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2008 Nissan Sentra - Engine bogs

2008 SE-R Spec V 2.5 engine. Car bogs or loses quite a bit of power and is a little jerky when the engine gets completely warm. Almost like a plug is not fully firing. When cold it runs great until it warms up. I have replaced the catalytic converters, MAF, two 02 sensors, and spark plugs. Any suggestions?

Yes, tell us if the check engine light is on, tell us how many miles on the car, tell us why the cats were replaced,the MAF, 2 O2 sensors and spark plugs, too. Were these replaced in an attempt to fix this issue? Or why?

We could tell you a bunch of “Might Be’s” and you could replace those parts, but that’s just throwing money away.

Or you could take it to a shop and have them diagnose the problem, and go from there.

The reason I replaced the Catalytic converters is the car didn’t have any on it when we bought it from the dealer. The per-cat had been gutted and the rear was totally gone. I knew it had a code for converters but didn’t know they were totally gone. The MAF had oil on it from someone installing a K&N air filter. Some one had installed Autolite plugs instead of NGK plugs. The two 02 sensors was because they threw a code for each of them.

One of many possibilities is a single fuel injector might be partially plugged. When it’s cold the ECU demands more fuel. This may be enough fuel to seemingly run well at cold temps. As car warms and fuel is decreased. The injector might not supply enough fuel to fire properly. These things can be diagnosed at a shop with equipment. They can disable each cylinder to determine which one and why it is not firing. And see what’s happening with a scanner.

Keep going, you are halfway there… what are the codes now, how many miles on the car and one more… are you going to try and fix this yourself?

It isn’t showing a code right now, but the last one was P0138, that is when I replaced the last 02 semsor. The car has 138,000 miles on it. Yes I will have to fix it myself as I am on a fixed income.

I have a scanner, taking it to a shop is not an option. At this moment I know it isn’t the fuel pump or fuel filter as I am getting different readings on bank 1 and bank 2 of the LONGFT of each bank. If it were the fuel pump or filter they would read the same and they don’t. I am suspecting a vacuum leak as of now. I will follow that route until I prove that wrong.

I will check the injectors and see how that goes. I really appreciate all the help from you fellows, thank you.

You have a strange engine configuration… a 4 cylinder with 4 O2 sensors.

The P0138 code tells you the voltage of the downstream bank 1 sensor is high, or a rich condition. If your Long term fuel trim is negative for bank one, you might have a leaking injector. If it is high, it may be a failing injector. @tcmichnorth is on the right track, you need to run a balance test. Prop the throttle open enough to boost idle to 1500 rpm or so and disconnect one fuel injector at a time and note the drop in rpm. If one doesn’t change as much as the other 3, swap positions and re test. If the problem follows the injector, replace it. If it doesn’t it might be a coil or an internal engine issue. Run a compression test to verify.

You can run the same test by unplugging the spark to each cylinder one at a time as well. Can identify a bad coil on plug or a dead cylinder.

That is a great suggestion, I will do all that today, hopefully. I did a compression test all 4 cylinders are hitting 150 psi each. I will have to have someone hold the peddle down to keep it at 1500 rpm, if you open the butterfly manually you have to relearn the throttle body and that is a royal pain to say the least.

I would suggest starting the engine and blocking the butterly open a bit more. This should not require a relearn. It will be hard for a helper to hold a steady throttle.

Check to see if your scanner can set to 1500 rpm

Flaky coolant temperature sensor? Does your code reader give you coolant temperature?

I have a new temperature sending unit on it’s way now. I did a vacuum leak test today and found nothing at all. I am going to take the injectors out and see what they look like, I will almost bet they are shot, but that is just a hunch.

Would clogged injectors cause the car to use more gas than normal?

What are the long term fuel trim values on each bank?