Need Help Diagnosing Poor Running

[Vettezuki]

Took the Vette out tonight to go to the gym. It sounded funny, and was WAY down on power. I'm guessing a couple, maybe few cylinders are not firing. However, the check engine light did not come one. If so the cylinders in question are either not getting spark or fuel, or both. For those who don't know my Vette, it's a Frankstein H&C LSx motor setup basically like a 2001 F Body.

[Damian]

Id check the plug wires.

[94cobra69ss396]

Id check the plug wires.

Same here. This is the same issue I just went through with the Cobra. Check to make sure that none of the wires are sitting on the exhaust. Another way to check if the plug wires are arcing is to get a spray bottle and fill it with water. Pull your car in the garage where it's a little darker and lightly spray water mist near the wires. If any are bad you'll see the spark arc through the mist.

If the wires are fine pull the plugs and make sure the porcelain looks good. When we were putting the 383 in Phil's Jimmy we had one plug that the porcelain was loose and it was arcing causing a misfire. You couldn't tell it was loose by looking at it but when you held it you could feel it.

[Vettezuki]

Thanks guys. I'll check this out tomorrow afternoon and report back.

[SeanPlunk]

Thanks guys. I'll check this out tomorrow afternoon and report back.

Paul said two other possibilities would be a bad coil pack, or clogged cats.

[Vettezuki]

Paul said two other possibilities would be a bad coil pack, or clogged cats.

The packs and cats came off fairly high mileage cars, so definitely a possibility. I wondered about that too. :huh:

[Damian]

It would be nice if you could get a CEL to help narrow things down to a single cylinder, or two. Also, Id check your fuel pressure. Maybe your not misfiring, maybe starving your engine of fuel and/or air? My GTO was running like crap without a CEL (bad fuel pump), so I went on the freeway and put the petal to the floor until I got a CEL. Granted mine is under warranty still, so that may be an iffy way to pop a CEL light for you.

[joedls]

I think I remember you saying you use an octane booster. Octane booster has been known to foul plugs. You might wanna pull your plugs and check them.

[Vettezuki]

Well, what do you think? Click on pic for gory details. I only pulled No. 1.

http://motorgen.com/pic/data/500/DSC_0022.JPG

Plug wires themselves are pristine, are not in contact with exhaust and have heat shields to boot. These plugs only have only about 9,000 miles them from when the motor was put together. This includes tuning period which included many gnalry AFR passes. And yes, I run a small amount of Torco, Mach Fuel Accelerator.

These were not cheap plugs, AC Delco Iridium.

[joedls]

I would bet that is your octane booster causing that.

[Vettezuki]

I would bet that is your octane booster causing that.

Is that plug dead and gone? In other words, should I suspect plugs as the cause of my problem?

Next question, money no object (plugs aren't all that much) what is the best choice for my application? Mid-high compression somewhere in the 11.x:1, all motor.

[SeanPlunk]

Is that plug dead and gone? In other words, should I suspect plugs as the cause of my problem?

Next question, money no object (plugs aren't all that much) what is the best choice for my application? Mid-high compression somewhere in the 11.x:1, all motor.

I have NGK TR6's on the Cobra. They've been great so far.

[joedls]

Is that plug dead and gone? In other words, should I suspect plugs as the cause of my problem?

Next question, money no object (plugs aren't all that much) what is the best choice for my application? Mid-high compression somewhere in the 11.x:1, all motor.

Yes, that orange color is exactly what I've heard others have experienced with octane booster. I don't know what plugs are best for your application.

[Vettezuki]

I have NGK TR6's on the Cobra. They've been great so far.

I'm sorry. Your' title and avatar are a little distracting. . . :lmfao:

Thanks for the tip though.

[SeanPlunk]

I'm sorry. Your' title and avatar are a little distracting. . . :lmfao:

Thanks for the tip though.

I hate all of you :lmfao:

[94cobra69ss396]

Is that plug dead and gone? In other words, should I suspect plugs as the cause of my problem?

Next question, money no object (plugs aren't all that much) what is the best choice for my application? Mid-high compression somewhere in the 11.x:1, all motor.

I just run regular Autolites in both the Chevelle and the Cobra.

[Vettezuki]

I just run regular Autolites in both the Chevelle and the Cobra.

Anything about temp range, etc.?

[Leedom]

I'm sorry. Your' title and avatar are a little distracting. . . :lmfao:

...... nuf said!

[94cobra69ss396]

Anything about temp range, etc.?

