I just had this pop up today when I was out. It is blowing black smoke out the exhaust pipe and runs rough at idle. The check engine light was flashing intermittantly as well. What would I start to look at first to fix this? When I shut it off and start it up it runs smooth but as soon as I put it in gear, it starts to run rough and spew black smoke.
PO300 code
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Originally Posted By: NHGUY
Bad plug,bad coil,sticking injector.Its flooding the cat con with fuel.
Im going to pull the plugs out and have a look at what one is covered in soot and take it from there. If its an injector, how hard is that to replace, any idea?
Bad plug,bad coil,sticking injector.Its flooding the cat con with fuel.
Im going to pull the plugs out and have a look at what one is covered in soot and take it from there. If its an injector, how hard is that to replace, any idea?
Make and model? Have the codes read at the parts store. Hard to tell w/o more info.
This is on my 2004 Silverado with the 4.8 engine. Parts stores here don't read codes that I know of. I have my own code reader and that's what it told me.
Random misfire. I would start with the coils and check for intake and vacuum leaks.
A live data steam would be helpful with this code, so you may need to bring it to a repair facility.
A live data steam would be helpful with this code, so you may need to bring it to a repair facility.
Originally Posted By: Zaedock
Random misfire. I would start with the coil.
There is 8 coil packs, how do you test them?
Random misfire. I would start with the coil.
There is 8 coil packs, how do you test them?
Originally Posted By: xxch4osxx
Originally Posted By: Zaedock
Random misfire. I would start with the coil.
There is 8 coil packs, how do you test them?
I edited my post. A live stream while it's running will be most helpful.
I just repaired an Audi TT with multiple misfires and it was a large vacuum leak on the PCV system.
Originally Posted By: Zaedock
Random misfire. I would start with the coil.
There is 8 coil packs, how do you test them?
I edited my post. A live stream while it's running will be most helpful.
I just repaired an Audi TT with multiple misfires and it was a large vacuum leak on the PCV system.
Originally Posted By: Zaedock
Originally Posted By: xxch4osxx
Originally Posted By: Zaedock
Random misfire. I would start with the coil.
There is 8 coil packs, how do you test them?
I edited my post. A live stream while it's running will be most helpful.
That I have no way of doing, unfortunately.
Originally Posted By: xxch4osxx
Originally Posted By: Zaedock
Random misfire. I would start with the coil.
There is 8 coil packs, how do you test them?
I edited my post. A live stream while it's running will be most helpful.
That I have no way of doing, unfortunately.
Try unplugging the MAF and start it. Post the results. You may have a bad MAF or a large vacuum hose has either come off or broken.
ls1mike
$50 Site Donor 2024
A random misfire P0300 on an LS motor is generally not a coil.
How many miles?
I would start with plugs and wires if they have not been done. Easy Peasy.
The GM motor will generally tell you what coil is misfiring. If it were a coil you see the following P0301, P0302 all the way to P0308 which would tell you what coil is bad.
If you have a random misfire P0300 and P0301 to P0308 you can tell where it is. If plugs and wires don't work. You can test each coil.
Three other things will give you that code. A bad CPS, a bad MAF, a leaky intake gasket or vacuum leak like Trav mentioned.
You will usually get the MAF code as well but not always.
How many miles?
I would start with plugs and wires if they have not been done. Easy Peasy.
The GM motor will generally tell you what coil is misfiring. If it were a coil you see the following P0301, P0302 all the way to P0308 which would tell you what coil is bad.
If you have a random misfire P0300 and P0301 to P0308 you can tell where it is. If plugs and wires don't work. You can test each coil.
Three other things will give you that code. A bad CPS, a bad MAF, a leaky intake gasket or vacuum leak like Trav mentioned.
You will usually get the MAF code as well but not always.
I have seen Generic Random Misfire's with Code P0300 after the air induction system or throttle body has been cleaned. Clearing the code immediately brought things back to normal for a smoothing running engine than before the maintenance procedure.
Update: I pulled the plugs out of the passenger side and all 4 were carboned up and the 4 on the driver side are clean. I replaced the plugs and wires back in Novermber 2012 with OEM parts, AC Delco Iridium plugs and AC Delco wires. There is only 26,000kms on those plugs and wires. The truck has 262,000kms on it. I have never replaced any coil packs since I have owned it from 2008.
