Engine Failure at speed... Options

[DM_2000]

Define cranks slow, does it constantly crank slow ( too much friction overall ) or does it spin fast between compression strokes then goes slow over compression ( like the timing is advanced too far ) ? Did you turn the motor over by hand with plugs in and out?


This is a V8 Chevy LS as noted in the vid title correct? As an initial test, I'd check valve events against crank position to make sure they are believable in case a timing chain hopped over. ( this usually results in low compression however )

It is possible for an engine to overheat, pistons swell and grab the bores. This does not make any noise but power does noticeably drop off over a few minutes.

If you instantly lost oil pressure, the bearings could melt and grab the crank especially if they are aluminum. This causes surprisingly little damage as the crank does not get a chance to be scared up. ( think gluing the rods to the crank. ) If this occurred, I'd check the rods for bending.

[Rand]

I would think the first thing to do is check for spark before digging into anything deeper. But yeah, the slow cranking thing needs an answer (unless the electrical fail means low battery or something.)
I figure Tony knows how to troubleshoot though. (IMG:style_emoticons/default/wink.gif) Good luck.

[IronHillRestorations]

That car is amazing. I hope it's nothing major.

[Cracker]

Thanks for that thoughtful insight...just to clarify my claims of regarding the cranking. It was our initial thought that something bad happened on the bottom end; maybe a timing chain for instance. I pulled the valve covers to inspect the rockers - all valves are properly activated. There is no way the timing chain jumped a tooth on this motor...we are running a double roller Katech unit with aftermarket gears. I called the engine builder today to confirm this and he agreed. This means the timing chain failure is out - big deal since that tears up heads, pistons and cylinders. The engine didn't turn over nicely with or without plugs but the battery was also compromised and registered 10.5 volts. I am going to check spark but already know there is none. If that IS the case, I will check power on the ECU circuit and determine if my hypothesis is true. If so, I will install a jumper wire on that circuit to see if we light the shift light with ignition (and fuel pump) - should fire. I really believe the root cause is the female fuse block receptacle has "slipped" down and cut contact with the fuse. Just a hunch since we had the same thing occur with a bank of coil packs earlier this year.

Tony

Define cranks slow, does it constantly crank slow ( too much friction overall ) or does it spin fast between compression strokes then goes slow over compression ( like the timing is advanced too far ) ? Did you turn the motor over by hand with plugs in and out?


This is a V8 Chevy LS as noted in the vid title correct? As an initial test, I'd check valve events against crank position to make sure they are believable in case a timing chain hopped over. ( this usually results in low compression however )

It is possible for an engine to overheat, pistons swell and grab the bores. This does not make any noise but power does noticeably drop off over a few minutes.

If you instantly lost oil pressure, the bearings could melt and grab the crank especially if they are aluminum. This causes surprisingly little damage as the crank does not get a chance to be scared up. ( think gluing the rods to the crank. ) If this occurred, I'd check the rods for bending.

[Cracker]

On a totally unrelated topic/video...I came across this just now - its worth the time. Sweet driving and an 8000 rpm 3.0 with a slick close-ratio trans to boot! Enjoy.

T


https://www.youtube.com/watch?v=bgBcaKPhKbI

[jd74914]

If your battery is 10.5V is your alternator charging? If voltage dips too low, typically in the 10.5VDC, many ECUs (high-end aftermarket ones at least) will start cutting as a self-protection method to avoid over current faults on the coil drivers.

[Cracker]

Hmm? Solid observation Sir...now that you say that, I noticed a slightly "jumpy" water temp gauge the day before that was unusual - it eventually settled down. I bled the cooling system thinking it might have been air in the line - took a little water. I recall, however, seeing my volt meter show just under 14 on Saturday. Definitely something to look at for sure. Thank you!

OK: I can definitely see my volt meter over 12 at the time of shut-down...it is to the far left of the dash. Hard to see..

Tony

If your battery is 10.5V is your alternator charging? If voltage dips too low, typically in the 10.5VDC, many ECUs (high-end aftermarket ones at least) will start cutting as a self-protection method to avoid over current faults on the coil drivers.

[jd74914]

Hmm? Solid observation Sir...now that you say that, I noticed a slightly "jumpy" water temp gauge the day before that was unusual - it eventually settled down. I bled the cooling system thinking it might have been air in the line - took a little water. I recall, however, seeing my volt meter show just under 14 on Saturday. Definitely something to look at for sure. Thank you!

