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Code P0300 Misfire


TONYUBALDO

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You are going to do both of these

1) put a fuel pressure gage on the schrader valve, start the car check fuel pressure, expect 42 to 45, turn car off, watch needle, does it hold? Quickly dropping pressure potentially indicates a leaking injector, if you can not afford a gage, do #2, but even if you do this, do #2 also, you have to determine why your CAT is glowing red.

Can the FPR still be bad, yes it can, check it again

2) remove the fuel rail retainers, gently lift fuel rail, turn on the key (dont start), look for leaking,

I am glad to see that your mechanic is thinking the same

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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You are going to do both of these

1) put a fuel pressure gage on the schrader valve, start the car check fuel pressure, expect 42 to 45, turn car off, watch needle, does it hold? Quickly dropping pressure potentially indicates a leaking injector, if you can not afford a gage, do #2, but even if you do this, do #2 also, you have to determine why your CAT is glowing red.

Can the FPR still be bad, yes it can, check it again

2) remove the fuel rail retainers, gently lift fuel rail, turn on the key (dont start), look for leaking,

I am glad to see that your mechanic is thinking the same

ok i will defitnely do this 1st thing tomorrow morning and i will let you guys know what happends.

i just came back from my car and took some pics of the nuts i have to take off to remove the fuel rail. i found two in the back and two in the front..is that correct????

also i look in the fuel rail and i found a valve it looks like the one from a bikes tire. is this the schrader valve????

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You are going to do both of these

1) put a fuel pressure gage on the schrader valve, start the car check fuel pressure, expect 42 to 45, turn car off, watch needle, does it hold? Quickly dropping pressure potentially indicates a leaking injector, if you can not afford a gage, do #2, but even if you do this, do #2 also, you have to determine why your CAT is glowing red.

Can the FPR still be bad, yes it can, check it again

2) remove the fuel rail retainers, gently lift fuel rail, turn on the key (dont start), look for leaking,

I am glad to see that your mechanic is thinking the same

ok i will defitnely do this 1st thing tomorrow morning and i will let you guys know what happends.

i just came back from my car and took some pics of the nuts i have to take off to remove the fuel rail. i found two in the back and two in the front..is that correct???? YES THAT APPEARS TO BE CORRECT

also i look in the fuel rail and i found a valve it looks like the one from a bikes tire. is this the schrader valve????

YES, SLIGHTLY BIGGER BUT YES, IT MAY HAVE A CAP ON IT

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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hey guys i have a quick questions... i have my friends OBDII and i was looking through all the options and i came across the freeze frame.......what does that do or show???? this is what came up on the freeze data frame.

DTC that caused freeze frame p0300

throttle position 0.0%

engine rpm 817 RMP

load value 2.7%

mp sensor 44kpa

ignition timing adv, 17.5 degrees

commanded secondary air status ATMOS

short term fuel trim1 0.0%

long tem fuel trim 1 0.0%

short term fuel trim2 0.0%

long tem fuel trim2 0.0%

short term fuel trim3 50%

long term fuel trim3 -38.3

long term fuel trim4 -45.2%

short term fuel trim4 57.0%

fuel system 1 open2

fuel system 2 open 2

i will be doing the fuel rail test and pressure test later today got off from work at 7 a.m. and i had to get some sleep..lol

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ok guys i just got the call fromt he mechanic and everything is running fine. the injectors and fuel rail and FPR are working fine. he said that one of the coil packs is messed up he doesnt know if its the front coil pack or the one on the back. he said they cost about $275.00 each. so what should i do ?? how can i test the coils?? any idea? any help???

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ok guys i just got the call fromt he mechanic and everything is running fine. the injectors and fuel rail and FPR are working fine. he said that one of the coil packs is messed up he doesnt know if its the front coil pack or the one on the back. he said they cost about $275.00 each. so what should i do ?? how can i test the coils?? any idea? any help???

Hey, good. If you know that's what it is, your computer should be able to tell you which cylinder, right? Even is front, odd is rear. Autozone has the coil packs for $199.99 each, so $275 is typical mechanic price padding.

