Compression past spark plug.

[The Devils Own Chariot]

I know this question may be really hard for you to answer.
I cross threaded a plug on the head closest to the driver. Dont ask me how because I couldnt tell ya.
I re tapped the hole and the plug seems to fit in there very snug. It took me a bit to get it tapped all the way. Before I got it tapped I used a hose to hear if the compression was pushing past the plug. It was.
Like I said I got it tapped all the way in. The plug goes in harder than the rest but it seats. I can hear no leaking around the plug at idle. At least from what I can hear with the hose to the plug and to my ear.
The truck runs great until after 20psi and it started to miss really bad. I’m wondering if it’s that spark plug. Is it possible compression does not leak past it until 20 psi? I never had this issue until that plug got crossed.
It’s not the gap. Plugs gapped to .025
It’s not the plug. Tried CR42TS and CR43TS ACDELCO
Tried new plug wires. No change
Checked the cap and rotor, looks great no black marks
The plug in the cross threaded cylinder looks brand new after operation.
Datamaster shows no codes.
Stock injectors are at 120% DC

Help!

 

[dgoodhue]

Re: Compression past spark plug.

I know this question may be really hard for you to answer.
I cross threaded a plug on the head closest to the driver. Dont ask me how because I couldnt tell ya.
I re tapped the hole and the plug seems to fit in there very snug. It took me a bit to get it tapped all the way. Before I got it tapped I used a hose to hear if the compression was pushing past the plug. It was.
Like I said I got it tapped all the way in. The plug goes in harder than the rest but it seats. I can hear no leaking around the plug at idle.

If you want to test for an air leak. I would use one of the spark plug fittings that connect to compressed air AThe ones often used to hold the valves up with changing springs/valve seales). Fill the cyclinder up, turn off the compressor and listen for an air leak around the plug You might have to unbolt the valve cover and disconnect the rockers. I have also found sometimes you have to whack (hammer) the valves for them to completely seal with the deposits over time.

My friend tried what you did on 4 cylinder (not a boosted motor) and his plug came flying out and dented his hood

 

[Bill Z]

Re: Compression past spark plug.

Please allow me my 2 cents.

To properly test to see if the plug is leaking compression is difficult, however I have been somewhat successful by taking ½ children’s bubble soap and ½ water. Applying the soapy water around the plug snug in the hole on a cold engine. Starting the engine up and watch for bubbles. You have to look and find the bubbles before the heads get too hot or it cooks out the soap. You may have to block the breeze from the fan from blowing on the plug.

Give it a try and let us know.

 

[dgoodhue]

Re: Compression past spark plug.

Please allow me my 2 cents.

To properly test to see if the plug is leaking compression is difficult, however I have been somewhat successful by taking ½ children’s bubble soap and ½ water. Applying the soapy water around the plug snug in the hole on a cold engine. Starting the engine up and watch for bubbles. You have to look and find the bubbles before the heads get too hot or it cooks out the soap. You may have to block the breeze from the fan from blowing on the plug.

Give it a try and let us know.

That is a good idea. At my work we test our sensor probes for leaking that way.

 

[The Devils Own Chariot]

Re: Compression past spark plug.

Please allow me my 2 cents.

To properly test to see if the plug is leaking compression is difficult, however I have been somewhat successful by taking ½ children’s bubble soap and ½ water. Applying the soapy water around the plug snug in the hole on a cold engine. Starting the engine up and watch for bubbles. You have to look and find the bubbles before the heads get too hot or it cooks out the soap. You may have to block the breeze from the fan from blowing on the plug.

Give it a try and let us know.

I can give that a try. Sure seems like it only acts up at high boost. Thanks for the info guys.

 

[The Devils Own Chariot]

Re: Compression past spark plug.

Did the soap test. Did not see any leaking. Now what? Think probelms on high boost only and it has to be warmed up.... I dont understand!

 

[MikeRenz]

Re: Compression past spark plug.

do you have a datamaster log to look at? I wonder if you're just running out of fuel.

 

[sy#2716]

Re: Compression past spark plug.

Mike that is what i was just thinking becasue his duty cycle is at 120% and that means they are sautrated. I would change injectors and see if that helps out any.

 

[Quickstop [UK]]

Re: Compression past spark plug.

why not just try a compression test on the cylinder? If it is way down then you know you've got a leak.

I doubt it's your plug though.

