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Discussion Starter #1
I'm wondering how exactly ECU controlled boost works.
In all my previous turbo vehicles, boost is limited only by the wastegate spring.

When manifold pressure surpasses the static force of the spring it is forced open and out goes the exhaust pressure. So a 14psi spring would allow 14lbs. of boost plus or minus. I also understand how a bleed can be used to extend boost beyond the wastegate spring rate by bleeding some of that pressure off.

What I don't understand is how my 87' T1 car opens the wastegate under that spring pressure. As far as I know my "small" wastegate can has a spring that requires about 14psi to open. I also know that my manifold pressure line is routed through a bleed solenoid before heading to my wastegate.

I know that the stock ECU and the FWD-performance Stage-1 ECU I'm using now, limit boost below a certain throttle position and in lower gears (auto 3-speed).

I don't understand however, how it opens the wastegate at all (to limit boost) without a pressure source?

For example if the stock ECU limits boost to 4psi in first gear how does it generate 14psi of pressure to open the wastegate at 4psi.

I realize I'm missing something fundamental or I'm misunderstanding something. I would like to switch to a dual stage mbc. So that I can maintain a low boost (+/- 4psi) setting for daily commuting, and a high boost (14psi) setting for occasional fun.

I'm finding that even with the stage-1 ECU (12lbs.) I rarely make even 2psi while daily driving, and if I put my foot into it (75% to WOT) I can make about 6psi under 4k rpm (which is as high as she gets revved on account of me babying her).

My wastegate is free moving and closed at start, and the actuator is connected and working properly. My vac. line for the wastegate goes from manifold to wastegate solenoid to wastegate can. So I'm operating under the assumption that the system is functioning properly.

I do understand that because of the ECU controlling the boost it is slow to build hence looking into an mbc. However I just don't understand how that wastegate can be opened with less manifold pressure than required.

I'm hoping someone here can shine a light on this for me..?

P.S. sorry post is so long, and I dually apologize if it's in the wrong forum.

Thanks in advance.
 

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Discussion Starter #2
So it would be impossible then to maintain a lower boost than the 6-7psi.
How is my engine managing to open the wastegate under that pressure.
For instance my car will make nearly no boost at all until I depress the throttle at least 50%. I can literally feel the wastegate close and boost builds within seconds.
How is it staying open up until then.

My turbo is the stock .48 trim Garret for an 87' T1 car. Which according to Chrysler made peak boost of 9lbs. @ 3900rpm under ECU control. So how come with exhaust, intake, and ECU upgrades I can't make 9psi @4k?

And how come ECU boost is so much slower to build, people always suggest an mbc to improve spool time claiming that the ECU is slow to respond.

But it seems to me if the ECU can have no boost lower than the 6-7psi spring-rate than up to that point an mbc should provide no gain?
 

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Discussion Starter #3
OK, that really helps.
I'm a big fan of "know how it works and if it's working properly, before you touch it".
Basically I like the boost I have now for cruising, but the wastegate is open at least partially almost all the time. Knowing that I went over the most common fail points for lack of boost. Boost leak, wastegate actuator, vac. lines. Nothing comes up irregular. The turbo can be heard spinning and there was no play or difficulty rotating last time I inspected it. No leaks, however I do have a stripped turbo to manifold stud, however there is zero detectable exhaust leak there and the contact between the manifold and turbo is good.

So I'm wondering how the car can make so little boost, that plus being able to feel the wastegate close under hard throttle makes me think the ecu is opening the gate.
So that helps a lot in understanding what's going on here.

So i guess next up is a boost controller that will work in line with the factory bleed solenoid to switch between ecu controlled boost and a manual setting (12psi like the ecu).

Two questions, does a wastegate spring so badly weakened that it will open at 2-3psi need to be replaced?

And does the ECU not read that the car isn't making the boost limit and start to bleed the vac line from the manifold to compensate?
(I read somewhere that's the problem with bleeding the vac. line instead of a full on mbc, every time the ecu is reset by battery disconnect it loses what it's learned about the bleed and allows too much boost until it's re-learned.)
 

