Cracked Coilpacks

[steeldawg_69]

Hey guys, I am having some problems with my gtr motor and would love some help. To begin with the engine was yanked, pistons changed, rod bolts changed to arp, headgasket was the cometic superstreet hg. My engine management is power fc (got a used one from my engine builder). Head was ported and polished, tomei procams installed with tomei solid lifters, valve springs and retainers etc.. I have been having very low compression since the build, pretty much 90-95 psi across the board. Now here lies some of the other problems, the car has been mildly tuned and when I get on the car the idle becomes really rough and it takes a little while for it to clear up. I started to get compression readings of 0, 30, 90 and now 50 psi on number 4 cylinder. The other cylinders hold at 90 psi. I get no smoke so it leads me to think that the problem is in the head. I am going to be taking the motor out in a couple days to see what's going on but my new problem is now this, yesterday while driving the car it started to give me the "subaru sound" when I stopped I noticed that number 5 was not firing, I have injector pulse and the plug is wet. I also noticed the coilpack had a huge crack on it. I tried to tape it up and the replaced it with the coilpack from number 4. I also changed the plug. I cruised home and when I got home, decided to check the coilpack again, where I saw that the replaced coilpack also cracked! So now I have TWO cracked coilpacks. I have use the gtr manual to check the wiring and also the ignition relay, I ran out of time but I will be checking the power transistor when I get home. Do you think that the power fc is the problem and has anyone else had this problem? The engine is from a 96 gtr and is in a 97 240sx. Going to post a picture.

Edited April 30, 2011 by steeldawg_69

[DVS JEZ]

Check that the coilpack cradle is sitting correctly. Also what spark plug are u using? Maybe the spark plug is too long or not completely down in the spark plug well/thread. Check this very carefully.

Does the spark plug screw all the way down?

Check the thread

As for the compression pour some oil down the bad cylinder and see if the compression test result is higher.

If not then maybe the valves arent lapped in correcty or maybe the valve is beeing held open by incorrectly fitted shims

[steeldawg_69]

Forgot to mention that I had poured a capfull of oil in the faulty cylinder and there was no change in compression. The plugs I am using is the NGK iridium BKR8EIX. I used to use the 7 series and changed them for the colder plugs.

[DVS JEZ]

ok, let us know if there is an issue with the spark plug height,

also before you pull the head off check the cam lobe to shim clearance with a feeler gauge set and see if the is insufficient clearance or if its ok.

[steeldawg_69]

Ok will definately do that. I checked to see if there was anything hindering the plug from going in. It went in without hassle. I just cant figure out what would make two coilpacks pop like that within 15 mins of each other. I'm going to recheck all my grounds. I almost forgot, the builder could not find my shims and he had the machine shop make some, now I'm starting to think......oh boy!

Edited May 1, 2011 by steeldawg_69

[steeldawg_69]

I had forgotten to ask, what could be the reason for the compression to be in the 90's? The hg was 1.2mm.

[steeldawg_69]

Anyone?

[DVS JEZ]

Might be a dud tester.

Try another compression tester gauge.

Also make sure the throttle is completely open when cranking. Don't stop cranking until the gauge stops moving

[Thelen]

'Low' compression isn't a problem so much as constant compression, as mentioned in other threads and in here due to dodgy testers or badly done.

The problem is, as you have, when one or more are vastly different than the rest.

Good luck with the fix.

[MrStabby]

Did you speak to engine builder about the compression? Is it actually a problem?

You need to address the coilpack issue completely first, and only once that's done work out if you have a real problem. If it were me, i'd put it back on the dyno once the coilpack issue is fixed and see if it makes the right power. If not, ask the engine builder why you're getting those compression test results.

Big cams can effect compression results, so maybe get a leak down to back it up.

[steeldawg_69]

Update............ I tested the power transistor today and it turns out number five resistance reading was off (dead short). I ordered one so now I wait. Thanks to all that answered my post, I'll keep you guys posted.