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ok guys i just got the call fromt he mechanic and everything is running fine. the injectors and fuel rail and FPR are working fine. he said that one of the coil packs is messed up he doesnt know if its the front coil pack or the one on the back. he said they cost about $275.00 each. so what should i do ?? how can i test the coils?? any idea? any help???

Hey, good. If you know that's what it is, your computer should be able to tell you which cylinder, right? Even is front, odd is rear. Autozone has the coil packs for $199.99 each, so $275 is typical mechanic price padding.

I wish the computer would tell me which one is bad but i guess im having a multiple misfire and the mechanic is not sure which one it is. im guessing it might be the back one because when i changed the sparkplugs the smelled funny. but who know. lol anyone know how to test the coil packs???

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Cool, as I said above in post #24

"The P0300 must be tracked down, that includes checking the coils, coils not firing will cause unburned fuel also"

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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ok i just got back from the mechanic, he said he checked everything motor is fine, no injectors arent leaking.

he said that one of the coil pack is bad. he didnt know which one it was.

he said he would charge me $600.00 to change both coil packs. but they were both going to be used.

i can get new ones from ACDELCO for $300 each. .

I called a junk yard and they sell them for $150 each with 30 days of warranty. + they come with the ignition module. (whatever that is)

He also told me that since i was driving my car while the cylinders were misfiring that cause for it to use too much gas and thats why my cat was GLOWING red.

what do you guys think i should do??

Is there a procedure or way to check the coils?? so i dont have to buy both coil packs???

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First, your ear might be able to tell you which. Try a long coil, like the cardboard tubes that fabrics come on (you can probably get one from your local JoAnn Fabrics or department store bulk fabric area for the asking) and hold one end at hour ear and put the other near each coil while the engine is idling. If you can hear arcing in one of your coils, that is it.

Another way is with a timing light. Each coil has two wires attached to it. Clamp the timing light on each plug wire in turn and see if you can see if any of them give a weak spark signal. A pair that correspond to one coil gives it away as the bad one.

From your local auto parts store such as Pep Boys, you can get visible spark gap testers that plug in over each individual spark plug. Again, a pair of plugs identifies each of your four cols.

The simplest old-school way is to pull the plugs and look at them. Be sure and label them so you know where each of them came from. Any significant miss will leave plugs dark or even wet with a gasoline smell. Again, pairs of plugs are hooked to each of four coils. The downside is that it's hard to get at the rear plugs and IMHO it's bad luck to put old plugs back, and new ones are about $7 each.

There's also the possibility that you have arcing from plug wires and that the coils themselves aren't bad. Your listening tube can help you there. Another good way is to let the car idle in the dark with the beauty cover off and simply look for the arcs in the dark.

Probably the best way is with an ohmmeter. The secondary is a wire between each plug wire connection and it's a high resistance. The primary is between two terminals on the connector from the coil to the wiring harness, and is a low resistance. There should be an open circuit between the primary and secondary. I can look up the resistances and the connector terminals in my 1997 FSM if you want to go that route.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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First, your ear might be able to tell you which. Try a long coil, like the cardboard tubes that fabrics come on (you can probably get one from your local JoAnn Fabrics or department store bulk fabric area for the asking) and hold one end at hour ear and put the other near each coil while the engine is idling. If you can hear arcing in one of your coils, that is it.

Another way is with a timing light. Each coil has two wires attached to it. Clamp the timing light on each plug wire in turn and see if you can see if any of them give a weak spark signal. A pair that correspond to one coil gives it away as the bad one.

From your local auto parts store such as Pep Boys, you can get visible spark gap testers that plug in over each individual spark plug. Again, a pair of plugs identifies each of your four cols.

The simplest old-school way is to pull the plugs and look at them. Be sure and label them so you know where each of them came from. Any significant miss will leave plugs dark or even wet with a gasoline smell. Again, pairs of plugs are hooked to each of four coils. The downside is that it's hard to get at the rear plugs and IMHO it's bad luck to put old plugs back, and new ones are about $7 each.

