Eric Brumley

I've been playing the parts toss lottery with my 87 GTA (LB9 / 700R4).











I have a vibration at 2000-2500 rpm that comes and goes. Somedays its bad, others it isn't. When I can feel it, it does it when the car decelerates as well.


Without boring anyone, I've eliminated ignition, motor mounts, trans mount, harmonic balancer, belts, water pump, timing chain, trans, driveline, suspension, wheels and tires, brakes and steering as possible causes. The only thing that affects the vibration is adjusting the timing. It reduces it but never eliminates it.


Im now thinking injectors may be the culprit. I plan on ohm testing the injectors.


Any ideas or tips?

aliceempire

iTrader: (14)

Judging by that statement you have not eliminated the possibility of it being ignition related....

My guess is the mis is there all the time, it just makes the most problems when you're at those rpms/load. You don't state what you did to the ignition to assume it's good so I'm not too sure what to advise on checking.

If it were mine, I'd do a compression test to help rule out engine health problems as well.

alex722607

iTrader: (3)

What speed at 2200-2500, because I had a vibration with my TPI above 75 and got worse, almost like lockup wasnt there or was malfunctioning

Eric Brumley

Alicempire.... All new ignition system from distributor to plugs. New coil. New ECM. The vibration comes and goes. Someday its bad and others its barely noticeable. Never thought compression test. Ill run that too when I'm running the injector test. When I say timing affects it but doesnt eliminate it i mean it just reduces the violence of the vibration not the frequency or when it vibrates. Are you thinking burnt valve seat? It does fine when giving it WOT from a standstill until it gets to 2500 rpm.

Alex722607.... New converter too. Flywheel is fine and bolts are tight. TV cable was way out of adjustment when I bought the car. That was my first fix after I bought it. No idea how long they drove it like that. It shifts a bit funny but not really strange.

If I sneak up on 70 and above (very light throttle inputs) the vibration isn't bad. But if you really gas it its nearly undrivable.

alex722607

iTrader: (3)

Is the connector on the side of the trans plugged in. (Not the speed sensor one on he tailshaft, but the white one on the body of the trans.

A transmission shop forgot to connect that once for me, so that's why I am asking

aliceempire

iTrader: (14)

Maybe a burnt valve. Whats the vacuum look like at idle? Odd that would affect it so differently from wot at 1500rpm and 2500 rpm. Conventional thinking would be something so wrong would have an affect at all or more rpm ranges.

Did the problem occur after the new torque converter? I'd wanna blame that if it was after.

Extra thought...driveshaft out of balance? Or does it shake revved up in park too?

Eric Brumley

Alex.... All plugs on trans are connected. I still haven't eliminated that the OD valve or valve body isn't plugged or jacked up in someway. Also the trans mount is OEM rubber and in good shape.

Aliceempire. ... Vacuum seems fine. I would also think that that would cause a power loss especially at WOT.
Vibration was there before new TC was installed and did nothing to change it. I had a driveshaft from an 83 Firebird and switched them out. No difference. Also new u joints in original driveshaft and axle bearings. The vibration is just barely there at 2000 rpm in park. That's why I keep coming back to injectors. I'll run the injectors tonight (I work nights so I'm used to being up all night). I'll post results tonight.

Parts also replaced.... Harmonic balance, all belts, all pulleys run hot straight and true, motor mounts, nearly all sensors (O2, TPS, AICS, temp sensors) EGR and EGR temp sensor, fuel filter, tires (also speed balanced and rotating them makes no change).

Thanks for the replies. Its always good to bounce ideas off of other car smart people. I might as well just order the injectors and new regulator from southbay and be done with it. Lol

Eric Brumley

Finally got off my posterior and check the injectors. Checked while at operating temp. All were between 16.3 and 17.0 ohms. So its not them. I think I'm pretty safe in saying my fuel system is good then. If the regulator or fuel pump were bad i would think that it wouldn't run at all or very poorly.

Ill do a compression test and see what I find. Ill post results this weekend.

Johnny*G

hello there!,
I have a similar problem. ever figure out this vibration?

darbysan

An old thread, but I have the same problem, with no solution yet. Anyone find the problems yet?? I've changed pretty much everything the PO did. I notice a slight improvement when timing is set to 0 vs 6 degrees, but it's still there. Almost a drone in the cabin as well at specific speeds, all starting right at 2000 RPM.

GeneralDisorder

iTrader: (1)

Check torque converter to flex-plate bolts for tightness, and proper clamping. Also re-clock the converter and see if it changes. Try all three orientations and see which one gives the least (or no) vibration.

GD