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Old 08-10-2022, 01:04 PM   #1
volvoloco
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The car is a 1994 940 factory turbo
megasquirt running perfectly fine and dandy
do88 intercooler,
ipd cam
wasted spark
630cc siemens
gt28 t3 turbo
greddy 10 row oil cooler
as far as everything else goes this is a maintained and healthy engine, no leaks, popping dipstick, literally perfect car that does not overheat in the summer with ac on or any problems at all

But, im a total dumbass and while hammering on the limiter one night, (i will include datalogs)
engine died

If you look at the log, as soon as it hits fuel cut for the last time, map value goes straight to 100kpa and stays there

The car nno longer starts, it turns over like it has ZERO compression
It will crank fine, nothing nasty sounding
But only i think 2 cylinders pop out the back
3" turboback straight pipe

What did i potentially do?
Timing marks are bang on, ive never checked the valve clearances but something must have obviously broke.
they did leak
some

not much though

cam turns with starter inspected from oil cap hole.
idk

DATALOG
https://drive.google.com/file/d/1azJ...ew?usp=sharing


TUNE
https://drive.google.com/file/d/1bGl...ew?usp=sharing
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Old 08-10-2022, 01:10 PM   #2
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Does the cam turn when you're cranking?
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Old 08-10-2022, 01:11 PM   #3
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Do a compression test just for the hell of it, but I'm pretty much thinking you're going to need to whip the head off and take a look. If you can tell the starter isn't working itself over compressions any more, and the cam belt isn't broken (and it's still in time), then something srs bzns happened, and taking the head off is the first step.

I'd say you might want to double check the TDC mark on the front pulley, since that can wander around, but the odds of the timing belt slipping and the pulley slipping as well to match is pretty low. Still, it's a possibility, maybe that bolt came loose and they both scooted on the crank together. Take the #1 plug out and verify TDC with something like a straw stuck into the hole to feel for the piston. There really isn't much keeping the timing gear/front pulley in place other than the tension from the bolt, those little nubs are just an assembly guide.
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Old 08-10-2022, 05:07 PM   #4
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A compression check is a good start. If needed a leakdown test will further diagnose any mechanical issues. That is if you have verified the cam timing hasn't slipped. Valve float can do some damage. If the engine has a lot of miles the red line isn't as high as it was when fresh.

Edit:Don't forget you can take a look in there with a bore scope.
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Last edited by dl242gt; 08-10-2022 at 05:08 PM.. Reason: add comment
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Old 08-10-2022, 06:01 PM   #5
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I'd start by making sure you didn't shear the roll pin on the cam, or break the crank gear.
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Old 08-10-2022, 07:33 PM   #6
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I'd start by checking that your MAP hose, and others, are still attached.

You can also run a MS Tooth Log during cranking as a simple compression check - the speed variation / tooth time variation for all 4 cyls should be about the same. This is from someone else's log of cranking-to-running with the factory 60-2 wheel (and some tooth detection problems once running):
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Old 08-10-2022, 10:25 PM   #7
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Quote:
Originally Posted by bobxyz View Post
I'd start by checking that your MAP hose, and others, are still attached.

You can also run a MS Tooth Log during cranking as a simple compression check - the speed variation / tooth time variation for all 4 cyls should be about the same. This is from someone else's log of cranking-to-running with the factory 60-2 wheel (and some tooth detection problems once running):
You're saying that the tooth logger can catch the bum cyl. in the graph? How does that work though, when everythings connected at the crankshaft?
I am still pretty new to things and tunerstudio literally describes nothing.
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Old 08-10-2022, 10:28 PM   #8
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Originally Posted by redblockpowered View Post
Does the cam turn when you're cranking?
yeah it does, first thing i checked, but i have to check the timing still, i pulled the plugs and thankfully not one of them appeared to be anywhere near a melted piston and that is nice, but its just a matter of finding my 1/2" socket adapter and turning #1 to TDC with a cpl straws in there and see what's what