For the Chevelle I'm using the ones for a 1967 427 Covette because it came factory with 12.5:1 compression and they were the only ones I found that didn't protrude too far into the chamber to the point that it hit the piston. On the Cobra I'm running 1 step colder plugs than what came on it stock. I also modify the ground strap by rounding the sharp edges just to be on the safe side. The Cobra is right on the edge of pinging so I don't leave anything to chance.

[Vettezuki]

For the Chevelle I'm using the ones for a 1967 427 Covette because it came factory with 12.5:1 compression and they were the only ones I found that didn't protrude too far into the chamber to the point that it hit the piston. On the Cobra I'm running 1 step colder plugs than what came on it stock. I also modify the ground strap by rounding the sharp edges just to be on the safe side. The Cobra is right on the edge of pinging so I don't leave anything to chance.

Do you mean like a gentle de-burring of the strap or an actual rounding of the edges? Also, exactly what problem does that solve?

[joedls]

Do you mean like a gentle de-burring of the strap or an actual rounding of the edges? Also, exactly what problem does that solve?

Sharp edges in the cumbustion chamber create hot spots and promote detonation.

[94cobra69ss396]

Sharp edges in the combustion chamber create hot spots and promote detonation.

Exactly.

[BRUTAL64]

Well, what do you think? Click on pic for gory details. I only pulled No. 1.

http://motorgen.com/pic/data/500/DSC_0022.JPG

Plug wires themselves are pristine, are not in contact with exhaust and have heat shields to boot. These plugs only have only about 9,000 miles them from when the motor was put together. This includes tuning period which included many gnalry AFR passes. And yes, I run a small amount of Torco, Mach Fuel Accelerator.

These were not cheap plugs, AC Delco Iridium.

So what did you find?

[Vettezuki]

So what did you find?

Well, I guess that plug was toast. I'll replace them and see what happens.

[BRUTAL64]

Well, I guess that plug was toast. I'll replace them and see what happens.

The limit of miles on "regular" plugs (with high compression) is 6,000 to 10,000 miles. Now your fancy type plugs you have should have gone longer before breaking down.

[Vettezuki]

The limit of miles on "regular" plugs (with high compression) is 6,000 to 10,000 miles. Now your fancy type plugs you have should have gone longer before breaking down.

Is that primarily because of the high combustion temps?

[BRUTAL64]

Is that primarily because of the high combustion temps?

Actually has to do with pressure. The higher the compression the higher the cylinder pressure the harder to jump the gap for the spark. Temp is secondary here, unless you go lean and spike the temp and melt the plugs and pistons.:boggled:

[Throttle Crazy]

Is that plug dead and gone? In other words, should I suspect plugs as the cause of my problem?

Next question, money no object (plugs aren't all that much) what is the best choice for my application? Mid-high compression somewhere in the 11.x:1, all motor.

Give my friends Chris or Bruce over at Custom Built Motors in Rancho Cucamonga a call. They specialize in building LSX motors from mild to wild. 1700 Hp. They also do all there own installs, programming and dyno runs. If you ever need Ls parts these guys have a ton laying around. They build alot of sand car stuff but also do cars, trucks and boats.http://www.cbfunforyou.com/

[Vettezuki]

Give my friends Chris or Bruce over at Custom Built Motors in Rancho Cucamonga a call. They specialize in building LSX motors from mild to wild. 1700 Hp. They also do all there own installs, programming and dyno runs. If you ever need Ls parts these guys have a ton laying around. They build alot of sand car stuff but also do cars, trucks and boats.http://www.cbfunforyou.com/

Can they do exhaust in house? Maybe they can hook me up with some headers and install them on site when the time comes. I'll have some tricky fitment issues putting LS headers in a C3 body.

[enkeivette]

I'm with Joe, I remember reading that reddish plug is caused by the type of fuel. The fouled plugs is likely the cause of the slower acceleration.

Another advocate for the cheap Autolites, copper conducts better than platinum. Then again, platinum resists fouling better. Which might do well for you.

If your wires are burned though to the headers and are arcing, you'll feel a rougher acceleration. If you have an intake manifold leak or some sort of stuck lifter problem, the exhaust will prob sound different. From my experience.

If it feels the same just slower, and your fuel filter is not clogged, prob just bad plugs. I doubt your cats are clogged. Your motor is clean and that would happen slowly over time, not noticeably and all of a sudden.

[enkeivette]

Also, your comp needs to see the error so many times before it will throw a code. So if the plugs don't fix it, keep driving it, you'll see the code sooner than later.

[Vettezuki]

Also, your comp needs to see the error so many times before it will throw a code. So if the plugs don't fix it, keep driving it, you'll see the code sooner than later.

