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Old 04-07-2018, 10:15 AM   #1
242Bleek
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Default 245T No more than 7 PSI

Hi all, im making this post because im at wits end with this car. Its a 1983 245ti, b21ft with kjet. Car has had virtually every single k jet component replaced, new cpr, fuel distributor rebuilt by cis flowtech, bosch gold injectors, new pumps and 255plh in tank, new engine harness, new o2 sensor, new everything base fuel pressure is at 95psi, control pressure is at 40psi hot.

As far as mods, care has a smallish precision t3/t4 with .63 ar turbine and stage 3 wheel internal gate. Ported 90+, b21f intake, all new piping. Basically stock engine with an m47 and clutchnet red clutch.

The car runs great but simply refuses to make more than 7-8 psi in boost. I have literally devoted months trying to figure out why, been through 3 intercoolers thinking there were leaking at the tanks, did smoke test. Pulled turbo to check if wastegate flap was seated and it very much is, all new manifold gaskets so no pre turbo leaks. No sign what so ever of it leaking boost and the boost stays rock solid on 7 psi and doesn't creep or move, its pretty much self regulating even with the wg line pulled. I will add that I have a stock exhaust with no cat and Ive also ran it open dp and made no difference. I have a dual port actuator on the wastegate with only the one line in use which ive read is fine.

At this point I just really don't know what else it could be, if a boost leak were that major k-jet will surely let you know about it by running like garbage, but the car runs just like a 7 psi car should. Can someone shed some light please? You think the intake track to the fuel distributor doesn't like this bigger turbo? Thanks in advance
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Old 04-07-2018, 10:22 AM   #2
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There's an overboost pressure switch above the brake pedal (aka charge air overpressure switch). I forget where it trips (it's different between the non-intercooled and intercooled cars) but 7psi seems a bit low. When it trips, it turns off lambda and fuel pumps. I think that if you search for "adjusting hobbs switch" you can find out more.

edit: Bentley says it should be at 10psi for non-intercooled and 15psi for intercooled.
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Old 04-07-2018, 10:29 AM   #3
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I know what you mean, that thing has long been unhooked, doesn’t act like it’s experincing fuel cut either, pulls hard to redline
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Old 04-07-2018, 10:41 AM   #4
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Have you checked that your boost gauge is accurate? 7psi is really 7psi? Otherwise, it seems like your turbo is simply not capable of over 7psi. I really don't know turbo parts, but any chance that a wheel has been replaced with an undersized part? Any chance that it's binding?

And have you stuck a hand vacuum pump on the actuator to confirm where it opens?
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Old 04-07-2018, 10:50 AM   #5
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It’s accurate, tried two different gauges. The turbo is brand new and spins freely. I have applied pressure to the actuator and it works as it should, I don’t know it’s opening pressure but it’s new as well. Either way it shouldn’t matter if the wg signal is pulled and it remains shut it’s gotta make unlimited boost till something breaks unless I’m missing something
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Old 04-08-2018, 10:43 AM   #6
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#1 go to harbor freight and get a regulator. and air gun
regulate air to 10-20PSI. and hit the waste gate with some pressure.

does everything move the way it should?

#2 grab some wire. and wire the wastegate arm shut so it cant move and disconnect the lines to it and plug them

do you get more boost? or same boost?

#3 get/make a smoke tester and boost test/smoke check the intake again.


question. how does it sound/feel? does it sound like the turbo is WORKING/spooling hard?

I had a clamp that would leak only under boost.. i could tell there was a problem because i could HEAR the turbo spool up hard and loud and fast.. but only got 5-7 PSI .

you might wanna get a boost leak checker IE: a cap to put on the compressor inlet on the turbo with a tire valve sticking out. then hit the intake with the smoke and pressure.

had to do it all the time with the TT VR4. so many pipes.. so many leaks.
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Old 04-08-2018, 10:55 AM   #7
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Itís accurate, tried two different gauges. The turbo is brand new and spins freely. I have applied pressure to the actuator and it works as it should, I donít know itís opening pressure but itís new as well. Either way it shouldnít matter if the wg signal is pulled and it remains shut itís gotta make unlimited boost till something breaks unless Iím missing something
Melted cat?
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how psi stock cna support?

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Old 04-08-2018, 12:20 PM   #8
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Melted cat?
Stock exhaust with no cat and he tried open DP, made no difference.

This sure is weird, I look forward to the results.
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Old 04-08-2018, 01:21 PM   #9
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Is there a CBV built-in to the turbo? separate CBV? leaking or adjusted to 7psi?
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Old 04-08-2018, 01:23 PM   #10
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I always believe 9 times out of 10 its the simple solution. That being said it sounds like you've replaced a lot and if it were me I would check and recheck the work. To me it sounds like something is giving way under boost and 7psi is it's max.
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Old 04-08-2018, 02:15 PM   #11
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Old 04-08-2018, 02:54 PM   #12
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Intake hose partially collapsing?
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Old 04-08-2018, 03:11 PM   #13
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Old 04-08-2018, 03:44 PM   #14
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Thanks for all your helpful replies guys. I have put pressure to the wastegate arm and it functions just the way it should oppens and closes. The way the boost feels limited is so consistent and really feels like it’s the wastegate doing it but that’s one area I’ve beat to death looking for leaks and it’s all airtight. I thought about maybe the actuator spring was letting the flap open under boost but I don’t see how as that thing is damn near impossible to move by hand an it’s preloaded like crazy. I but I will do a boost leak test, still baffles me.