@Linuxman if the cam gear roll pin were to have sheared, would the bolt just roll along without holding it all in place?
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Old 08-10-2022, 10:40 PM   #9
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With the roll pin sheared, it's possible for the cam to have slipped on the gear, but still be snug enough to turn the cam? Another quick eyeball check you can do once the timing cover is off before taking things further apart.
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Old 08-10-2022, 11:26 PM   #10
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With the roll pin sheared, it's possible for the cam to have slipped on the gear, but still be snug enough to turn the cam? Another quick eyeball check you can do once the timing cover is off before taking things further apart.
Of course! I over(under?)think things a lot!
If i'm honest, i had already landed on the same page as you said in your post earlier, about the head coming off; But i was hopeful id find something easy

Last edited by volvoloco; 08-10-2022 at 11:33 PM..
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Old 08-11-2022, 09:02 AM   #11
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I looked at your log and agree with Kenny et. al. As you said, you were bouncing off the rev limiter: -6deg advance for most the the pull, with an occasional spark cut. AFR drops and then sticks at ~10 (except for a brief bump from spark cut).

If the cam gear rotated on the cam shaft slightly, or it skips a few timing belt teeth, the valves are no longer opening/closing at the right time, and the pumping efficiency of the engine drops. In other words, the VE drops. MS has no way of knowing that VE has dropped, and continues fueling based on the VE table. This would explain the AFR dropping and sticking at ~10. [BTW, a MAF-based setup would show the drop in airflow immediately.]

--------
Tooth logger picture:
During cranking, the cranking speed varies as each cylinder reaches TDC of the compression stroke. It gets harder to turn the crank as pressure builds. Once it rotates past TDC, the cylinder pressure pushes the piston down and makes it easier to spin the crank.

This shows up in the Tooth Logger picture as the wave-shaped pattern of tooth times. The valley of the wave is the fastest cranking speed, just after TDC when the cylinder pressure is helping spin the crank. The peak of the wave is the slowest cranking speed, as cyl pressure builds.

If you look at the shape and peak/valley of 4 waves in a row, you're looking at the 4 cylinders. If one, or more, of the 4 waves is significantly different, that corresponds to a compression difference. If all 4 waves look about the same, then compression is fairly even across the board. This won't tell you if all 4 cyls are equally low, but it's a quick and easy test if you don't have a compression gauge, or you don't want to pull all the plugs.
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Old 08-11-2022, 09:25 AM   #12
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You can also do a shade tree compression test where you just pull a coil wire and crank it around a few times, and listen for the starter slowing down on all 4 cylinders evenly. Or not evenly. If it's some sort of uneven syncopated beat, something is wrong.
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Old 08-11-2022, 08:43 PM   #13
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I really appreciate the responses guys

One thing I might add is that where I live I cannot work on my car, so I barely even can check **** out without risk of being evicted
But anyways

I was going over **** today and when #1 is at TDC, looking down into the lower timing belt cover with a light I see no where on the topside of the crank gear washer a timing nib
I think it’s safe to say that the gear slipped indeed
I haven’t checked the cam gear yet cause like I said I cant
But I’m either gonna tow it to my shop or (tell me if this is dumb) reset timing and go
Is that possible to get them timed up and still safely drive now that the locating pin(s)are sheared ?

I’d want to at least start it , and drive it onto the street where I can change it at home even, (I have a spare crank gear and washers for this very reason )as long as it doesn’t play as risky
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Old 08-11-2022, 09:02 PM   #14
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Quote:
Originally Posted by JohnMc View Post
You can also do a shade tree compression test where you just pull a coil wire and crank it around a few times, and listen for the starter slowing down on all 4 cylinders evenly. Or not evenly. If it's some sort of uneven syncopated beat, something is wrong.
After I had originally died all I had was a pair of pliers so I had to call for a tow
And while I was waiting for a truck to come I tried starting a bunch and it was turning over as if the plugs were out
It was as you describe as “evenly across 4 cylinders” turning over
Lol the tow truck driver asked me if I had a compression release switch
Didn’t know cars ever did
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Old 08-11-2022, 09:56 PM   #15
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So it's not cranking normally, but like it has no compression. And all 4 cylinders are pretty even? That's probably pointing toward a valve timing issue of some sort. It's very unlikely that all 4 cylinder would suffer some sort of compression loss through broken rings/holes/valves/HG failure in such a way that all 4 would have roughly the same very, very low compression.

