Cadillac Owners Forum banner

1 - 20 of 47 Posts

·
Registered
1999 Deville 85,000
Joined
·
85 Posts
Discussion Starter #1
I'm getting a Miss fire code on my 1999 Cadillac Deville 4.6 Base 86,000 Miles

At first the car would shake a lot until the car was warmed up. I would get the PCM P0300 code every so offend.
So I did a tune up and wow all that power that I was missing.
Now I still get the PCM P0300 code but the engine is Rock steady cold or warm.
the last codes I got this morning was PCM P0300 and RFA U1000.

How can I tell what Cylinder is the one misfiring? shouldn't the code say what is misfiring?
If I can find out I would start with changing the coil pack. I could change all 4 to rule that out but would rather not spend the money were I don't have to.
Thanks for any help
 

·
Registered
98 DeVille, 97 DeVille d'Elegance
Joined
·
7,345 Posts
Built in reader does not tell cylinder missing unfortunately (major GM pooch screw). Any parts store will scan and be able to tell you the cylinder missing. Any brand coil will do as the are not unique to this car. I just replaced one last week from a box o coils i keep laying around.
 

·
Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
·
19,864 Posts
Re: 1999 Cadillac Deville 4.6 Base Miss fire code

I'm getting a Miss fire code on my 1999 Cadillac Deville 4.6 Base 86,000 Miles

At first the car would shake a lot until the car was warmed up. I would get the PCM P0300 code every so offend.
So I did a tune up and wow all that power that I was missing.
Now I still get the PCM P0300 code but the engine is Rock steady cold or warm.
the last codes I got this morning was PCM P0300 and RFA U1000.

How can I tell what Cylinder is the one misfiring? shouldn't the code say what is misfiring?
If I can find out I would start with changing the coil pack. I could change all 4 to rule that out but would rather not spend the money were I don't have to.
Thanks for any help
=======================
I agree with rodnok -
P0300 is a generic misfire code -
our on-board code readers will not display WHICH cylinder/cylinders is/are misfiring -
only that there IS a misfire -

take the car to any large auto parts store - they will check your codes for free -

P0301 is a misfire in cylinder #1 - P0302 is cylinder #2 - P0303 is #3 - etc -

once you discover WHICH cylinder is misfiring - diagnosis becomes much easier -
 

·
Registered
1999 Deville 85,000
Joined
·
85 Posts
Discussion Starter #5
Re: 1999 Deville 4.6 Base Miss fire code

I went to Autozone here in Brooklyn NY and they said we will not be able to tell you what cylinder is miss firing with a p0300 code, its a generic code
The code you are getting means you need a tune up. I said I just did a tune up spark plugs and wires.
They said I will have to replace the packs I said all 4, yes all 4.
the car runs great if not for the miss fire code.
Do I ignore it until I get a true code on what cyl.
Could it be a Dirty intake?
 

·
Registered
98 DeVille, 97 DeVille d'Elegance
Joined
·
7,345 Posts
Re: 1999 Deville 4.6 Base Miss fire code

While it is possible to only have 0300 code, any cylinder misfiring will set a code in these so BS flag for that auto parts store... go someplace else and have them pull the codes.
 

·
Registered
1999 Deville 85,000
Joined
·
85 Posts
Discussion Starter #7

·
Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
·
19,864 Posts
Re: 1999 Deville 4.6 Base Miss fire code

I went to Autozone here in Brooklyn NY and they said we will not be able to tell you what cylinder is miss firing with a p0300 code, its a generic code
The code you are getting means you need a tune up. I said I just did a tune up spark plugs and wires.
They said I will have to replace the packs I said all 4, yes all 4.
the car runs great if not for the miss fire code.
Do I ignore it until I get a true code on what cyl.
Could it be a Dirty intake?
============================
I went to Autozone
IDIOTS -

they said we will not be able to tell you
what cylinder is miss firing with a p0300 code,
its a generic code

IDIOTS -
did they connect their scanner to your car?

I agree with rodnok -
RARELY - but sometimes - a P0300 code can be set -
and not store the specific cylinder/cylinders that are misfiring -

take the car to a different store -
 

·
Registered
1999 Deville 85,000
Joined
·
85 Posts
Discussion Starter #10
Tell me about it Same thing at another Autozone but this time he did it for me.
Got these codes p0300 we know about that one
p0171 and 0174 according to the print out they game me p0171 is the powertrain control module uses the oxygen sensor to calculate the air/fuel reto to the engine. the computer has recognized a rich or lean condition on one engine bank only
possible causes
1- if bank one and two set together suspect fuel pressure or MAF sensor
2-oxygen sensor defective
3- ignition miss fire-repair
4- fuel injector problem

and the other code p0174 is bank 2 so I was thinking its number 1- if bank one and two set together suspect fuel pressure or MAF sensor
So I ask the guy you still have a free tool lending program including a fuel gauge with shredder vale connector Sure we doo. its a $140 deposit. I said A WHAT. You used to take the drivers license and when we returned it you gave back the license.
that was 10 years ago sir. we except Credit cards.
now if I was able to put $140 on a credit card or give that in cash I would have just brought it to a repair station.
I will have to wait until my SS check comes in next moth until I check the fuel pressure.
in the mean time I do have a fuel filter I'm going to change now..
 

