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Not Firing All Cylinders, Code P0300.

marc_w

Full Member
Joined
Jun 5, 2002
Messages
1,112
Location
Douglas, MA
Well, this weekend something weird happened.

First, the weather. ?Very nice Saturday, about 60-65*F. ?Saturday night, lots and lots of rain. ?Cooler, in the 40's. ?I did some driving in the rain, and there were some large puddles I drove through. ?Sunday morning, in the high 30's, and still raining hard.

I went to fire up the truck Sunday morning here at the g/f's house, in the pouring rain, and I kind of accidentally didn't hold the key on long enough. ?The engine sputtered and died. ?I've done this before. No biggie.

I turn the key again, and the engine turned over for a good 6-8 seconds with nothing but sputters. I let off, and ?I turn it over again. ?I know it's fuel injected and all, but it wasn't going to start so I played with the throttle to get it running.

The truck was only running on 4-5 cylinders (I felt what 6 feels like on an V8 before, and this was not 6!). ?It sounded AWEFULL and would not idle. I had to play with the throttle to keep it running.

I shut it down, and became quite mad. ?My g/f has some problems with mice making temporary residence in her car's engine compartment. ?(Her driveway is near a neighbors horse-barn.) ?I pop the hood expecting to see some fuel injection wires chewed up or something, but nothing...... Except for one of my MSD wires which was rubbing on the steering shaft. ?It was almost worn through the insulation, and I knew this wasn't a good thing, but also not the cause of this frustration.

I twisted the wire to stay out of the way. I took off the cover to the underhood fuse box, wondering if maybe a FI or Ignition fuse blew for one of the banks. ?Nothing. ?I slam the cover on in frustration. ?By now I'm drenched, and I can't find anything obviously wrong.

I start the truck up again, and rev the heck out of it. ?It was making a noise similar to a Harley trying to rev with it's choke on. "brak Brak BRAK BRAK BRA-BROOOM" ?It's spewing tons of white/grey smoke that reaks of fuel. ?I'm wondering if my block or head cracked for some reason, and I've got coolant getting in the cylinders. EDIT: ?:p ?Maybe some injectors are stuck open? I could also hear a distinct "Pfft Pfft Pfft Pfft Pfft" as the truck "idled". It sounded like a carbureted engine with an it's air cleaner removed...

I keep my revving up for a minute or two, trying to clean the thing out. ?It was finally able to idle on it's own, VERY ROUGHLY at about 400-500 rpm.

I go inside to talk to the g/f. ?I come out a minute later, and the trucks idling fine. ?I drove home with all 8 cylinders firing.

I get home, and pull a P0300 "Random Multiple Misfires Detected" code.


Anyone had these problems before? ?

What do you think the issue was?
 
Something got wet in all the rain. On my old chevy truck when I take it to the car wash sometimes It will get wet and die. I always have a can of moisture displacer with me. Open the hood and spray the wires and it will start right up. Hope this helps.
 
Hi Marc,

I had similar problems once. You are lucky it happened while the truck was cold. If the catalytic converters had been up to operating temp the extra fuel would have caused a meltdown, been there.

Two things to check;

There are little thread on terminals on the spark plugs. If these are loose you can get cylinder misfire. Did you put dielectric grease in the boots when you put on the MSD wires? Even though the grease is conductive it makes things worse if the little terminals are loose.

Poking around the wiring harness connectors with a test probe will cause problems, looking for an "ignition hot" wire for example. It's amazing how touchy those connectors are. I screwed mine up looking for a hot wire in one of the coil banks.

The service manual for the truck actually has a WARNING about using voltmeter probes in the wiring connectors.

If you've done nothing except plugs and wires I'd check there. The wires may not have been seated fully also! It can be hard to tell if they've snapped on to the terminals. They may be "close enough" when it's dry but moisture offers a better path to ground. The poor running session may have provided enough heat to dry things out.

kw
 
First, I found this off on some site, in regards to Coil On Plug (COP) ignition systems.

The most common trouble codes you?ll encounter with COP systems on OBD II equipped vehicles are P0300 series codes such as P0301, P0302, etc. that indicate a misfire in a particular cylinder. The important point to remember here is that a general misfire code (P0300) is probably not ignition related but is due to a vacuum leak or fuel delivery problem.

A code that indicates a misfire in a single cylinder (such as P0304), on the other hand, will usually be due to a fouled spark plug, weak coil, dirty or dead fuel injector, or loss of compression (burned vale or leaky head gasket).

If a misfire is due to a bad coil, you should find a coil code that corresponds to the same cylinder (P0351 to P035:cool:.

If a misfire is fuel related, you should also find a code that indicates an open or shorted injector in that cylinder (P0201 to P020:cool:.

