[MM Alexander]

About 3 weeks ago, while driving home from work, my 4 back cylinder ( 5, 6, 7, 8 ) abruptly stopped firing (found this out once I made it home to diagnose it).
I tested the coils for 12V and spark as well as tried switching the coils and plugs around, no change.
Limited on time to diagnose (I had to travel for work the next day) I left it at that point.
Fast forward to this afternoon and I go back at it. I first test the injectors to make sure they have both 12v and a neg pulse from the computer. Both being present, I pulled the injectors out and energized them with a battery to make sure they all sprayed/worked. I then swap the front 4 around with the back 4. No change, the back 4 cylinders still aren't combustible.
I read somewhere (I've done a bit of searching ) that it could possibly be the CKPS (crank position). I've only dealt with one of those on a Mercedes I owned. When it went bad, the car simply shut off and would not start at all.
So, I'm asking if anyone has seen this (or similar) and if not, any ideas on what I could possibly check out next?
I'm literally at a stopping point and out of ideas.

 

[Raymond Luxury Yacht]

I think the CKP would throw a code if it was off.

Have you tried disconnecting and reconnecting the battery (I'd leave it off for 30+ minutes)

 

[Konnie the Goat]

CKP and CMP failures can ghost to other issues. but i doubt thats the case here. 1-8-7-2-6-5-4-3

i bolded the failed cyls in the firing order. If we'd lost 8,7,5,4, id say check the CMP and CKP patterns.

But i dont have other ideas beyond what youve done. So check the CMP and CKP signals. you need an O-scope to do that.
they are hall-effects, so its a digital square wave.

Oh, and do a compression test. Its rare, but i have seen cams snap in half. Never on an LS though.

 

[MuhThugga]

Is fuel getting into the combustion chamber?

That'd probably be a quick indication if the cam is effed-up. It won't get in there if the valves are closed.

 

[yellow.nc]

Wow, I've never heard of this before. Usually I'd have a couple of thoughts, but I can't come up with anything. Good luck, and let us know what it is, I'd like to know just for the hell of it.

 

[St.Mary]

Try pulling one valve cover and crank the motor by hand (crank pulley with big wrench). That'll give you a quick idea if anything is funny in the top end (like a broken cam).

Are you sure it's getting spark? Pull the plugs, reconnect the plug wire, place the plug on a rag and ground it out with a screwdriver against the block. That'll rule out the spark thing.

Are you sure it's getting fuel? You mentioned you jumped the injector but was it still hooked up to the factory rail? It's probably not the best way, but you could pull out one side of the fuel rail with injectors, crank the motor, and see if fuel sprays. A towel or bucket may be in order to clean up the mess If you somehow clogged a fuel rail maybe you'd see it here.

What other things run in series to the back of the motor that if they get plugged, the rear 4 cylinders would stop firing?

 

[MM Alexander]

You guys are fantastic

First off --- THANK YOU ALL for the replies!!! I don't think that is said often enough on forums (when questions are answered).
Okay, now ...

I think the CKP would throw a code if it was off.
Have you tried disconnecting and reconnecting the battery (I'd leave it off for 30+ minutes)

I did that (was hoping the computer had went "stupid" on me). I actually didn't get a code my whole ride home (about 30 minutes from when the cylinder combustion dropped). I have a CEL now but I'm sure it relates to the misfires.

CKP and CMP failures can ghost to other issues. but i doubt thats the case here.
But i dont have other ideas beyond what youve done. So check the CMP and CKP signals. you need an O-scope to do that.
they are hall-effects, so its a digital square wave.
Oh, and do a compression test. Its rare, but i have seen cams snap in half. Never on an LS though.

Don't have access to an Oscilloscope here in the office. Though it was my best friend out in the field while working in Woodward, Oklahoma the past few weeks. I'm a Wind Turbine Service Engineer for Siemens and we had a high fault rate on one of our RPM sensors (which is a Hall effect Square Wave as well). Denmark (wind division head quarters ... bunch of stubborn know it all's) refused to believe it was a manufacturing defect. Took readings from about 15 towers to prove my findings ... Totally off topic/subject I know BUT it's still a hot button with me (still fresh on my mind, LOL).
Funny you mention the snapped cam. A friend of mine thought the same thing as well. We were actually driving in his truck (with a worked 350 in it) about 5 years back and it snapped the cam (literally broke in two ). We both had ruled it out this time because like you, never heard of it happening to a LSx based motor.

Is fuel getting into the combustion chamber?
That'd probably be a quick indication if the cam is effed-up. It won't get in there if the valves are closed.

