Lack of power

[koenig]

Hey guys. When my engine is cold it seems to run better. I have better acceleration and the power seems to increase as i rev higher. But when the engine is warm the power seems to be less. Cant feel the power increase just kinda stays the same. Anyone have any idea what might be causeing this? Thnx

[1991S13]

Most cars (if not all) run better when it is cool. Operating temp is cooler, and cold air is more dense, so your engine is getting more air. And of course, more air = more power. I think you mean before the car warms up, not having anything to do with the outside temp...

Is your temp gauge on hot, or is it in the normal area when you think you are losing power? When was the last time it had a good tune up (plugs, wires, etc)?

Also remember not to take your car to high rpm's and drive it real hard before it has warmed up. There are a couple reasons, one being the piston hasn't expanded yet (like everything else does when it gets hot) so driving hard when the engine is cold could cause oil to leak past the piston rings.

BTW, Im assuming this is a 240sx but what year?

[koenig]

Yes i did mean when my engine is warmed up. My temp gauge is on warm not hot when i lose power. I keep very good care of my car. My plugs are due for a change(but that will happen when i go turbo) and my wires are realitively new. I rarely rev past 5000 especialy when engine is cold. Could it hace something to due with my compression only being 155 avg.? Yes its a 1992 240

[Checkered-Member]

Do a compression check, see if everything is normal with the engine internals

[koenig]

I did a compression check and the average was 155. I guess i should replace the rings. Would this be the cause of the power loss?

[InsanityInc]

You could have bad rings, but it's unlikely. I have 212k miles on my 240, and the compression is 190 across the board (it's modified).

My guess would be that your camshafts are a bit out of whack. I had really low compression before I fixed mine. If your intake valve is opening a little late or closing a little late, it can have a dramatic impact on compression test numbers. You should do a cylinder leak test to make sure it's the rings.
Modified by InsanityInc at 1:29 AM 6/16/2005

[BigBore240]

If I was in your shoes, i would think about checking the thermostat first. It could be damaged a little and that would cause it to give your computer the wrong information which could result loss of power with a warm engine. It's a lot easier than messing with your cams and it's only like 8 bucks to replace it. Worst comes to worst you'll have a new thermostat and then you can go from there. I have learned the hard way to check the easiest/ least expensive stuff first and then focus on major components. Hope you can fix it!

[JPG0511]

Also check your MAF sensor. Plull it off the car and clean it out with carb cleaner. It may not be your problem but it only cost about a dollar or two for the cleaner. Mine was dirty inside and it made my car run a little rich.

[koenig]

Well my car has 255 XXX kms on it so its gettign up there. I did have to turn my timing down to like 16 to stop detonation. Would the cams be a cause of this? This winter my water pump went so i replaced the thermostat at the same time so i doubt its that. Ill try the MAF clean. Could the MAF cause my car to run rough and hesitate while accelerating at lower altitudes? It is also drier air at the lower altitude. At higher altitudes my car runs really smooth. Not sure what to do.

[InsanityInc]

Well my car has 255 XXX kms on it so its gettign up there. I did have to turn my timing down to like 16 to stop detonation. Would the cams be a cause of this? This winter my water pump went so i replaced the thermostat at the same time so i doubt its that. Ill try the MAF clean. Could the MAF cause my car to run rough and hesitate while accelerating at lower altitudes? It is also drier air at the lower altitude. At higher altitudes my car runs really smooth. Not sure what to do.

No, but 16btdc timing WILL make your car run rough. Hell, if mine's more than 2 degrees off, it backfires and is about as fast as a civic HX. At higher altitudes, the air pressure is lower so you could be not having detonation since you're getting a lower cylinder fill. Also, are you sure you were detonating before? If you get an ECU code for the knock sensor, that doesn't mean your knock sensor was activated, it means there's something wrong with it. Are you using high grade gas? The car calls for premium (91+) for a reason.

[koenig]

Well my car was knocking cause i could hear it! And i use 91 octane. I can handle the rough idle but i still wanna know why the car loses power while warm. So u dont think it would be the low compression?

[koenig]

I just had an idea. My car seems to only run rough and stumble when it is hot outside. I was thinking that it would probably have something to do with the maf not working correctly or dirty. What do u guys think?

[SlidnSideways]

Also check your MAF sensor. Plull it off the car and clean it out with carb cleaner. It may not be your problem but it only cost about a dollar or two for the cleaner. Mine was dirty inside and it made my car run a little rich.

^ Did you do that? Seems like a good place to start.

Also, im not quite sure i understand why you set your timing back. I thought timing was only really supposed to be adjusted if the use of alcohol or something like that was being used or under boosted situations. On a NA motor running no mods to mild mods isnt timing supposed to stay the same? Ive heard you can even keep timing the same on a boosted KA up to like 5 psi..

Am i wrong?

--Tim--

[InsanityInc]

Well my car was knocking cause i could hear it! And i use 91 octane. I can handle the rough idle but i still wanna know why the car loses power while warm. So u dont think it would be the low compression?

Describe the sound. What you think was "knocking" could just be valvetrain noise, or a faulty chain guide. If your car is actually knocking at stock timing with 91 octane, you have a bigger problem that you need to address.

[koenig]

It was a deffanite pinging sound and when i turned back the timing the knocking stopped. Im pretty sure it was knocking. I have never touched the cams... maybe the previous owner did.... Dont really have the time right now to work on the car and take the valve cover off and check the timing or put in new rings due to the fact that im working atleast 20 days straight!!!! Hmmm well atleast ill have money to burn

What are the symptoms of running lean. cause i was thinking that if the maf wasnt working correctly and the outside temp goes up the maf doesnt cool down as much, which makes the ecu think that less air is coming in and accordingly reduces the amount of fuel. Could this be the problem?
Modified by koenig at 4:05 PM 6/22/2005

[InsanityInc]

It was a deffanite pinging sound and when i turned back the timing the knocking stopped. Im pretty sure it was knocking. I have never touched the cams... maybe the previous owner did.... Dont really have the time right now to work on the car and take the valve cover off and check the timing or put in new rings due to the fact that im working atleast 20 days straight!!!! Hmmm well atleast ill have money to burn

What are the symptoms of running lean. cause i was thinking that if the maf wasnt working correctly and the outside temp goes up the maf doesnt cool down as much, which makes the ecu think that less air is coming in and accordingly reduces the amount of fuel. Could this be the problem?

Modified by koenig at 4:05 PM 6/22/2005

If the wire is hotter, the MAF is going to think there's less air coming in, but the car has an intake air temperature sensor which compensates for it. You could have a broken intake air temp sensor.

[koenig]

How would i check it?

[InsanityInc]

How would i check it?

That, I don't know. It doesn't seem to have a diagnostic for it in the FSM.

[Golden]

check your air intake for air leaks (big black plastic air duct) feel around it with one hand while revving the engine with your other hand on the throttle thing.

[koenig]

K ill try that