Update to ignition problem

[PMan_S13]

Ok, this is an update from a problem i've had for a while.. I've just tried ignoring it as best I can until I can really take things apart this summer and hopefully get it sorted out.

I just wanted to run somethin i find interesting past you, but first the symptoms..

ok, motor ('95 KA24DE turbo charged, not stock at all) misses at low engine speeds. Mostly at idle it is most evident (and annoying) can be bad enough that it will die and usually does if I don't flick the gas every few seconds. If you hold the rpms up you can hear and feel, from shaking, the misses. The missing is not consistent in any way. It starts ok, but will die right after the initial firing if you don't rev it up a little. Usually misses a lot at first and then runs fine with no missing for about 15 secs to a few minutes, but starts missing after that. Driving with load on the motor, you really don't feel or hear any missing, and it will boost fine. Pretty much the lower speeds, low load stuff that is causing the problems.

Ok, here is the interesting thing. I just happened to get the car on a good moment where it would idle nicely and started playing with settings to see if anything would change. A/F is good at like 14-15 at idle and doesn't change the missing when richer or leaner. BUT when I pull back on the brights (the headlights that is) the missing immediately sets in horribly and the idling goes up and down stumbling back and forth until I let off. Now that has to be an electrical problem of some kind. I get the same response when I use all 3 power windows (driver, passenger and sunroof) from the high electrical load.

I know electronics, but not how to troubeshoot them without looking at each part individually. So here is where I look for some answers..

thanks-Phil

[NISTECH]

when you apply a load to most newer fuel injected cars the ECM adjusts the idle via the FICD or IACV to compensate for the load. It sounds to me as if the compensator is not functioning properly. But it is getting a signal from the ecm as you state the idle fluctuates back and forth like its trying to. I would take a look at the IACV and see if all is ok with it. do you have a service manual you can reffrence for testing?

[PMan_S13]

well I have a FSM for the s13 but not one for the s14. I know a lot of things are the same and some things are different. For one, the plugs for the iacv aren't in the same orientation or even the same color as on my old s13.

But I don't think this is the issue. Let me make the problem a little more clear..

Ok, when you hit the brights, it's the missing itself that kills the car. It doesn't just idle down to 0. And the idling up and down is more like missing till like 250rpms and then picking up again and revving up to like 1100, stablizing for a second, and then missing again. Usually it will do this and then die after it falls too low.

I could see the idle valves being the problem if it was just dying off, but when it doesn't miss it runs fine. The missing is what I want to rid myself of and the idle valves wouldn't control that, unless I am somehow mistaken.

I'm guessing that something isn't getting enough power. The coil is my number 1 suspect, but I really don't know.

this might be a side issue, but when driving I get volt readings starting at like 13.8-13.9 and it soon drops to 13.1-13.3, but if I disconnect the battery while running it holds 13.5-13.6 the whole way. I know how the alternator works, I just don't know if this is normal or not.

thanks

[NISTECH]

If your enigine does not receive enough air it will rich misfire, if your enigine receives to much air it will lean misfire. The IACV controls the amount of air entering the engine.Your O2 can also cause this if it is fluctuatiing to slowly.

[PMan_S13]

well I have a wideband and it seems to read alright except just after it misses it will read richer, lik 12-12.5 until it stabilizes again. I figure that is just the unburnt fuel tripping the sensor. It will miss when you cruise at really low rpms too.. like less than 2000 and the AF reads perfect even when missing.

I understand how the idle valve opens or closes to let in more or less air, but that still doesn't control the a/f ratio. The air flow meter is still reading when more air draws in and adds fuel to compensate. So for it to lean misfire or rich misfire it would take more than just the iacv because it still is only indirectly affecting the engine. I mean, the valve could be wide open and it should still run with the right AFR it would just idle really high and likewise it could be completely shut and it would only run with your foot on the gas after warmed up, but it would still have the right afr. So I just don't see how it could possibly be that valve..

I know the valve doesn't actually stay open to idle, it flucuates open and closed really fast, more or less so depending on how much idle you need. Maybe the valve is going dead for a few millisec? That would be similar symptoms, it isn't really misfire, just not getting fuel or air for a few milliseconds.

[NISTECH]

You do realize those AFR devices are not acurate right? they are very lazy and sample at a very slow rate. unburnt fuel does not show up as rich but as lean. Those devices are based off O2 input and the O2 looks at oxygen content in the exhuast, oxygen content decreases when fuel is burnt and increases when it doesnt. If you were lean misfiring the o2 voltage would drop sending your AFR reading up, and the opposite would occur if you were rich misfiring voltage reading would go up and AFR reading goes down. Now if your O2 is not functioning right niether will your AFR device.

[PMan_S13]

I'm not trying to offend you, if that's how I'm coming a cross I apologize..

I'm using a wideband O2 sensor, not the stock O2. It's the same kind of sensor they use in town on the dyno so I'm pretty sure it's somewhat accurate at least. The sample rate is a little less than real-time I'll admit though. I'd say it only updates 3-4 times a sec, plenty of time for a miss to go undetected.

But that is all besides the point. Missing is going to cause the AFR to do something other than 14.7 and just changing the idle valve to be more open or more closed will not do that. That will only affect the level of the idle, not the way it runs, unless something else is messed up. This is very possible, but it is that other thing that I want to know about.

[left channel audio]

Im not a certified "auto mechanic", but I am a certified electronics pro. I would check your grounds and have your batt. tested. A quick check is to hook up jumper cables to a buddies car along with yours "like your gonna jump start your car, and just leave them hooked up run you car and see if anything changes.

A bad chassis ground can mess with sensors badly. Also poor charging circuit can allow for insufficient voltage to your 12 volt components causing a voltage drop.

[PMan_S13]

I've kind of been wondering if my battery was not grounded very well. I had to move the battery to the trunk to fit the front mount. Maybe I'll try moving the ground to a different part of the frame and see if I get better results

thanks