amanlikemike

Hooooo-kaaay... So.

First off - as a long time lurker and owner of a less-than-cooperative rig - I would just like to express my deep appreciation for the wisdom of this forum.

Secondly, I'd like to jump into the fray and ask for y'alls' opinion on what I am most likely to have destroyed by monstrously - yet innocently - overreving my motor here (see attached "EEEEEK" video).

Backstory is: during an overhaul promoted by a rough and erratic idle (along with various other electrical issues), I did a wideband 02 sensor conversion [correctly] and was testing the voltage in & out of it at various points in the rev range via my (wonderful - if you don't already have one, get one!) REM II+ Renix reader. Right at the end of the test I [brilliantly!] decided I needed to see how it behaved at WOT, and duly buried my foot, fully expecting the needle to safely bounce back somewhere shortly after 5 grand on the tach...

It was at this point I discovered that Renix XJs do not have a goddamned-friggin-summ***** rev limiter.

As you will witness, just a momentary stab at the skinny pedal was enough to send the revs deep into uncharted territory and possibly all the way to the end of the line for the engine in its current configuration.

As terrifying as this was, I thought I'd got away with it until the BAD noises kicked off back in the safe zone on the decel.

Immediately after I stomped her into the stratosphere, she wouldn't start - just crank, wheeze at the intake, fart out the pipe and crank again(see "no starty" video here - please excuse engine bay wiring, which I was in the process of checking and re-looming etc).

No change since then and no engine faults reported by the REM while cranking (in the overrev video the warning light on the REM was - I think - due to the o2 sensor getting out of spec).

Before things went s**t-shaped I was about to clean out the TB and associated sensors, adjusting the TPS (which was reading a tad low) in the process, and do a general spring clean/spruce up. At that time, I was getting an intermittent CPS error, which I confirmed with a voltage test at the connector and was going to resolve, but other than that - and the TPS being a wee bit under spec - it was looking like the o2 sensor was the main cause of my fueling woes, which were close to being over... Gaddamnit!

Sooooo... I guess my question is: what do you reckon crapped out [first], based on what you can hear in the video? To me, it sounds like valves having an ugly fit, but I'm praying there could be another - less serious - possibility...

More than likely the valve floated at some point, but with this being a non-interference engine, I'm hoping that massively reduces (or even makes nigh-on impossible?) the chances of a piston clattering any of them. But - with revs that high - who knows?

Aside from the possibility of bent valves - and with the timing chain apparently still in one piece - I'm guessing the other "options" are damaged (but not thrown because block and oil pan are still sans dents/holes) conrod, popped piston skirt or blown gasket.

I suppose I'm hoping to hear that it could be anything other than catastrophic engine failure e.g. I could have melted the catalytic converter or fried the CPS entirely or anything other than that...

Noted, this is probably just wishful thinking.

So far, I've pulled the valve cover and everything looks normal under there. Oil is still all inside the vehicle and the dipstick isn't showing any signs of it having coolant in it, related relays and wiring appear unmelted. Plugs look OK, I'm getting strong spark and fuel (haven't checked fuel pressure yet but pump primes, injectors are still on duty, the o2 sensor still checks out and exhaust gas is reading rich according to the REM). ECU is trying to dump a lot of fuel into the motor while cranking. I'm trying to avoid pulling the head until I'm sure I need to (I know I probably should regardless...) and am instead I'm [vainly?] trying to rule out worst case scenarios. I will still be running a compression test as soon as I get chance, and borrowing a borescope to check for anything nasty-looking in the cylinders (will post findings).

Oh yeah! Punchline is: newly, professionally rebuilt engine with only a few thousand miles on it. FARK!

Any educated guesses would be greatly appreciated. Light at the end of the tunnel would be nice, but I am fully prepared for it to be a ten-mile-long freight train).

Meanwhile, I'm off to kick myself in the nuts for a bit.

UGH.

superj

dang. that was an odd couple of sounds at the end. every time i have went over on vehicles and things got messed up, it sound way more metallic and bad. yours sounds like something became disconnected. do you have any holes in the block on either side? maybe you just jumped the timing chain or spun the distributor out of whack. (not sure if that is even possible, the distributor part)

BruceB

distributor and/or timing chain.
Leaning more to distributor
Start with draining your oil to look for metal bits...
Pull the distributor and inspect.

EZEARL

"I've pulled the valve cover and everything looks normal under there."
Everything is moving as it should when engine is turned over?
In the no start video to me the cranking actually sounds normal. Firing seems out of time though. If all looks normal with the valvetrain I'd do this:
http://cruiser54.com/?p=65

awg

do a compression test..if the valves have contacted, this will be revealed

EvanM

Spark plugs themselves may have a story to tell.

I drive a cummins and a jeep 2500 is over reving to me.

BlueRidgeMark

While I won't go so far as to say that no cars have rev limiters, I will say I have never heard of one that does, except big rigs. Seems a strange assumption to make.

third coast

As an FYI I believe many modern vehicles have a rev limiter. I have one on a 2001 Audi that I have accidently hit a couple of times doing autocross runs - sort of forgot to shift up while focused on those darn cones. With a small displacement turbocharged engine it can get there fast in low gear. Modern marine motors also have rev limiters so that when the prop cavitates or comes out of the water and unloads the engine you don't overstress things.

I have not looked at the video yet but I am surprised that a relatively quick throttle stab would catastrophically kill something that was not already well on its way to a failure. You may have just forced it sooner rather than later. High on my “wishful thinking” list would be a check for a distributor related problem, maybe gear or rotor issue. I am optimistic that it is not super bad. It is possible that your engine rebuilder didn’t do something right. If there is a warranty remaining you might want them to take a look before you go too far.

Dave51

I believe it's possible to jump a 4.0 timing chain if you take out a few teeth.

Looking forward to hearing compression numbers.

Dave51

Although not necessarily this many:

cruiser54

There are some people that can bend a digging bar in a sand pile.

IJM

Since the engine was popping on deceleration and making those noises while cranking, it sounds like it either jumped valve timing or the distributor isn't happy. Or both. It sounds like a BMW at 7 grand.

I've never heard of a car (gas, at least) made in past 25 years that didn't have a rev limiter. Back in the old days before EFI, sure.

The 1.8Ts in the B5 A4s were geared pretty short, so it would be pretty easy to run out of second gear on the course without realizing it.

superj

@amanlikemike
whats the story? did you find anything? you had the whole weekend and we are here anxiously waiting to hear what happened

cruiser54

I'm gonna bet it wasn't revs that caused the OP's failure.
The auto trans will shift at 4,800 RPM. I had my MJ with an auto trans and 3.55 gears, just the same as a Cherokee, with the speedo needle pointing straight down and I wasn't near 4,800 RPM.

IJM

This happened in neutral, no?