Originally Posted By: Trav
Try unplugging the MAF and start it. Post the results. You may have a bad MAF or a large vacuum hose has either come off or broken.
Ok, I will try that, thanks. Any idea what vacuum hoses I should look for that may be a culprit?
Try unplugging the MAF and start it. Post the results. You may have a bad MAF or a large vacuum hose has either come off or broken.
Ok, I will try that, thanks. Any idea what vacuum hoses I should look for that may be a culprit?
If the problem is specific to one side that leaves you with two things to look at before anything else:
-restricted exhaust
-major vacuum leak
There are other things that can cause this sort of thing, but look for those two first. If the misfires are mostly at idle, intake is more suspect. If misfiring gets worse with speed and load, suspect exhaust restriction more.
-restricted exhaust
-major vacuum leak
There are other things that can cause this sort of thing, but look for those two first. If the misfires are mostly at idle, intake is more suspect. If misfiring gets worse with speed and load, suspect exhaust restriction more.
Last edited:
ls1mike
$50 Site Donor 2024
Vacuum hoses are limited. The big one is the Brake booster.
P0300 will not be specific to one side on an LS motor.
P0300 will not be specific to one side on an LS motor.
ls1mike
$50 Site Donor 2024
3 LS1 F-bodies. 2 LS trucks. A 5.3 and 6.0.
They all work the same as a 4.8. Check your plugs and wires first.
The only P0300 I have had were on the 6.0 Truck and two of the F-bodies. All were plug wire related. Heat had and aged had killed them.
The other ones were friends with trucks that had bad manifold gaskets.
Did you list your vehicles mileage?
They all work the same as a 4.8. Check your plugs and wires first.
The only P0300 I have had were on the 6.0 Truck and two of the F-bodies. All were plug wire related. Heat had and aged had killed them.
The other ones were friends with trucks that had bad manifold gaskets.
Did you list your vehicles mileage?
Originally Posted By: xxch4osxx
Originally Posted By: Trav
Try unplugging the MAF and start it. Post the results. You may have a bad MAF or a large vacuum hose has either come off or broken.
Ok, I will try that, thanks. Any idea what vacuum hoses I should look for that may be a culprit?
Chances are all 4 coil packs didn't go bad at the same time or the injectors all on one side.
As all the plugs are black the O2 on the right bank is reading lean for some reason.
Any other codes? It might be throwing a manufacturers specific code eg P1133, P1139, P1153, P1404 etc but you need a scanner capable of reading the enhanced codes.
Originally Posted By: Trav
Try unplugging the MAF and start it. Post the results. You may have a bad MAF or a large vacuum hose has either come off or broken.
Ok, I will try that, thanks. Any idea what vacuum hoses I should look for that may be a culprit?
Chances are all 4 coil packs didn't go bad at the same time or the injectors all on one side.
As all the plugs are black the O2 on the right bank is reading lean for some reason.
Any other codes? It might be throwing a manufacturers specific code eg P1133, P1139, P1153, P1404 etc but you need a scanner capable of reading the enhanced codes.
Originally Posted By: ls1mike
3 LS1 F-bodies. 2 LS trucks. A 5.3 and 6.0.
They all work the same as a 4.8. Check your plugs and wires first.
The only P0300 I have had were on the 6.0 Truck and two of the F-bodies. All were plug wire related. Heat had and aged had killed them.
The other ones were friends with trucks that had bad manifold gaskets.
Did you list your vehicles mileage?
I doubt the plugs and wires are bad as they were new just 26,000kms ago and were OEM. It has 262,000kms on it. Thanks for the input though!
3 LS1 F-bodies. 2 LS trucks. A 5.3 and 6.0.
They all work the same as a 4.8. Check your plugs and wires first.
The only P0300 I have had were on the 6.0 Truck and two of the F-bodies. All were plug wire related. Heat had and aged had killed them.
The other ones were friends with trucks that had bad manifold gaskets.
Did you list your vehicles mileage?
I doubt the plugs and wires are bad as they were new just 26,000kms ago and were OEM. It has 262,000kms on it. Thanks for the input though!
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