The engine is misfiring I changed spark plugs

Yes, the plugs will act that way when the engine is misfiring. Can you pull all plugs and line then up in order? This will show us which cylinders are misbehaving. I believe you have an injector that is out but we need to see the plugs to start. It sounds like you might need a tune up or have a bad spark plug-coil (common), injector or low compression to be sure which one it is please follow these videos and guides.

https://youtu.be/QTE8k06MzwQ

and

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

and

https://www.2carpros.com/articles/how-to-tune-up-a-car-engine

Let us know what happens and please upload pictures or videos of the problem.

Please let us know what you find. We are interested to see what it is.

It was an upper oxygen sensor bad.

Thank you for the update.

Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help.

Cheers, Ken

I have a 2004 silverado 1500 5.3L that I took to the dealership i purchased it at to have it checked. It was ideling very rough. When they ran diagnostics on it, it came back with P0300 code and missfire counts on cylinders 1,3,5,7. (the entire left bank) Cylinder 1 had 40,000 missfires and they intermittenly decreased to 16,000 on cylinder 7.

This thing idles rough, at road speeds it's fine.
I took the throttle body off and cleaned it really well, checked for vaccum leaks on the intake manifold. No problems i could find there. Spark pllugs are all good.

The service techincian had no clue what to do with it.
I searched on the net and found that this is becoming a problem with this motor, but no one seems to be able to figure out how to fix it.

You guys have any clues?

I've had this problem before,try this info:Check Engine Light with a P0300 due to 2 - 4 cylinders misfiring on the same bank of the engine. DTCs P0171, P0172, P0174 or P0175 may also set for the misfiring bank.

Recommendation/Instructions:
If the published misfire diagnostic does not isolate the cause, perform the following suggestions as necessary:

Perform a fuel injector balance test for all 8 cylinders. If a fuel injector concern exists, it is possible to misfuel an entire bank of the engine, causing multiple cylinders on the same bank to misfire even though the root cause is a single fuel injector.
Inspect O2 sensor connections on the misfiring bank for corrosion or water intrusion. If water intrusion is found on the right bank, it may be due to the AC Evaporator Condensation dripping onto the O2 sensor harness. If this condition is found, reposition and shield the harness to prevent a repeat concern and repair the connections.
Check for excessive exhaust backpressure using the restricted exhaust diagnosis from SI.
Swap the Position 1 O2 sensors side to side to see if the misfires move to the other bank of the engine. If so, replace the O2 sensor.also perform an exhaust back pressure test on that bank,a plugged cat converter can cause this also.post back with what you find.

Ok, Did like you said, started by flipping the o2 sensors...bingo! New O2 sensor and bam..problem fixed! Thanks!!

My friend has the truck listed above, he is getting a P0300 code (random misfire) so I suggested on changing plugs and wires for starters but still no change. We also checked the compression and changed fuel pump also the filter so everything is good but still the misfire is still there there and I am starting to question maybe the ECM is defective or if the catalytic converter is clogged. I will also add when we clear the code for the check engine light to go off and drive it the light will come back on but flashes.

Hello,

The random misfire is due to mixture problems which is caused by the MAF or a vacuum leak, here are some guide to help you get the problem fixed.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

and

https://www.2carpros.com/articles/how-to-replace-a-mass-air-flow-sensor-maf

The MAF can be bad and not light the check engine light btw.

Please let us know what happens, we are interested to see what it is.

Cheers, Ken

miss-fire in the morning when the engine is cold. Check Engine turns on. The truck runs fine after few minutes of running and it will not miss-fire for rest of the day. The code that I get is P0300 only. I have changed spark plugs back 30,000 miles. I have replaced PCV. I have checked for vacuum leaks and there aren’t any. Someone said that it could be fuel pump but I am not convinced since it only miss-fires in the morning and it runs fine afterwards. Besides the pump is $250.00 and I want to be sure be fore I change it.
Please help me if anyone has any ideas.

although the fuel pumps are very common. i dont think yours is bad. i would check your fuel pressure regulator. its located on the fuel rail where the injectors are under the hood. it has a vacuum line going to it. usually you will find when you take off the vacuum hose you will see gas. if you see gas or the vacuum line is soft, replace the fuel pressure regulator. what happens is when the truck sits, the regulator leaks raw fuel into the intake, causing it to be slightly flooded when you first start it.

This guide can help us fix it

https://www.2carpros.com/articles/engine-misfires-or-runs-rough


let us know what you find.

Had a multiple cylinder misfire code and right bank running rich code. Truck was very hard to start. Also, truck was burning up rotors and caps. Found somewhat worn distributor, changed it. New plugs and wires. Coil checked okay. Cleared codes. Codes came back, changed upper intake gasket and injector spider valve (upgraded model changes from poppet valves to actual injectors) truck now starts like a champ, but running worse than it ever has. No more multiple cylinder misfire code. Now shows misfire on number six and injector pressure code. EGR cleaned and works well. Found carbon buildup in intake. Cleaned best I could. Not sure where to go from here? Plugged catalytic converter? Dropped valve? Timing chain?

