I am trying to figure out why my car is misfiring. I hooked up a OBDI reader and am only getting 0300 codes (random misfires). The car doesn’t misfire when the car is cold, only when hot. I can drive it for an hour with no problem, but then when I shut if off and try to start again, it misfires like a blind sharpshooter. It has a new fuel filter, plug wires, new-ish plugs, cap, rotor. I have no idea where to begin now that these basic tune up items. There are a lot of things on this car that could be causing misfires: sensors, fuel delivery, timing, vacuum leaks…I can’t possibly replace everything! Any ideas where to start looking?
I am going to guess there may be a bad temperature sensor.
Test the ignition coil, and rule it out, since everything else in the ignition system is new.
If that isn’t it, then you need to check the EGR system, and the fuel system.
nissan had a bad run of coils around the time your car was built. I would replace yours.
Thanks for the replies.
I checked the temperature sensor because that’s exactly what someone else recommended. It was OK.
I am going to do the plugs before I get really into this. Started thinking and it might have been a while since I did them. I mean, it seems like last summer but time sure flies when you’re living life. I cannot find my receipts for the plugs, so I’d better assume they are bad before I go throwing time and money at the car.
The car has a distributor, not coils. It’s a 2000, the year before they switched to ignition coils. But, if the plugs don’t fix it, I guess checking the distributor/timing then EGR, then fuel pressure is the course of action.
I’ll follow up with the results.
It should still have an ignition coil. Something’s got to make the spark - the distributor just “distributes.” (Its just not as distributorless coil “pack” which is probably what you’re thinking came about the next year).
Many auto parts stores can test various kinds of coils. And your problem sounds exactly like a “heat soaked” coil. You drive and everything gets really hot. You park and it all sits there and gets much much hotter. Under the heat the coil can’t handle it - resistance increases, insulation can’t insulate, etc. So don’t cross the coil off the list.
Does it keep misfiring, or does it just run rough for a brief period and then go back to smooth? If so I’d be looking at a fuel system problem that produced flooding after hot shutdown (leaking fuel pressure regulator or injectors) or a bad check valve in the fuel pump.
what you describe sounds very plausible. I searched around quite a bit and could not find an ignition coil for the 2000 pathfinder though. I understand what you mean though, something has to be generating the high voltage. The Haynes manual doesn’t really even mention it for the 3.3 engine. I’ll keep looking though.
I replaced the plugs last night. The car isn’t misfiring anymore, and the MIL turned off. Good news there. But, the car still idles pretty rough when started hot. When I go to accelerate, it hesitates just a bit. After driving for a few minutes, it’s all better.
I went to the garage to do some more diagnostic work. The EGR diaphragm doesn’t seem to move as the Haynes manual describes.
I am beginning to suspect vacuum leaks. The plugs I changed out looked like they had been running lean/hot (insulator seemed to have little white bumps on it, it looked blistered. Not as extreme as the picture in the back of the haynes manual though). It would seem that a vacuum leak could cause this. Also, the Haynes manual’s troubleshooting section suggests vacuum leaks as the first thing to check for a rough idle.
What do you all think about that?
The thing about suspecting vacuum leaks is that they would present a problem whether the car was hot or cold. Given what you described (the car can be driven for quite a while with no problem and then the problem presents on hot restart) a vacuum leak doesn’t really fit.
I suppose I wouldn’t rule out an EGR problem entirely only b/c the EGR is only supposed to operate when the car is hot. When cold and at idle the EGR should be doing nothing. So you’d be looking at a control side problem. Furthermore, if this had something to do with it, it wouldn’t wait until you shut it down to show up. Most any of those issues should also set a code.
Find whatever wiring feeds the distributor and check it out.
Find the fuel pressure regulator and the next time you’ve had it running a while pull the vacuum line and look for gasoline in that line. If you fine any actual gasoline replace the regulator.
have an ignition coil for your Nissan.
I’d have to agree not to rule out the EGR system. Although I wouldn’t rule out an oxygen sensor either. When the engine is cold, the ECU bypasses the Ox sensor loop to allow the engine to run rich, and that could mask either an EGR problem or an oxygen sensor problem. I would also not rule out a temp sensor problem. Sorting through these three thoughts, the EGR and the oxygen sensor should not be affected by the “stop and restart” protocol, but if the temp sensor were bad the protocol might upon restart not recognize that the engine is already hot, bypass the oxygen sensor, and cause operating problems.
By teh way, you need an OBDII reader. All vehicles starting withe the model year 1996 have OBDII systems. An OBDII reader may just help you find the problem.
thanks for that link, I do indeed see one there. Courtesy Nissan parts doesn’t seem to have one. My Haynes manual doesn’t reference it. I’ll keep looking for it though.
I don’t have an ODBI reader but I do have access to one. The only codes I have ever seen on it are p0300 (random misfires, which the plug job seemed to clean up) and once several months ago it showed an 02 sensor as a fault (don’t recall the exact code). But I suspect that was due to the misfires and that code hasn’t come back since.
Would 02 sensors cause this, though? Everywhere I look, the answer seems to be no. Seems like you think that could be causing this? If so, I guess I could try replacing them.
OBDII, not OBDI
OBDI computers only have minimal diagnostic functions and do not have datalogging capability on board. There are many OBDII blocks that are not accessable on these ECUs.
The “upstream” sensor, forward of the cat converter. The “downstream” sensor only monitors the performance of the converter and doesn’t affect the fuel metering.
