View Full Version : sohc high-end rpm problems. help anyone?

05-23-2002, 12:12 PM
It doesn't really sound like a miss (ignition problem) so you probably have a clogged old fuel filter. Try replacing that first.

05-23-2002, 10:34 PM
hmmm. That thought never crossed my mind. Thanks, I'll have to look into it. Oh yeah, I forgot to add that the check engine light is on. Ran a diagnostic but nothing came up.

05-23-2002, 10:38 PM
also check the plugs, sniff the exhaust, might be running too rich, small problems w/ the fuel system might cause this. If it's really running too rich, the mileage will be crap too. Remember KA24E motors had top feed injectors w/ seal problems. Running rich is a symptom as well has high fuel usage. Of course, don't take out the injectors unless you have a set of seals standing by incase you rip into one. Plus, those seals might need to be changed anyway since the car is pretty old.

If it's too lean, you can see it in the plugs as well. check the vac hoses for leaning.

Bad timing could also be a factor. Also check the throttle body to see if it's dirty and gunked up or if the MAF sensor is dirty either.

05-23-2002, 11:24 PM
Ok, here is the dilemma. I went to test drive an 89 240sx yesterday. The low-end power seems stronger than my old 90 240sx but at a high rpm, starts at around 5k and up, the rpm starts jumping and seems to be having a hard time going up to redline. The owner, which is a friend of a friend, told me that he had the motor replaced not too long ago. I was wondering what the problem could be and if it is anything major. Could it be that there isn't enough fuel at the high rpm range? If it's not anything major, I might consider buying it. And if this topic has been covered before, I apoligize to the moderators for re-posting it.

05-24-2002, 07:18 AM
It's hard to tell without driving what the prob could be. By your desciption, I'd agree. It sound s like one of the following in the fuels system;

- Clogged Fuel Filter
- Dirty Throttle Body (if that motor has a TB)
- Dirty injectors(if that motor has injectors)
- Some sort of bad fuel supply

Also, you may want to have the MAF looked at and/or diagnosed to see if it's bad and causing the ECU to do some funky stuff. But the fuel is more likey the problem. ( Forgive my ignorance on that particular motor.) Deffinately check the entire fuel system starting with the easiest parts to access, and pull your plugs to look for lean or rich symptoms.

05-25-2002, 03:47 PM
Thanks for the response guys, I'll have to look at the car closely the next time I check it out again. Since the car belongs to a friend of a friend, maybe I might hook up an air/fuel ratio gauge to see how the fuel is running. Once again, thanks for the help and response.