: Bbob, question about a P0300



dloch
11-30-04, 09:04 PM
I get a P0300 code every once in a while but only if I am driving slow, like in stop and go traffic and only have to barely touch the gas before stopping again. I had the same thing happen with the old engine. The few things that I used over from the other engine was the injectors and the plug wires, which were new Delco wires.

The original engine would also throw a P0300 if I were start it and let it idle to get the car warm. (You being from Michigan can understand that)

The car never throws a code any other time, I haven't tried starting and letting idle for an extended period of time other than when I put the engine back in.

Any suggestions?

Thanks

BeelzeBob
12-01-04, 12:48 PM
Don't know what to tell you. The misfire code is pretty robust so I would be fairly certain that you are getting a consistent misfire under those conditions. If you are sure the plug wires are good by checking continuity and resistence on each one then I would consider the injectors.... Possibly score a single new injector and keep swapping it into different locations to see if the code disappears when any given injector is replaced.

The code works by looking at the engine RPM on a continuous basis. The engine RPM in real time constantly changes with an increase in instantaneous RPM when a cylinder fires and then a decrease in RPM until the next cylinder fires. The misfire code tracks each instantaneous RPM spike and assumes that a misfire occurs if the instantaneous RPM spike that it is anticipating does not occur for any given cylinder. The code has logic so that it needs to see multiple "failures" before it sets a code so there is a countup/countdown logic for misfires that is constantly tracking misfire failures. This caues it to take longer to set the code at idle due to the longer time interval between cylinder firings.

Katshot
12-01-04, 01:04 PM
Chances are you have a lean mis-fire. The two points in time that you mentioned are typically lean points and tend to stress the ignition secondary the most. I'd start by looking at your secondary KV and troubleshoot from there. It's also possible to have the miss narrowed down to a specific cylinder via a scan tool.

oldgamer
12-01-04, 02:47 PM
...The code works by looking at the engine RPM on a continuous basis. The engine RPM in real time constantly changes with an increase in instantaneous RPM when a cylinder fires and then a decrease in RPM until the next cylinder fires. The misfire code tracks each instantaneous RPM spike and assumes that a misfire occurs if the instantaneous RPM spike that it is anticipating does not occur for any given cylinder. ...

That is very interesting to know. So, I think next step PCM should do is locate which cilinder has a misfire and have more miningfull code. GM can do that.

BeelzeBob
12-01-04, 03:04 PM
That is very interesting to know. So, I think next step PCM should do is locate which cilinder has a misfire and have more miningfull code. GM can do that.

Already in the sytem. That is why the Tech tool can show it. The Fed's dictate what trouble codes are displayed since the implementation of the OBD2 requirements. That is their call not GM's as has been reviewed before.

BeelzeBob
12-01-04, 03:11 PM
Chances are you have a lean mis-fire. The two points in time that you mentioned are typically lean points and tend to stress the ignition secondary the most. I'd start by looking at your secondary KV and troubleshoot from there. It's also possible to have the miss narrowed down to a specific cylinder via a scan tool.

Maybe....maybe not.

Off idle could be a lean condition (when you have to use the throttle slightly after being at closed throttle as you mentioned) causing the misfire. If so, the first thing I would suspect would be the EGR system being lazy. You might try cleaning the EGR valve pintle shaft as has been described before to make sure the EGR is not sticking in the least and is opening correctly. If the EGR is not delivering the calibrated amount then that momentarily forces the ssytem lean to some extent. This is minimized on the 96 and later cars with the MAF sensor but it is still a momentary possibility.

At idle, lean is not likley...especially on a long idle or warmup. The closed loop control system is pretty quick to correct any leaness in a situation like that and would easily correct a gross lean condition before the misfire detector counter could set the code. Besides, idle is set to be at 14.7:1 which is stochiometric certainly not lean. Deliberate lean idle might be the case on a 70's car but not anything into 80's or from the 90's.

A misfire at idle is more likely due to a plug/wire/coil/injector kind of thing and not a gross lean condition.

dkozloski
12-01-04, 03:33 PM
bbobynski, the misfire detection system sounds amazing. I have often wondered how it worked. How many times per revolution is the RPM measured?

Katshot
12-01-04, 04:41 PM
Maybe....maybe not.

Off idle could be a lean condition (when you have to use the throttle slightly after being at closed throttle as you mentioned) causing the misfire. If so, the first thing I would suspect would be the EGR system being lazy. You might try cleaning the EGR valve pintle shaft as has been described before to make sure the EGR is not sticking in the least and is opening correctly. If the EGR is not delivering the calibrated amount then that momentarily forces the ssytem lean to some extent. This is minimized on the 96 and later cars with the MAF sensor but it is still a momentary possibility.