I’m considering the oxygen sensor because this aounds like it may be a fuel metering problem, but the fact that it only does this when turned off and restarted suggests a temp sensor. I’m theorizing that the temp sensor is not telling the ECU when you start that the engine is already warm, the ECU is bypassing the oxygen sensor and running the fuel mix rich, and spraying the excess fuel into the hot engine is what’s causing the misfiring “like a blind sharpshooter” (I like that analogy).
But, again, see if you can get a reader that will read OBDII. You may have some stored fault codes in the ECU unaccessible by the OBDI reader that could help analyze the problem.
yep, all good points on the vacuum leak/egr. I’ll keep tracing that back from the distributor. There is a plug on the side of the distributor which has wires that come out of a tube which has other wires that go to other places…long story short, tracing back from the distributor is no easy task. But I guess that’s what I’ll have to do.
Out of desperation, I took the car to a nissan dealer and paid them for a diagnosis a few weeks ago. The insisted I needed a carbon flush first, which I grudgingly agreed to (because I really wanted a solid diagnosis and if that’s what it takes, well). They never gave me a solid diagnosis, and when I pressed them the guy just kind of blurted out the distributor. I am not trying to disregard the professional advice; that’s why I took the car there in the first place. But before I sink that kind of money into fixing something I want to understand how that could cause my specific symptoms. I felt like they were just trying to sell me stuff and just gave me an answer to make me go away. I asked if he could briefly explain to me why that would cause the problem and he got all defensive and told me that “a nissan mechanic with 18 years of experience said that, so you’d better take it.” I think it’s interesting that complete strangers online will patiently explain things for free but a dealership mechanic I am PAYING wants to get all tight-lipped and defensive. That’s off-putting and makes me suspicious.
I did not include this story above because I didn’t want to color anyone’s ideas.
Does someone here think the distributor could cause this type of problem? Can you please help me understand how?
Sorry, I was calling it the wrong thing. It’s one of these: http://www.autozone.com/autozone/accessories/Actron-OBD-II-and-CAN-Professional-trilingual-scan-tool/_/N-25iq?itemIdentifier=98817&_requestid=321705 A friend has one, and that’s what I used.
No apology necesssary. It can be confusing.
Yup, that’s the correct tool. The “Random/Multiple Cylinder Misfire Detected” code that you alluded to could be caused by a fuel metering problem.
I may have answered my own question. There may be a reason that I cannot find anything about the coil in the Haynes manual. All of the coils at that site have a pin that looks like it accepts a plug that would connect to the center pin of a distributor. I see nothing like that under the hood of this car. The distributor has no center pin. According to this, http://en.allexperts.com/q/Nissan-Repair-825/2000-Nissan-Pathfinder-3-1.htm the ignition coil is an internal distributor part. I don’t see one in the exploded view at Courtesy Parts, and I didn’t see one when I took the thing apart. But, if the distributor has an internal coil, that would actually point to the distributor.
well, the thing is that the car doesn’t seem to be misfiring anymore. Since I did the plugs the other night, I have driven it quite a bit. It’s better, and the MIL is no longer on. It’s just still that rough idle when I start the car hot. Not quite a miss, just a rough idle and a bit of hesitation that clears up after a few minutes of driving. I do realize though, that the fuel side could still be the fault. I guess hooking up a fuel pressure gauge is the way to go? Any other way to troubleshoot the fuel side?
Maybe this is caused by a loss of fuel pressure when the car has been turned off. The missing and running rough could be due to air in the fuel lines which takes a minute or so to get burped out of the system.
Generally a loss of fuel pressure is caused by a faulty check valve in the fuel pump although it could also be caused by an injector leaking off. A fuel pressure gauge to see if the system is maintaining residual pressure might be a good idea as this is not a rare problem.
I drove the car around today, made a few stops. After the last stop it started running rough and kept hesitating (no MIL though, so I assume no misfire. It’s running better than when it was when it was definitely misfiring). It fluttered a bit in P and N, and in D and R is was more pronounced. I drove it home, pulled into the garage, and left it running, put in park and set the parking brake. I opened the hood to see what I could see.
With the hood open, every time the engine stuttered, I could hear a clicking coming from the EGR area. Each engine falter corresponded with a click. 2 or 3 fast clicks, then about 15 seconds of smooth idle. I grabbed a few socket extensions and used them to listen to specific parts. The clicking was coming from the EGR Backpressure Transducer Valve. What do you think, cause or effect?
Also, I pulled some vacuum hoses while the car was running. Some would just kill the car outright. Others would have no effect. Specifically, pulling the hoses from the EGR backpressure valve had no effect.
I also ran the engine and held a propane torch (unlit) near the various vacuum hoses. No engine revving, so I think I have ruled out a vacuum leak in and around the hoses. Not on the intake manifold or anything. But now that I know what a vacuum leak sounds like, I am starting to doubt this as the cause.
A few have recommended checking the fuel pump/regulator. I am not ignoring this advice. But I am simply proceeding from things that are simpler and cheaper for me to fix. If checking the EGR, vacuum doesn’t pan out, then I will have to get a fuel pressure gauge and try that next. It’s just that the fuel pump/regulator are more expensive and I have to buy tools just to test the fuel system. Also, replacing the fuel pump is pretty nasty on this car and I’d like to save that as a last resort. It’s about $250 and I have to remove seats and then go into the fuel tank (and somehow exhaust the fuel vapors from my garage). No fun there.
I do appreciate all of the suggestions.