Good morning,

I would start by checking the compression. Make sure there is no internal issues with the engine.

https://www.2carpros.com/articles/how-to-test-engine-compression

Also, I would check the fuel pressure. That is the most common cause for a misfire code.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Roy

I have the truck listed above that's coming up code p0 300 which comes back is a multiple cylinder misfire. not quite sure what to do to fix it. I've replaced plugs, wires and next step will be coils even though that I had them tested and they tested okay. any ideas? there's no vacuum leaks and I changed my EGR valve as well.

What's the true mileage? If it's over 100,000, a real common but elusive cause for multiple misfires on GM vehicles is the injectors. They are not defective, so don't waste your time trying to test them. (That's something professionals never waste their time on). The problem stems from different flow rates.

Most commonly the code will specify one or two cylinders that are having the misfires. In that case, you can switch two injectors, erase the fault code, then see if the code sets for the cylinder you moved the suspect injector to.

When you have a code 300, the misfires are occurring in more than one cylinder, so another good suspect is low fuel pressure.

Here's a link to a related article, if it will give you more ideas:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

If it looks like injectors are the cause of the misfires, replace them with rebuilt injectors in a flow-matched set. There used to be a specialty shop near the Indianapolis Speedway that rebuilt injectors and matched them. It was owned by Jim Linder, and his last name was part of the business name. It appears he has retired, but I'm sure there are other sources for rebuilt injectors.

The EGR valve you mentioned was another good suspect. Rather than replacing it, you can loosen it, then slide in a thin metal shim to block the ports. If the misfires still occur, you can remove the shim and continue looking at other causes.

Vehicle will start and run fine when temperature is normal here in texas. When weather gets cold like in 50s vehicle will have long crank and once it starts it misfires causing CEL but once it warms up it will start and run no problems. Items that have been replaced include: sparkplugs, wires, cap, rotor,Coil, FPR, fuel filter, fuel pump. I need your opinion. PLease advise. Codes that it shows is multiple cylinder misfires, bank1 sensor 1 heater circuit malfunction.

Have the ignition module tested at most autoparts stores for free. If good you may have bad crank/cam sensor.

The other code is the O2 sensor. These are heated sensors and it is indicating the sensor is not at operating temp. when it is supposed to be. So the element that heats the sensor, is probably burnt out.

[quote:73148ed660="coyotte82"]Engine Performance problem
2001 Chevy Silverado 6 cyl Two Wheel Drive Automatic 120000 miles

Vehicle will start and run fine when temperature is normal here in texas. When weather gets cold like in 50s vehicle will have long crank and once it starts it misfires causing CEL but once it warms up it will start and run no problems. Items that have been replaced include: sparkplugs, wires, cap, rotor,Coil, FPR, fuel filter, fuel pump. I need your opinion. PLease advise. Codes that it shows is multiple cylinder misfires, bank1 sensor 1 heater circuit malfunction.[/quote:73148ed660]

It was the camshaft sensor, thanx guys

Check engine light keeps coming on after I clear codes after a few cycles. Has new coil packs, plugs, wires. But the speedometer went to 100 mph. Couldn't figure out what was going on. Then I beat on the PCM and it went to 0. Still get check engine light. Could the PCM terminal need cleaned?

Hi,

Anything is possible. What codes are you finding when you scan the computer? As far as the misfire, it could be many things such as a vacuum leak, fuel pressure, and with the mileage it could be a stretched timing chain or low compression.

First, let me know if you found any codes. Next, check to see if there are any vacuum leaks on the engine. Here is a link that explains how it is done:.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Next, if there are no leaks, check fuel pressure to make sure it isn't high or too low.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Do these things and let me know what you find.

Joe

I have 2000 silverado 4.3 that has been acting up. It idles fine and always starts right up but when ur accelerating right before it shifts around 3500 to 4000 rpms it misses. Some times it just shudders and chugs sometimes it just falls completly on its tail and loses all power and will either go on die or it will catch back up and take off sometimes it will backfire. Once it has started messing up alot it will do it if ur just cruising or coasting but alot worse when ur accelerating at higher rpms. Its like it just loses fire I have checked fuel preasure, tps, changed plugs and plug wires,dis cap and checked resistance of the coil. Nothing helped. It seems to only do it when its warmed up and is worse when it is hot outside like 100 deg. Thanks

Has it ever set a check engine light when it is running like this? If so have it scanned fo rcodes.If not it could be many different things.You may have a crank sensor that is breaking down when hot and giving bad readings to the PCM, if the fuel pressure is good then it is usually a sensor issue if it has to be warm/hot to act up, that is usually when they start having problems.Does the tach ever jump around when it is acting up?

This guide can help us fix it

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Please run down this guide and report back.

Only light it gives is random misfire and p1351 and the tack just falls.

That is a code for the IC (ignition coil) control circuit, it can be set by a number of different items from the crank sensor to the coil to the PCM or the wiring in between. Try moving the wiring harness around while engine is running to see if it responds, also enhance/clean/inspect connections at the coil, coil module

The truck listed above is 1500 with a 5.3L engine. i have a random misfire and i can't find the problem.

