Vacuum leak
09-08-2004, 11:33 PM
#1
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Join Date: Sep 2004
Location: Oregon
Posts: 17
Vacuum leak
1990 240SX - KA24E - Auto
ok, I'm pretty sure I have a vacuum leak somewhere. My idle sometimes is really lumpy and low, although other times its fine. Sometimes when I rev to say 3 or 4k rpms in neutral, the rpms will bounce up and down 1000 revs give or take. Sounds like a classic vacuum leak to me. I can hear an air whoosing sounds somewhere in the area of the big red circle in the picture below.
I checked all the vacuum lines under the intake elbow and I can't find a leak there. However if take the line of the top nipple where I drew the little circle and arrow, and cap off that vacuum hose, the air leaking sound stops. If I connect it up again the leaking sound starts up again. However the leak is definitely not at the point of connection between that hose and the nipple. Maybe the leak is in the valve that the nipple is connected to? I'm not sure, it sounds like the leak is coming more from the area where I drew the big circle, but I could be wrong. What is that little canister where I drew the arrow to? There are 3 vacuum connections on it. One I think is the Charcoal canister, but I'm not even sure of that. Anybody have any ideas for me?
Thanks in advance for any help.
ok, I'm pretty sure I have a vacuum leak somewhere. My idle sometimes is really lumpy and low, although other times its fine. Sometimes when I rev to say 3 or 4k rpms in neutral, the rpms will bounce up and down 1000 revs give or take. Sounds like a classic vacuum leak to me. I can hear an air whoosing sounds somewhere in the area of the big red circle in the picture below.
I checked all the vacuum lines under the intake elbow and I can't find a leak there. However if take the line of the top nipple where I drew the little circle and arrow, and cap off that vacuum hose, the air leaking sound stops. If I connect it up again the leaking sound starts up again. However the leak is definitely not at the point of connection between that hose and the nipple. Maybe the leak is in the valve that the nipple is connected to? I'm not sure, it sounds like the leak is coming more from the area where I drew the big circle, but I could be wrong. What is that little canister where I drew the arrow to? There are 3 vacuum connections on it. One I think is the Charcoal canister, but I'm not even sure of that. Anybody have any ideas for me?
Thanks in advance for any help.
09-08-2004, 11:40 PM
#2
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Join Date: Dec 2003
Posts: 109
yes that is the charcoal canister you are referring to! there is a large 1/2 in. or so hose that runs from the bottom of it to your frame rail underneath it, could be that its leaking somewhere down there! should be 2 vac lines to the top, 1 line that just goes atmosphere, and the one on the bottom. disconnect the charcoal canister from the car, but leave the vac lines attached. then try again trouble shooting by sight or sound. easiest way to telll whats wrong is to get it out and see it and study it! good luck,
sage
sage
09-10-2004, 01:01 AM
#3
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Join Date: Sep 2004
Location: Oregon
Posts: 17
Thanks, I'll try that when I have time Saturday. The problem seems very intermittent. It was doing it constantly the other day, and today it only happened to me once. It doesn't seem to matter if the car is warm or cold. I just got the car on Monday, so I'm trying to read up on all I can right now to learn about it. I used to be a rotary nut until I sold my RX-7 almost 3 years ago. Since then I've been driving daily beaters to support my racing habit. This is the first "cool" car I've had since then and I only paid $1000 for it.
09-10-2004, 10:32 AM
#4
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Join Date: Dec 2003
Posts: 109
hey well good for you (switching away from the rotary )
...........something more reliable which gets better mileage and is much more reliable,(well generally 
) feels good huh! ok that problem you describe can also be related to the tps adjustment, try adjusting that if doing the other suggestions doesnt work first, also try adjusting the idle (using fsm procedure, im not sure what it involves) that causes the revving symptoms you are describing in honda's!
-sage
...........something more reliable which gets better mileage and is much more reliable,(well generally ) feels good huh! ok that problem you describe can also be related to the tps adjustment, try adjusting that if doing the other suggestions doesnt work first, also try adjusting the idle (using fsm procedure, im not sure what it involves) that causes the revving symptoms you are describing in honda's!-sage
09-10-2004, 11:05 AM
#5
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Join Date: Sep 2004
Location: Oregon
Posts: 17
Actually my NA 13b was dead reliable and I drove the **** out of it for 3 years, constantly revving beyond 8000rpms. Never had a single problem with it. But its nice to learn about other cars and new engines. This thing called "torque" is pretty new to me coming from rotaries. 
I downloaded a factory service manual for the KA24DE, I hope its close enough to be able to diagnose problems for the SOHC. If anyone knows a link for the KA24E FSM, let me know please. I'm going to check the TPS this weekend, probably replace the O2 sensor, and I've heard a few people mentioning the IACV and EGR as possible causes of rough/low idle as well, so I'm gonna check out those possibilities as well. Strangely though trhe problem seems to have cured itself, but I know its an intermittent thing and it will come back. It was really bad two days ago, sometimes the engine would actually stall when I'd apply a little gas from a stop. But today and last night it has been fine. Intermittent problems are the worst to diagnose because every time you try to find out whats causing it, it doesnt show the symptons. The symptons only happen when you are on the road away from your tools. Doh!!
I downloaded a factory service manual for the KA24DE, I hope its close enough to be able to diagnose problems for the SOHC. If anyone knows a link for the KA24E FSM, let me know please. I'm going to check the TPS this weekend, probably replace the O2 sensor, and I've heard a few people mentioning the IACV and EGR as possible causes of rough/low idle as well, so I'm gonna check out those possibilities as well. Strangely though trhe problem seems to have cured itself, but I know its an intermittent thing and it will come back. It was really bad two days ago, sometimes the engine would actually stall when I'd apply a little gas from a stop. But today and last night it has been fine. Intermittent problems are the worst to diagnose because every time you try to find out whats causing it, it doesnt show the symptons. The symptons only happen when you are on the road away from your tools. Doh!!
09-10-2004, 07:10 PM
#6
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Join Date: Dec 2003
Posts: 109
dont we all know it!
"Intermittent problems are the worst to diagnose because every time you try to find out whats causing it, it doesnt show the symptons. The symptons only happen when you are on the road away from your tools."
oh and rotaries, i was speaking about the turbo version in particular, i know the NA ones are quite a bit better, but ive heard the rotor seals still wear out after 60-70k even on those.
-sage
"Intermittent problems are the worst to diagnose because every time you try to find out whats causing it, it doesnt show the symptons. The symptons only happen when you are on the road away from your tools."
oh and rotaries, i was speaking about the turbo version in particular, i know the NA ones are quite a bit better, but ive heard the rotor seals still wear out after 60-70k even on those.
-sage
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