A COP engine that cranks but fails to start, in many cases, will often have a problem in the crankshaft position sensor circuit (code P0320). Loss of the camshaft position sensor signal (code P0340) may prevent the PCM from properly synchronizing the fuel injectors, but may still allow the engine to start and run in a limp-in mode.

I find the last sentence of the first paragraph intriguing. That weird "Pfft" noise I heard sounded a lot like a vacuum. I just thought it was the fuel injectors firing in a dead cylinder or something.

Redshift - Yeah, I was thinking about the cats... I was hoping the dang things would go so that I have an excuse to get that aftermarket y-pipe and header sections. :) I was surprised I didn't even see any complaints about the O2 sensors or emissions. Maybe because the engine wasn't up temp yet.

Spark plug terminals - I'm still using factory plugs, so they have the permanent stud/mount/thing.

I'm not using dielectic grease... I'm about as sure as I can get that all of the spark plug wires connections are good. :)

I haven't done any poking around the electrical system, but that's a good thing to know. I was going to start interrogating the TPS soon, make sure it's adjusted spot on... (totally unrelated - just doing this for S&G's)
 
More "non-fun" stuff. ?:rolleyes: :)

"A P0300 code indicates a random misfire that jumps around from cylinder to cylinder. The cause here would likely be something that upsets the engine?s air/fuel mixture, such as a major vacuum leak, leaky EGR valve, low fuel pressure (weak pump or faulty pressure regulator) or even water-contaminated gasoline."

Edit: And similarily:

"When the vehicle is diagnosed, the technician finds a P0300 random misfire code which would normally be set by a lean misfire condition due to a vacuum leak, low fuel pressure, dirty injectors, etc., or an ignition problem such as fouled plugs, bad plug wires, weak coil, etc. The OBDII self-diagnostics tracks misfires by individual cylinder, and considers up to a 2% misfire rate as normal. But water in the gas or variations in the additive package in reformulated gasoline in some areas of the country can increase the misfire rate to the point where it triggers a code."
 
Hi Marc,

I don't think the Av is a true "coil on plug". My 99 Trooper actually had a coil sitting right on each plug. No plug wires at all.

All four cylinders on the left bank quit on mine and I got the P0300 code, my reader said "random, multiple misfires". I didn't get any individual cylinder codes. After I found the loose wire in the connector I still had 2 cylinders not firing smoothly (loose terminals). I still didn't get a specific code for those cylinders.

Smelling the raw fuel leads me to think the injectors were working but not getting ignited. There are not a lot of vacuum lines on the beast, power brakes, PCV, emission solenoid, fuel pressure regulator pilot. I can't think of a reason they'd be an intermittent problem.

I'd soak the engine down, start it in the dark, and look for the light show.

Doctors have a saying, "when you hear hoofbeats don't think of zebras". Meaning it's probably something common. I'd still bet on the plug wires. The coil boots on the MSD wires are so tight that air gets trapped in them and pops the connection loose.

Good luck

kw
 
Dunno if this will help you any, but I had a similar vacuum problem on a 69 VW Bug. When starting it would idle VERY roughly and it took a lot of finesse with the accelerator/clutch to keep the thing running when driving it. After examining the engine I found a hole on the back side of the carburator almost as big around as my pinky that sounded like it was sucking air. I put my finger over it and sure enough there was a vacuum draw there. Soon as I had covered the hole the idle smoothed right out.

Now for the resolution. After going to a shop that specialized in old bugs (this was in San Jose, CA btw) they said that VW designed these carbeurators with a "pressure release valve" in the form of a very thin metal plug that covered that hole. If you ever get a backfire that could damage the carbeurator it blows out that metal plug instead. The bad news though was that this piece is supposedly not something that can be replaced, you have to buy the whole carbeurator.

The mechanic's suggestion was that I should let him diagnose to see what (if anything) was wrong with the ignition that had caused the apparent backfire and then at the very lease replace the carbeurator with a rebuilt one plus any other work they find needs being done while they are in there. Total before they found any work aside from the carbeurator was going to be ~$500.

Sooo... instead of dumping that kind of money into an old car I stopped by Home Depot on the way home and picked up a small package of rubber stoppers like you might have seen in the tops of test tubes in high-school. Cost about $0.50 for a package of 4 of them. I placed one in the hole and squeezed it in just a bit and put the rest in the glove box. That way I'd have 3 replacements in case the backfire problem returned and I got stranded somewhere. Problem solved, new rubber pressure release valve $0.50. Saved $499.50 and a lot of pride and never had a problem with it again.

 
I hear ya Redshift... I'm just tossing all of my thoughts out there, unreasonable or not...

The truck's been running like a top since the incident. (I took a carload of kids in a Mitsubishi Eclipse last night. ;D :rolleyes: )

I haven't touched anything under the hood since that morning. All of the plug wires were on there nice and snug. Nothing was obviously wet.

