Possible motor knock

[Black2003Vert]

First problem I had was my motor blew off sparks plug tips off of cyl 2 and 4. Replaced the plugs, then my motor would not do faster than 140 mph. Had the car retuned and they said it was misfiring. I had either one or two coil packs bad. Installed granatelli coil packs, took car for a ride and it wouldnt do faster than 120 mph. Started misfiring, brought it home. #2 cyl blew tip off plug again. Last two days motor started knocking for first couple of minutes when you start vehicle then go's away. Did a compression test again and all cyl's are good. Any ideas?

 

[Buds03Cobra]

What si you Fuel PSI?
Sound like your lean.
Bad pump?
Filter cloged?

I would think injectors are good because it random. I would watch fuel PSI

 

[Black2003Vert]

Why would this make the motor knock if it fuel? I just had the car retuned about two weeks before the knock started and they said that the fuel was extremely lean. They did richen it up.

 

[HISSMAN]

A lean condition is the most common cause of knock on these cars. Of the two main things that cause pre-detonation the fuel trim is the most common because setting correctly the timing is much easier.

-Jeff

 

[03CobraEG]

First problem I had was my motor blew off sparks plug tips off of cyl 2 and 4. Replaced the plugs, then my motor would not do faster than 140 mph. Had the car retuned and they said it was misfiring. I had either one or two coil packs bad. Installed granatelli coil packs, took car for a ride and it wouldnt do faster than 120 mph. Started misfiring, brought it home. #2 cyl blew tip off plug again. Last two days motor started knocking for first couple of minutes when you start vehicle then go's away. Did a compression test again and all cyl's are good. Any ideas?

damn dude, that is crazy, my car is doing the same shit, but i put brand new plugs and coil packs in my car, all 8. then i pullied it and got a tune, but its always been missfiring, then i pulled the plugs cause missfire got real bad...#3 cyl spark plug tip was broken and some of the porcelain was broken too, and then my car started having the head tick problem, from what i think it is, cause it does the tick 24/7 never goes away... sounds like a knock, and my car right around 120mph its stops pulling, rpms will not move in 4th gear...

so im pulling the head off soon to see what the problem is, hopefully its not a knock....but i still dont know why my car miss fires...

 

[03CobraEG]

Why would this make the motor knock if it fuel? I just had the car retuned about two weeks before the knock started and they said that the fuel was extremely lean. They did richen it up.

you found anything out???

 

[WDW MKR]

Stop beating on the car until you get to a dyno and verify WOT A/F and timing.

The cold-start noise may just be piston slap common with forged aluminum pistons, but damaging those plugs is a definite sign of pre-ignition detonation. I would lean towards the latter due to only damaging the plugs. Pre-ignition can be a lot more violent.

 

[Black2003Vert]

The car sat at home for a week or so. Towed it out to Henderson performance in New braunfels where Bryan did a boroscope test. Found #2 cyl. swimming in oil.

 

[virginiafiveo]

ouch....that sucks bro...what happened to cause that? blown out rings?

 

[Black2003Vert]

I pulled toe motor in my garage. It's down to bare block. There was no oil in the cyl.'s just melted pistons. I guess I leaned out the motor. Seven out of eight were melted. One had a ring snapped in two, and another had the ring melted to the piston.
Which pistons should I go with and should I do thirty over on the block?

 

[01cobravortech]

Man 7 of 8 pistons melted? Wow. I'm still knew to the 03 Cobra scene and getting to know my Cobra but I can't hear anything above the loud supercharger whine. If you were hearing any knock above the loud ass whine then its comforting to know that knock can be audible if there is a serious tuning or A/F related issue. Just curious...did you have the cooling mod on the driver head. I know its not the cause of your piston failures but just wondering how you're finding the balls to do what appears to be several 140mph runs on the Cobra?

 

[Black2003Vert]

I have not done this since my car started acting up. It was later after I had the car retuned that the motor started knocking. Thanks Murillo motorsports.

 

[WDW MKR]

I pulled toe motor in my garage. It's down to bare block. There was no oil in the cyl.'s just melted pistons. I guess I leaned out the motor. Seven out of eight were melted. One had a ring snapped in two, and another had the ring melted to the piston.
Which pistons should I go with and should I do thirty over on the block?