Like these?
http://www.summitracing.com/parts/FRM-5245/?image=large

At that price I could just change them with the oil.

[enkeivette]

Like these?
http://www.summitracing.com/parts/FRM-5245/?image=large

At that price I could just change them with the oil.

Yuppers. You might want to go a few steps colder if you have problems with pinging.

I run the... 3923s I think.

[Vettezuki]

BTW, Wolfram Alpha is one of the coolest information engines on the interwebs.

http://www22.wolframalpha.com/input/?i=copper+vs.+iridium+vs.+platinum

[enkeivette]

If those are your plugs I would guess that 5244 would be one step colder, 5243 two steps.

[Vettezuki]

If those are your plugs I would guess that 5244 would be one step colder, 5243 two steps.

Nothing with those numbers. . . :huh:

[enkeivette]

Nothing with those numbers. . . :huh:

Jump on LS1forum or call Autolite then. My plug numbers were sequential.

[Damian]

Im running the NGK TR-55s in the GTO amd I love them. i changed them out at 45k and noticed better throttle response over the factory ACDelcos. I recommend those.

Also, what gap are you running?

[Vettezuki]

Im running the NGK TR-55s in the GTO amd I love them. i changed them out at 45k and noticed better throttle response over the factory ACDelcos. I recommend those.

Also, what gap are you running?

.040 is stock.

My AC iridiums were toast at less than < 10k miles. I think I'll try the AutoLite and just check them with each oil change and see how that goes.

[Vettezuki]

Jump on LS1forum or call Autolite then. My plug numbers were sequential.

I used this guide:
http://www.power-21.com/AutolitePower21i/RelatedInfo.aspx?b=A&f=Autolite/Plugs/HeatRange/ASP2009AutoliteHeatRange.pdf

One colder for the 5245 is 5144. Go figr. I'll give these a whirl.

[94cobra69ss396]

Yuppers. You might want to go a few steps colder if you have problems with pinging.

I run the... 3923s I think.

I believe the 3923 is what I installed in the Cobra.

[94cobra69ss396]

Like Phil suggested give Chris or Bruce over at Custom Built Motors a call (909) 390-9130 and tell them what happened and what you have done to the engine. Then see what plug and gap they suggest. Make sure you let them know that Phil Cooper referred you to them. It will only take you 10 minutes to call them and then you'll have an answer from the experts.

[Vettezuki]

Didn't catch your post till now Ron. But I ordered and installed a set of Autolite 5144 (colder version of 5245, OEM replacements). Gapped .040, OEM gap.

This ain't the problem. It did the same thing and this time intermittently while driving a little bit. I'm confident the plugs and wires are ok. The problem is packs or earlier. Tonight it did flash the CEL while on the freeway, then went out. There was no difference in driving response (poor) before during an dafter the CEL. Unfortunately we can no longer check out scanners. :mad:

[Vettezuki]

Well finally made it over to ls1z28's to do a Tech II scan, etc.

Fuel Pressure: ok at around 58~psi

Scan shows #8 missing quite a bit. Turns out to be an injector sticking. I think all he did was check that it was firing, probably a little bit of a continuity problem. :huh: Then I put in a can of Sea Foam in the tank (that stuff has got me out of a couple binds) and she purs like a kitten again. Many thanks Paul!

When I have spending money again, I'm going to get a flow matched set from our pals at InjectorsPlus.

[enkeivette]

:thumbs_up:

[94cobra69ss396]

Well finally made it over to ls1z28's to do a Tech II scan, etc.

Fuel Pressure: ok at around 58~psi

Scan shows #8 missing quite a bit. Turns out to be an injector sticking. I think all he did was check that it was firing, probably a little bit of a continuity problem. :huh: Then I put in a can of Sea Foam in the tank (that stuff has got me out of a couple binds) and she purs like a kitten again. Many thanks Paul!

When I have spending money again, I'm going to get a flow matched set from our pals at InjectorsPlus.

How many miles do you have on your injectors?

[BRUTAL64]

Glad to hear you have fixed the problem. Now BACK in the day, we used ATF to clean injectors.:jester:

[Vettezuki]

How many miles do you have on your injectors?


Miles from origianl owner plus 8~k. WELL below 100K, which is the service life of most GM parts.

[D.denly]

one of the easiest things to install and you need help?

you dont deserve that srt-4/.....gimme it to me

[BADDASSC6]

Back in my supercharged mustang days I used to keep a code scanner in the car with me. It will tell you there is an issue and which cyylinder(s) are miss firing even before there is a check engine light.

I also run the NGK Iridium in the vette, but I ran the Autolite copper plugs in hte mustang.