There's also the possibility that you have arcing from plug wires and that the coils themselves aren't bad. Your listening tube can help you there. Another good way is to let the car idle in the dark with the beauty cover off and simply look for the arcs in the dark.

Probably the best way is with an ohmmeter. The secondary is a wire between each plug wire connection and it's a high resistance. The primary is between two terminals on the connector from the coil to the wiring harness, and is a low resistance. There should be an open circuit between the primary and secondary. I can look up the resistances and the connector terminals in my 1997 FSM if you want to go that route.

the mechanic said he removed the spark plugs and he found all of the ok. none had oil and none smelled like gas.

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First, your ear might be able to tell you which. Try a long coil, like the cardboard tubes that fabrics come on (you can probably get one from your local JoAnn Fabrics or department store bulk fabric area for the asking) and hold one end at hour ear and put the other near each coil while the engine is idling. If you can hear arcing in one of your coils, that is it.

Another way is with a timing light. Each coil has two wires attached to it. Clamp the timing light on each plug wire in turn and see if you can see if any of them give a weak spark signal. A pair that correspond to one coil gives it away as the bad one.

From your local auto parts store such as Pep Boys, you can get visible spark gap testers that plug in over each individual spark plug. Again, a pair of plugs identifies each of your four cols.

The simplest old-school way is to pull the plugs and look at them. Be sure and label them so you know where each of them came from. Any significant miss will leave plugs dark or even wet with a gasoline smell. Again, pairs of plugs are hooked to each of four coils. The downside is that it's hard to get at the rear plugs and IMHO it's bad luck to put old plugs back, and new ones are about $7 each.

There's also the possibility that you have arcing from plug wires and that the coils themselves aren't bad. Your listening tube can help you there. Another good way is to let the car idle in the dark with the beauty cover off and simply look for the arcs in the dark.

Probably the best way is with an ohmmeter. The secondary is a wire between each plug wire connection and it's a high resistance. The primary is between two terminals on the connector from the coil to the wiring harness, and is a low resistance. There should be an open circuit between the primary and secondary. I can look up the resistances and the connector terminals in my 1997 FSM if you want to go that route.

the mechanic said he removed the spark plugs and he found all of the ok. none had oil and none smelled like gas.

Remember, his car has the coil over plug coil packs, so no plug wires to check with timing light. You could test by ear as said above, but a non-contact IR thermometer might tell you. They usually have a laser to help aim, so shoot for a spot as low on the head as possible if you can't shoot it directly at the exhaust port. The one that's cooler than the others isn't working.

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Well the mechanic is wrong, because IF your CAT is GLOWING RED you MUST have plugs that smell like GAS, as they are NOT firing because of a bad coil pack... something is wrong here

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Well the mechanic is wrong, because IF your CAT is GLOWING RED you MUST have plugs that smell like GAS, as they are NOT firing because of a bad coil pack... something is wrong here

yea thats true. and to top it off he doesnt know which coil is bad. so i guess ima have to buy both of the coil pacls black and gray and im crossing my fingers they do the job.

oh i almost forgot he also told me that a leaking injector wont cause the misfire and that the fuel rail has nothing to do with the misfire.

(he just said that if im having the misfire from the coil packs and im forcing to drive the car like that; i guess its using to much raw unburned gas and thats causing for the CAT to get hot.)

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Well the mechanic is wrong, because IF your CAT is GLOWING RED you MUST have plugs that smell like GAS, as they are NOT firing because of a bad coil pack... something is wrong here

yea thats true. and to top it off he doesnt know which coil is bad. so i guess ima have to buy both of the coil pacls black and gray and im crossing my fingers they do the job.

oh i almost forgot he also told me that a leaking injector wont cause the misfire and that the fuel rail has nothing to do with the misfire.

(he just said that if im having the misfire from the coil packs and im forcing to drive the car like that; i guess its using to much raw unburned gas and thats causing for the CAT to get hot.)