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Just to clarify what's being talked about here ... you're dealing with two issues of pressure imposed on the wastegate. It's important to note that indeed the actuators spring can be moved to open the flapper with as little as 5-7psi imposed on the actuator through the vacuum line. The force required to move the spring by the pressure in the turbine housing is much greater than 5-7psi. ... can be as high as 25psi (large can). All the ECU has to do is modulate air pressure to the actuator using the solenoid.

boostcontrol
 

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Discussion Starter #5
I understand what you've written.
What I'm trying to understand is how my car is able to open the wastegate at such a low pressure (1-3)psi. There is no boost leak, nor any issue with the wastegate plumbing, or actuator.

Yet I will only make 2-3psi under heavy load and acceleration. If I don't depress the throttle half way or more I have almost no boost. And then under WOT I will only make about 5-6psi by 4k rpm.

I won't even make 2psi unless I have at least a slight incline and I gass it for about 5 seconds.

What I don't understand is why it feels like the wastegate is suddenly closing to make that 2psi. As if the wastegate is partially open all the time unless 50% throttle or more is applied.

From what I'm reading here, it could be that my actuator spring is severley weakened.
But even then the wastegate should be closed up until it's overcome by 2-3psi of manifold pressure. So how come it feels like it's open all the tie unless I floor it?

Should I be checking anything else?
Or is this normal for an 87' 2.2 T1.
Mods above.
 

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The flapper is always closed (default position). Weakened spring combined with a bad WG solenoid? .. maybe.
Is your vacuum line routing as per OEM? (the right solenoid is connected, etc?)
Is the actuator arm actually attached to the flapper pivot?
If you detach the arm does the flapper move easily? .. can you hear the flapper making contact with the orifice in the swing valve?
 

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Discussion Starter #7
The vac routing looks correct per the diagram under my hood, I had the retaining pin between the arm and actuator dissapeer a few weeks ago didn't even notice the difference that's how little boost I'm making daily.

When I replaced the pin, I checked the pivot mechanism, and the flapper could be heard and felt making a good closed contact, also moves freely.

The wastegate actuator can be pulled on when disconnected, the spring feels strong, it takes some force to extend it.

It is in the closed position when I start the car, the vac line between solenoid and is good. Not that it should matter as improper routing and/or a leak would only hold the wastegate shut.

I guess it's possible I'm either loosing exhaust between the turbo and manifold. I have a single stripped stud there I need to replace. However there is zero leak between idle and 2k with no load and the surfaces look very flush, no change in turbo sound since I got the car 15k miles ago so I doubt that, also the other three are on there tight.

Or maybe my wastegate spring really is that weak (1-2psi) and during part throttle its forced open at least partially and only closing under heavy throttle?

This is so odd, zero possibility of boost leaks, I suppose I could have missed a pin-hole in a vac line but again that would only help close the gate. Up until I installed a bosst gauge recently I just thought the ECU was limiting boost and this was normal. When I installed alky injection and the FWD (12lb.) ECU I thought it would make more. Hence the query on how the ECU could be holding boost that low. Now that I understand, I know something is irregular.

I should readily be making more than 1-2psi at part throttle, and more than 6psi under WOT at 4k. Need to do some more reading...
 

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if U want to rule out the WGA side of the problem,
disconnect the WGA, then wire the WG flapper so it CAN"T OPEN

now, carefully drive it, giving mor throttle gradually, so you dont overboost lol

see if problem goes away ...
 

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Discussion Starter #9
Connecting the wastegate directly to the manifold net's the same boost.
So it's not vac. line or routing issue.

Disconnecting the wastegate entirely net's the same boost.
So it's not a wastegate issue.

This leaves only boost leak, exhaust leak pre-turbo, or turbo issue.
Since a boost leak at 2psi would be easy to catch and there is only a single hose between turbo and manifold this is unlikely.