At idle, lean is not likley...especially on a long idle or warmup. The closed loop control system is pretty quick to correct any leaness in a situation like that and would easily correct a gross lean condition before the misfire detector counter could set the code. Besides, idle is set to be at 14.7:1 which is stochiometric certainly not lean. Deliberate lean idle might be the case on a 70's car but not anything into 80's or from the 90's.

A misfire at idle is more likely due to a plug/wire/coil/injector kind of thing and not a gross lean condition.

Agreed, but a lean condition is very possible at a cold start even with the enriched open-loop settings, especially if there is a slight vacuum leak or something. Seen this a bunch of times in the field. "Usually" it's a case of the car starts and runs ok but once it drops into closed-loop it starts idling rough but I HAVE seen it go the other way too.
Bottom line, this kind of stuff "usually" gets traced to either an ignition system issue that is tipped-off by the misfire, or a lean condition caused by some sort of vacuum leak that then causes a lean miss.

dloch
12-01-04, 07:23 PM
Katshot, changed the coils from other motor to this one. Still got the intermittent code.

The EGR is the same one from the old motor....
As I said the injectors are from the original motor. I tried the injectors that came with the other motor but they were all gummed up and only 3 of the 8 worked.

It has to be something that was carried over from the 1st motor and the EGR and the wires are about the only thing I used over. I bought the wires to try and correct the code at idle. With the motor I took out the code was the least of my worries.

Wish I had a tech 2 to see if it's the same cylinder that keeps running up the misfire count. That would at least tell em which one to look at with regards to an injector or wire. If it's random then I would lean towards the EGR.

There are times that it does seem to idle rougher than others which to me would point towards the EGR pintle shaft.

I'll try removing the EGR and cleaning the pintle shaft.

Other than this little problem the car runs great.... love that loose converter.

Thanks for the replys.

dloch
12-01-04, 07:36 PM
Another thing I found interesting.... when the car throws a P0300 the PCM won't allow the converter to go into lock-up, with good reason. What I didn't know was that if you are driving and you clear the code it still won't allow lock-up until you cycle the ignition to off then re-start the car.

Found that out going out to Brighton one day. Got stuck in stop and go traffic because of an accident and it threw the code. I cleared it while I was driving but noticed that the RPM was higher than usual for the speed I was traveling..... ~ 80 or so... generally the RPM is around 2500 -2600 or something in that area. Well it was close to 2900 - 3000, stiff head wind and loose converter that wasn't in lock-up. Got off the freeway cycled the ignition and got back on again cranked it up to ~ 80 again and the RPM was down where it generally runs...

This wouldn't be a problem with a car that has a standard converter but it could be a problem with a car that has a ~3000 stall converter and the converter doesn't lock-up.

eldorado1
12-01-04, 10:11 PM
This wouldn't be a problem with a car that has a standard converter but it could be a problem with a car that has a ~3000 stall converter and the converter doesn't lock-up.

Not to hijack the thread or anything, but how's that treating you? Are you able to do burnouts? :bouncy:

dloch
12-02-04, 04:44 PM
Not to hijack the thread or anything, but how's that treating you? Are you able to do burnouts? :bouncy:



Yes until the traction control catches up, which is rather quickly if it's wet outside. With TC off the car still pulls great off the line. If the grounds wet the tires break loose very easy even in 2nd with TC off.

When the motor gets close to 3500 it becomes a different animal, if the tires break loose it will torque steer real bad so you need to stay on top of it. If/when I buy another caddy with a bad motor I want to put a 3500 stall in it. I believe that will be the best of both worlds. If anyone were to ask me the best bang for the buck in terms of performance I tell them to change the converter. The different is somthing you can feel with the butt dyno as soon as you hammer it, which I do a lot...... :rolleyes: I have surprised a number of people when they try to jump me away from a stop light... them cadillac ain't suppose to run that good.

One of the things I have noticed is that the motor will bang the rev limiter on the upshift from first to second if you leave your foot flat to the floor. The reason for this I believe is that the PCM is comparing, among other things, TPS to MPH. Well with the looser converter the motor bangs the rev limiter before the MPH gets to what the PCM is looking for before it shifts to 2nd. Like I said if you lift the throttle ever so slightly it shift right about where you would want it to shift and in most cases it will spin the tires on the upshift.

eldorado1
12-02-04, 05:05 PM
So lets say you're crusing down the road at 30mph... To maintain that speed, do you have to keep the engine at 3k? (I.e. does it feel like it's in neutral until 2.5-3k?) btw- this place got a number/website?

