Cylinders 3 & 4 not firing

[kahl23]

I'd love to hear some thoughts on this one because I'm stumped. The car has a new engine in it (6 bolt in a '95 GSX), ran great when I first started it up. Continued to run great while I calibrated the MAFT for idle and rev tuning. I then had to put the car away for a couple of weeks because life got in the way, when I went back and started her up, she started backfiring all over the place at idle. After swapping out the plugs, I discovered that cylinders 3 & 4 don't have spark. What could be causing this? I know that the coils go 1&4 and 2&3, so it can't be them (I also just put in brand new OEM coils last fall and this car isn't a DD). I thought that when the transistor dies, it also stays within the 1/4 and 2/3 pattern. Am I wrong there? Could this be a CAS problem?

 

[jstgon]

A bad plug or two? Test the coil pack.

 

[rstchris]

If it were the CAS you would lack spark on all cylinders, like stated previously I would test the transistor and coils. Though usually when you loose a coil the 2 cylinders that share that channel would go out and not just one of each.

 

[kahl23]

I'll check the coils but like I said, they're brand new so I doubt that's the problem. Thanks for the thoughts.

 

[snowborder714]

Do you have the random misfire box unchecked in DSMlink?

I'd also check the coils, transistor, and wires. I also agree if the CAS was bad, it'd cause all spark to go out.

 

[anmGST]

I'll check the coils but like I said, they're brand new so I doubt that's the problem. Thanks for the thoughts.

Did you try the transitor( AKA ignitor) on the back of the manifold.. I had some spark issues before and that was bad. also did you check the wiring and the ground for the coil pack? Here is a pic of what it looks like.

 

[blcknspo0ln]

Although 3/4 is not common (as you said, 1/4 and 2/3 are the spark patterns), It would suggest pretty much anything. I'd go back and check all the wires that lead to the transister, coil pack, etc. It also doesn't hurt to do a quick resistance check between the coils, they should read ~30k ohms.

 

[FlatBlackTerror]

Although 3/4 is not common (as you said, 1/4 and 2/3 are the spark patterns), It would suggest pretty much anything. I'd go back and check all the wires that lead to the transister, coil pack, etc. It also doesn't hurt to do a quick resistance check between the coils, they should read ~30k ohms.

Also you might wanna check the wires. Also start the car up and night and see if you can see the spark plug wire bleeding off spark against a ground. If the insulation of the wire deteriorates for whatever reason it will do this causing a misfire.

 

[kahl23]

Do you have the random misfire box unchecked in DSMlink?

I'd also check the coils, transistor, and wires. I also agree if the CAS was bad, it'd cause all spark to go out.

Enlighten me, what does the random misfire box do?

Coils are fine. Wires are fine (already did the nighttime bleed test). Haven't had a chance to test the transistor, I'll do that tonight. Blackspooln, when you say check the wires, are you talking about breaking open the harness and looking through all the individual wires for chafe, etc.?

 

[snowborder714]

With having a 6 bolt swap in a 2g, you commonly get the random misfire CEL. This feature tells the ECU to not look for that CEL.

 

[blcknspo0ln]

With having a 6 bolt swap in a 2g, you commonly get the random misfire CEL. This feature tells the ECU to not look for that CEL.

Random misfires most definitely happen with 6bolt/2g, but if cyl 3/4 are not getting spark *at all*, then I suspect that is not the issue.

Yes, I suggest looking physically at your wires to see if there is anything going on with them. When diagnosing problems, always start with the basics (especially those of which you've done ).

 

[snowborder714]

Random misfires most definitely happen with 6bolt/2g, but if cyl 3/4 are not getting spark *at all*, then I suspect that is not the issue.

I agree, but figured it'd be another thing to check.

 

[Jeff99GS]

How are you 100% sure that it is those two cylinders that aren't firing?

Are you pulling the wires while the car runs or something? Pull the 3 wire off the plug and hold it to the side of the spark plug hole...see if it sparks when you do that. Repeat this with the 4 wire.

A good way to tell which cylinders are firing is to get some brand new plugs and run the car for a min then pull them out. The ones that are still minty fresh are the one not firing.

My guess is it is something to do with the power transistor. Are all your grounds okay?

 

[kahl23]

Grounds are solid. I did a double whammy firing test. Put new plugs in, pulled them out and three and four were still "minty fresh." Then put them on top of the valve cover (one at a time) and tested them visually. I tested the transistor. It checked out but I'm still not confident that's not my problem. I'll try to source another one and see if that fixes it. The last thing I want to do is dive into the wiring harness.

 

[blcknspo0ln]

Did you do the magnus rewire for the CPS/CAS? I would check there first. Besides, the wiring harness isn't so bad.

 

[kahl23]

I did use the Magnus rewire. What should I be looking for there? As for the harness, every time I've started cutting through the loom, I've started questioning my love of cars.

 

[turboglenn]

well if 1 and 2 are firing then 3 and 4 have to unless the problem is in the wires or plugs on those cylinders this is virtually impossible for entire sparek energy to only travel down one half of it's passages to ground (unless that plug wure is broken), this is not going to be coil related, transistopr related or wiring harness issues... this has to be the plug wires going to these cylinders... ... .


THe reason i say this is that # 3 fires on the same coil as #2 and at the same time every time no matter what if it's working it's puts spark to both at the same time (a.k.a. wastefire). Number 1 and 4 fire together as well (the car can't fire half the coil, the whole thing strikes) I would be more apt to believe that you are not getting fuel to those 2 cylinders before i would believe that 1 and 2 are firing and 3 and 4 are not...it's virtually impossible if the system is firing it's opposing jugs...they would have to pair up as 1 and 4 not firing or 2 and 3 not firing.... If you don't believe me just stick # 1 plug wire on the post for # 4 on the coil (do the same swap with 2 and 3) I bet the car runs the same but you've ran the other sylinders off the coils for the dead ones... you're either missing fuel or compression and if it were compression you would be throwing smoke and makingsome sort of noise from them but not a healthy one i'm sure

MY guesses from here are to check the injector wires for both +12v and that the grounds from the ECU to said injectors are pulling their signal down... (if you pull the cas out, turn the key one and then spin the cas by hand you can see the sparking and injection happening in real time under the hood and slow enough to check what is and isn't happening

 

[Jeff99GS]

Yeah Glenn makes a good point. I would do an OHMS test on the spark plug wires.

Also do an ohms test across all 4 injectors. If they are all the same resistance then the injector coils them selves are OK. However still check to make sure they are getting 12v and a signal.

 

[kahl23]

Thanks for all the help. Even though the transistor tested out, it was the problem. A new one fixed it.