This one's had my head scratching. I've got a turbo setup, with an AEM ecm, and 440 injectors. If the injector duty cycle falls to less than 15% while cruising, the car runs like total piss. It sputters and starts stumbling. This usually happens around 2500 in all gears with 3%-10% throttle. If I give it some gas, get the revs up to around 4000, and then let off the throttle, it'll also sputter and stumble although the injector duty cycle is up around 20%-25%. I pulled the plugs and noticed it was running lean, so I bumped the fuel pressure up some. It didn't help the stumbling any unfortunately. I borescoped the cylinders and didn't notice any major detonation. If I'm cruising out of those rpm ranges the car runs fine. My next thought was putting an analog meter on my throttle rheostat and checking for any unusual deflection. Beyond that though, I'm stumped. Fast Idle Control Valve maybe? I did notice it happens more after about 5-10 minutes into driving.

 

well doesnt the fast idle control valve only control the idle being bumped up when you use things like lights etc? How about the throttle position sensor? I knew someone who was having probs with hesitation and it turned out to be that but I never got around to finding out why etc etc.... also do you think it is possible an injector can be fouled in any way? Cause when you are at 3-10% throttle and if its fouled you wont get the pressure that you should, but when you punch it then even if its fouled it will get decent pressure....

 

Doesnt sound like the Fast Idle thermo to me... But it sounds like u are on the right path to fixing it. I would say to check your wiring and make sure the numbers are correct on the TPS. I assume your running a stock ecu so none of the fuel map numbers have been changed around?

 

AEM computer that until recently had been running fine. I found it stumbles on accelleration now too. It feel like it'll struggle until it hits a certain point when you step on the gas, then it'll accellerate normally. The decelleration stuttering happens at a certain point too, when the exhuast note changes.

 

My 88 CRX si engine does that cuz i have a cracked exhaust manifold gasket, so my O2 sensor is bad. ECU Code Blink : 1.

 

It seems like every time I make a post nailing the problem down, it gets worse. Now its got a rough idle, all of the other symptoms and its misfiring in all driving profiles. Oh well.

 

I really dont know anything about the EMS system but does is throw trouble codes?? Is the idle jumpy or just rough? Idling too high or low?

 

Check your igniter!!!!!! had this problem once on a B18c - it wouldn't run smooth below 2500 rpm. If in doubt have a tune up shop scope the ignition. Most hondas derive injector pulses directly through the distributor output signals.

 

civicon, it doesn't throw codes, but I could monitor the cylinders, spark, and fuel injectors from a laptop if I had one. I CAN watch the injector pulse width (I'm guessing the #1) and Throttle Position from my Apexi boost controller. Both of those are normal. The throttle position doesn't really jump around or anything... it stays within .3% probably caused by my jittering foot. It doesn't read anything with the gas pedal let off, like it should. The idle is jumpy in that the engine is misfiring. I've never heard detonation in a honda, but it doesn't sound like pinging. It sounds like a popping sound coming out of the exhaust.

doc, when you say "igniter" do you mean my spark plugs or the distributor? The plugs were fine when I last checked them, and I pulled the cap off of my distributor today, to find everything looking pretty much how it should. There was a little blackening on the face of the rotor that arcs to the contacts, but it didn't look abnormal.

Thanks for the help guys... keep the suggestions coming.

 

The igniter that I'm refering to sits in the distributor - the little 4 prong thingy held in with 2 screws that fires the coil. These are very notorious for causing all sorts of crazy drivability problems. The problem is that it ties into the feedback of the ECM for spark timing and duration as well as injector trigger to ECM, so if it acts up, then it can even cause your ignition timing to shift around and make the injectors cut out. It's just a basic thing you can check before you rip all the hair out of your head. The car I had mentioned before I had worked on had almost everything replaced as far as sensors go. I hope this helps you out a bit - Good luck Rooster!