Well I went and broke my Miata

Stephen Westerfield · **Posted:** Mon Feb 28, 2011 9:45 am

JamesShort wrote:

I guess if you think about it, it is MUCH more impressive blowing up a BP miata engine than a Subaru, so I guess Milko is still in the lead

.

We need something more impressive than some dirty gap less spark plugs. We need to see holes in blocks and such. Keep working on it.

Steven Carter · **Posted:** Mon Feb 28, 2011 10:14 am

JamesShort wrote:

Well looks like two James' blew engines due to detonation/AFRs in 1 week. Do we get to share the burnt piston award this year?

Easy there, Cowboy....your car doesn't spew smoke anymore, had *decent* compression and still ran well. I think you're a pretty distant second at the moment. Blow up your Honda engine, then I'll be impressed.

JamesMilko · **Posted:** Mon Feb 28, 2011 10:15 am

I put my hand behind the tail pipe at idle and it turned black with oil. There was a black spot in the paddock where the tailpipe exited.

George Bright · **Posted:** Mon Feb 28, 2011 10:33 am

Years ago I broke a ring or 2 in the L16 in my 510. It was a bug fogger when you got on it after idle. I was even pulled over by Raleigh PD but the guy let me off witha warning because I was headed to swap the motor at Bob Kendrick's house and had the new motor sitting in the passenger seat. The hard part was getting the motor downd the stairs from my apartment and into the passenger seat by myself.

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

JamesMilko wrote:

Oddly enough my MS install was almost 4 months old to the day on saturday. I got everything together for the Oct 26th Autocross but wasn't totally ready for the 15th at CMP.

I'm pretty confident it was detonation now. No idea why I got detonation though, I'm leaning towards that I was running the colder of the two OEM plugs.

I'm pretty sure this is the incident that regapped the plugs. This is the first spot where the car started having issues. My AFRs for the rest of the session look like the first second of the graph rock solid right on target.

Can you tell me if I'm reading these charts right?

- Cursor is at about 398.9, you're full throttle in 4th gear
- Target AFR (white line)looks like it's around 14?
- At about 399.0 "something" changed which caused AFR overall to jump to maybe 18 and start oscillating from 16-20
- At about 399.0 you felt this and then backed out of the throttle at about 400.0

2 questions:

1. Was the screwy AFR the cause or the symptom of the problem? Is it possible that for example you detonated the motor THEN the AFR spiked? It only took you 1 second to notice and back out, and I don't see any indication of problems before 399.0... leads me to think the AFR is a symptom. But who knows.
2. If the AFR caused the detonation/broken motor, what could have caused the AFR to suddenly spike? Fuel pump went bad? Obstruction on the filter? Failed FPR?

Just cusious

Ryan Holton · **Posted:** Mon Feb 28, 2011 11:30 am

Also 122 mph in 4th gear? Holy crap!!! :shock:

JamesMilko · **Posted:** Mon Feb 28, 2011 1:17 pm

Ryan Holton wrote:

Also 122 mph in 4th gear? Holy crap!!! :shock:

The gear numbers are fuzzy, it's just RPM * effective gear ratio. I was likely near redline in 3rd or 2nd for the 122mph. Fastest I get at VIR is ~110-115 indicated.

Quote:

Can you tell me if I'm reading these charts right?

- Cursor is at about 398.9, you're full throttle in 4th gear

Correct

Quote:

- Target AFR (white line)looks like it's around 14?

13.4 is the target. The number at the bottom of each section is the current value at the cursor.

Quote:

- At about 399.0 "something" changed which caused AFR overall to jump to maybe 18 and start oscillating from 16-20

The change was actually at ~393, before that the AFRs looked like the first second of the graph.

Here is the end of 3rd and beginning of 4th for preceding that log. There are some lean spots. I changed some data points to be more useful. PW = pulse width to the injectors, MAT/CLT = intake air/coolant temps.

Quote:

- At about 399.0 you felt this and then backed out of the throttle at about 400.0

Correct. To give you an idea of where I was the 0 throttle bit at the end should be about the 1 marker on the back straight. Fuel was 3/4 so it wasn't starving on the uphill part of the back straight.

Quote:

2 questions:

1. Was the screwy AFR the cause or the symptom of the problem? Is it possible that for example you detonated the motor THEN the AFR spiked? It only took you 1 second to notice and back out, and I don't see any indication of problems before 399.0... leads me to think the AFR is a symptom. But who knows.
2. If the AFR caused the detonation/broken motor, what could have caused the AFR to suddenly spike? Fuel pump went bad? Obstruction on the filter? Failed FPR?

1. That's what I'm wondering, chicken or egg. Not sure if I have enough data to know for sure. I haven't pulled down the data from parade laps/last session/drive home to see what they look like but based on what the 2nd half of the log file looks like if it was a fueling issue it was transient. I wasn't recording video for that session either so I can't see what my reactions were at the times indicated.
2. I'm starting to think the detonation was caused by plugs that were too cold. Not sure if I'll ever be able to know this for sure. Might just have to be lesson learned run it richer next time.

