General engine question

[ThePmMan]

Hi all,
I have a stock 1993 240sx. I have just over 80k mile on it. It seems sometimes, I have this problem that seems like the car is only running on 3 cylinders. It does not stall, but it shakes, and I can't seem to figure out what the problem is. I've jiggled wires around the distributor, and the fuel injection, but it still does it.And it only happens some times not always. Any suggestions ?

[StryfeS13]

Check injector O-rings, and test injectors to see if one is faulty

And do a basic tune up and see if it fixes anything..change your fuel filter, rotor, cap, wires, plugs, oil, oil filter

[AZ89two4Tsx]

Check all the vacuum lines. If a few are disconnected/broken, it can make the car run TERRIBLE.

[pj]

do everything listed so far, check all vacuum lines, check the plug wires as well as plugs for spark. check all injectors as well as the wiring going to them, the pigtails from the injector plugs get corroded and loose, and stop signaling the injector.
if you have to find a multimeter or somthing and use that.

[costa_rican13]

all of the above^^

[SHIFTrl240]

Easy way to check if it is an "injection"(air/fuel/spark into a single cylinder) problem or a "delivery"(getting that air/fuel/spark to the entire engine) problem:

With the engine running, carefully pull out the first spark plug wire about half way. The engine should noticeably shake more harshly. Replace the wire.

Repeat this for each cylinder, if at some point you pull the wire and the engine doesn't noticeably shake more, then you know you have an "injection" problem on that cylinder. If nothing changes for any of them, you most likely have a vacuum leak or some other "delivery" problem.

[alms24sebring]

Sounds like a misfire so I would do the tune up stuff first, then if nothing, check vacuum by listening for whistles or spraying brake cleaner. There has to be a check engine light, check that too. it might tell u your problem.

[motoman399]

had this happen on a friends RB25. it turned out to be the fuel injector wires at the ecu plug were really loose in the plug. had to unpin them all and crimp them tighter.. may want to check that.

[ThePmMan]

How would I go about checking the injectors ? I changed all the spark plugs. 2nd one in appeared to have been fouled. It runs better but still shakes.
The cap, rotor & wires are only about 8000 miles old, would they be bad already ? The check engine light is not on. I appreciate everyone's input. Thank you !

[motoman399]

you can check the injectors by simply unplugging them. if one of them doesnt affect how the car runs, then that one needs to be replaced or you need to check the wiring on the ecu for that injector. if the wiring is loose then it will have symptoms like that.

[ThePmMan]

Actually, after talking to a friend, and telling him that there was oil on on of the spark plugs, It has been determined that I have a blown head gasket. The car acted like it was running on 3 cylinders . oh well......now I have to save to have that done. Thank you everyone for your input.

[alms24sebring]

whoa whoa. Oil does not mean head gasket. If there is oil on the plugs, the valve cover gasket is most likely done. Check for oil to be running down into the tubes. I think it would have to be alot of oil too. I also think a bad injector might would a code.

If all tune up parts seem to be good and plugged in tight (make sure of that) I think the next step would be for a compression check especially on cylinder 2. Dont forget to look at the vacuum lines either.

Is there any smoke from the tailpipe? What do RPMs look like at idle?

[motoman399]

was there oil on one of the tips of the spark plug or on top of the spark plug? did you have oil on your spark plug wire where it goes into the head?

may just be a bad valve cover gasket.

[ThePmMan]

There was oil midway on the plug, no oil on the spark plug wire. Temp is fine. not overheating. No smoke out of the exhaust. RPM @ 1000 at idle, but shaking alot. If it was a bad valve cover gasket - would I notice anything else ?

[ThePmMan]

Thank you to everyone ! I replaced the #2 fuel injector after downloading a service manual. I will tackle the valve cover gasket next !