• The site migration is complete! Hopefully everything transferred properly from the multiple decades old software we were using before. If you notice any issues please let me know, thanks! Also, I'm still working on things like chatbox, etc so hopefully those will be working in the next week or two.

someone help? p0300 code

E

ericg1181

New member
today i was driving went to change lanes and it just started flashing the check engine light at me. if I am going at easy highway speeds everything is fine. if I have to cut the wheel at slow speeds or attempt to climb a hill it sputters really bad and kicks. sometimes just easy driving does this also but if I let off the gas and ease back into it levels out. I had the code read and of course it is the generic p0300 code.
I had replaced wires and coils about 3 or 4 months ago but the plugs looked fine so I let them alone. any ideas?
 


Replace the plugs, it's what I'd do first.

Check for any damage to the wires and corrosion on the coils. Remove them and see if there are any cracks along the side of them.

Lastly would be the ICM, thats under the coils. It controls were the spark goes, it can go bad aswell.
 
When you changed the wires did you put the dielectric grease on the plug and coil contact pints and boot electrical contact surfaces? Some people mistakenly put the grease on the contact surfaces, it's an insulator and should only be but on the ID of the boots. Just a light coating applied with a Q tip to keep moisture out. What you are describing sure sounds like weak spark from either bad wires or bad connections on either the plugs or coil connections. I had a 67 Mustang convertible when I was in college, that had an engine replaced with a used 302 V8 by a garage that had pulled it from another Mustang they were building up for drag racing. The engine I got had been sitting outside for a while. It ran horribly after a while just like you described. Put new wires on it and then it ran perfectly.
 
just put new plugs in still does the same thing. wires, coil, and icm all look fine. no I didn't use grease they looked light coated when I got them.
possibly the cat?
im lost I don't know what to try. I have no power though and it just happened today when it was 65 degrees out. if I take off slow its fine so I tried giving a little more gas I couldn't get it above 2000 rpm I felt safely any way. I don't want to blow anything. it just sputters and kicks when I try to give it anything over barely pressing the throttle. so I put it in neutral and sat there for a while the rpm gauge was struggling to just stay at 1000 when I put the load on the engine it dropped below 500 bounced back but roughly.
 


Try cleaning the contact points on the ICM/Coil plate. Had this issue before and helped many others with this issue personally. It may not work but the ICM plate usually caused those issues when working with several GMs.
 
can I ask what of my problems makes you guys think electrical? ill put new wires and icm on if I know that's the right way to go. I was reading somethings online that it might be the cat or vacuum. what difference would I have how do I distinguish those differences?
 
I put autolight wires on it but when I changed the icm I didn't have a lot of cash so that is a bwd. not what I wanted but that's all I could afford at the time. I just put the autolight plugs in it even though most of them looked pretty good 2 of the front ones had a little orangish color to them but not terrible.
 
DO NOT PURCHASE an ICM unless you really need one. They are a little pricey. You could have defective plugs or wires. Check the harness to the ICM and make sure there are no broken wires. Coil packs could be shot too. As for the cat, it's very unlikely. Vacuum? It would have to be a pretty big leak. Are your upper/lower intake gaskets leaking? I've seen 2 really bad cases of intake gaskets leaking and causing the plugs to misfire.
 
I can honestly say I have not checked for any leaks wasn't sure where to start. I just put coils on it when I did wires a couple of months ago just did plugs tonight checked coils and icm everything looked clean and tight nothing cracked or corroded.
 


Starting to look like clogged cat to me from what you are reporting. Do you have rough or smooth idle? Weak acceleration on upgrades? Weak quiet exhaust at end of tailpipe? Can you put a vacuum gauge on the intake manifold? Can you remove the upstream o2 sensor and see if it gains some power due to providing a place for the exhaust to go ahead of a clogged cat? Just went through all of this..in the end it was all due to a clogged cat...
 
Is P0300 the only code you're showing? Assuming you are using stock temp properly gapped plugs, I too would say it could be a cat or vaccuum issue.

To check for vac leaks, get a can of starter fluid. After the car has sat and cooled down for a while, start it and spray around the intake and vaccuum lines. If the idle changes, you have a vac leak. Make sure not to get it on the headers, as it is flamable.

A quick way to check the cat would be to shake it. If it makes a noise like something came loose inside of it, replace it.
 
rough idle yes, it is like it struggles to hold it. acceleration yes I really have to baby it if I hit a hill I have to keep pushing the throttle in and letting it out as this seems to stop the kicking. the p0300 is the only code it is throwing. do cats always glow red? I haven't checked it yet guess I will find out this morning
 
When I am climbing a hill I tried to keep it at 2000 rpm but the car kept wanting to go to 1500 where it would begin to kick. I let off and ease back into it right back to 2000. Fuel problem?
 
Let's think about what has just recently happened. It went from super crappy cold to nice and warm. This can be a cause of condensation. Did you recently get fuel? Literally 2 minutes ago a woman at work came to me and said "My car bucked the last two days, what is it?" My first suggestion.... put a can of dry gas in the tank and give let it run a while.

Being a multiple misfire out of nowhere, you have to think about all the various things. I haven't seen a lot of ICM's go bad, could be..but not typical for these motors. A coil would cause only one/two cylinder issue. A vacuum leak, possible and again, not likely that something just happened without anyone messing around under the hood.

Me.. I'd be lazy and try drygas
 


After doing that I idles a lot smoother. Not sure if the rest will take time to get through the system. Still doesn't want to go up hills and as soon as it does the first kick my boost gauge goes all the way up
 
You must log in or register to reply here.
Back
Top