I do have a stripped turbo to manifold stud, but this problem began before I stripped it, and as I've said the other three are on tight and surfaces are pretty good. No detectable exhaust leak at all at idle. So this is unlikely but not impossible.

This leaves the turbo, which spun freely 5k ago when I last inspected it. No irregular noises coming from it, just the slight whistle of spool like always.

Is it possible that bearings on the turbo could be holding up more boost beyond what I'm seeing (i.e. turbo on it's way out)? Has anyone ever experienced declining boost from a turbo before it fails?

Or should I be looking elsewhere (i.e. turbo stud)?

What would you guys check first?
Car makes only 2psi under heavy throttle, if I get on the freeway and go WOT It will make about 5psi.
 

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if U want to rule out the WGA side of the problem,
disconnect the WGA, then wire the WG flapper so it CAN"T OPEN

now, carefully drive it, giving mor throttle gradually, so you dont overboost lol

see if problem goes away ...
Detobias already told you what to do.

Asking questions and not trouble shooting isnt going to get you anywhere but annoying people into not helping.
 

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Discussion Starter #12
Detobias already told you what to do.

Asking questions and not trouble shooting isnt going to get you anywhere but annoying people into not helping.
Listen I'm sorry if I annoyed you. I realize my posts are lengthy.
That being said I gotta say that's kinda harsh.
I did do some troubleshooting earlier, ruling out two possible fail points for sure. I'm not going too justify why I didn't have time to do any more work today, no one wants to hear it and I sure as hell don't feel the need to. I appreciate the help I get on here, if I write to much I'm just trying to be precise, in an effort to avoid wasting your time and mine.

Moving on, I will isolate the wastegate actuator tomorrow.
Any opinion on the possibility of say worn bearings in the turbo.
I've never seen bearings slow something that much without failing completely, but I'm no expert either...
 

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when yur working on it 2morrow, pull turbo inlet tube - you can reach right in and wiggle turbo shaft with yur fingers

its possible turbo bearings may be SO LOOSE that comp wheel is fouling out on comp housing, or similar with turb side, and not allowing turbo to spin up
 

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What are you using filter wise ... pre-turbo? Only other thing that would make sense is the turbo not being able to breathe. A restriction on either side could cause this.
 

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Discussion Starter #15
Stock 87' T1 intake w/ K&N filter.
I'll pull the air-box when I take a look at the impeller tomorrow.
Doubtful anything's in there but anything's possible.
Thanks for the suggestion.

Have you ever heard of carbon build-up on the wastegate flap itself preventing a decent seal? It felt and sounded like it closes securely but obviously I can't see it.

Also is there a difference in the lengths of the different wastegate shafts on different TD wastegates, mine looks like a standard "small" can and the rod itself is one-piece non-adjustable so I assume it's the factory original, possible it's been replaced with a later model which may have had a longer actuator?

What about the can itself possible something is preventing the spring from returning the piston all the way closed?

Oh well, know more tomorrow.
 

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I have the exact same problem,,to a T,, ,yesterday i put in the stg 1 ecu and vacuum gauge,,, I have an 86' Lebaron 2.2 turbo ,,and i understand the fustration. I have yet to make any headway. ,,but i believe most of the solonoids are shot(3out 4) i know the map solonoid is shot and even tho its detriment,,,, i drive with it bypassed. Could the waste gate solonoid be be shot? Or turbo solonoid for that matter,,, 2 issues are different but i feel its just cause of age. ,,,,the throttle body to turbo tube collapses slightly when running in idle,,,,?,, and a mildlyrough idle |slight miss,, very slight ,,,, check lines. All of them, leaving out alot but just wanted to relate,,,,,,i have the same boost problem. Exact.

Same readings at same throttle position
Thanks
 

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I had some boost tiny problems like this and it wouldnt spool much at all when I floored it it did and then it didn't... Two mice crawled up and died near the turbo inlet and when I floored it turned them to mush on the intake
 
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