My guesses right now:

1st: It's my fault - I shouldn't have touched the throttle, and given the engine more time to light.

2nd: The rain and puddles. Maybe I *did* drench something under the hood, and sitting overnight let the water get where it shouldn't have been.
 
Marc_w,,,

Educated guess here...

You were dumping raw fuel in the motor after the ignition triggered, but because it was wet out, it didn't start as easy, and you let off the key on the first start attempt (moist air resists ignition more so) ... ?Now you had a charge of raw fuel in some cylinders ... You hit the key again, now you have a double charge of fuel, fuel soaked plugs, and wet weather ... Eventually when the heads built some combustion temp due to some cylinders firing, the other cylinders expelled the raw fuel and the plugs dried out and started firing...

Please note, if a cylinder is not firing for some reason, the pcm doesn't have the ability to stop that injector's fuel delivery to the dead cylinder... The injectors will pulse whether it's corresponding cylinder is firing or not ... Hence filling that cylinder with fuel ... You are lucky the plugs dried out ... Normally when an injected motor wets the plugs, you're in for a long wait ...

The DTC's were because the Hall-Effect sensors under the timing cover were detecting mis-rotation ... These sensors (beyond their tooth error correction) are pretty sensitive buggers, and will see the misfires and set a code for each cylinder ... I'm surprised that the only code you pulled ... ?>:D

No biggie... Next time, I would just let the truck sit for 10 minutes unless you want to be like Redshift... LOL

Make sure you change your oil asap too ... You may want to unhook the battery overnight to clear all the memory in the PCM as long as everything is ok ... If you don't and you have a new mechanical failure, the dealer might confuse your prior issue with the new one ...

11H
 
Thanks 11H...

Yeah, my general thought was that I fouled the dang plugs on my own. ?I was surprised the cleaned out also. ?With my single or dual cylinder toys, if the engine doesn't light, you pull the plug(s), and if any are wet --- they're DONE! No starting for you! :) ?This is the first 2+ cylinder vehicle I've fouled up, so I was surprised at the results. ?I was ready to limp home with it running horrible, hop on my bike and get some new plugs.

Yeah, I realize each dead cylinder was still pulling in fuel... just like a carbureted engine... but:

When you mentioned the charge of raw fuel - It sounds like you're saying each time you trip the starter, you get a heavy dose of fuel in the cylinders? ?Like and old-fashioned primer? ?I had a sled with one of them (actually a 1998 ), and it was a female dog to start if you got too much fuel in the cylinders. ?Get it right, and it starts mid-pull of the recoil. :)

I was under the assumption that (in the truck) you get a heavy amount of fuel, but it was the equivalent to what the engine needed at the time of (cold) starting. ?Like a 'choked' fuel-to-air ratio... not quite a raw dumping?

I pulled and deleted the code with my scanner... so that should be all set. ?I was a little surprised I didn't see any specific codes too.
 
Marc,,,

It sounds like you're saying each time you trip the starter, you get a heavy dose of fuel in the cylinders?

If yer on the key, it's giving fuel just like if it were idling... The IAC will close off a little more even to choke during a COLD start, so you are getting an even richer mixture at startup ... Considering that the fuel Pressure is consistent at the rail and not variable, the PCM "MAY" shorten the pulse time on the injectors at a cold start, but I doubt it... The PCM is pretty much a lame duck until the engine is actually running especially in open loop...

11H
 
I hear ya. (Do you mean 'lengthen' the pulse though? Putting in extra fuel...)

I'm under the impression that out trucks have a cold-start 'map'.... the computer senses that the truck is cold, and judges what parameters to use to get the engine lit in the split second the key is in the on position, to as the engine is cranking over.

My buddie has an older 4.3 that needs a "cold-start sensor" replaced... I haven't had a chance to dig into what the heck it actually does. ???

They've got to have SOMETHING that richens the fuel:air... These engines fire right up at any temp. :)

I know motorcycles that run a open loop system have the above features... that's why I was figuring our more advanced closed loop systems do the same...
 
Has anyone else had this problem lately? My 03 had a slight stumble when I would stop at a traffic light, but smooth as silk once I started moving. This went on for a week then yesterday it almost stalled at a light but again, ran smooth when started to move. This morning seemed to be OK but threw engine light. Onstar was useless so when I got home scanned to find the P0300 code. I am hoping its just some crappy gas. My 02 trew a light with only 700 miles on it but that code was a specific cylinder and it turned out to be a pinched wire that happed during assembly. The coil assembly was installed with a wire pinched. Any one else had it be more than crappy gas?

Mike
 
Oh, and I have 18k on the truck and have had MSD wires for the last 10K.