 

[ryanman]

Re: Compression past spark plug.

120% DC, holy shit man!!! Buy some MUCH bigger injectors, lol.

 

[The Devils Own Chariot]

Re: Compression past spark plug.

AFR is 11 at 25 psi. Im sure the injector are running out but the alky is making up for it. Im using the alky as fuel. The truck also goes rich like its not firing. For example the AFR is 11 and then drops to 10 when it starts breaking up. I do have 50# injectors but I cant tune for those yet. I dont have the knowledge yet or the equipment. I do have Datamaster but its not telling me anything.

 

[MikeRenz]

Re: Compression past spark plug.

how much timing @ 20psi

if it's breaking up at 20psi...why are you staying in it to get to 25psi?

why are you even allowing yourself to run 25psi on a stock motor?

 

[The Devils Own Chariot]

Re: Compression past spark plug.

how much timing @ 20psi
if it's breaking up at 20psi...why are you staying in it to get to 25psi?
why are you even allowing yourself to run 25psi on a stock motor?

Whats wrong with 25psi on the stock motor? I have an upgraded turbo that flows 65 lbs/min and is efficient to 30 psi. I have an AFR of 11 and 15 deg of timing no KR intake temps at 80 deg. The truck only made 255 whp at 18 psi. I dont think 25 psi is making dangerous Hp levels. Maybe 300 whp or 350 whp at most. I thought Jeremy ran 11.9 on 30 psi with the stock turbo and built tranny?
I can get a few runs in at 25 psi before it gets fully warm and it just sings. After like three pulls it acts up. Like its heat realted. Is it possible the ultimate is shutting me down? Its not killing fuel its killing spark from what I can tell.

 

[SCWolverine]

Re: Compression past spark plug.

Have you tracked temps from run to run?

Nothing wrong with 25#, unless you're breaking up at 20#.

 

[The Devils Own Chariot]

Re: Compression past spark plug.

Have you tracked temps from run to run?

Nothing wrong with 25#, unless you're breaking up at 20#.

Its breaking up rich after 20 from what I can tell. My engine temps get well into the 200's if I dont let it cool down between runs. The FMIC is restricting cooling and I need to get electric fans that pull more. Running a 160 stat. Might go back to the clutch fan.

 

[WyoSyclone]

Re: Compression past spark plug.

I'm no expert at running Alky..although I'll be installing Julio's kit soon....
Question...
If you're running at 120% injector DC at high rpm/wot, is it probable that you're transitioning from firing a mainly gasoline mixture, to one of firing a mainly alcohol mixture? I would imagine the spark/ignition system requirements to properly fire each mixture are quite different.
If your gasoline/alcohol mixture remained in the same ratio to one another throughout the run it's probably that you may not see the breakup??

...just a thought.... if you can follow it!

 

[MikeRenz]

Re: Compression past spark plug.

The truck only made 255 whp at 18 psi.

pretty sure people make more than that with the stock turbo @ 18psi.

What alky setup do you have? How's it regulating how much alky to dump in?

You're running an ultimate chip that is programmed for not your build. IMO it'd make more sense to get yourself some 50 or 65# injectors and a tune to go with it...rather than bandaiding yourself by dumping in alky to make up for your injectors not keeping up.

Also have you tried opening your gaps to maybe .27? .25 sure seems tight..maybe you just aren't having enough spark to keep up

 

[bezerk]

Re: Compression past spark plug.

i think if you only made 255. you got to begin at lower boost again. and tune it your way up without extra boost, now you are adding boost and ''try'' to tune it. it's the other way around.

 

[The Devils Own Chariot]

Re: Compression past spark plug.

Well first off. The 255 whp was made on a dyno dynamics AWD dyno. If I was to go to a dyno jet like everyone else it makes 300 whp and 400 ft/lbs of tq. I'm sure thats what the majority of the dyno runs are on. That number is severely inflated on a dyno jet. Around 18 to 25% inflated on a dynojet.
http://forums.nasioc.com/forums/showthread.php?t=286440

 

[gkrcr882]

Re: Compression past spark plug.

IIRC, anything past 80% DC and the injectors are essentially flowing all the time. 120% DC? Time for bigger injectors and some good tuning for them. In order to make power with the amount of air you're (attempting) to cram through the engine, you need the fuel to do it. Even if the A/F ratios are correct, something doesn't add up.