Generation IV External Engine - LS2 120 RWHP loss

Hi,
I have an LS2 ( all mods in sig) Dynoed at 535 RWHP. After about 2 weeks or so I knowticed some power loss but wasn't sure because I don't drive it much. Maybe 2 or 3 times a month. brought it back to the dyno to find that it was down to 410 RWHP. the computer said that #6 spark plug was skipping. also the tune was rich. do you think it could be that the spark plugs are fowled or something?

I will be doing a compression test next weekend.
What else could it be?

HELP!!!!!!!
Al

Replace the spark plug and reduce the amount of flow at the fuel pump. Sometimes it takes a little while for an engine to get "Broke In," and the fuel pump could've just started for that very reason.

Replace the spark plug and reduce the amount of flow at the fuel pump. Sometimes it takes a little while for an engine to get "Broke In," and the fuel pump could've just started for that very reason.


Do you realy think that one spark plug could cause the motor to loose 120 Hp?
What do you mean reduce the flow on the pump? it is dyno tuned to 11.5 AFR give or take approx .3

Pull the plugs first, that will let you know a lot. That said 120 HP is a lot to lose, sounds like a cylinder or 2 isnt firing.

And maybe a boost leak too.

Is your car M6, it could be a slipping clutch under WOT conditions.
Any funny smell after you go WFO on the throttle?

Pull the plugs first, that will let you know a lot. That said 120 HP is a lot to lose, sounds like a cylinder or 2 isnt firing.

And maybe a boost leak too.

The guy that dynoed it said that 3 and 6 ware skipping but 6 was real bad.

Is your car M6, it could be a slipping clutch under WOT conditions.
Any funny smell after you go WFO on the throttle?

No it is a 99 SS camaro.
But you bring up a valid point about the clutch slipping. no smells but it has a kevlar clutch and may not smell if it slipps, not sure.
The clutch has about 2500 - 3000 k on it should be ok
we did put it under load on the dyno and it was consistant so I will have to think about this one more

Is your car M6
No it is a 99 SS camaro.

lol M6 = Manual 6-Speed

not BMW M6

A BMW M6 with an LS2 would be sweet though

well obviously if 2 cylinders arnt firing correctly its not gonna produce as good HP correct? change plugs check wires and possiably coilpack

sounds like 2 cylinders are out...

something is down-120 is a lot to loose with just plugs-

well obviously if 2 cylinders arnt firing correctly its not gonna produce as good HP correct? change plugs check wires and possiably coilpack

What is the procedure to check the coil packs? do I just ohm them? if so, what should they ohm? also what should the wire ohm out to?

lol M6 = Manual 6-Speed

not BMW M6

LOL!

:bang:

check the plug wires and plugs. Ive had wires pop off the plug and believe it or not, one plug not firing will cause you to loose 100+ hp. think about it, you have 7 cylinders dragging one dead cylinder. :D

Hi,
I have an LS2 ( all mods in sig) Dynoed at 535 RWHP. After about 2 weeks or so I knowticed some power loss but wasn't sure because I don't drive it much. Maybe 2 or 3 times a month. brought it back to the dyno to find that it was down to 410 RWHP. the computer said that #6 spark plug was skipping. also the tune was rich. do you think it could be that the spark plugs are fowled or something?

I will be doing a compression test next weekend.
What else could it be?

HELP!!!!!!!
Al

Math lesson - 535hp/8 cyl = 67hp/cyl x 2= 134hp loss.
So if 2 plugs arent doing there job you can lose substantial power. Not only do you lose power production, but the other cyl now have more load to handle, so they become less efficient also.
Since they fire on occasion you are not getting the full loss, but it is a big loss no matter what.
Good luck!

Math lesson - 535hp/8 cyl = 67hp/cyl x 2= 134hp loss.
So if 2 plugs arent doing there job you can lose substantial power. Not only do you lose power production, but the other cyl now have more load to handle, so they become less efficient also.
Since they fire on occasion you are not getting the full loss, but it is a big loss no matter what.
Good luck!

Thanks for the info.
Yes I had figured this out, just didn't post it

Do you realy think that one spark plug could cause the motor to loose 120 Hp?
What do you mean reduce the flow on the pump? it is dyno tuned to 11.5 AFR give or take approx .3

I don't think so. 535rwhp/8 = 66.88 or 630bhp/8 = 78.75
Each cylinder is making approximately 78.75hp.

I don't think so. 535rwhp/8 = 66.88 or 630bhp/8 = 78.75
Each cylinder is making approximately 78.75hp.


Can you explain this to me? I don't get the jump from RWHP to BHP. Are you talking 630*.85 = 535.5? and are you talking 630 BHP at the crank now.

Forget all the stupid calculations, just have your plugs, wires, and coilpacks checked. To check the wires and packs all you really have to to to pull one wire off the plug when the engine is running and hold the end of the wire up to some metal on the motor, you should see the spark arc across the wire and jump to the engine. I would just go ahead and replace the plugs though.

If all the checks ok then do a compression test.

Forget all the stupid calculations, just have your plugs, wires, and coilpacks checked. To check the wires and packs all you really have to to to pull one wire off the plug when the engine is running and hold the end of the wire up to some metal on the motor, you should see the spark arc across the wire and jump to the engine. I would just go ahead and replace the plugs though.

If all the checks ok then do a compression test.

Ya now I know you have lost it.
You want me to pull the coil wire off, while the car is running.
Don't you think that the spark is going to jump to whatever ground it can find?
Including me if I am the least path of resistance.
There must be a safer way to check the coil than this method.

something is down-120 is a lot to loose with just plugs-

I lost over 100rwhp with 1 plug... but im running a bit more boost then he is.

Misfires could be a variety of things: plugs, plug wires, bad coil, clogged injector. These things can be checked by the process of elimination. But a cylinder misfiring can cause your O2's to read a lean condition, then adds more fuel to make the other cylinders too rich, losing even more power.

It is not crazy to pull a plug wire off while the car is running to see it misfire.

Misfires could be a variety of things: plugs, plug wires, bad coil, clogged injector. These things can be checked by the process of elimination. But a cylinder misfiring can cause your O2's to read a lean condition, then adds more fuel to make the other cylinders too rich, losing even more power.

I had a simular though but mine was that if the cylindar missfired it was not burn the fuel causing a rich mixure at the O2. then the O2 would compinsate by leaning it out. but wouldn't this cause the light to come on at the dash?
not sure just a thought.

It is not crazy to pull a plug wire off while the car is running to see it misfire.

You can also use a test probe, connected to a ground, and make a small poke through the plug boot to see if the plug is firing or not. If the idle drops and hunts, that plug is firing. If it doesn't change at all, that plug wasn't working in the first place. GL!

You can also use a test probe, connected to a ground, and make a small poke through the plug boot to see if the plug is firing or not. If the idle drops and hunts, that plug is firing. If it doesn't change at all, that plug wasn't working in the first place. GL!


poking holes in boots = not such a great idea. You could always just go to NAPA or advance auto parts, or autozone or wherever and by a 3 dollar spark tester. It just plugs into the end of your boot like a spark plug and then clips onto some ground. You adjust it for the proper gap you want, and crank the car and voila. If it arcs the gap you have spark so the coil/wire combo is good. If it doesnt, change it with a different wire, if still no spark coil and or coil power/ground is bad. If it has spark and that cylinder is misfiring, you have either a fuel injector issue, or a bad spark plug. very simple, very cheap diagnosis without dumb math calculations or just buying new everything until you've spent $200 and still have a damn misfire.

poking holes in boots = not such a great idea. You could always just go to NAPA or advance auto parts, or autozone or wherever and by a 3 dollar spark tester. It just plugs into the end of your boot like a spark plug and then clips onto some ground. You adjust it for the proper gap you want, and crank the car and voila. If it arcs the gap you have spark so the coil/wire combo is good. If it doesnt, change it with a different wire, if still no spark coil and or coil power/ground is bad. If it has spark and that cylinder is misfiring, you have either a fuel injector issue, or a bad spark plug. very simple, very cheap diagnosis without dumb math calculations or just buying new everything until you've spent $200 and still have a damn misfire.