Yeah, I kind of suspected that (see original thread link at the bottom of this thread) since the plugs I pulled from the non firing cylinders weren't wet.

Good luck, and let us know what it is, I'd like to know just for the hell of it.

Yeah, you and I both. I "think" I'm going to go down as having the first (that I know of) broken cam'd LSx (and that Comp cam has been in there for close to 2 years and about 18K miles problem free).

Try pulling one valve cover and crank the motor by hand (crank pulley with big wrench). That'll give you a quick idea if anything is funny in the top end (like a broken cam)

I planned on pulling the valve cover, riggin' up the coils and running the motor with the covers off. I can't a more clear indication of valve events than that (I figure).

Are you sure it's getting spark? Pull the plugs, reconnect the plug wire, place the plug on a rag and ground it out with a screwdriver against the block. That'll rule out the spark thing.

I'm getting great spark. I have one of those in line Spark testers. It fires like a champ on all cylinders.

Are you sure it's getting fuel? You mentioned you jumped the injector but was it still hooked up to the factory rail?

I pulled each injector, place a bit of fuel in each one, power it up from a battery and blow thru them. They all squirt fuel with a very nice pattern.

What other things run in series to the back of the motor that if they get plugged, the rear 4 cylinders would stop firing?

Exactly what I was looking to figure out and to be honest... Nothing outside of the fuel rail. The fuel rail and injectors are both clog free.

My first thread concerning this issue
http://www.ls1gto.com/forums/showthread.php?t=388860

 

[Konnie the Goat]

Thank YOU, for the quality and comprehensive testing, and laying it all out nicely.

Ive only seen cams snap twice, personally. And It does throw you. Much like the Spanish Inquisition, nobody expects it.

 

[mistermike]

Thank YOU, for the quality and comprehensive testing, and laying it all out nicely.

Ive only seen cams snap twice, personally. And It does throw you. Much like a knobber from Rosie O'Donnell, nobody expects it.

Fixed.
Big 10-4 on a great example of how these threads should go, but seldom do.

 

[St.Mary]

Hmmm. I'm still not sold on the way you are testing your injectors.

It sounds like you've shown that your injectors work individually, but not that they are spraying fuel when connected to the OE harness and fuel rails.

If your fuel rail was somehow blocked, the injectors could still be working fine, but if no fuel is getting in...no fuel is going to get out.

You mentioned that the fuel rails were clog free, but how did you check that?

Fuel, Air, Spark....gotta be one of those 3

Could it just be really low fuel pressure? Maybe you are getting enough to feed the front half of the rail but not the back?

Edit: Ok, looked at the car. Fuel rail is fed by in the middle of the driver side bank in the middle of the rail. I have no idea how you'd clog up only the back two cylinders on each rail.

I think you still need to make sure the injectors spray fuel when hooked up to the rails. Make sure something isn't fudged where the computer isn't telling the injectors to open in the back 4 cylinders.

 

[Konnie the Goat]

He said he'd switched the injectors around, and 'noid lighted them.

Power wise, they are fed by bank, IIRC. Individual control (ground) circuits, and loosing 4 is just too weird.

Not any weirder than losing the back half of the cam, however.

 

[EricBlueGTO]

Maybe I missed it, but how did you determine it is the back 4 cylinders that are dead? Did you see if the header primaries have any heat?

The most common sense check is to pull one of the valve covers and turn the motor over. If the valves are actuating, then you narrow it down to fuel or spark. If you have four dead cylinders and the plugs look normal, then it would seem at a glance that they are not getting fuel.

 

[MM Alexander]

You guys are STILL great! Much Appreciated Fellas!

He said he'd switched the injectors around, and 'noid lighted them.
Power wise, they are fed by bank, IIRC. Individual control (ground) circuits, and loosing 4 is just too weird.
Not any weirder than losing the back half of the cam, however.

Exactly ....
The coils & injectors for 2,4,6,8 are powered by Red > Pink for injectors ( S154 )
Red to coils ( S137 )
1,3,5,7 are powered by Lt. Grn > Pink for injectors (S155)
Lt. Grn to coils ( S138 )
I pulled the valve cover on yesterday to check the valve events while it was running. They are all fine so the cam is still in one piece. It also showed me that the reason for the plugs NOT being wet was not from the valve being in the way (from a fubar'd cam).
I even went so far as to change the fuel rails (I have a complete LS3 package waiting to go on). I figured why not, with it being literally a 10 minute job. No change to the situation.
With the injectors being supplied both 12v Pos and a Neg pulse from the computer ... fuel rail not clogged/blocked and injectors being swapped from working locations (1,2,3,4 >>>> 5,6,7,8 ) great spark (verified twice ) and still no combustion on the back 4 ...
Wonder what would cause the obvious lack of fuel???