OK: I can definitely see my volt meter over 12 at the time of shut-down...it is to the far left of the dash. Hard to see..

I've been burned by that a few times so I figured I'd throw it out there. Once after loading a car on the dyno and planning to spend the day there. (IMG:style_emoticons/default/wacko.gif)

Ahh, I didn't even notice it in the video. That wouldn't seem to be the issue then. Your slipping fuse connection seems like a good thought. Definitely seems electrical based on the video.

[Cracker]

The electrical narrative is boosted by the loss of power to "all things powered by the ecu" - that are visible from the onboard camera. The fuel pressure gauge is the white faced unit just to the left of the shift knob. I have fuel pressure indicated at about 10:30 (which is a correct and accurate indicator) and by the time I turn into 10a - it is at zero or 7:30. Conclusion: Either the ECU DIED at that moment or the ecu lost its lifeblood - power. I can only hope that there wasn't collateral damage caused by an abrupt engine cut...

PS: I thought I locked up the fronts again and you can see me glance in the rear view mirror - I was looking for a trail of smoke. Felt very similar to that prior experience but without the engine noise - it was kinda weird.

Tony

[Chris914n6]

I can only hope that there wasn't collateral damage caused by an abrupt engine cut...

Tony

Millions of cars do that everyday (IMG:style_emoticons/default/smile.gif)

Only issue would be if you lost sparks at that RPM and it was still squirting fuel, which could be ignited by the cat, which I doubt you have, and burned it.

Awesome racing video, but boy does that look like a rough track to do a bunch on laps on.

[Cracker]

I have a process and technique to slow the car - its not only the brakes that accomplish it...off-throttle at that speed with the engine cut is what I am referring too. THEN, I proceeded to shift through the gears, as I normally would - THEN, I tried to jump-start the engine just prior to turning into T10a - I used 3rd gear. It didn't catch and I JUST had enough momentum to crest the hill and on down to the pits. But you already knew all of that... (IMG:style_emoticons/default/biggrin.gif)

T

Millions of cars do that everyday (IMG:style_emoticons/default/smile.gif)

[gms]

Tony,
I hope it is just a simple electrical problem
(IMG:style_emoticons/default/beer.gif)

[DM_2000]

The engine didn't turn over nicely with or without plugs but the battery was also compromised and registered 10.5 volts.

Your battery is either fully discharged or you have shorted a cell. ( Actually electrically shorted not an electrical "open" that many call "shorted" ) I have had batteries with a shorted cell crank all day but a bit slow and unable to properly operate a FI system. A fully charged "12" V with a shorted cell is 10.5 V.

Here is a handy chart to determine a lead acid battery's state of charge ( how full the "tank" is) . Note, this only works if the battery has been siting for 8 HR since the last time it was charged / discharged and the numbers can vary a bit. This does not test battery capacity, you need a load tester for that. ( how big the tank is )

Using an accurate digital volt meter, testing at the battery terminals.
12.66 full charge ( This is 2.11 V per cell )
12.42 75% charge
12.18 50 % charge
11.90 25% charge ( Go below this on a regular basis and the battery will degrade )
11.70 0% charge ( Go below this more than a couple of times and the battery will be damaged )

[Rand]

If feels to me like people are talking basic 101 with someone who is way past that. Surely Tony would have swapped batteries or hooked up to something before delving into such detailed meter testing. Don't you think? And hopefully that car isn't using a lead acid battery.

[DM_2000]

If feels to me like people are talking basic 101 with someone who is way past that. Surely Tony would have swapped batteries or hooked up to something before delving into such detailed meter testing. Don't you think? And hopefully that car isn't using a lead acid battery.

And stop calling him Shirley. . .

I don't know the OP, but I would not even try to crank an electronic FI engine if the battery was 10.5 V. With a carb engine you "might" have a slight chance of catching it.

Even if the battery had a shorted cell while driving, the alternator would keep voltage up while running so I'd tend to think the alternator quit charging and the car ran out of electricity.

I've seen ( and fixed ) too many cars that went from shop to shop without a positive result because the basics were missed / others assumed that so and so would have checked item X.

[Cracker]

Its all good...keep it coming. We noticed voltage and went to cables. You never know WHO would be reading this and gain some benefit! Thanks!

