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From: laughingatDesertBob on 29 Jun 2007 08:14
to those of you who own and drive one of these great GM V-6 engines,
here's a few free power/tuning/maintenance tips:

1. unplug the EGR valve connectcor, located just behind the throttle
body near the firewall- your 3.4 DOHC will WAKE UP and make about
20-30 more HP at part throttle driving conditions- it will literally
glide along on level roads at 70 mph with the EGR disconnected- and
will not require as much throttle input to pull from a dead stop or
uphills- most "low power" complaints on the DOHC can be totally
eliminated by simply unplugging the EGR valve- it will throw a code
and turn on your "check engine light"- but will not harm the car in
any way- after removing the EGR plug, run premium fuel for best
performance and to eliminate any ping/spark knock. The DOHC is a
relatively high compression engine 9.6:1, and really should have
premium fuel.

2. the DOHC uses both a timing belt on the overhead cams, and a
standard timing chain behind the front cover- with age, the timing
chain will stretch about 4 to 6 crank degrees- even though the belt is
NEW and replaced. Don't simply mark the cams and put a new belt on,
where the old one was. That will put the cams BEHIND (retarded) in
timing, due to the timing chain stretch. (you only changed the belt,
not the chain). Make sure you lock the cams, unbolt the timing
sprockets (use a stout 6-point impact socket and breaker bar, to get
the cam cog bolts loose)- and retime the cams to the crank. When you
do this, make up for the timing chain stretch, by rotating the crank
forward to take the play out, aligning the balancer mark with arrow on
timing cover, THEN locking the cams in place. My timing chain had
about 4 degrees of slop, when I retimed it.

3. It's a lot easier to time these engines, with the inner fenderwell
plastic cover and right wheel removed, and a hole cut in the inner
fender so you can see the timing marks. This way, you won't have to
remove all the front engine accessories and belt, to see the marks-
and you can look at the marks "straight on", instead of at an oblique
angle from the top. You can cut the sight hole in the inner fender
with a hole saw, or sawzall.

4. Use BOSCH 4-tip platinum plugs- I have put 55,000 miles on a set of
these plugs, and I could have left them in and run it another 50,000-
but changed them for good measure. They really work- require no
gapping- and they don't foul. They are pricey, $5-7 per plug, but
well worth it in maintenance time saved.

5. Use synthetic oil- I use Amsoil 10-30 or 10-40, this will extend
your oil change intervals to 25,000 miles, with oil filter change at
12,500 miles, and add oil in between for what you may use/burn off.

6. Use a K&N lifetime air filter, so far I have 55,000 miles on one of
those filters as well.

7. Oil leaks- if you DOHC 3.4 gets up in mileage, over 150,000 miles,
it would pay to have the top end of the engine removed and gaskets
replaced. Replace cam carrier gaskets, cam seals, head gaskets,
intake upper/lower gaskets, oil distribution block gasket (between
heads in valley, like a valley cover), and also replace the oil pump
drive plug O-ring. Under the oil pump drive plug itself, place a GM
Chevy distributor gasket, for good measure. Some of these DOHC
engines have oil cooler lines near the oil filter adapter (my 1995 did
not)- replace the lines and oil filter adapter gaskets, and your DOHC
engine will be leak-free.

8. Use synthetic oil in the automatic transmission.

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