap set of wires. Put them on but no difference. However I borrowed a tool to check the wires for current to see when they were firing. All were firing properly!

A friend recommended a possibly bad fuel injector. I had a spare set from another 86 camaro I parted out. I changed the injectors today.....same vibration at idle.

I tried changing the computer...same vibration.

I am pretty much at wits end here. and further ideas?

 

my car did the same thing would run like crapwhen pushing the gas and all it was...1 of my spark plug wires was rubbing agianst my exchaust manifold and it burnt through..took it off drove down the road and it ran bad a$$

 

My car did the same exact thing. At first I thought it was something with the distributor. The root of the problem actually turned out to be a dirty throttle plate. Cleaned it up and adjusted the minimum idle and it stopped shaking at idle.

Give cleaning your throttle plate a try, hopefully that'll solve your problem.