MightyBright1
12-02-04, 11:08 PM
For My Info... Would a bad HG letting coolent into the cylinders couse a P0300. Thanks.

BeelzeBob
12-03-04, 02:30 PM
So lets say you're crusing down the road at 30mph... To maintain that speed, do you have to keep the engine at 3k? (I.e. does it feel like it's in neutral until 2.5-3k?) btw- this place got a number/website?


No, not at all. The higher stall speed comes into play when the engine is at WOT and making max power. Under light load the converter doesn't allow the engine to rev that high. It will seem to "slip" or feel a little "looser" than the production converter in normal driving but it still hooks up to some extent well below the stall speed.

If you hold the brakes firmly and hold the throttle to the floor while in drive you can measure the stall speed of your production converter. You'll probably see around 2000 RPM or so. So...it is a 2000 stall speed converter. That doesn't mean that nothing happens in the converter until 2000. It just means that at full stall the converter will let the engine rev to 2000 RPM. Same with the 3000 or 3500 stall speed converters. If you use common sense driving them (they are not ideal for towing obviously and you really don't want to hold the car on a steep hill at a red light with the throttle against the torque converter) driving a high stall converter on the street is very easy...and fun.

Katshot
12-03-04, 02:45 PM
Yeah, I came close to replacing my OE one with a higher stall one in an effort to get better ET's at the track but since my tires are as big as I can fit on the rear now and I STILL manage to break them lose, I figured why bother. A big difference in "around town" driveability was made by limiting my converter lock-up to 50mph and over. I did this via LT1-Edit and my lap-top, I think you'd be limited to getting a custom flash done though.

turbojimmy
12-03-04, 03:17 PM
The stall speed is also a function of the torque the engine is making. A 3k stall converter may not actually stall at 3k RPM if you wind the engine up against the brake because the engine isn't making enough torque to stall the converter. Higher stall converters = more slip = more heat = more trans wear. If you switch to a higher stall converter it's not a bad idea to install an auxilliary trans cooler.

I put a 3600 stall converter in my GN and it's amazing (moved from a 3000 stall). Keeps the turbo spooled and allows the car to operate in its powerband. You do need a bit more RPM to get moving, but it's pretty docile around town. Locked on the highway and it's like stock (I also manually lock it at the track which is very hard on the drivetrain parts but is good for another tenth or two in the quarter).

Jim

dloch
12-09-04, 09:18 PM
For My Info... Would a bad HG letting coolent into the cylinders couse a P0300. Thanks.

The engine has been replaced. New HG's and timeserted.
It was doing on the old engine as well.

Took the EGR off and cleaned it.... I'm waiting for the next stop and go hold up.

dloch
12-09-04, 09:22 PM
No, not at all. The higher stall speed comes into play when the engine is at WOT and making max power. Under light load the converter doesn't allow the engine to rev that high. It will seem to "slip" or feel a little "looser" than the production converter in normal driving but it still hooks up to some extent well below the stall speed.

If you hold the brakes firmly and hold the throttle to the floor while in drive you can measure the stall speed of your production converter. You'll probably see around 2000 RPM or so. So...it is a 2000 stall speed converter. That doesn't mean that nothing happens in the converter until 2000. It just means that at full stall the converter will let the engine rev to 2000 RPM. Same with the 3000 or 3500 stall speed converters. If you use common sense driving them (they are not ideal for towing obviously and you really don't want to hold the car on a steep hill at a red light with the throttle against the torque converter) driving a high stall converter on the street is very easy...and fun.


On my caddy if you hold the brake and hold the throttle to the floor it will flare to about 2800 and hold for about 2 seconds then drop down to about 1800. I believe the PCM has detemined what you are doing and pulls timing so as to not damage the trans. Bbob correct me if I'm wrong.

BeelzeBob
12-10-04, 12:15 AM
Yes, there is some "abuse protection" software in there....LOL....try revving it up in neutral and pull a "neutral drop" and see what happens. Go ahead. Try it. It won't hurt anything as the PCM instantly realizes what the high schooler is doing and retards the spark severely momentarily to kill the engine torque and actually decelerate the engine to kill the inertia of the engine at high RPM and then the trans will engage. You can pull a full throttle neutral drop and the trans will just plop into gear and drive away.

