I get a severe shake when going over 65 and I speed up to pass someone. When
drops out of overdrive and then goes to slip back in after the pass has been
the whole drive train shakes like hell. If I let up on the gas and then
gently step on the gas
to maintain speed, it will go away. The service light will come on and it
always reads the
same code. Misfire 5th cylinder. I've changed the plugs, wires and
distributor. I took it
to the dealer and they said it needed a tune up. They replaced the parts I
had just changed 3 months
earlier. The problem is still there. Now they tell me it's a stuck valve.
This has been going on for
2 years now. When I first felt it, it only happened when the truck was fully
loaded and going up
a hill or passing someone. Now it's doing it when the truck is empty and
much more often. Could
it be a stuck valve and if so, what's the best way to fix it?
do not run it in overdrive unless you are in a nearly flat long stretch.
the overdrive clutches are the weak spot in that 4l60e transmission.
soon you will face a 2300 dollar rebuild.
You wrote on Mon, 3 Sep 2007 00:02:24 -0400:
With best regards, firstname.lastname@example.org. E-mail: email@example.com
It is not so much the 4L60 being a weak design as it is as they ship
them with too tall of gears in drive axles for false high EPA MPG
ratings that do not pan out in real world and that strains OD badly at
times. A 3.42 is pretty tall for a heavy burb with a SB and it has to
strain a lot at times to maintain headway and hunts around. THis is
also compounded by GM's knock sensor that retards spark to control
knock before you hear it which reduces availble power in OD in warmer
weather which can also make engine ruff at times under times a severe
knock control. (the knock sensor masks true octane requirements at the
expense of power and MPG) Make no mistake that without a knock sensor
and ECM retarding spark that engine would rattle like it was full of
marbles with 87 in it in summer. Retarding spark does stop knock but
it really hurts power too. BTW, I have a old 89 burb that I bought new
and I have run it for years on 93 and it runs sweet even after 180k
plus miles. It has 3.73 gears and stock type tires and it pulls OD
really well rarely downshift and will step right out in OD too when
called on to do it. I averages 17 MPG or better on trips too using
The Dealership is adamant that the transmission is not causing the shake. I
trailer package with the 3.73 gear ratio so the OD doesn't really strain at
Code the service code reading of 5th cylinder missfire be caused by a sticky
There's a lot of homework that can be done before teardown.
Swap injectors. See if the problem follows the injector.
Do a compression test.
Make sure all electrical connections are clean and solid
Make sure the injector is receiving electrical pulses
Pull all the spark plugs and compare their appearances
> Thanks for the list of things to check before spending the $ on a
> One other item
> I forgot to mention earlier is that this shaking appears to occur
> is high manifold pressure.
Not so very likely, but, better check for a broken engine
mount as well. And as the engine rocks in the direction
opposite torque, make sure electrical connections aren't
This could all be a wild goose chase, but these are easy
compared to a tear down and you'd sure kick yourself if
there was an easy fix discovered after a major expense.
Check for TSB's here, there was one for this condition for the valves being
too tight in the guides causing them to stick hence the misfire,. Not sure
whether it went up to 99, symptoms are similar, once ign and injector issues
Yes, a sticking valve could cause a missfire in cylinder #5.
Easy 5 minute diagnosis with a labscope and a vacuum transducer.
More common would be failing intake manifold gaskets, a plugged
injector or crossfiring in the distributor cap.
Is this diagnosis with a labscope and vacuum transducer something I could
should I ask a garage to do it. I have access to an oscilliscope, if that is
the same as a
labscope, and could alsways buy a vacuum transducer. Just need to know what
it up too and what to look for.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.