Don't jump to conclusions, hang out here, someone will help. I am not 100% familiar with coil packs... I have a different system. I do believe that there is a way to determine which coil pack is bad.

Logan keeps a coil pack in the trunk they go bad. Is is true that the front bank and rear bank packs are different? There must be a way to test these. Hold on someone will help you out... You are getting close.

I have a program called Autotap, it would show misfires by cylinder, I am SHOCKED your mechanic does not have the proper tools to diagnose this

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I know that my OBDI car doesn't show misfires, but I thought OBDII ones could, right down to which cylinder. Is that not something that can be shown on the DIC?

The front and rear coil packs are different according to my research (AutoZone.com). Beyond just color difference, I think that the channel they fit into on the cam cover is a different shape on each bank.

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I know that my OBDI car doesn't show misfires, but I thought OBDII ones could, right down to which cylinder. Is that not something that can be shown on the DIC?

The front and rear coil packs are different according to my research (AutoZone.com). Beyond just color difference, I think that the channel they fit into on the cam cover is a different shape on each bank.

All you'll get is a P0300 (misfire detected). I think with a Tech II you can get P0301, P0302 etc, telling you which cylinder is misfiring.

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Some models display the codes that tell you which cylinders are misfiring, some don't. I believe that reporting which cylinder has the misfire started sometime after 2000. I don't have any information about which makes, models and years support these codes. I don't think that they are mandated by law. They are most useful in diagnosis with coil-on-plug so I expect that these models would be most likely to support those codes. Others will most likely simply give us P0300.

I thought that I had a misfire last year because I thought that I felt a hesitation at idle occasionally. My mechanic, who has an aftermarket PC-based professional equivalent of a Tech II for all makes, told me that the 1997 Cadillac PCM was very sensitive to misfires and that no trace of a P0300 history code or snapshot was present, but that my model didn't support reporting of individual cylinders that might have a miss. It turned out to be a cracked element in the cat, and when the ceramic shifted the PCM would adjust the timing, throttle, and mixture almost instantaneously, which I could feel at idle.

Some months later when I got a cat efficiency code, he verified a cat problem by checking the difference between the waveforms from the HO2 sensors at the front and back of the cat, and he found the cracked element when he changed the cat. There was no miss. The PCM caught the problem early enough with the cat efficiency code so that only a white powder was coming out the back of the cat and no other exhaust system work was necessary. Apparently my car goes months at a time without a miss, according to my mechanic's OBD II software.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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My $200 Autotap program that a member ranked on recently, will give current and historical misfires by cylinder... Very easy to detect what cylinder (s) are misfiring

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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My $200 Autotap program that a member ranked on recently, will give current and historical misfires by cylinder... Very easy to detect what cylinder (s) are misfiring

hey guys, well thanks again for all your support.... i will definetly find a place where i can get that checked out again. i hope we can get it working ASAP......

i'll let you guys know what happends....

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Good Morning guys,

Well i have good news the car is finally up and running. i changed both of the coil packs. and now its running. =] thank you guys soo much for all your feed back.

Now im just have another question. when i turn my car the rmps are always above 1000 and than like 2 mins later it settles down. but once i put it on reverse or drive the spms go below 1000 close to the 500 rpms and in park rpms always go higher?????? any ideas??????

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What are you saying, when you TURN?, your RPMS increase to 1000?

OR are you saying when you start your car, your RPMs are above 1000 RPM and it takes 2 min to return to normal say 625

It should be 625-650 in drive

Have you cleaned your throttle body and the idle port and pindle?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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What are you saying, when you TURN?, your RPMS increase to 1000?

OR are you saying when you start your car, your RPMs are above 1000 RPM and it takes 2 min to return to normal say 625

It should be 625-650 in drive

Have you cleaned your throttle body and the idle port and pindle?

lo...yes im sorry..when i start my car my rpms go a little over 1000 and once in drive or reverse i drops back to about what you said "625"

no i havent done those 3 things...where can i read to lear how to do that? i dont know whats the iddle port or the pindle lol..... sorry

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