Ranger
12-10-04, 09:40 PM
Yes, there is some "abuse protection" software in there....LOL....try revving it up in neutral and pull a "neutral drop" and see what happens. Go ahead. Try it. It won't hurt anything as the PCM instantly realizes what the high schooler is doing and retards the spark severely momentarily to kill the engine torque and actually decelerate the engine to kill the inertia of the engine at high RPM and then the trans will engage. You can pull a full throttle neutral drop and the trans will just plop into gear and drive away.
Interesting. I'm sure many a tranny have been saved by GM being there when dad isn't. :worship:

oldgamer
12-10-04, 10:25 PM
Yes, there is some "abuse protection" software in there....LOL....try revving it up in neutral and pull a "neutral drop" and see what happens. Go ahead. Try it. It won't hurt anything as the PCM instantly realizes what the high schooler is doing and retards the spark severely momentarily to kill the engine torque and actually decelerate the engine to kill the inertia of the engine at high RPM and then the trans will engage. You can pull a full throttle neutral drop and the trans will just plop into gear and drive away.

That's very interesting to know. Of course, it's an "automatic", not a manual, so it shiould be this way. But I remember once I shift too fast from R to D (the car isn't stoped completely yet) and it was a kinda hit. I promised myself to do that more carefully next time.
Sure I beleive in that software protection (smoth shifting is a proof of it already), but some parts in my car are too expensive just to test... If it was a test car, yeah, why not?

BeelzeBob
12-10-04, 11:36 PM
That's very interesting to know. Of course, it's an "automatic", not a manual, so it shiould be this way. But I remember once I shift too fast from R to D (the car isn't stoped completely yet) and it was a kinda hit. I promised myself to do that more carefully next time.
Sure I beleive in that software protection (smoth shifting is a proof of it already), but some parts in my car are too expensive just to test... If it was a test car, yeah, why not?


The trans will do that to protect itself. A "hard" shift is a quick shift and that actually puts less wear and tear on the clutches than a soft shift. So, in the event of a shift event like rolling backward and putting it into drive the trans will "hit" hard to keep from burning the clutches up. It forces the clutch to engage quickly to minimize heat buildup and wear. Other cases of "abuse" are handled differently.

oldgamer
12-12-04, 01:10 PM
If this is a case, I think the PCM "knows better" than somebody else what to do. I still think that if I was a PCM :canttalk: I interrupt fuel for a bit more time, wait untill RPMs drop a little more, cause I can see a car still moves back, that shift transmission to forward. The algoritm should count actual moving direction too not just RPMs. And very possible it does. I understand it very hard to adjust software for all driving conditions. I'm a programmer and It still amased me how PCM can manage everything. :hmm: So much "IFs".

BeelzeBob
12-12-04, 11:28 PM
Lots of things happen during shifts and for abuse protection.

In the case of rolling backward and shifting into drive there is a threshold where the trans will shift hard to protect the clutch pack from wear and above that it will actually cut fuel briefly and retard the spark to employ torque management.

Usually when the car is rolling the assumption is that the vehicle is in traffic and interrupting power is not desireable. In a quick revers to drive situation the driver may be turning around and hurrying in traffic so the intent is to allow the trans to shift if at all possible. It just shifts hard to protect the clutch.

If you were to do a severe rock cycle maneuver you would get into the protection mode you envision.....like trying to rock the car free from a snow bank. If the throttle is held open and the trans shifted from reverse to drive to reverse repeatedly the PCM will employ some dramatic torque management to protect the trans. The spark is actually ADVANCED severely just as the shift occurs so that the compression actually slows the engine rotation to kill the spin energy in the engine as simply cutting fuel would not elimnate the inertia the engine had at higher RPM.

There are many more protection and abuse elimination modes. Too many to cover all them here.

oldgamer
12-13-04, 10:25 AM
...The spark is actually ADVANCED severely just as the shift occurs so that the compression actually slows the engine rotation to kill the spin energy in the engine as simply cutting fuel would not elimnate the inertia the engine had at higher RPM...

Wow! I didn't think about that possibility!
Thank you very match for an explanation. :thumbsup:

turbojimmy
12-13-04, 10:56 AM
I have a P0300 error, too. I have a couple of others as well that I don't think are related - TPS and EVAP system. I think the TPS is because the cruise control cable wasn't seated in the bracket properly and had the throttle propped open. The EVAP could be just about anything - it's probably full of water. My car is a recovered flood. It ran fine when I first started it up after changing the fluids. There was a fair amount of moisture in the combustion chambers. It idled smooth and when you gave it a little throttle it was fine. I'd let it idle for about 15 mins at a time over a period of a couple of days to get it up to operating temp and dry things out. On the 2nd day it developed a dead miss. It's definitely a single cylinder not firing at all. Without a $4,000 scan tool, how would you suggest I start to narrow this down?

