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View Full Version : Occasional stumble under partial throttle.



hobbie2k
10-18-2013, 05:40 AM
The car is a '96 Nissan Pulsar SSS, SR20DE with a manual.

Occasionally I can feel a slight stumble under partial throttle. It usually just feels like the car is a little down on power then it recovers and picks up again. My wife says she can't feel it, but it's definitely there. It seems more common when cold, but can happen hot, too.

I have replaced the cap, rotor (I couldn't believe how much trouble replacing a rotor could be), wires and plugs (gapped and indexed) along with the fuel filter. Followed by a computer reset. It appears that the fuel rail was replaced recently and the injectors may have been done with it, but I can't say for sure.

My current working theory is a vacuum leak. I've tried using a spray bottle to mist a little water around various tubes while listening for changes in running, but haven't found anything. I've also tried listening and feeling for air, but am hard of hearing so have been unsuccessful.

Any other theories or ideas on how to diagnose would be appreciated.

MrWOT
10-18-2013, 03:09 PM
An unlit propane torch is the easiest way I've found to find a vac leak. Work way better than liquids.

Shadowlife25
10-19-2013, 04:19 AM
See if any of the shops in your area have a smoke machine. That will find most leaks in a hurry. :)
MrWOT is correct in his use of propane as well for vacuum leaks. Give that a try as well.

Could it perhaps be a dead spot in the TPS sensor? Just putting some other ideas out there.

underscore
10-19-2013, 05:47 AM
Nay gentlemen, the easiest way to find a vac leak is a boost leak tester. Pressurize the system up to a couple PSI and you'll find any leaks.

hobbie2k
10-20-2013, 02:58 AM
Thanks, I'll give them a shot.

celica9303
10-20-2013, 03:40 AM
I am dealing with the same type of issue with my 5sfe. Though my stumble is more like hitting a brick wall then recovering. Narrowed it down to ignition related im preety sure. Leaning toward the coil in the distributor going bad. Havent had time to pull it apart to test yet.

Id look there on the Nissan too

hobbie2k
10-21-2013, 01:03 AM
I am dealing with the same type of issue with my 5sfe. Though my stumble is more like hitting a brick wall then recovering. Narrowed it down to ignition related im preety sure. Leaning toward the coil in the distributor going bad. Havent had time to pull it apart to test yet.

Thanks, I'll keep that in mind, too.

hobbie2k
12-28-2013, 01:17 AM
I think I've finally got it dealt with.

Started by replacing a couple EGR vacuum lines that were a little cracked at the ends even though I wasn't seeing any leaking, that led me to remove the EGR valve and BPT to clean them, which allowed me to see another rubber EGR line that is very cracked. It crumbled in my hand as I removed it. I then removed the entire metal EGR tube and cleaned it out. There was a clog in one of the sharper bends. That seemed to improve things. Then I decided to try cleaning the O2 sensor before I replaced it. That seems to have dramatically improved the situation. The only thing left to do is replace the EGR valve gasket which was in rough shape (I would have done it a while ago, but it seems an EGR gasket is a difficult thing to get a hold of here...)