·
Registered
2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
Joined
·
26,323 Posts
Those aren't code definitions, those are the descriptions that AutoZone prints out of possible things they can sell y.... I mean possible reasons that the code has been set.

Most likely reason for both of those codes, you have a vacuum leak effecting both banks. A leak after the MAF, a manifold leak, manifold overpressurization valve leak, PCV system leak...
 

·
Registered
1999 Deville 85,000
Joined
·
85 Posts
Discussion Starter #12
Came inside to see if I can find the fuel filter and after going under the car saw a hose hanging from the compressor for the rear shocks. it leads to the Tee on top of the compressor but I can't find the other end there is no home or connector that I can find at the possition the hanging hose reaches.
Does anyone have a diagram of the hose route.
I was looking for both a location of the gas filter and the air ride hose routing but having no luck.
the gas filter I know is supposed to be by the tank next to the steel beam (cant think of the proper name LOL)

----------

Found the gas filter and changed it.
Found were the hose goes it goes to a filter attached to the body above.

Question if I get a code p0300 and the check engine light goes on would the check engine reset and go off?
because after a refill of the gas tank the light went off with out resetting it manually.
 

·
Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
·
19,864 Posts
Tell me about it Same thing at another Autozone but this time he did it for me.
Got these codes p0300 we know about that one
p0171 and 0174 according to the print out they game me p0171 is the powertrain control module uses the oxygen sensor to calculate the air/fuel reto to the engine. the computer has recognized a rich or lean condition on one engine bank only
possible causes
1- if bank one and two set together suspect fuel pressure or MAF sensor
2-oxygen sensor defective
3- ignition miss fire-repair
4- fuel injector problem

and the other code p0174 is bank 2 so I was thinking its number 1- if bank one and two set together suspect fuel pressure or MAF sensor
So I ask the guy you still have a free tool lending program including a fuel gauge with shredder vale connector Sure we doo. its a $140 deposit. I said A WHAT. You used to take the drivers license and when we returned it you gave back the license.
that was 10 years ago sir. we except Credit cards.
now if I was able to put $140 on a credit card or give that in cash I would have just brought it to a repair station.
I will have to wait until my SS check comes in next moth until I check the fuel pressure.
in the mean time I do have a fuel filter I'm going to change now..
------------------------
MYSTERY SOLVED -

P0171 and P0174 means you have a big vacuum leak -
and THAT is causing occasional - sporadic - misfires -

with the engine running -
use a can of carb cleaner - with the little hose on it -
and spray around the intake and throttle body -
when the idle changes - you found the vacuum leak -

while you're there -
clean the throttle body -
 

·
Registered
1999 Deville 85,000
Joined
·
85 Posts
Discussion Starter #14
Excellent I will get carb cleaner and test it

on my other question:
if I get a code p0300 and the check engine light goes on would the check engine reset and go off?
because after a refill of the gas tank the light went off with out resetting it manually.
thanks
 

·
Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
·
19,864 Posts
Excellent I will get carb cleaner and test it

on my other question:
if I get a code p0300 and the check engine light goes on would the check engine reset and go off?
because after a refill of the gas tank the light went off with out resetting it manually.
thanks
==================
check your codes again -
see if the P0300 went from Current to History -
 

·
Registered
1999 Deville 85,000
Joined
·
85 Posts
Discussion Starter #16
Checked codes again and it went to history. then my wife told me check engine light came on and no new codes all history codes (didn't clear the last set). So today I sprayed Throttle body cleaner around the intake and around the throttle body and no change in idle.
I took opened up the throttle body and cleaned it with throttle body cleaner. Was not so bad just black and junky inside the flap and around the body. cleaned it with a toothbrush and cleaner until aluminum showed.
Cleared the cod due to sensors being disconnected.
Will see if I get another code and go from there.
 

·
Registered
1999 Deville 85,000
Joined
·
85 Posts
Discussion Starter #19
Got the Check Engine light again today.
Checked Codes and got
P0300
p0171

What else should I look at?
oxygen sensor?
 
1 - 20 of 47 Posts
Top