Mike
 
If you guys are having the misfires when using aftermarket plug wires I would take them off and apply a good amount of dielectric grease to both ends of the wires. If moisture condenses and gets in the wires it sure will cause these problems!

Butch
 
Right after breakfast I am gonna try that Butch. Even though I have a wire remover, I just yanked off the OE wires breaking most of them, so I dont have those to put back on. I am sure if i visit the the dealer they will put the fault on the wires even if it is not so I would like to figure it out witout them. The Helm books shows a flow chart to follow as well listing causes such as vacuum hoses, throotle body or intake leaks, PCM grounds and fuel contamination, which I hope it is.
 
With a full stomach I found what I belive to be the problem. I scanned it again and got another code. P0200 which is fuel injector circuit. I removed intake cover and began to gently twist/pull on the injector plugs. Got to number 5 and it came up in my hand. Was not seated. If you are famililar with the plug, to diconnect it you first have to pull a release tab up, and then push another tab in to remove it. In other words, our mexican friends strike again. I guess 7 out of 8 is good :8:
At least they did not pinch any wires this time. I will still go ahead and follow your advise butch and dielectric the plugs wires anyway. that is aways a good idea.

Mike
 
I have the P0300 code. I have cleared it twice in the last month using my predator programming.

I will be taking it in to the dealer on monday.

I am just curious from what I have been reading that the P0300 code can come up for a variety of reasons. Right here in NJ it is very cold out, so I cannot do any research inside my engine compartment.

What can be done to stop the P0300 code from coming up again?
 
I was just outside and started my Av to go to the store and the service engine soon light was no longer on. It was on this moring when I went out and stayed on until I returned home. Interesting. I am confused.
 
Hello, I though I would just let you know about my experience. I had a check engine light come on, and I called onstar, and they told me it was a p0300 code. I got some new gas and fuel injector cleaner. The code went away for about 2 weeks, then it came back. This time with a p0303 code. I got new taylor wire ( i had been meaning to do so anyways) and it still was idling like crap, really rough. I then changed all the spark plugs. #1 and #3 were verybad looking. Lot's of carbon and black/grey. Almost like they were running rich. Now it runs fine. Any idea what may have caused only those 2 cylinders to foul? I have about 35000 miles on my truck, and I would like to be sure it's fixed before my warranty runs out. Thanks a lot. Andrew R.
 
Hey all, had to rejoin cause my last profile went AWOL.
I have a 02 ZR71 avalanche (120000 kms) which I stopped driving over the winter cause i had a company car.
I started in once a month to keep it charged. Problem now is it's running rough, and CEL is lit up. It's lit steady to about 35 mph than it blinks above that speed and you really feel the lack of power.
I check my codes and I see P0300. Is it safe to assume the gas evaporated despite using some gas stabilizer?
Checked my plugs, they are fine and the truck was running fine before parking.
Any suggestions will be appreciated,
Thanks
 
mikeb52 said:
Hey all, had to rejoin cause my last profile went AWOL.
I have a 02 ZR71 avalanche (120000 kms) which I stopped driving over the winter cause i had a company car.
I started in once a month to keep it charged. Problem now is it's running rough, and CEL is lit up. It's lit steady to about 35 mph than it blinks above that speed and you really feel the lack of power.
I check my codes and I see P0300. Is it safe to assume the gas evaporated despite using some gas stabilizer?
Checked my plugs, they are fine and the truck was running fine before parking.
Any suggestions will be appreciated,
Thanks

Sounds like the cat(s) may be plugged. However, then, you have to think that something has plugged the cat(s), like maybe a bad downstream O2 sensor causing a rich condition. I would run the gas out of it, and then replace the two downstream O2 sensors. However, it may be too late, and the cat(s) are plugged and need replacement. Definitely get fresh gas in it.
 
Thanks for the reply..
If it is the cat(s) and it was due to the fuel, now that I've changed it out and run it gently for a while, it still really shudders under load.
A buddy recommended take it out for a good hiway blast to blow out the cats.
But I dunno, would that work maybe or cause wose damage? Their isn' ta legitimate misfire if it's clogged cats right so would there be any harm?
Thanks again
 
If the Cats are going out the OBDII system will let you know.  You will get a Catalyst effecency below threashold code (sry cant remember the number)  The P0300 code is random misfire detected and that usually means that you have air/fuel issues more than ignition or exhaust issues.  I would check your airbox for debris or a furry critter making a nest in your box.  Your mass airflow sensor could be going bad and or not getting proper airflow around it to give the proper readings.  Another issue could be fuel delivery with clogged injectors or a bad fuel filter.  Try using a QUALITY fuel injector cleaner like Lucas injector cleaner, Check and replace plugs as needed, your fuel filter may not be servicable so if you dont see one dont worry.  I think the problem will be a simple one, just check the basics first.

Massey
 
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