Cadillac Owners Forum banner
1 - 20 of 25 Posts

·
Registered
Joined
·
15 Posts
Discussion Starter · #1 ·
Hi everyone, hope you can help cause I'm running out of easy ideas.

It's an 05, with the 3.6, 226k kms. Plugs and injectors and coils were new a year ago, says the old owner.

I have the old P0306. So far I've checked fuses, swapped coils around, swapped injectors around, replaced plugs, polished up both levels of intake gasket and checked for anywhere else a vacuum leak could come from, traced the wiring harnesses back checking for any visible damage, unseated and reseated every electrical connector that might be involved, and probably some other things I'm not remembering.

I can't get the code to move to a different cylinder. I plan to borrow a multi meter, hoping I can check the wiring more thoroughly soon.

Anything else I should be looking at or that you know is a usual culprit?

Thanks!
 

·
Registered
2003 Cadillac CTS
Joined
·
356 Posts
Besides the code, how's the car running?

After doing all of that I'm leaning towards the ECM being evil.

Sent from Earth II using Tapatalk V
 

·
Registered
2007 CTS 3.6 >140k miles
Joined
·
1,056 Posts
I would try a new plug first, then proceed with further testing.

Also, what brand plugs and coils were installed? If generic ones from ebay, you are lucky that 5 out of 6 work! I always buy local...Advance Auto, NAPA, etc and use their rebates (Rockauto.com and Summit Racing also legit). Never ebay, Amazon, etc for critical parts...too many counterfeits there.
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #4 · (Edited)
Thanks for the replys.
The car is definately running on five cylinders. Easy to tell at idle, when driving sometimes it seems like it's doing better, sometimes the check engine light goes out even, but I don't know if that's just the engine speed hiding the fault.
Only other code is 0300. Wouldn't there be more codes of the computer were having trouble? Maybe not..
I've replaced the spark plug a couple times, it's NGK Iridium all around. The coils are AC Delco.
What do you suggest next for further testing?
Edit; is there a way to check if the computer is sending the required signals to the coil and injector on 6?
 

·
Registered
2007 CTS 3.6 >140k miles
Joined
·
1,056 Posts
If you replaced the plug and moved coils but the problem persisted, it is safe to day that the issue is somewhere in the wiring or ECM. I would probably remove the ECM and check for broken wires in the harness. It's kind of a crap shoot but important to rule out rodent damage before investing a lot of time or money. Also check the wiring and plug at the coil.

One more thing...I don't know your level of expertise so this may be unnecessary, but be sure to disconnect the neg battery cable before doing any electrical work.
 

·
Registered
2003 Cadillac CTS
Joined
·
356 Posts
If you replaced the plug and moved coils but the problem persisted, it is safe to day that the issue is somewhere in the wiring or ECM. I would probably remove the ECM and check for broken wires in the harness. It's kind of a crap shoot but important to rule out rodent damage before investing a lot of time or money. Also check the wiring and plug at the coil.

One more thing...I don't know your level of expertise so this may be unnecessary, but be sure to disconnect the neg battery cable before doing any electrical work.
What he said

Sent from Earth II using Tapatalk V
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #7 ·
Cool thanks guys.

I'm going to do a compression check before pulling the trigger on the computer, just since I can borrow the tool for free.

Will post back after the weekend!
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #8 ·
Sorry for the delay, can only work on this in spurts. I got a refurbished computer and the problem unfortunately persists. I'm pretty much out of ideas.

To summarize so far:
New refurb computer
New plugs, proper ones
New AC Delco coil
Swapped 6 and 5 injectors
Checked from the block up for vaccum intake leaks
Checked everywhere else for vaccum leaks
Wire harnesses seem perfectly fine
Everything else seems up to snuff


Still misfire on 6 that stays on 6 no matter if I move parts around.
Thanks for any input you can think of
 

·
Registered
2004 CTS Lux Sport and 2014 ATS 2.0T AWD Lux
Joined
·
1,186 Posts
You noted a replaced computer. Did you have it "re-flashed"? A mechanic told me he had to do that after a coil replacement.
 

·
Registered
2003 Cadillac CTS
Joined
·
356 Posts
You need to follow the number 6 coil's wire. Cut all the loom off and follow it until you find the issue. It's the only thing that I can think of that would still be unrepaired...

...but...

...There are ways to test the coil output while on the vehicle but not on the plug. Granted I've only done it on my Mercedes.

Anyone have experience with that on this car?

Sent from Earth II using Tapatalk V
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #12 ·
Thanks for the reply. I'm thinking next step will be to do the noid light and in line spark tester. If either shows an issue that give me a harness to remove and check through. I'll report back.
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #13 ·
Ok so did the noid light and it went blink blink. Did the spark checker and it went blink blink. I guess a compression check is about all that's left.

Anyone know what the actuator on the back of the intake manifold does? Looks like there's a little a door between banks inside the manifold. It's close to the back of the engine and the trouble cylinder is the only really I ask. Doubt it would be big enough of a deal to cause a constant issue like this.

Will report back after a compression check when I get the time to do one.

Thanks all
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #15 ·
That's the thing yep. Don't know what it's supposed to do but I manually actuated it open and left it unplugged on the last test drive and it made no change, except added another engine code - intake actuator open. So I assume it was working right and I've added to the long list of things that aren't broken.
 

·
Registered
2003 Cadillac CTS
Joined
·
356 Posts
That's the thing yep. Don't know what it's supposed to do but I manually actuated it open and left it unplugged on the last test drive and it made no change, except added another engine code - intake actuator open. So I assume it was working right and I've added to the long list of things that aren't broken.
Long ago I had to Goggle around to find out what that part is on my '03.

Sent from Earth II using Tapatalk V
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #17 ·
I'm certainly learning a lot through all this. More than I intended. Good for the confidence but also want to be able to drive my car again. It's a fun unit when it's working.
 

·
Registered
2003 Cadillac CTS
Joined
·
356 Posts
I definitely understand. I miss driving mine too. The deeper I dig while repairing one thing or another, the more things I find in need of repair.

It's a rabbit hole.


Sent from Earth II using Tapatalk V
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #19 ·
Hello I'm back with some numbers, in case you're looking for something to read about

1-110PSI
2-150PSI
3-30PSI
4-150PSI
5-145PSI
6-0PSI

Tried a dollop of oil in 3 and 6 with no change. Never had the computer tell me there was any issue with 3 before and the spark plug looks as good as the others (except 6) so that was a surprise. No blow-by at all comming out of the oil fill when running. I guess valves are next.
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #20 ·
Got the valve cover off and the springs all look great. Rotated the engine and felt each one and everything seems to be in order. Lobes all look normal and the same along the bank. Let me know if you can think of anything to check while it's open. Thanks


Here are a couple pictures, first one is the rear most #6 exhaust (by way of a shaving mirror) and the second is the forward #6 exhaust.

Automotive tire Motor vehicle Automotive design Rim Auto part

Hood Motor vehicle Automotive design Automotive tire Automotive exterior
 
1 - 20 of 25 Posts
Top