Help diagnosing P0300
07-10-18, 10:23 AM
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Help diagnosing P0300
So my brother has a 08 ISF with about 117k on the odometer. It had the cats replaced due to a bad odor in the car under heavy acceleration. After the cats were replaced and the car was broken in properly, I took the car out for a drive. I had driven the car after he first got it, it had about 97k then, and I fell in love with the power. This time when I drove it, it felt mostly the same, but you could feel that it wasn't 100%. I took it onto the freeway in sport and manual. Started at about a 40 roll in 2nd, mashed on it up to 6k. Up into 3rd to 6k again and as soon as I shifted into 4th, bam, "check VSC" comes up and CEL blinks, limp more ensues. Luckily I had my scanner with us. Pulled over, pulled the code and it had the P0300 random misfire. Changed all plugs with OEM replacements. Cleaned MAF with carb cleaner, cleaned TB throat. Took it back out and it'll do the same thing when taken to the limit. When driven normally the car drives fine. Had plenty of power and everything seems normal. Then next step I guess is to start replacing coils. But I wanted to see if anyone else has had any similar problems or anything I could try.
07-10-18, 05:08 PM
#2
Swapping coil packs is not likely to help as a failed coil pack would repeat and be flagged appropriately.
What shape are the engine mounts in? Any chance under WOT it's getting a vacuum leak from the engine moving?
Granted it should produce other errors but under WOT its ignoring fuel trims and perhaps other things.
Open the hood and powerbrake it while in drive. Does the engine raise enough to pull any vacuum hoses or intake tube?
The next big hitter would be fuel starvation. Torque Pro will read fuel pressure. Take a look at that. No clue what WOT values should be. Ask other members.
What shape are the engine mounts in? Any chance under WOT it's getting a vacuum leak from the engine moving?
Granted it should produce other errors but under WOT its ignoring fuel trims and perhaps other things.
Open the hood and powerbrake it while in drive. Does the engine raise enough to pull any vacuum hoses or intake tube?
The next big hitter would be fuel starvation. Torque Pro will read fuel pressure. Take a look at that. No clue what WOT values should be. Ask other members.
07-10-18, 05:35 PM
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Swapping coil packs is not likely to help as a failed coil pack would repeat and be flagged appropriately.
What shape are the engine mounts in? Any chance under WOT it's getting a vacuum leak from the engine moving?
Granted it should produce other errors but under WOT its ignoring fuel trims and perhaps other things.
Open the hood and powerbrake it while in drive. Does the engine raise enough to pull any vacuum hoses or intake tube?
The next big hitter would be fuel starvation. Torque Pro will read fuel pressure. Take a look at that. No clue what WOT values should be. Ask other members.
What shape are the engine mounts in? Any chance under WOT it's getting a vacuum leak from the engine moving?
Granted it should produce other errors but under WOT its ignoring fuel trims and perhaps other things.
Open the hood and powerbrake it while in drive. Does the engine raise enough to pull any vacuum hoses or intake tube?
The next big hitter would be fuel starvation. Torque Pro will read fuel pressure. Take a look at that. No clue what WOT values should be. Ask other members.
I haven't checked condition of mounts, but in theory I guess that could be happening.
Would a large enough vacuum leak cause a random misfire though? At idle it is smooth.
What do you mean by power braking? Just to put it in drive and press on the brake while standing still? Or like from 10ish mph and hard brake and see if engine moves?
Wish I still had an android to use Torque. That was my favorite app by far. But ill see if I can get my hands on a good scanner. Thanks for the advice. I will look into those points.
07-10-18, 05:37 PM
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07-10-18, 08:15 PM
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I'd save your money on coil packs. Something else is happening here. If the plugs haven't been touched in a while, start there.
Coils if bad would misfire under load when pulling and repeat. Just saying there is no way 4 or more are failing at once but only at WOT.
Backing up I'm thinking fuel starvation at the tank. Data could support this from both o2 sensors and fuel pressure readings. The computer has this data to stream live.