Tony

[ottox914]

I've had a few similar electrical mystery problems in the past. Car would crank but not start until you let off the key, and on that last portion of revolution of the motor, it would usuallly start. After that it would start just fine all day. Just that first start. Used a basic volt meter in the morning, battery was 12+ volts. Borrowed a load tester and the battery fell on its face. Seems letting off on the key lightened the draw enough that the aftermarket ecu saw enough voltage to operate- there just wasn't enough to turn it over and power ecu at same time. After a start and charge, you could generally start again with no problems or symptioms.

New battery solved that one. Took awhile to figure it out.

At an autocross the car just stopped dead mid run. No warning. No painful motor sounds. Rolled off track and hit the key- no fuel pump could be heard. Checked all fuses, all were good. Nothing looked wrong. Ran wires for + and - from the relay up to the pump. Maybe a wire had grounded out. Still nothing. Trailered it home. Next day found a 15 yr old crimp between a ground wire and ring terminal for the ecu had let go, and I lost ground to the ecu. No ground, no crank signal. No signal, the ecu would not trip the relay to power the pump. 5 minutes later it was all good again.

Not hearing the fuel pump was not the problem, just another clue. That I didn't see for what it was.

Electrical can by tricky. One clue can mask another problem and get you thinking the wrong way. You can have the answer right in front of you and miss it.

Based on no sounds of mechanical death, I'm thinking electrical also. Look at your clues carefully, test theories. My experience is that electrical issues are seldom a smoked board or other big deal repairs. Generally something simple- a battery or ground in my case.

Good luck, and great car. Fun to watch it eat up track. And whoever happens to be in front of you.

[DM_2000]

Its all good...keep it coming. We noticed voltage and went to cables. You never know WHO would be reading this and gain some benefit! Thanks!

Tony

I don't know what gauge your cables are, but most consumer grade ones are more battery charging cables than true jumper cables.

The consumer stuff is 10 to 6 gauge with thick insulation and poorly connected copper plated steel jaws. High end cables are a minimum of 4 G with 2 or 0 G being even better and have well terminated solid copper jaws.

With real jumper cables, an engine should be able to be easily started without a battery in the car. If the cables can't do this, they are charging cables.

With the car running, the battery voltage should be in the 13.8 - 14.2 V range, I looked at the vid and it looks like you are at 12 V ( difficult to see ) , this is too low.

In any event, the battery voltage is too low, attempt charging then do a load test.

[Cracker]

Busy work week! Normally the gauge reads right at 14v...I am not even pulling the car out the hauler until Saturday. My cables are CABLES...they were built specificatlly to be used on our 1100 hp/600ci mile car.

Tony

Its all good...keep it coming. We noticed voltage and went to cables. You never know WHO would be reading this and gain some benefit! Thanks!

Tony

I don't know what gauge your cables are, but most consumer grade ones are more battery charging cables than true jumper cables.

The consumer stuff is 10 to 6 gauge with thick insulation and poorly connected copper plated steel jaws. High end cables are a minimum of 4 G with 2 or 0 G being even better and have well terminated solid copper jaws.

With real jumper cables, an engine should be able to be easily started without a battery in the car. If the cables can't do this, they are charging cables.

With the car running, the battery voltage should be in the 13.8 - 14.2 V range, I looked at the vid and it looks like you are at 12 V ( difficult to see ) , this is too low.

In any event, the battery voltage is too low, attempt charging then do a load test.

[Cracker]

Update
Well...it doesn't look good. I checked power at the fuse panel and have ignition, fuel and spark - Hell, I got power everything. The engine started up and then died within seconds; a second attempt led to the engine dying even more quickly. After the third start (again having difficulty turning over but catches) it made a strange noise as it shut down - a rotational scraping type noise. I did not hear it the two times it ran.

At this point, unfortunately, I believe my original assessment at the track may unfortunately be true - something is likely wrong on the bottom end. Oh well.

One interesting observation: When the ecu primes the high pressure fuel pump the gauge will "hold" that pressure for startup; however, right now that pressure is dropping immediately after the pump cycles off. Hmm?

I plan on getting the car up on the stands tomorrow afternoon and pull the pan - I'll be looking for bits and pieces that shouldn't belong. If I have anything that warrants pictures I'll share the gory details.

Tony