Well So far I like this option the best.

Ok so I have changed the spark plugs, tested the spark and did a compression check. The spark plugs are gapped at .040 and the compression was 128 - 135 cross all cylinders. I did find a missing vacuum hose but the car still doesn't pull as hard as it used to. What do I check from here?
Thank
Al

well first off, i don't understand how you have all the stuff done to your car but you don't even know how to check for spark.

but anyways why is your gap so small? on all my supercharged cars I ran ~.053

do you have a boost gauge? are you still getting 10 psi??

how about your meth. is it still spraying? if your getting KR you will loose quite a bit of power. I have had grounds go bad where it says I'm spraying but no fluid is coming out.

also when you pulled the plugs, was #6 damaged at all? was the electrode bent or at a different gap from what you set it?

<Off topic>
It's funny, I've seen people pull plug wires off the car while running 100 times, but I'm still too pussy to do it. :lol: :emb:

Maybe Z Angel or some other car chick should post a pic of herself with an arching wire in her hand with a caption, "Just do it, wussy!" :lol:
</off topic>

<Off topic>
It's funny, I've seen people pull plug wires off the car while running 100 times, but I'm still too pussy to do it. :lol: :emb:

Maybe Z Angel or some other car chick should post a pic of herself with an arching wire in her hand with a caption, "Just do it, wussy!" :lol:
</off topic>

Yes I agree
You are waaaaay off the topic
:offtopic:

Ok so I have changed the spark plugs, tested the spark and did a compression check. The spark plugs are gapped at .040 and the compression was 128 - 135 cross all cylinders. I did find a missing vacuum hose but the car still doesn't pull as hard as it used to. What do I check from here?
Thank
Al

That .040 gap is too much with a boosted motor. I'd tighten the gap to .025 or at least .030 I think thats your trouble, alot of boost and not enough voltage at the plug results in a spark that is virtually blown out when your boostin on it.

Good luck to ya...

That .040 gap is too much with a boosted motor. I'd tighten the gap to .025 or at least .030 I think thats your trouble, alot of boost and not enough voltage at the plug results in a spark that is virtually blown out when your boostin on it.

Good luck to ya...

Thanks for the reply
The thing that I don't under stand is, it worked just fine before. something has changed but I'm not sure what? Just trying to get some insight on what to look at
thx
Al

That .040 gap is too much with a boosted motor. I'd tighten the gap to .025 or at least .030 I think thats your trouble, alot of boost and not enough voltage at the plug results in a spark that is virtually blown out when your boostin on it.

Good luck to ya...

I run 0.35 gap in My plugs & Have no issues @ all with my boosted motor

I also found this
http://www.ls1tech.com/forums/showthread.php?t=443369
But I'm running 10 PSI boost so I need to go smaller gap.

Yes I agree
You are waaaaay off the topic
:offtopic:As was your post there. As is this post here.

Guess you're just sour since you're a pussy too.

another method of testing spark is a using a -spark tester-
sold at autozone for less than 5$
connect spark plug wire to spark tester instead of spark plug-
displays a spark arc encapsualted in glass chamber
if no spark then coil is bad

I had a simular though but mine was that if the cylindar missfired it was not burn the fuel causing a rich mixure at the O2. then the O2 would compinsate by leaning it out. but wouldn't this cause the light to come on at the dash?
not sure just a thought.

a o2 sensor does not read fuel. it wiil read the unburnt AIR in the exhaust and correct by trying to add fuel thus making the condition worse. none of that matters anyway cause at WOT it is in open loop not reading the sensors anyway. i would pull the valve covers and check for a broken spring since the ignition and compression are checking out.