I attached the testing for the p0300 code. This code is just telling us that the PCM is not seeing the crankshaft accelerate as it should after each time the spark plug fires. This is on various cylinders and not one repeatedly.

So this means we need to check the things that each cylinder has in common first. This is fuel pressure and ignition issues. This could also be o2 sensor issues or simply a crank sensor issue.

The only way to know for sure is to run through this testing and find out where the issue is. Let us know what you find and we can go from there. Thanks

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

My 99 silverado 2500 6.0 is having misfire issues. It has misfires in every cylinder. Some rarely misfire and some misfire a lot. I've changed plugs wires and 3 coil packs on the worst cylinders. Checked fuel pressure and flow. Could it be the ecu? Or maybe valve springs or lifters?

It sounds like you have a weak furl pump or the MAF sensor needs to be replaced but to be sure this guide can help us fix it.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Please run down this guide and report back.

A new fuel pump fixed it for me, thanks for the guides .

Truck was missing so I replaced the plugs and wires and still missing, only when I give it gas though. Is it gas or the ignition coil?

Hi,

This sounds like a weak spark condition so it is very likely the coil is the issue. The coil has low voltage and high voltage windings. I suspect the secondary (high voltage) side as an issue and is not delivering a strong spark.

If it were me I would just go ahead and replace the coil and see what happens. They are not that expensive and in my opinion is worth taking a shot at it. If that is not the case, we can dig further into fuel pressure and compression.

Let me know what you find and we can go from there. Thanks

I've changed fuel filter, plugs, wires, rotor, distributor cap, ignition module and it still isn't fixed what else is it

Are you getting any other codes beside that one?
With that mileage have you taken a compression test?

This guide should help us fix it

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Please run down this guide and report back.

just the p0300 code compression was about 120

120 is a bit low but that's expected at that mileage. You have something that is effecting all cylinders. You probably should use a scan tool and examine the sensor data very closely to get an idea what is triggering it. It could be lean fuel, restricted exhaust, crossed firing order, distributor not set correctly (that should set a P1345). There are many things that can lead to random misfire. You need to narrow down the condition triggering it.

bad coil was it thanks, runs great again.

Truck listed above is a k1500 5.7 TBI. Engine missing pretty bad hot or cold in park and drive. has new TPS, MAP, EGR, IAC, temperature sensor, plugs, wires, and distributor. A/C is unhooked.

Good afternoon,

I would start by doing a compression test to be sure there is no internal issue in the engine. The pressure should be 140-160 on each cylinder.

https://www.2carpros.com/articles/how-to-test-engine-compression

I would also do a fuel pressure test to be sure enough fuel is to the injectors.

Ignition ON Engine OFF .................... 62-90 kPa (9-13 psi)

https://www.2carpros.com/articles/how-to-test-engine-compression

Roy

5.7L (350CI) Throttle Body Injected automatic with 126,000 miles. A while back I had bad misfiring (sputter, missing, and stumble) while accelerating and in the last gear under greater load i.e. going up a hill (truck would shake and stumble) but not much while idling (slightly if at all) Replaced plugs (two plugs and ash deposits and one plug had oil on it) and fuel filter (filter poured out brown gasoline) and it ran like a champ for about a week.

Started doing the same thing again and also missing more at idle. Replaced wires, distributor cap, and rotor button. Wires had arcing spots, distributor cap was corroded and worn, rotor button was rusted onto the distributor and had lots of black deposits, the circular metal plate where the cap screws down on was solid green with corrosion,removed as much as possible but unable to remove it all. Solved the problem and ran wonderfully for a couple weeks to a month.

Now it is miss firing again while idle (worse than before) and while accelerating and cruising in last gear under load i.e. going up a hill EXACTLY as before. Hoping it's not a warped or burned valve, especially since it ran like a champ for a while after every repair.

(As a side note, kind of unrelated, after the wires and distributor cap and rotor button, I had the intake manifold gasket replaced for leaking, valve cover gaskets replaced for good measure, and driver side exhaust manifold replaced because of a crack, done by a shop. The mis firing started a week or two after these repairs)

No black or blue smoke.

Stumped, any help would be greatly appreciated, Thanks in advance!!

P.S. After replacing wires, the plastic clips unavoidably broke, some of the wires are touching metal brackets connected to the block, and I caught a couple wires touching the block, so I tied them back out of the way with zip ties. should I wrap them in plastic electrical lume where ever they contact the metal brackets to prevent arcing??

Try to avoid allowing the plug wires to touch the engine block where they can melt and arc. Check fuel pump pressure. Check crank sensor.

The odd thing about this is the fact that it works good for a period of time then changes back to the start. Therefore, I don't feel it is anything internal. I really feel it is ignition related. Check the things I mentioned. Also, if the new wires have any signs of arcing, they need replaced again. Also, I just re-read your comment about the metal brackets. There should be rubber grommets between the wire and the steel bracket.

Check out the guide below

https://www.2carpros.com/articles/engine-misfires-or-runs-rough