Random Miss/Weak Spark

[schroder]

Alrighty, I knew I had a miss so I've gone through what I can think of to find it. New plugs, New wires, new coils (did not include the 1990 harness with the tach signal), and a compression check. Several sets of plugs and wires later, with 2 sets of coils gone through, and 185-190-190-190 compression (2g pistons/rods) I still have this miss. Its ONLY in cylinder number 4, the one with 185 compression. I believe the compression to be dropping because its not burning all the fuel it should be and the cylinders are beginning to wash, so I REALLY need to fix this problem. I finally got my hands on a tool my buddy has that you can touch to the spark plugs and it flashes a red LED everytime it sparks. I had very FAST spark in cylinders 1,2, and 3, but not 4. I tested at the coil and at the plug with the same result no matter where the sensitivity on the tool was. I know my old coil used to have alot of oil around/on it because the old owner was an idiot to say the least. Could the Tach signal box on the the coil pack be whats causing my problems if there is oil on/in it? I know the coil has the power wire running to it, but I thought that would effect both cylinders attached to that coil. If not, what could this be. I'm getting tired of spending money where it shouldn't be spent (although, I'm sure I needed the parts.) Any help would be great! Thanks guys!

 

[schroder]

Ive also gone through 2 ECUs and a few different Eprom chips including the factory one and that has not helped/hurt the problem. Thanks!

 

[aeffdgst]

ah when you find this misfire lemme know because im finding the same problem...

 

[Jimmer307]

Might be a stupid idea but, did you gap the 4th spark plug correctly? When i bought my car they were not gapped correctly and my car ran like shit. I was missing on cylinder 1, but i got all new plugs gapped .028-.031. Now im running great.

 

[schroder]

because i'm running 23psi on a big 16g, I have the gap set to .025, but its that way on all cylinders. I've run the gap at .028-.031 on stock heat range and 1 step colder. Nothing helps the miss. The only thing I can think of is that there was so much oil around/on the coil pack and intake manifold that some of it may have gotten into the tach signal box and that could be causing some problem somehow because the hot wires for both coils run to that box. The only thing that confuses me is that all the other cylinders (even cylinder 1) have GREAT spark, its just cylinder 4. Could it be the tach signal box, or a cas (I figured CAS would cause poor spark over all cylinders because of timing issues, not just 1 cylinder)...or am I missing something else. All the connections are hooked up, I've gone through the connections MANY times, and I've had the motor out 3 different times to fix problems. Every time it goes back in, I have the same problem and its getting really old. Thanks again in advance!

 

[schroder]

I should also note that my CAS wires are 205k old and have some wire actually showing. Its possible the current could be arcing to the head, but I dont know if that would only cause one plug/coil to fire weak. Thanks again in advance all!

 

[aeffdgst]

i have a hard time believing its your cam angle sensor...im having the same problem with a first gen motor....im looking into the MAF MAS and the o2 snesors... if you disconnect your tps does the problem stop?

 

[aeffdgst]

also check your physical timing just to make sure for some reason that the physical timing isnt off if it is that is what is pretty much causing my problem by my knowledge and the CAS is out of position so its not sparking right...

 

[schroder]

I didn't think about the TPS, but I"ll unplug it to see if it stops. If I unplug it, can I still drive the car or will it not really allow me to? The physical timing when grounded out is at 5*, when off ground its between 9 and 12* (maybe higher?) at idle (750 rpm). I've gone through different ECUs and Tunes and I'm currently on an Evo MAF so I dont think its anything there. I've heard that at idle the timing should float around 7-9* advance, so mine is a little off. But I'll go out and try unhooking the TPS and see if that works and post up on it in a minute!

 

[schroder]

Well, after unhooking the TPS its not that, and I find it hard to believe that a TPS would actually cause me to have a weak spark in cylinder 4. I strongly feel that it could be the CAS as thats got a major control on timing, so spark and fuel. Either that or possibly the tach signal box as its had a good ammount of oil go through it. If theres an OG on the site that has an opinion please chime in! Is there a way to test the CAS thats not "Take it off and spin it to make sure the injectors fire"? I know they fire, and I know there IS spark, i just need to know whats causing it to be weak. Thanks!

 

[aeffdgst]

it has to be something in the wiring then check for loose wires grounded out wires and bare wires seriously the CAS would cause a misfire but the miss would be VERY suttle check the mechanical timing now also make sure its top dead center on #1 and then make sure all your timing marks line up....

 

[schroder]

Ok...again its dead on. Its not mechanical as I only have WEAK spark in cylinder 4. Somehow, the spark is either not getting the same signal, or something is causing the spark to be weaker. It has nothing to do with mechanical timing as that, again, has been checked and again, its only weak on one cylinder. If it was mechanical, it would be all 4, or cylinders 1 and 4. So please, its not spark plugs, wires, compression, or anything that wouldn't cause a weak electrical pulse in the 4th cylinder. Is there anyone else with any ideas on it being the CAS, the Tach Signal, or SOMETHING else that I'm not thinking of? Thanks!

 

[schroder]

Well, it turns out cylinder number 4 AND cylinder number 2 have weak spark. My thinking is continuing to lean farther towards the CAS, but I'd like another opinion either confirming or possibly denying my theory. Thanks in advance!

 

[schroder]

Seriously, any help from any Mods or Admins, or people with different opinion (or the same one as mine), or people with a 1g, or Anything?

 

[aeffdgst]

ah check the signal coming from the CAS see if unplugging it does anything i dont know my best guess yet is that if 1/2/4 have a weak spark the 3 also does meaning its probably your CAS especially if your CAS is stock and never been changed find a half effect one the black top and wire it in with your origional they a proven to be the best to use...

 

[schroder]

1 and 3 have Great spark. 2 and 4 (the back side of the firing order) have poor/weak spark. This is what is causing my miss, and if its not, I'll determine the miss later. I believe it to either be the CAS or the transistor, but I've heard that when transistors crap out, they simply crap out. The cas and the wiring, along with the transistor, are 207k old. The wires are brittle and slightly exposed right at the CAS. So in summary, the CAS's wiring blows, the front of the firing order *1, and 3* are good and the back half *2 and 4* are weak. Thanks again in advance!