03 Trailblazer 4.2 runs like crap!

teehee

Full Member
Joined
Jan 9, 2007
Messages
98
Likes
0
Points
6
#1
Please fill out the following to ask a question.

MAKE:chevrolet
MODEL: trailblazer
YEAR
:2003
MILES: 169000
ENGINE
:4.2
DESCRIBE ISSUE....Rough idle, won't rev past 3,000 rpm in park, flashing CEL

I've changed two coils that were supposed to be bad, all the plugs with denso iridiums, cleaned throttle body (removed).... I'm wondering about the cat???
 

billr

wrench
Staff member
Joined
Mar 12, 2007
Messages
6,138
Likes
65
Points
48
#2
What codes are set? Generally, a flashing CEL indicates that something is bad that it will soon hose the cat... don't delay in getting this resolved.
 
Joined
Mar 1, 2002
Messages
3,452
Likes
46
Points
48
Location
Kentucky
#3
"hose the cat" My cat eventually learned to stay out of the garden when my wife was watering the plants. Flashing CEL? Got codes? Recommend exhaust back pressure test. Shade tree test for backpressure....remove upstream O2 sensor, (cold engine?) start engine , or have a helper start it. If your can block exhaust flow at idle very easily with a finger, 1-2 psi, exhaust flow probably ok. If you need to press more firmly to block flow, and you get a 1/2 second "whoosh" when you remove your finger, you may have a backpressure problem. CAUTION...hot exhaust coming out of an O2 hole can melt things you don't want to get melted.
 
Joined
Nov 14, 2006
Messages
4,802
Likes
50
Points
48
Age
118
#4
CEL flaashes to get ATTENTION now as cat damage is likely.
out of an abundance of caution check eng oil for excess fuel. - EASY QUICK
Fuel pressure test AND with KOEO observe leak down rate likely a leaking component..
Next step-
A billr said get codes do not delay... gets expensive fast
 

teehee

Full Member
Joined
Jan 9, 2007
Messages
98
Likes
0
Points
6
#5
It's my daughters truck, she took it to A#$zone, and they scanned it...don't know the codes off hand but they pertained to:

Crankshaft position sensor
Camshaft position sensor
Intake air temp sensor
Misfire cyl #3
Wheel speed sensor
 

Gus

wrench
Joined
Dec 8, 2006
Messages
2,421
Likes
0
Points
36
#6
Flashing CE light mean you have a bad misfire than can damage the cat.... Check output at the ends of the boots with a spark tester? Since this is coil on plug set up, are the boots OK? Who determined which coils were bad?

If spark is ok, and plugs were not cracked on installation(I prefer OEM), next step is check for compression on all cylinders.....If ok, then we have a possible injector problem.....

A scan tool would tell you which cylinder is misfiring to make diagnosis easier...

Not sure, but 3K could be the rev limiter in Park....
 
Joined
Nov 14, 2006
Messages
4,802
Likes
50
Points
48
Age
118
#7
reread my post above.
with a known p0303 #3 cylinder is a place to start- how does plug look- wet, dry, black,tan?