TraviZ06

One thing after another. I feel cursed.
If I have learned anything in the car community is not to not ask diagnostic questions without first attempting all logical tests and inspections. I had a sudden misfire and rough running engine after a highway pull. I babied it home the mile or so to my house. I was going to ask what it could be but my own research pretty much lead me to knowing I have no choice but to pull the head after discovering no compression on #5. The rest of the cylinders had perfect compression ranging between 145-160 and 95-120 on first stroke.

So my question now is why would only #5 be so torched and the rest look fine? I ohm'ed my injectors and they were all 11.9-12.7 with #5 injector as 12.4.

RonSSNova

Supercharged?
Do you monitor air fuel ratio?

That looks like hot from lean possibly.

Or it detonated, broke a piece out of the ring land and just melted from there.

Looks amazingly clean. Like on E85 possibly.

racebum

i've done this before...twice actually

one was too much timing in the fuel map and the other was an oil burner that lit up the ringlands while doing a 1/4 mile pass.

too much timing and not enough octane are often the culprits

whoever tuned the car would be my 1st suspect

TraviZ06

Supercharged, 12psi.
I dont monitor my AFR. I have a racetronix pump and kenne bell boost-a-pump. It was dyno tuned 5k miles ago with the new boost (from 6 to 12). Motor has overall about 8k miles on it. Just California 91 octane. No knock showed on the dyno but it was peaked at 17 degrees timing but the tuner said there was no signs of knock detection. I have a feeling it may have been detonation as well. I am just curious why #5 took it so hard.

Do you think that cylinder wall can be salvaged and a new piston popped in?

racebum

depends on how bad the cylinder is. if it's still smooth and you can't feel anything at all you can ball hone it with a hone on a 1/2" milwaukie 800rpm drill and install a new piston and rings. make sure you shove some rags down at the bottom of the cylinder to catch the fine metal flakes and grime from honing. also be liberal with the hone oil

also make sure you buy the correct grit ball hone for the rings you use. they come in various grits and some rings like a rougher /smoother hone than others

that picture is absolutely detonation. the question is what caused it

also no idea why one cylinder lights up and others don't. it just happens. i took out a turbo honda the same way. only variable was a brand new spark plug in the hole that died. i traced that car down to too much timing for the given octane

keep in mind with pump gas if you ever get a bad batch and are boosted bad things can happen. if i ever boost a car again on pump i'm going to make sure either it's a lower compression engine or timing is a couple degrees under what the tuner thinks is safe.

hot hot days also increase the chance of detonation

ps buy an AFR meter. you really should have one in the cabin

something like http://www.jegs.com/i/AEM/017/30-411...5ShBoCq1Xw_wcB

TraviZ06

Thanks. I do own a ball hone already and will see if it is correct for these Medium tension springs that came in my motor. This was a low compression motor as well, built for 9.5:1 CR with the 12 psi in mind. I do think I will go with a wideband such as innovate so I can still piggyback my stock o2 plug into it to keep the ecu happy.

Is digital or analog gauges better for monitoring AFR? I am thinking a digital would seem more logical.

Secondly, I think I should start my own tuning. I have tuned efi's on my old Iroc before. I learned alot with megasquirt and then transitioned to Holley's HP EFI which was super user friendly and I had my 383 procharged iroc running on that quite well into the 10's quarter mile.

HP tuners a safe choice for adjusting afr and timing?

racebum

talk to those in the know for the c5 on which way to tune but generally people seem to have better luck doing their own tunes IF they are the mad scientist sorts and smart enough to learn how to do it correctly

grit on the hone depends on ring thickness and material. old cast iron rings often go a bit rough where as a super high rpm race engine with thin tool steel rings usually requires a fine hone to seat. most ring makers have suggestions for their rings if you call tech

TraviZ06

On monday I am taking my injectors to be flow tested to see if #5 had any faults. Also, I ordered a new ball hone in 240 grit to clean up that cylinder. I think it can be saved. All the roughness in the picture feels external, not engraved.

racebum

sounds like a smart idea, i also was able to save that honda that had the same problem.

Mike Beck

Makes me wonder if you could stick a Holley HP or Dominator in there to control the engine and leave the stock ECM in there to do it's other things......

racebum

gas mileage would be crap and longevity of the engine compromised. with EFI you can tune the AFR across the rpm range. with a carb it's all about WOT. this means part throttle is often extremely rich. no biggie if it's a drag car but horrible for a street car. rich engines usually have a short ringlife, excess gas promotes ringwash and fast wear.

this particular car just had detonation and i'm sure the OP is really digging into why and how to make sure it doesn't happen again.

TraviZ06

I believe mike beck is referring to the HP and dominator line of efi kits, not the carbs. Which I would love to do with its auto-learn function. However though I believe I have the ability to wire it in piggy back, I don't know how the stock PCM would react

printmanjackson

If I were you I would purchase a good wideband and tuning software like HPTuners or EFILive and learn how to tune and monitor your engine. Just because you have it dyno tuned means its all good as you can see.

TraviZ06

I just got ahold of a innovate lc-1.
I'll look into tuning software once I repair the motor

ajrothm

#5 & 7 are usually the first ones to go. 12 psi, 17* timing and no meth on 91 octane is a melt down waiting to happen. I am not surprised at all..

1) Fire your tuner
2) Get a wide band & fuel pressure gauges at a MINIMUM, watch them religiously.
3) Get Alky control meth and learn how to stay on top of the maintenance on it.
4) Find a good tuner.
5) Make sure to connect steam cross overs on the rear of the heads and tie them into the front cross over. This "may" help with the steam pockets and coolant flow around #5/7. Kurt Urban makes a nice kit for this. I believe Trick Flow also makes a kit and its much cheaper.

This will atleast give it a chance at living.

Best bet is to get HP Tuners and learn how to datalog, just to keep tabs on it.

Good luck on the rebuild. We've all been there.... I'm about to be on my 3rd motor.

RonSSNova

I agree 100%

Ron