3500 Swap - help me solve the shakes!

[jmgtp]

First some history:
-3500 LX9 motor swap (all stock)
-3400 exhaust manifolds
-2.5” exhaust, high flow cat, stock mufflers off a 97 GTP
-Modified to fit 3.4 dohc throttle body (63mm I believe)
-1997 Lumina air box (from 3100 motor) and paper air filter
-3400 fuel injectors
-GEN II/III ICM/Coil packs and aftermarket external crank trigger
-1997 Lumina Dogbone Mounts. 3x00 solid motor mount and, in addition, a 3.4 dohc rear mount
-Getrag 284 5 speed manual
-tuned by Ben of WOT tech

Symptoms:
-Hot idle is steady, however engine ‘bounces around’ just a bit
-5th gear, under 2500 rpm (say 60 mph), and a small load (passing someone) causes a lot of vibration. Once it exceeds 2500 rpm (over 65mph) it smooths out. At 70mph and above it runs great. I can also cruise at 60 mph in 5th without any shakes so long as I am maintaining speed and not attempting to accelerate.

Potential Cause:
-Ignition problem
-Fueling problem
-Motor mount problem
-Issues with the ecm Tune

What I’ve tried so far:
-New spark plugs and wire set
-Swapped ICM/Coils with a spare set
-Ohm tested injectors
-Ben assures me the tune is looking good

So… there you have it. At hot idle, I can see the engine bouncing around a bit, I notice it on the accessory side of the motor, I can see the rubber in the dogbone mount allowing the motor to dance. At idle it is moving around +/- quarter inch. BUT, at speeds under 65 mph and in 5th gear the vibrations feel much much worse. And something like 50mph in 5th, forget about it!

Any thoughts? Should I try to shore up the passenger side dogbone mount? If so how? I don’t see myself shelling out $80 for a poly dogbone, especially since I don’t know if that will fix the problem. Do you think I have another problem?

Driven normally it is running pretty well, it is smooth and quiet. It has a bit less torque then I expected from 3.5 liters and the WOT performance is something between a GenII 3.1 and a stock 3.4 dohc. In a drag race, I would hands down give it to the 3.4 dohc. But, cruising around town, 30-45 mph, it is quiet, smooth and I think fairly efficient. The injectors are of unknown mileage. I purchased them on ebay, they were listed as 3400 Monte Carlo injectors. They do ohm out ok, but I’m not sure if they are flowing correctly. The 5th gear vibrations are really what is keeping me from driving the car regularly right now.

[Superdave]

the 3500 makes more power than the 3.4 DOHC stock for stock.. however you put some less than ideal exhaust manifolds on it so it may be down a little.

the shakes in 5th are probably just too much spark advance at that engine load, easy fix for the tuner.

[Wallace]

Does the ECU allow you to run any diagnostics? If so I'd try the cylinder balance test, it sounds like you may have a miss. Have you checked compression on each cylinder?

[pocket-rocket]

Does the ECU allow you to run any diagnostics? If so I'd try the cylinder balance test, it sounds like you may have a miss.

He's running the OBD1 system that came in the car from the factory. So yes, he has the ability to run diagnostics, but no, it can't do a cylinder balance test like OBD2 can.

[mickaz]

when you 'punch it' does it feels like it wants to stall? or does it feels weird? ( I mean not smooth?)

another thing, I had my cam sensor disconnected and it was shaking a idle a little more...when I reconnected it it was alot smoother.maybe that's the same thing your having, since your engine dosent have is cam sensor? kinda like the old school 3.1

maybe you could have 2 things that are looking as one prob? like a drivetrain related and something else?
what about if you rev it from idle??

i'm just throwing idea arounds lol.

[jmgtp]

Depsite the 3400 exhaust manifolds I was expecting more out of this motor. When my 3.4dohc was bone stock, it would run circles around the 3500 I have now.

I'll see what Ben thinks about the spark advance causing a case of the shakes.

I haven't checked compression. I thought about it, but due to the difficulty of reaching the rear bank I didn't do it. I don't think it is a mechanical issue. It is a 50k 60v6, only thing I did was replace the LIM gaskets - and yes I got the pushrods right. Engine runs quiet, (no ticks, pings, etc).

My OBD I ecm does not utilize a cam sensor.

Reving from idle is fine, revs smooth and sounds powerful. This is with the clutch in or out - so that includes spinning up the trans. Keep in mind it runs fine in 5th gear so long as you dont put any load on the engine so I think the issue is the engine and not the trans.

[mickaz]

Depsite the 3400 exhaust manifolds I was expecting more out of this motor. When my 3.4dohc was bone stock, it would run circles around the 3500 I have now.

I'll see what Ben thinks about the spark advance causing a case of the shakes.

I haven't checked compression. I thought about it, but due to the difficulty of reaching the rear bank I didn't do it. I don't think it is a mechanical issue. It is a 50k 60v6, only thing I did was replace the LIM gaskets - and yes I got the pushrods right. Engine runs quiet, (no ticks, pings, etc).

My OBD I ecm does not utilize a cam sensor.

Reving from idle is fine, revs smooth and sounds powerful. This is with the clutch in or out - so that includes spinning up the trans. Keep in mind it runs fine in 5th gear so long as you dont put any load on the engine so I think the issue is the engine and not the trans.

I know OBD1 dont use a cam sensor but MPFI on a engine that was made for SFI might make it feels like it shake a little more at idle... ( superdave said something about a sfi car with a wild cam that felt smoother)
what about your axels? maybe one is out of balance, evens out at higher speedd?

maybe its because you have a heavier vehicule that you feel that its slower?but the 3500 as a torque advantage over the 3.4 DOHC...so it must have some tuning issue.

[SappySE107]

ROFL