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Can you show a graph of PW from 392 to 405?

JamesMilko · **Posted:** Mon Feb 28, 2011 2:04 pm

Sure. It's uneventful though.

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

JamesMilko wrote:

Sure. It's uneventful though.

Wouldn't that mean that your injectors are maxed out?

If not the ECU should be trying to dump more gas to correct for the lean factor... What does the value 31 actually correlate to in %?

JamesMilko · **Posted:** Mon Feb 28, 2011 10:24 pm

MikeWhitney wrote:

JamesMilko wrote:

Sure. It's uneventful though.

Wouldn't that mean that your injectors are maxed out?

If not the ECU should be trying to dump more gas to correct for the lean factor... What does the value 31 actually correlate to in %?

My Megasqurit doesn't do closed loop EGO correction at large throttle/load/idle. It can be done but the map mine is based on has EGO correction turned off for TPS >70 or when the engine isn't making much vacuum.

13ms PW is around 55-65% duty cycle. They were at 60% duty cycle when everything went sour.

Charlie Guthrie · **Joined:** Thu Aug 28, 2003 8:14 pm **Posts:** 832

Just a layman's observation here, but there is repeated mention that you suspect detonation may be related to using a colder plug. This is counter to what I have been taught. Typically one wishes to run the coldest plug that doesn't foul. A "hotter" plug will run cleaner but also runs hot enough to sometimes create a hot spot that can cause preignition. I would rule out the cold plug as the culprit.
What I want to know is what mechanically occurred to close the gap on the plugs. That seems very rare without some sort of contact. Has anyone ever heard of over reving an engine sufficiently to stretch the rods enough to reach the plugs? Otherwise, are these plugs the proper length? My first impression upon seeing the closed gaps was that the plugs were actually extending too deep into the engine and got "touched" just enough to close the gap. Since the contact could be very slight the piston could have enough carbon build up to mask the contact.
Opinions, opinions, opinions,
I've got one too.
Charlie G

Vincent Keene · **Posted:** Tue Mar 01, 2011 2:20 pm

Charlie Guthrie wrote:

Just a layman's observation here, but there is repeated mention that you suspect detonation may be related to using a colder plug. This is counter to what I have been taught. Typically one wishes to run the coldest plug that doesn't foul. A "hotter" plug will run cleaner but also runs hot enough to sometimes create a hot spot that can cause preignition. I would rule out the cold plug as the culprit.
What I want to know is what mechanically occurred to close the gap on the plugs. That seems very rare without some sort of contact. Has anyone ever heard of over reving an engine sufficiently to stretch the rods enough to reach the plugs? Otherwise, are these plugs the proper length? My first impression upon seeing the closed gaps was that the plugs were actually extending too deep into the engine and got "touched" just enough to close the gap. Since the contact could be very slight the piston could have enough carbon build up to mask the contact.
Opinions, opinions, opinions,
I've got one too.
Charlie G

Charlie, you do know what 'non-interference' means right? :wink:

JamesMilko · **Posted:** Tue Mar 01, 2011 2:54 pm

Charlie Guthrie wrote:

Just a layman's observation here, but there is repeated mention that you suspect detonation may be related to using a colder plug. This is counter to what I have been taught. Typically one wishes to run the coldest plug that doesn't foul. A "hotter" plug will run cleaner but also runs hot enough to sometimes create a hot spot that can cause preignition. I would rule out the cold plug as the culprit.
What I want to know is what mechanically occurred to close the gap on the plugs. That seems very rare without some sort of contact. Has anyone ever heard of over reving an engine sufficiently to stretch the rods enough to reach the plugs? Otherwise, are these plugs the proper length? My first impression upon seeing the closed gaps was that the plugs were actually extending too deep into the engine and got "touched" just enough to close the gap. Since the contact could be very slight the piston could have enough carbon build up to mask the contact.
Opinions, opinions, opinions,
I've got one too.
Charlie G

You're right Charlie. I misspoke. I'm running the hotter of the two OEM plugs "BKR5E." Mazda also lists "BKR6E" as a correct plug which is the next heat range colder. Plugs are what the car ships with so they should be good. It's likely the most common plug in a BP motor.

Even on a non-interference motor the piston should never hit the spark plug, the plug never moves.

Charlie Guthrie · **Joined:** Thu Aug 28, 2003 8:14 pm **Posts:** 832

Yeah, Vincent I do

Quote:

Charlie, you do know what 'non-interference' means right? :wink:

What intrigued me was the possibility of reving the engine so fast that the connecting rods actually stretched a few to many thousandths of an inch. I would think that the rpm required to do that would be in excess of 10K, but what the heck....inquiring minds want to know. When forces exceed the design parameters, things move in unexpected ways.
Charlie G

THSCC Forums

Well I went and broke my Miata

Who is online