I can smell raw fuel at idle so I'm presuming the problem is electrical (getting gas but no spark). I can smell what I think is probably a very hot exhaust system (raw fuel igniting in the cat) so I don't run it anymore. I put a stethescope on each injector and they're all clicking. The plugs looked pretty crappy when I first pulled them (before the car ran for the first time) they were carbon fouled and wet from moisture. I haven't looked at them again since the miss developed. I guess the easiest thing to do is to replace the plugs and see what happens. I'm pretty sure it's not a mechanical issue (stuck valve, for example) because it's not making any nasty noises nor popping through the intake or exhaust.

There may have been water in the fuel, but if there was it wasn't much. I pulled the pump out and took a look in the tank before I started it. There wasn't much fuel in it and I put 5 gals of fresh fuel in it. Plus bad fuel wouldn't cause a single cylinder to stop working - it'd be rough overall.

I have the dash out of it now so it'll be another week or so before I try to run it again.

Suggestions would be appreciated.

TIA,
Jim

dkozloski
12-13-04, 12:00 PM
To find a dead miss, spray a little water on the exhaust manifolds where they bolt to the heads after the engine has run for a while to find the cold one. In a pinch you can just spit on the cylinder outlets one at a time to accomplish the same thing. Now you know where to concentrate your efforts.

turbojimmy
12-13-04, 12:09 PM
To find a dead miss, spray a little water on the exhaust manifolds where they bolt to the heads after the engine has run for a while to find the cold one. In a pinch you can just spit on the cylinder outlets one at a time to accomplish the same thing. Now you know where to concentrate your efforts.

Thanks - I'll give that a whirl once I get it running again. This is an '01 DTS so it's tough - but not impossible - to get at the manifolds. In the meantime I'll pull the plugs. Hopefully one of the plugs will be obviously different from the rest, but my luck usually isn't that good.

Jim

mcowden
12-13-04, 04:01 PM
You don't necessarily need a $4000 scan tool to see it. I use my $300 AutoTap and can see all the misfire information and history. www.autotap.com If not for troubleshooting, I still would have bought it for the learning potential. Lots of interesting data available and it makes you appreciate what the car's computers do to keep things under control.

M C
:cheers:

turbojimmy
12-13-04, 04:34 PM
You don't necessarily need a $4000 scan tool to see it. I use my $300 AutoTap and can see all the misfire information and history. www.autotap.com If not for troubleshooting, I still would have bought it for the learning potential. Lots of interesting data available and it makes you appreciate what the car's computers do to keep things under control.

M C
:cheers:

I didn't know that - thanks for the info.

Is there any way to get body codes? Or can I get those from the DIC?

Jim

mcowden
12-13-04, 05:48 PM
You can get those from the DIC for free, or the AutoTap will show you all of the codes and what they mean. The base AutoTap software and interface can't tell you misfire data, but the Enhanced Parameters for GM can. It's $100 on top of the $200 for the tool and the laptop or Palm to run it, and that's what I would use to troubleshoot the misfire if you have the money. No, I'm not a spokesperson for AutoTap, I don't own stock in the company, I don't sell anything to anybody and I have absolutely no interest in the product other than I think it's very useful for a reasonable cost.

M C
:cheers:

turbojimmy
12-13-04, 08:28 PM
I'll try the DIC first for the body codes. I have an Equus OBD-II scanner that will at least give me the generic codes, but not the enhanced data and graphs the AutoTap would. If this misfire (or anything else) stumps me I'll look into the Autotap stuff. Seems like a good deal.

Thanks again,
Jim

dloch
12-19-04, 02:41 PM
You don't necessarily need a $4000 scan tool to see it. I use my $300 AutoTap and can see all the misfire information and history. www.autotap.com If not for troubleshooting, I still would have bought it for the learning potential. Lots of interesting data available and it makes you appreciate what the car's computers do to keep things under control.

M C
:cheers:

Thanks mcowden...... I think I will get a copy of it. I want to see if it's one cylinder or if it's random like a vac leak would indicate.

caddywhizkid
12-19-04, 07:32 PM
Regarding the p0300, a while back I had a car in with a misfire condition, I dont remember the details, but I know I couldn't figure it out. So I called tech assistance, and they said replace the belt. I thought to myself no way, as well my coworkers. Well anyway I replaced the belt problem solved. All the techs I work with remember that one.

Ranger
12-19-04, 09:37 PM
Regarding the p0300, a while back I had a car in with a misfire condition, I dont remember the details, but I know I couldn't figure it out. So I called tech assistance, and they said replace the belt. I thought to myself no way, as well my coworkers. Well anyway I replaced the belt problem solved. All the techs I work with remember that one.
Ok kid, you or someone is gonna have to "splain" the theory behind this one because in my wildest imagination I cannot come up with a logical explaination. I don't doubt your word. I just don't understand it.