Some kind of ignition problem

[PMan_S13]

Motor is missing at low throttle/idle. Kind of like rrrrrrPArrrPArrrrrrrrrrrrrrPA. Sometimes it's just one miss every few seconds, but others it misses a whole bunch over and over.

Already have done all the simple things. Plugs, Wires, Cap, Rotor. Still about the same, runs just a bit better.

Tested the spark with a timing gun. If the light doesn't blink consistently, it's not firing at all times. According to this method, it is missing on all cylinders sparatically. So from this I am pretty sure it is a general problem with the ignition system.

I checked the ground at the back of the block.. looks fine to me, but I'll probably add another one just for peace of mind.

I think it's the distributor coil crapping out on me.. anyone have a good way to diagnose? any other opinions are welcome of course.

This is on a 95 s14 with a turbocharged ka24de, btw.

[s13sr20chris]

i would not throw out the possibility of rich or lean conditions either. does she do it under load? how about the injector connectors are they corroded? try the good old wiggle test.

[PMan_S13]

at about 25% or more throttle (in gear) it doesn't miss at all... it only misses real bad at idle, or if you give it low throttle while driving. It's especially bad in first gear. In third or above, I don't think it misses at all, regardless of how little gas you give it.

I'll clean up the injector connections, but I don't think that is it. Each injector is ticking every revolution.

I don't think it is a rich/lean condition... the car has a s-afc2 on it and I went from 50% rich to 50% lean (the motor really doesn't like to run when you do that, btw) and the missing never changed. It ran worse either way of my settings, so I am fairly certain it is an ignition problem and not a problem with the fueling.

[s13sr20chris]

yeah, that does sound like ignition except that ignition misfires usaully get worse under load. never the less, it could very well be ignition related. if so, it sounds more like its in the dist. i have seen some distributors get oil inside them and only miss at idle. try taking the dist cap and rotor off. then remove the plate under it. finally clean the rotor plate and all around it. you may not see anything on the rotor but it could still be dirty.

[PMan_S13]

That's some great advice... I've never heard that about ignition missing before. I'll tear down the distributor and clean it asap.

Yeah, it definately is only missing at low throttle/low rpms. Once you give it some gas, or you're in 3rd or higher, it really is not present.

Here's something else it could be.. maybe just a really weak spark? If it actually is sparking, just weakly, wouldn't it be more likely to fire with more fuel and air in the cylinder? What I'm suggesting is that it is possible the low amount of air/fuel at low throttle might be resisting the weak spark's ability to combust.

BTW, I have the plugs gapped down to .027, to keep the turbo from blowing out the spark. The ignition can't spark on stock gapping anywhere above 8 psi very consistently.. just FYI

thanks

[s13sr20chris]

no spark jumps more easily with less pressure in the cyl. this means that more throttle or more boost gives the spark trouble.

[PMan_S13]

Hmmm... I've been trying to struggle with this on my own for a while, but Haven't gotten the results I'm hoping for.

I did find that the ground wire that comes off the passenger side of the motor (it comes out of the same harness as the fuel rail connectors) was not even close to tight. Fixing that seemed to help considerably, but not enough. It won't miss as bad in first anymore or really low throttle, but it still misses at idle and when crusing in low gear. It's about 2-3 misses per second, and it is reallly annoying. The missing goes away when you put a load on the motor, be it throttle or higher gear.

I would like to diagnose the ignition system, but I have my old '91 240sx FSM and this is a '95. So maybe there are things I can check if someone would let me know exactly what? I have a multimeter

I just checked for codes last night, just out of curiosity. Got a code 41 (air temp sensor. Which I didn't have when I swapped in this motor, but I doubt this could be it. Could it?), also got a 82 (Crank Pos Sensor, this one is intermitent... sometimes it gave me this code, but I checked it later and it didn't. But then I checked again, and it did!) and the last code was an 84 (A/T Diag Comm Line.. no idea what that is, but I think it's from the auto to manual swap. Something must not be hooked up or wired or something.)

I still wonder if it is a ground somewhere acting up. Maybe the ECU ground is no good?

Any ideas?

[NISTECH]

the 84 is saying that the ecm is not communicating with the tcm(which you likely removed) ignore that. the crank sensor code I believe is for the obdII misfire moniter sensor, not the actual firing pickup wheel in your dist(cam pos sensor).

what kinda plugs you runnin?