Power braking; apply both brakes and throttle while remaining stationary. Maybe these never break mounts but look anyway and verify there are no torn hoses.
PS - the engine will move some. It shouldn't move a lot. And its moot point if there are no torn hoses.
Coils if bad would misfire under load when pulling and repeat. Just saying there is no way 4 or more are failing at once but only at WOT.
Backing up I'm thinking fuel starvation at the tank. Data could support this from both o2 sensors and fuel pressure readings. The computer has this data to stream live.
Power braking; apply both brakes and throttle while remaining stationary. Maybe these never break mounts but look anyway and verify there are no torn hoses.
PS - the engine will move some. It shouldn't move a lot. And its moot point if there are no torn hoses.
07-11-18, 07:15 AM
#7
Get a proper obd2 port reader per your phone OS, Purchase OBD fusion, Purchase advanced PIDS.
Watch cylinder misfire counts to isolate the cylinder(s) the misfire is occuring on.
Pull plug and coil. Post a picture of said misfiring plug ( it will likely look like crap because of the miss). Label said coil that's misfiring, swap to another cylinder, monitor data list misfires and see if the misfire follows to suspected coil cylinder. (IE: misfire on cylinder 2, swap coils to cylinder 1)
Also see what your lamda sensors are reading at hot idle (voltage)
Watch cylinder misfire counts to isolate the cylinder(s) the misfire is occuring on.
Pull plug and coil. Post a picture of said misfiring plug ( it will likely look like crap because of the miss). Label said coil that's misfiring, swap to another cylinder, monitor data list misfires and see if the misfire follows to suspected coil cylinder. (IE: misfire on cylinder 2, swap coils to cylinder 1)
Also see what your lamda sensors are reading at hot idle (voltage)
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07-11-18, 09:35 PM
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07-11-18, 09:49 PM
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Get a proper obd2 port reader per your phone OS, Purchase OBD fusion, Purchase advanced PIDS.
Watch cylinder misfire counts to isolate the cylinder(s) the misfire is occuring on.
Pull plug and coil. Post a picture of said misfiring plug ( it will likely look like crap because of the miss). Label said coil that's misfiring, swap to another cylinder, monitor data list misfires and see if the misfire follows to suspected coil cylinder. (IE: misfire on cylinder 2, swap coils to cylinder 1)
Also see what your lamda sensors are reading at hot idle (voltage)
Watch cylinder misfire counts to isolate the cylinder(s) the misfire is occuring on.
Pull plug and coil. Post a picture of said misfiring plug ( it will likely look like crap because of the miss). Label said coil that's misfiring, swap to another cylinder, monitor data list misfires and see if the misfire follows to suspected coil cylinder. (IE: misfire on cylinder 2, swap coils to cylinder 1)
Also see what your lamda sensors are reading at hot idle (voltage)
And the plugs were changed very recently, I'm pretty sure they should all be in good condition, but it wouldn't hurt to make sure.
07-12-18, 03:19 AM
#11
Lexus Champion
Originally Posted by StockaF
Ok. Thanks for the advice. Do you know of a good OBD tool for iOS?
And the plugs were changed very recently, I'm pretty sure they should all be in good condition, but it wouldn't hurt to make sure.
And the plugs were changed very recently, I'm pretty sure they should all be in good condition, but it wouldn't hurt to make sure.
02-23-19, 12:51 AM
#13
Did you ever figure this out? I'm throwing P0300. Recently changed my spark plugs, cleaned my MAF and TB. I'm also getting:
P0171 (Bank 1 Too Lean)
P0172 (Bank 1 Too Rich)
P0174 (Bank 2 Too Lean)
P0175 (Bank 2 Too Rich)
P0125 (Insufficient Coolant Temp for Closed Loop Fuel Control).
Odd thing is my car seems to be running fine. Idles normal, drives normal and pulls hard.
P0171 (Bank 1 Too Lean)
P0172 (Bank 1 Too Rich)
P0174 (Bank 2 Too Lean)
P0175 (Bank 2 Too Rich)
P0125 (Insufficient Coolant Temp for Closed Loop Fuel Control).