And if you're saying that the lower timing gear seems to be the one that slipped, then it's possible to carefully line it back up and then crank down the front pulley bolt again. The little nubs on the timing gear down there are not there to handle torque, it's just for alignment purposes on install, the pulleys big bolt pinches the gear between the pulley and crank and that's what handles all the torque.
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Old 08-11-2022, 10:05 PM   #16
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So it's not cranking normally, but like it has no compression. And all 4 cylinders are pretty even? That's probably pointing toward a valve timing issue of some sort. It's very unlikely that all 4 cylinder would suffer some sort of compression loss through broken rings/holes/valves/HG failure in such a way that all 4 would have roughly the same very, very low compression.

And if you're saying that the lower timing gear seems to be the one that slipped, then it's possible to carefully line it back up and then crank down the front pulley bolt again. The little nubs on the timing gear down there are not there to handle torque, it's just for alignment purposes on install, the pulleys big bolt pinches the gear between the pulley and crank and that's what handles all the torque.

Right, it cranks over like it's sealing none of each cylinders at all.
Turning by hand, each compression stroke is barely noticeable in terms of resistance to turning.

I get it that bolt holds everything in place
Either the previous owner was to blame for that,maybe from a bad motor mount that has been pulling engine around at hard accel lately...it's been on my list to change it lol
On full throttle all I hear is belt squeal and the engine will pull hard to one side , this could be related to failure.


Now I just need to figure out how to torque this bolt. Car is an automatic,which makes me think I should be ordering the tool for this ,
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Old 08-13-2022, 02:42 PM   #17
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If you're running the IPD cam, the crank gear has slipped/moved, it quit running at rev limiter cut out RPM, it has no compression cranking, I think you can assume that you've bent valves in every cylinder. Do a leak down test, if you show massive leakage on intake side, pull intake manifold. Look down into the intake ports with a flashlight, rotate the crank through each intake valve cycle, you should be able to see the bent valves that are not seating in the valve seat, (it will be quite noticeable). If you only have leakage on the exhaust side, then pull exhaust manifold, and visually check, (a lot more work, that's why I recommended checking the intake side first). OR just pull the head off. Good luck
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Old 08-13-2022, 02:53 PM   #18
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Also, the belt squeal, may very well be your harmonic balancer hub that is spinning, under load, when you accelerate. The outer pulley section spins on the rubber between the outer pulley, and the inner hub.(It sounds just like a belt squeal). Need a new hub. Good luck
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Old 08-14-2022, 07:07 PM   #19
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Originally Posted by JohnMc View Post
So it's not cranking normally, but like it has no compression. And all 4 cylinders are pretty even? That's probably pointing toward a valve timing issue of some sort. It's very unlikely that all 4 cylinder would suffer some sort of compression loss through broken rings/holes/valves/HG failure in such a way that all 4 would have roughly the same very, very low compression.

And if you're saying that the lower timing gear seems to be the one that slipped, then it's possible to carefully line it back up and then crank down the front pulley bolt again. The little nubs on the timing gear down there are not there to handle torque, it's just for alignment purposes on install, the pulleys big bolt pinches the gear between the pulley and crank and that's what handles all the torque.
welp, i fired up today and it runs, no clattering no smoking, I have to adjust one tooth i think, might have retarded it a tooth as it runs, no poweer for a long while pulling onto the street lol

either that or there is actually som bent valves yikes

Last edited by volvoloco; 08-14-2022 at 07:16 PM..
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Old 08-14-2022, 07:08 PM   #20
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Also, the belt squeal, may very well be your harmonic balancer hub that is spinning, under load, when you accelerate. The outer pulley section spins on the rubber between the outer pulley, and the inner hub.(It sounds just like a belt squeal). Need a new hub. Good luck
definetly agreee with you there, its so loud

Last edited by volvoloco; 08-14-2022 at 07:16 PM..
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Old 08-21-2022, 06:46 AM   #21
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Could you set the cam pulley at TDC, take the valve cover off, and see if cam is also at TDC? Maybe you can also check through oil filler hole?
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