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Old 08-14-2020, 07:30 PM   #1
olov
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Default 940 falls on it's face in boost

93 940 turbo, lh2.4. have thelostartof fuel chip, was running stock spark. mbc to 12-14psi on 15g. was running fine but random miss/backfire. did a tuneup, plugs, cap, rotor, wires(had one full of corrosion at the cap). reset the computers(via battery disconnect). put in thelostartof spark box, car did not want to rev over 3k, pulled fine under that. so I tossed the stock spark in, same thing.

I can see some black smoke out the tail in boost, I can build 14psi of boost, but the second I pass 4psi it's like the car hits a wall. revs hold at 3k, so it's not the trans slipping. it's building boost(reference in the intake manifold) and I cannot find any visible tears or loose pipes for a boost leak. fpr vaccum line is dry(so it's not leaking), turbo isn't really leaking oil, I'm going to toss in another fuel ecu and see what happens. what else could it be?
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Old 08-15-2020, 01:17 AM   #2
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Plug gap?

WbO2 readings?
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Old 08-15-2020, 02:59 AM   #3
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Sounds like it is running full rich, check for vac and pressure leaks.

Also what is the rest of your setup? Injectors? amm?

Ideally you want to know what the afr's are. With a fresh reset of LH I typically drive 100-200 miles before getting into boost as things can run a bit rich as the ECU is learning depending on what parts you have.
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Old 08-15-2020, 08:13 AM   #4
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Check the coolant temperature sender for the LH, it might be best to back probe the connector at the LH computer. If it's bad it can make it think it's -40 out and run way too rich.
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Old 08-15-2020, 08:15 AM   #5
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Quote:
Originally Posted by thelostartof View Post
Sounds like it is running full rich, check for vac and pressure leaks.

Also what is the rest of your setup? Injectors? amm?

Ideally you want to know what the afr's are. With a fresh reset of LH I typically drive 100-200 miles before getting into boost as things can run a bit rich as the ECU is learning depending on what parts you have.
all stock except for the chips, 15g, and ebay ic. like I said, it was running fine, did a tuneup, reset ecu, then the problem, so I'm guessing it's something odd like a sensor or shorting wire/etc. planning on more, but not until it's running right

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Originally Posted by Sjeng View Post
Plug gap?

WbO2 readings?

didn't gap them, couldn't find my gapper, but it doesn't feel like blowout. plugs are ngk's whatever autozone says is stock. car has stock o2 narrowband. but like I said, the black smoke out the tail makes me think it's rich

Quote:
Originally Posted by VB242 View Post
Check the coolant temperature sender for the LH, it might be best to back probe the connector at the LH computer. If it's bad it can make it think it's -40 out and run way too rich.

will check, ty
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Old 08-16-2020, 09:22 AM   #6
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Have you checked all the boots on the inter cooler?
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Old 08-16-2020, 02:40 PM   #7
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Have you checked all the boots on the inter cooler?
just checked them again, felt no tears, pulled on them pretty hard, nothing

I'll try the temp sensor thing, maybe do a diy boost leak thing
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Old 08-16-2020, 03:15 PM   #8
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Check the pre turbo intake boot it could be collapsing.
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Old 08-16-2020, 04:07 PM   #9
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Check the pre turbo intake boot it could be collapsing.
now that is possible, it's very soft when it gets hot
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Old 08-16-2020, 04:23 PM   #10
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They get super soft with age and oil contamination.
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Old 08-16-2020, 05:08 PM   #11
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Haha it's true I also had that on my V70Rrrrr very strange indeed
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Old 08-16-2020, 07:44 PM   #12
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Quote:
Originally Posted by Harlard View Post
They get super soft with age and oil contamination.
but it's still building 12-14psi at the manifold(where the gauge pulls from) so it may be happening, but it must be getting plenty of air if it's getting boost to the manifold
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Old 08-17-2020, 04:23 AM   #13
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You likely just have a post-turbo air leak.

The most common leaks are at the intercooler and at the idle air hoses. Spray around with brake cleaner/something flammable and see if the idle changes.
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Old 08-17-2020, 07:06 PM   #14
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Are you sure the new spark plug wires are ok?

A friend just recently had issues with almost new wires actually, and after heavy fault tracing he put some random very old ones back in and it worked flawlessly (!!)
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Old 09-08-2020, 04:48 PM   #15
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Originally Posted by ZVOLV View Post
You likely just have a post-turbo air leak.
idle air hoses.
that's what I'm thinking, but I cannot find it

I pressurized the turbo to throttlebody pipes to 20psi and not one leak. I'm going to try and pressurize the intake manifold next, not sure how I can get the valves to close enough to do it though. I might just bypass the idle air motor just to test too

it's been raining a lot, and I've been busy remodeling the house. I just lowered the boost to wastegate and it's at least drivable

edit: finally found it, the idle air hose, was cracked in a way that it looked/felt whole till it hit boost. couldn't pressurize the intake, I tried and felt nothing. just took the hoses off and found it then. ran radiator hose for now and ordered the right hoses and problem's gone.

Last edited by olov; 09-11-2020 at 04:52 PM..
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