Engine Runs Rough Under Load.

[Peter]

Hi all! I have a 2003 Nissan Altima with a 2.5ltr. four cylinder engine. I bought the car with 135k miles and it now has 148k miles. It recently began losing power at lower RPMs (1000 to 2500 range) only under a load. Once it hits about 2500 RPM it is like someone hits a switch and it is perfectly normal. It is a standard and the problem is consistent through all gears. It idles and revs in neutral just fine. I looked in each spark plug well and one was filled with oil. I took it to a mechanic who fixed the bad gasket. The oil in the well also shorted a coil and this was replaced. This did make the problem better but it did not fix it. I researched problems with similar symptoms and found a fuel filter could cause issues like these. I replaced the fuel filter and pump. This perked the engine response and power but did not help the issue at all. All the spark plugs have been replaced as well. My thoughts are these. #1 Could possibly be another bad coil (but I feel it’s unlikely because it idles just fine.) #2 Bad fuel injector/s. #3 Leak in the fuel line which may be letting air in and skewing the mixture. Thank you for looking and please share your ideas with me. I’m not quite sure what to do.

Topic

[Hokiedad4]

Hi Peterbethea,

No check engine lights?

[Lee Ann]

This is a great place to start.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues

[Peter]

I apologize! Yes, the engine light is on and occasionally blinks if that means anything.

[Peter]

Thank you lar1996! I looked at the link and found I could take it to an auto parts store to get the codes ran. I’ll do that tomorrow afternoon and post the results I get. Again thank you both!

[Lee Ann]

[quote=”peterbethea” post=143745]Thank you lar1996! I looked at the link and found I could take it to an auto parts store to get the codes ran. I’ll do that tomorrow afternoon and post the results I get. Again thank you both![/quote]

Yes, do get that scanned as soon as possible. You may have a cylinder misfire.
You’re welcome. Keep us posted as to your progress. Thanks for using the ETCG Forum.

[Peter]

Ok, so I did go to Advance Auto and a very helpful gentleman ran my codes and told me that I had a bad Catalytic converter. I should have done more research but I went ahead bought it and put it on. After I did this, the car ran perfectly but the “service engine soon” light was still on. This all happened yesterday evening. This morning when I drove it into work, I could still tell the engine was rough. I took it back to Advance and this time a lady ran the codes and instead of saying what was wrong, she just gave me three codes. Here they are.

P0300 Random Misfire,
P1564 ASCD steering switch, and
P0031 O2 sensor

I would naturally think the one contributing to the rough running engine is the P0300 random misfire. I could be wrong though. The Catalytic converter did make a HUGE difference in power and response but is still not the main issue. I’ll do some more research on these codes to see what they mean but in the meanwhile, I am not quiet sure what to do. Any advice or recommendations would be GREATLY appreciated. Thank you!

[Peter]

I just got done testing the fuel injectors (via the screwdriver and ear test) and I also pulled each spark plug and examined them. I replaced them when this problem first occurred (early June) and so none of them should be faulty. However, each seemed to have a white-ish coating which I have heard means it is running hot. I understand that a bad mixture of fuel and air can result in this. A technician on YouTube showed how to use carburetor cleaner to check for any leaks in vacuum lines and intake. I did this (despite my fear of the whole engine igniting) and there was no change in the idle. The idle does not sound rough though it is just a little low. Maybe 700-800 RPM.

[Lee Ann]

[quote=”peterbethea” post=143914]Ok, so I did go to Advance Auto and a very helpful gentleman ran my codes and told me that I had a bad Catalytic converter. I should have done more research but I went ahead bought it and put it on. After I did this, the car ran perfectly but the “service engine soon” light was still on. This all happened yesterday evening. This morning when I drove it into work, I could still tell the engine was rough. I took it back to Advance and this time a lady ran the codes and instead of saying what was wrong, she just gave me three codes. Here they are.

P0300 Random Misfire,
P1564 ASCD steering switch, and
P0031 O2 sensor

I would naturally think the one contributing to the rough running engine is the P0300 random misfire. I could be wrong though. The Catalytic converter did make a HUGE difference in power and response but is still not the main issue. I’ll do some more research on these codes to see what they mean but in the meanwhile, I am not quiet sure what to do. Any advice or recommendations would be GREATLY appreciated. Thank you![/quote]

While the people behind the counter at the parts store can be very helpful and nice, remember that their main goal is to sell you parts. The first person should have just given you the codes, as the second person did.
With the info from the second person, I would have started by removing the O2 sensor and then take a resistance measurement with a digital multi meter (DMM). OL (outer limits=infinite resistance) on the screen would have confirmed for me that the O2 sensor needed to be replaced. After buying and then installing the sensor, my next step would have been to take it for a test drive to see/feel if that roughness went away and if the Check Engine Light (aka CEL) disappeared. Sometime the P0300 code for a random misfire is thrown as an artifact. The computer can’t always isolate the exact malfunction so it sets a code to try to give you enough direction to guide your investigation. However, 99.9 % of the time, the computer is spot on.

BTW It was the blinking Check Engine Light that told me you had a cylinder misfire and that your catalytic converter may have been compromised by raw, unburned fuel finding its way there and damaging the catalyst. With that situation, it is imperative to have it scanned and the root issue addressed as soon as possible.

Usually the engine running rough under load is due to an ignition problem. High resistance in the spark plug wires (or electrical arcing), or improper gap between the spark plug electrodes can sometimes cause this. An engine can run rough/idle rough due to something as simple as trapped air in the cooling system. Sometimes it is due to more complex mechanical failures resulting in cylinder compression loss.

I will include a few videos Eric produced as an edit to this post.

[Author]

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