No reason to go more than 0.020" on the overbore, which is what most consider the limt. If you have to go more than that, just get a new block. There are several good piston offerings from CP, Diamond, Ross and JE. I personally run Ross.

Most will say that CP are the strongest, but Diamonds have recently held up in severe detonation and are reportedly the quietest slugs out there. I would go with them if I were to do it over. Absolutely no complaints with the Ross. They are a strong piston, but a bit noisey in the aluminum block.

 

[racerat]

John if your block needs more than a .020 overbore to clean it up, I have a spare, stock bare block that needs nothing more than a hone.
I have CP 17cc pistons in my old block, no complaints whatsoever and it looks like they held up perfectly. I have JE's in my aluminum block now and so far, so good.
If you want to stay local, Kotzur has a lot of experience with these motors. Just be prepared to wait.

 

[txlen]

ok..lemme get this straight..yer car had lean issues..he cleared it up with the tune...then you had more issues a while later, which seemed to be lean issues also, did ya bother to change the fuel filter or anything??...maybe be bring it back and stick it on the dyno and have it rechecked??...you had issues but ya jus kept hammering on the car hoping they would go away???... and after ya beat on it knowing ya had probs now ya wanna blame someone else??...why not jus kick the horse after it falls down from being over worked??...

 

[Black2003Vert]

I was upset about the mis-diagnosis, not the tune. Yes, I beated on my car, but, when my car started melting the tips off of plugs, they said it was running lean and needed to be retuned. Had it retuned and Murillo said that I needed new coil packs. After that I never got the car under boost or out of 5th gear since my work is 5 min. away. The day before the coil packs come in, the motor starts to knock.
Again, I was upset at spending $500.00 on coil packs when I could have applied that towards new pistons.

 

[pb1302]

Mine just started with that damn piston slap....... it goes away after she warms up...... it never did it before so I only hope it is not going to get worse or a ring has broken or something. I will be pulling the plugs soon to see if I damaged any of them on my last spedo test....

 

[txlen]

I have not done this since my car started acting up. It was later after I had the car retuned that the motor started knocking. Thanks Murillo motorsports.

well..from the way i read this (and i think others will too) you seem to blame Murrillo for the prob...when the damage was prob already there he jus got the air/fuel and tune right and ya had the damage before from running it, but it ended up showing up after, and ya kept driving the car after he told ya it had probs... jus my .02 here... Len

 

[Black2003Vert]

Like I said, I'm more than convinced that the lean issue caused the problem prior. I just wish Murillo's diagnosis was correct, so I wouldn't of wasted 5 bills on parts I didn't need.That could of been my pistons, now, I have to save up the money because I'm not rich like some people.
I won't lie though, I'll probaly get my parts and info else where, ( Traci and Tim )

 

[MaximumVelocity]

I was upset about the mis-diagnosis, not the tune. Yes, I beated on my car, but, when my car started melting the tips off of plugs, they said it was running lean and needed to be retuned. Had it retuned and Murillo said that I needed new coil packs. After that I never got the car under boost or out of 5th gear since my work is 5 min. away. The day before the coil packs come in, the motor starts to knock.
Again, I was upset at spending $500.00 on coil packs when I could have applied that towards new pistons.

John, you should be upset about the tune! If a shop "tunes" your car...then tells you it is OK to drive???!!! How f'd up is that?
Then you have a collapsed plug electrode....which is purely a sign of detonation. Detonation is a timing /tuning issue, period. Or maybe a stretched rod due to over-revving a motor. Either way, this "shop" then sold you $500 worth of coil packs to "cure" a problem that didn't exist. Misfire my ass.
If Murillo can't tell a motor knock, then maybe he should start selling airfreshners...he'll do less damage.

If he had datalogged the car at all, he would've seen that it wasn't spark blow-out or misfire. It's just as obvious as blower belt slip if you have a dyno or know what your looking for. Hell, I don't have a dyno and I knew the ignition system wasn't the issue.

Cliff notes: Murillo tuned your car poorly, this cost you your motor.:kaboom: