Hello HT, I've come here hoping someone has ran into this problem and solved it. First off, I have a 1993 civic si with a SOHC ZC VTEC. Car is stock ,with the exception of a header and an AEM short ram intake. Here's what's happening...I was driving home on the highway a couple weeks ago, doing my usual 70 mph or so. As I'm a couple miles away from my exit, the car felt like it hesitated for a split second, then started losing power. It sounded like a wrx and felt like it was running on 3 cylinders. Even keeping my foot with the same amount of throttle pressure, my mph decreased by about 5. As I got of the exit, I turned off the car and turned it back on. It ran fine the rest of the way home. The next day I got back on the highway to go to work. Did the 45 mile drive perfectly, without a hiccup. The way home was a different story. About halfway home, the same thing happened. It never happens when I'm driving locally (40-50mph, stop and go). I ran a compression test and numbers were surprisingly perfect. Pulled the plugs and they show normal wear. No oil or gas on them. The wires are NGKs and I replaced them less than a year ago when I did a tune up. Cap and rotor were also replaced, along with the ignition coil as well. Fuel pump and filter were replaced a couple years ago with an OEM filter and walbro pump. Checked and cleaned all my grounds, but still no change. Every time it happens, I can restart the car and it goes away briefly. Does anyone know wtf this could be? Its driving me crazy at this point. I'm at the point of no return and she's about to go up for sale. Any and all feedback is much appreciated. Sorry for the long *** post.

 

It could be a failing fuel injector or injector driver inside the ECU. To check for an injector issue, the next time the "miss" occurs and you feel like you are running on three cylinders, pull over and raise the hood while the engine is running. Begin pulling spark plug wires one at a time (to try and keep the engine running without stalling) until you reach one that makes no change in how the engine sounds or idles. Once identified, drive on home and park the car. Remove the fuel rail and swap the offending fuel injector with a different injector... making note of where the potentially bad fuel injector is now placed. Now go and drive... and when the "miss" comes back, pull the spark plug wire of the cylinder that now is being fed by the bad injector. If no change in the engine operation occurs, then you have found the bad fuel injector and replacing it should fix your issue. If the engine shudders worse or stalls, try the spark plug wire where the offending injector originally came from. If this is still the same problem cylinder, then your ECU is bad and needs to be replaced.

Good luck.

 

first off, thank you for your helpful reply. I was suspecting a bad injector as well, so did the ol' listening to the injectors through a flathead move. Each one sounded like they were clicking consistently. Your process sounds like I'll be able to get to the bottom of it. Should I remove the plug wire at the plug, or the distributor? Also, I uploaded a pic of my spark plugs after I pulled them for inspection. There is one that is noticeably discolored from the others. Could that be an indication of the bad injector or cylinder?

 

Update: So I just came back from your recommended test and here are the results: pulled each wire at the plug, one at a time. Every cylinder was consistent when I pulled the plug. Consistent as in each one caused an idle drop and the car struggled to run. No one cylinder stood out from the other. Could it be that my ecu has just seen better days? Also, I've had no CELs pop up during this process. I even tried to run a test using the 2 prong connector and no codes popped up.