[PMan_S13]

if I recall correctly, I'm using oem plugs from NGK. They are gapped down to .027" to keep the boost from blowing out the spark (which it does if I don't make the gap small enough) They aren' very old, I'd hate to keep band aiding the problem if this isn't the real deal.

It threw the crank sensor code again today... So are you saying that this code is just letting me know that I am misfiring? LOL, that's pretty funny... I don't need a code to tell me that. The ol' butt meter can read that just fine =)

Any idea about the air intake temp code? I'd imagine it's nothing to worry about. Just wondering if I should source a sensor and hook it up, or just say screw it.

[NISTECH]

your car is a 95 pre obdII system with almost all the sensors required for obdII.All the code means is it is not seeing the correct pulse signal generated from the sensor at a specified engine speed. The intake sensor Is suppose to be for monitering also but i will pull up my service manual and give you any more info on it.

[NISTECH]

the intake air temp sensor as stated in the service manual is not for primary engine control, it is only for diagnostic purposes.

[PMan_S13]

hmm.. well the air intake temp sensor is not a problem.

Could not seeing the correct signal from the crank pos sensor cause the type of symtops I am seeing?

If not any other ideas?

[PMan_S13]

I think I'm going to get some new spark plugs today. I already had new wires that I haven't put on yet, so might as well make it a set. Then all the ignition parts will have less than 10 hours on them.

A long time ago, a crazy old man told me that when spark plugs get soaked with gas, they never really work again, even if they dry off. I thought he was just an old dirtbag, but maybe he's right? Weeks ago, this motor had a problem with the MAF, so it flooded the crap out of the motor. Like enough to have liquid in the cylinders. I pulled the plugs and cranked out the gas at full throttle, but the plugs had to have gotten soaked then.

[s13sr20chris]

i confess i did not look up your crank sensor code but i would guess that it is an effect of your problem rather than a cause. do you have a timing light? you could try watching spark on all the different cylinders while its skipping. better yet use a spark checker. sometimes you can get your problem to go away(temporarily of course) by turning the distributor(throwing your ign timing way out). i have seen dist. that were "iffy" and i was able to narrow the search down by playing with the timing. try checking the resistance across the temp sensor as well(hot and cold) record the resistance along with your temp gauge reading or the temp of the radiator(takeng with a thermometer of some sort). another thing is your iacv. if you are able to get it off and clean it out that could help your problem.

[PMan_S13]

well I got about 75% of the problem fixed..

I tested each plug wire as I removed and replaced them.. each one had 8.5-11 kohms when set on the 20k resistence setting. The new plug wires all came in under .9 Kohms a piece. Those wires had 10 times the resistance the new ones had.

It drives a lot better now, but it still has an occasional (1 about every 2-3 seconds) miss at idle. I tried tracing what cylinder it was from with the timing light, but they all seem to be firing. Strange. I'm wondering if an injector is not firing completely.

Also, if you hold it at 2k rpms under no load, it will miss a bunch still.

We're getting close. Just a little more and it will be completely fixed

[NISTECH]

hows the o2 in this car? if its lazy meaning it doesnt rise from.175 volts to .8v within 100ms when taken from full lean to full rich.

[PMan_S13]

not sure about the 02 readings.. I have a wideband, but I removed the sensor when it started missing really badly. Unburnt fuel is really bad for wideband sensors, so I've heard. Plus it can't read accurately when it's missing anyway.

I'm going to try and put it all back together today, if the rain stops here soon.

At the present I am just using the stock o2 run to the ecu. Could I diagnose it by just disconnecting it and see if it remains the same or not? or...?

[NISTECH]

yes you could as the ecm wont use it to fine tune the mixture. but it will be slihtly on the rich side. and a cel will result. If the o2 is lasy it will cause the car to go leaner or richer then it should as it thinks the car is still to far to one side then once it sees a good reading it switches to the otherside trying to keep up with what the o2 is sending. so you end up getting a slight lean misfire or slight rich misfire. the cycling misfire you mentions leans me toward that posiblilty.

[PMan_S13]

thanks for all the help.

I didn't get a chance to get the wideband put back on, but it will be shortly. It has a simulated narrowband output so the ecu doesn't freak out, so with it in place it will be much better.

I'm prety sure the remaining problem will be cured with new spark plugs.. if anything else, it is much more minor than it was to begin with

thanks