Maybe I missed it, but how did you determine it is the back 4 cylinders that are dead?

Link to thread I started about this a few weeks back when it first happens covers all that. (long version, LOL)
http://www.ls1gto.com/forums/showthread.php?t=388860

Did you see if the header primaries have any heat?

Yep Yep, cold to the touch (until the radiant heat from the other 2 tubes reach them) and the fact that I can disconnect the coil or injector with no change to the motor on those cylinders.

The most common sense check is to pull one of the valve covers and turn the motor over. If the valves are actuating, then you narrow it down to fuel or spark.

Yep Yep, been there --- done that (so to speak).

If you have four dead cylinders and the plugs look normal, then it would seem at a glance that they are not getting fuel.

Yep Yep, I'm in agreement with you on that (at this point since I've deducted/eliminated all other possibilities). Now I just need to figure out what's causing the lack of fuel supply.

 

[Steel Chicken]

At this point I would start diagnosing wiring issues or possibly a bad ECM. Its odd that its just half of two banks...usually wiring issues take out a whole bank.

 

[andrewzpsu]

This is absolutely nuts. I would go with Steel's point and say its gotta be wiring or a bad ECM.

I doubt you'd have 4 fuel injectors go back exactly at the same time. But you could always switch them around and see whats going on...

 

[Nmbr1GMfan]

At this point I would start diagnosing wiring issues or possibly a bad ECM. Its odd that its just half of two banks...usually wiring issues take out a whole bank.

Yes to above. Lots of good info here. If you have compression, the fuel and spark events are happening when they should combustion should occur.

 

[canttouchthis]

Just throwing this out there but could there be a major vacuum leak leaning out those 4 cylinders.

With the fact that it happened all at once, you would not think it would be injectors or coils. Another thing with a busted cam is it may still operate the valves if it broke crooked but it would be out of time enough to not fire those cylinders. I have seen an engine run on a busted crank. Usually it makes a knocking noise. I have never seen 4 components fail at the same time. Maybe I missed it but you did check compression on all cylinders right?

 

[Kingsize]

What Konnie said, also look into cracked reluctor wheel, and/or ground fault, or no ground to those circuts.

Seems to be alot of reluctor wheel failures as of late with similar symptoms, or symptoms at high rpm.

 

[MM Alexander]

At this point I would start diagnosing wiring issues or possibly a bad ECM. Its odd that its just half of two banks...usually wiring issues take out a whole bank.

At this point, I highly doubt it's a computer or wiring issue. The injectors aree receiving the 12V pos from the battery and the neg pulse from the computer. The injectors all work correctly (have been tested off the car and have been swapped around).
So the computer is getting the feedback it needs from other sensors to tell the injectors to fire.

Yes to above. Lots of good info here. If you have compression, the fuel and spark events are happening when they should combustion should occur.

Yeah, but now I'm quite sure the missing ingredient in the chain is the fuel.

Just throwing this out there but could there be a major vacuum leak leaning out those 4 cylinders.

Not a one ... One of the things i like about the LSx motor is the simplicity of it ... including the minimal amount of vacuum connections/hoses.

With the fact that it happened all at once, you would not think it would be injectors or coils.

Coils are fine (tested twice with my inline spark checker).

Another thing with a busted cam is it may still operate the valves if it broke crooked but it would be out of time enough to not fire those cylinders. I have seen an engine run on a busted crank. Usually it makes a knocking noise. I have never seen 4 components fail at the same time. Maybe I missed it but you did check compression on all cylinders right?

No knocking or any unusual noises. The car runs and drives (although not correct) especially once you get the RPMs up past 2300 (enough rpm to "mask" the dead cylinders) .
The only normal/logical check I haven't performed is that of a fuel pressure check. NEVER have I had a fuel pump slowly die that didn't moan and groan first. Nor have I ever heard of one being weak and causing half the motor supply side (injectors) to not fire or fire anemically. But ... you never know I guess.

 

[05 red tomcat]

i lost several cilinders about a year ago ,but it moved and was different cilinders .
one whole cill head ,then 4 cils randomly. i swaped coils from side to side , i finaly took the grounds off both heads sanded the head a little and put them back on ,problem is gone now for a year. the left side ground is on the back of the head ,a ratchet wrench works best .


http://www.ls1gto.com/forums/showthread.php?t=358820