Kjetsonaplane, one thing you mentioned was the timing could be too retarded under boost. One thing I forgot to mention was I removed the timing retard stop in the distributor. This may have been a bit extreme as I probably should have just ground it down. Could it be pulling too much timing under boost and actually limiting the engines exhaust energy and therefore overall boost pressure?

95 is a bit high, i’ll Probably remove a shim before I go any further and bring it back to stock.

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Old 04-08-2018, 03:58 PM   #15
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Old 04-08-2018, 04:04 PM   #16
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I second kjetsonaplane suggestion that you check the intake air cobra. If you have a car where someone only added an intercooler and did not add that cross support to the air intake cobra. Then it will suck it flat to the top of the airflow sensor. When the cobra turns down and changes to round hose. That section he mentioned as well can collapse.

There is a replacement for the cobra available from do88.
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Old 04-08-2018, 10:57 PM   #17
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Okay small update went and removed the cobra, looked everything over and it looks fine. Turns out years ago I did put a cobra from an intercooled car on this one and it does have the aluminum tubing inside as well as the cross reinforcement over the metering plate. Removed the upper portion of the airbox and there is no restrictions at all, metering plate has full range of motion, has a clean k&n replacement filter in there. So all is well on the intake side as far as I can see.

While I was in there I removed a shim on the fuel pressure relief valve and brought it back down to stock fuel pressure. Took it out for a drive and now instead of pulling hard to redline at 7 psi it now falls flat on its face at 7psi and around 4500rpm. Pulls okay then at 4500 it stutters and does nothing really.

Seems like it could be trying to produce more boost now if I get this issue solved. I’m thinking maybe the line pressure was disproportionately high for the control pressure and not allowing the plate to lift creating a major intake restriction. Any thoughts?
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Old 04-09-2018, 07:18 PM   #18
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Old 04-09-2018, 07:31 PM   #19
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"I have a dual port actuator on the wastegate with only the one line in use which ive read is fine."

That quote from your first post has me suggesting you try a different single port wastegate actuator. Also where are you taking the signal for the wastegate from? Stock it should be on the cold side interccooler pipe just after the coupler hose near the intercooler.
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Old 04-09-2018, 08:44 PM   #20
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Old 04-09-2018, 09:09 PM   #21
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Maybe the wastegate is getting pushed open from a weak spring in the actuator?

Try to safety wire it closed, or use a hose clamp or something...? Keep an eye on the boost gauge and see where it goes.
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Old 04-09-2018, 09:38 PM   #22
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Possibly an internally cracked turbine housing? The garrett exhaust housings cracked on a lot of stock 240 turbos.
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Old 04-09-2018, 10:10 PM   #23
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Is the coil hooked up right?
I had one 240T that was the slowest 240T I'd ever driven with a coil hooked up backwards. Took forever to figure it out.
But it would really sputter at 7-8psi (though oddly smoothly).
What's the pressure at now? 84psi? What's the warm control pressure? 50ish at sea level or whatever?

I hate K&Ns and wouldn't use them on anything! Fine beach sand and the like goes right through them and can cost you an engine! And with a bunch of oil on them they're a pain to clean and probably more restrictive than just a clean paper filter. I'll just keep buying Mann/ Mahle made in germany dusty shelf paper filters and never worry!
The more I look into this the more I donít think itís a wastegate issue itís reqlly acting as if itís starving for fuel after 7 psi, and or has a an intake restriction due to the metering plate not rising enough. As we speak I have the gauge on it again. System pressure is down to 87 psi and control pressure is hovering at 22psi on a warm engine at sea level which is very strange. The cars idle is not as smooth as it should be, you can hear slight variances in the in the tone of the engine, almost like a stumble of or richness and smells rich too. Think itís a bad cpr causing this mayhem? With control pressure that low I can expect rich but how would that starve it for fuel in the top end?
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Old 04-09-2018, 10:30 PM   #24
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Good grief. Sitting there watching the gauge and I started tapping the cpr with a wrench and control pressure rose to 40 psi before my eyes and stopped. Took it for a drive, same problem no difference, I get back and it’s still at 40. Close the valve and reopen and pressure drops back down to low 20’s and stays till I tap the cpr with a wrench again then it rose back to 30 and stops there. The bimetallic spring must be getting stuck or the cpr just doesn’t like getting tricked by the gauge.
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Old 04-10-2018, 12:13 AM   #25
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