Odd thing is my car seems to be running fine. Idles normal, drives normal and pulls hard.
02-23-19, 02:48 AM
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Did you ever figure this out? I'm throwing P0300. Recently changed my spark plugs, cleaned my MAF and TB. I'm also getting:
P0171 (Bank 1 Too Lean)
P0172 (Bank 1 Too Rich)
P0174 (Bank 2 Too Lean)
P0175 (Bank 2 Too Rich)
P0125 (Insufficient Coolant Temp for Closed Loop Fuel Control).
Odd thing is my car seems to be running fine. Idles normal, drives normal and pulls hard.
P0171 (Bank 1 Too Lean)
P0172 (Bank 1 Too Rich)
P0174 (Bank 2 Too Lean)
P0175 (Bank 2 Too Rich)
P0125 (Insufficient Coolant Temp for Closed Loop Fuel Control).
Odd thing is my car seems to be running fine. Idles normal, drives normal and pulls hard.
I haven't figured it out legitimately, but the only thing I can think of is that the car has been filled with cheap gas/Dirty fuel or something like that. To the point that the injectors are dirty or clogged or something like that. And I've come to the point that the injectors need servicing. And with your situation and codes I would be implied to suggest getting you injectors cleaned/ serviced. This is the same thing I told my brother as well. He has yet to do it, but I'm almost certain the injectors are the problem. The fuel system on the ISF is very sensitive because of the regular injection and the direct port injection system. So I believe that my brothers car is throwing this code because the injectors. His problem only occurs at WOT or heavy acceleration. And that leads me directly to the fuel delivery system because I've already addressed the spark/ignition system. The dealer blames engine sludge, which I can agree on, but also the only code that comes up is a “random misfire” not pertaining to any specific cylinder. So i am lead to fuel system because if it was the ignition system it would detect a specific cylinder.
02-23-19, 09:22 AM
#15
per identafix.
this is the list of possibilities when dealing with a p0300 code :
1. Open or short in engine wire harness
2. Connector connection
3. Vacuum hose connections
4. Ignition system
5. Fuel injector assembly for direct injection
6. Fuel injector assembly for port injection
7. Fuel pressure
8. Mass air flow meter sub-assembly
9. Engine coolant temperature sensor
10. Compression pressure
11. Valve clearance
12. Valve timing
13. PCV valve and hose
14. PCV hose connections
15. Intake system
16. ECM
happy hunting.
always start with the cheapest, ie checking work, checking connections checking hoses.
id assuming it be a vacuum issue. seal off the intake and pump if with smoke. or (ghetto way, and you dont have a friend that smokes) while running, hit it with carb cleaner, if there is a vacuum leak the leak will suck in the carb cleaner and you'll hear the engine tone change, it'll atleast give you an idea of where the leak is and work accordingly.
may be an issue under load where a hose could be contracting or expanding and exposing a leak. at that point maybe start with replacing all small vacuum lines?
this is the list of possibilities when dealing with a p0300 code :
1. Open or short in engine wire harness
2. Connector connection
3. Vacuum hose connections
4. Ignition system
5. Fuel injector assembly for direct injection
6. Fuel injector assembly for port injection
7. Fuel pressure
8. Mass air flow meter sub-assembly
9. Engine coolant temperature sensor
10. Compression pressure
11. Valve clearance
12. Valve timing
13. PCV valve and hose
14. PCV hose connections
15. Intake system
16. ECM
happy hunting.
always start with the cheapest, ie checking work, checking connections checking hoses.
id assuming it be a vacuum issue. seal off the intake and pump if with smoke. or (ghetto way, and you dont have a friend that smokes) while running, hit it with carb cleaner, if there is a vacuum leak the leak will suck in the carb cleaner and you'll hear the engine tone change, it'll atleast give you an idea of where the leak is and work accordingly.
may be an issue under load where a hose could be contracting or expanding and exposing a leak. at that point maybe start with replacing all small vacuum lines?
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