Losing turbo pressure when warm - MR2 Owners Club Message Board
 
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post #1 of 13 (permalink) Old September 19th, 2019, 13:52 Thread Starter
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Losing turbo pressure when warm

I recently purchased a 91 MR2 from a younger gentlemen that was not super mechanically inclined. The car wouldnt start when the key was turned and ran poorly when push started. I was able to get it started by cleaning up some corrosion build up on the battery terminals. The car smoked kind of bad and wouldnt stay running without feathering the gas. I looked over the engine bay and noticed that the mass air flow sensor was unplugged. Plugged it in and car idles great.
Took the car for a drive and the turbo gave the car a great hard pull. For the next couple of days the car drove like a champ. I went to put a radar detector in and nothing lit up. I decided to check to see if the cig lighter was unplugged. This might have been a mistake. I found a bunch of bare wire behind the lighter in a ball and barely attached to the lighter. Basically there was a bunch of wiring that was put in for the boost gauge and a couple of other wires that go in to the dash with unknown path. In order to see everything I took apart the center console. Doing so I accidently unplugged the boost controller and somehow blew the fuse to the stereo and controller. I tried to drive the car and had no boost power while i was hearing the turbo spool and blow off as it should. This is when I went back through and noticed the boost controller unplugged and plugged it back in.
I go for another drive and only have partial boost. It feels like it wants to pull hard it just won't. At this point I am generating 4-6 psi boost. I start going over the piping and end up replacing a few couplers and hose clamps. Get under the car and changed exhaust flange gaskets and bolts. Notice the alternator is zip tied in place. Correct that issue to correct 100 amp alternator.
Now I take off in the car and I hear the turbo spool correctly but dont feel the power until I start getting up to 4000 rpm. Is this normal?
Also, the psi the turbo is generating is greater during the first 8 to 10 minutes of driving. I am hitting around 10.5 psi during this time. As the car runs and gets fully up to operating temp I can no longer reach that same turbo pressure. If I come to a stop then get into it I can only get up to roughly 6 psi of boost. Dont understand this and am hoping someone can give me an idea of what is going on? I also noticed last night that I was reaching 4500 rpm I was at 5.8 psi and as I reached 5500 rpm the psi was dropping. I dont think its supposed to drop like that but this is my first turbo anything and am learning as I am going on this.
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post #2 of 13 (permalink) Old September 19th, 2019, 15:31
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There is a lot to process here, your post isn't easy to follow.

Post pictures of your engine, the mess of wires, boost controller, anything you think is important.

My first concern is what generation engine is it? A 2nd generation 3SGTE will not run without the air flow meter installed, it will start then immediately die. I cannot explain why you were able to keep it running with it unplugged. These engines don't have a hot wire mass air flow sensor, either a vane air flow meter or in the case of 3rd generation onward a MAP sensor.

I would start by cleaning up the known problems you have with the car now, remove the boost controller and clean up the wiring so you don't blow fuses that's priority one. I would also remove the hoses connected to the wastegate actuator, take all of it out and then once you get the car right reinstall it.

The alternator is zip tied in? I hope that's fixed that might be priority one don't get stranded because the alternator stops charging.

There is also the possibilty of the wastegate actuator getting caught on the downpipe and sticking open. It used to happen a lot in the past with poorly made Chinese downpipes.

I also wouldn't be redlining this engine until you get it fixed, there is obviously a problem and continuing to push the engine may cause more damage.

One last thought does the check engine light work and is it on? You will know the check engine light works because it will be lit when you turn the key to the ON position and if there are no problems it will go out when the engine is running.
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post #3 of 13 (permalink) Old September 20th, 2019, 12:27 Thread Starter
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Apologies for the difficult to follow post. There is a lot going on in the car. I have addressed the alternator issue and am goos to go there. There is a check engine light yes. It is showing codes 41, 43, 51 and 52. I am unsure of which generation the engine is. How would I be able to determine this?
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post #4 of 13 (permalink) Old September 20th, 2019, 13:44
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Post a picture of your engine is the easist way I can tell you what generation you have.

You need to fix the problems the ECU is telling you to, especially the code 52 which is knock sensor the ecu will go into limp mode with a code 52.

Incase you don't know what your current codes are...


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post #5 of 13 (permalink) Old September 21st, 2019, 03:23 Thread Starter
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Here are a few pics of the engine bay. How do I tell the generation of the engine?
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post #6 of 13 (permalink) Old September 21st, 2019, 10:19
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That's a JDM gen2, the JDM engines don't have an EGR and on the intake manifold they say "ceramics power" which means it came with a ceramic ct26.

There is a lot going on in that engine bay it's going to take some work to get it cleaned up.
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post #7 of 13 (permalink) Old September 21st, 2019, 20:48
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Post better pics specifically of the hoses around the intake and the wastegate.

Pull the back of the truck liner back and take a look at the ecu and wires there, see what the previous owner got up to.

I have a jdm gen2 MR2 hopefully I can help.

Last edited by T3HKMAN; September 21st, 2019 at 20:52.
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post #8 of 13 (permalink) Old September 22nd, 2019, 16:05
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Quote:
Originally Posted by J.harris View Post
That's a JDM gen2, the JDM engines don't have an EGR and on the intake manifold they say "ceramics power" which means it came with a ceramic ct26.

There is a lot going on in that engine bay it's going to take some work to get it cleaned up.
To be more specific, it's a 92-93 JDM GEN2 3SGTE. A few changes were made over the 89-91. Sort of like a GEN2.5.
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post #9 of 13 (permalink) Old September 23rd, 2019, 17:27 Thread Starter
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Does this engine have a MAP sensor?
I just got done installing a new knock sensor and am awaiting a throttle positioning sensor that should hopefully arrive tomorrow. Didnt notice any change with the knock sensor.
I also recently was told to possibly switch to a mechanical boost controller. Currently I have a digital that has a display and controls in the cab. Has anyone else had issues with the digital/electronic controllers failing?
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post #10 of 13 (permalink) Old September 23rd, 2019, 17:32 Thread Starter
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Answeres my own question I think. No MAP sensor. Is the air flow sensor the same thing as a mass air flow sensor?
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post #11 of 13 (permalink) Old September 25th, 2019, 16:07
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Air flow sensor is not the same as a mass air flow sensor. AFM usually refers to a vane type sensor that deflects a sprung door attached to a potentiometer. Measuring temperature and barometric pressure and sending that information to the ECU gives the mass flow rate. Mass air flow sensors detect mass flow rate directly, by heating a wire and measuring the change in resistance from air flowing over the wire. They only need an air temperature sensor as colder air with the same mass flow rate will cause a bigger change in resistance than hotter air.

The 3S-GTE gen 2 does have a MAP sensor but it is for failsafe only. If you overboost it will shut off fuel injection.
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post #12 of 13 (permalink) Old September 25th, 2019, 17:24
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MAP sensor sits up on the rear firewall close to the diagnostic port (grey box) and engine lid latch. Early gen 2's will have an orange-ish label on the top of it (MAP is a little box about 1" x 1" x 3/4" with a hose barb pointing down).
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post #13 of 13 (permalink) Old September 25th, 2019, 23:50
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Agree w everything above. In regards to the boost issue it *sounds* like you are hitting wastegate pressure, and you said there is a boost controller? My guess is one of the vacuum lines to/from the turbo, boost controller, and wastegate actuator is loose such that the you aren't bleeding off anything and the stock wastegate is opening as it should (without TVSV).
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