The infamous limp mode!!!(5psi)

Headlights to tailights and everything in between.

Moderators: Helpinators, Moderators

Post Reply
SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

The infamous limp mode!!!(5psi)

Post by SupaSubaru » Sun Sep 22, 2019 5:04 am

I will try and keep this as simple as possible

Ive got a 90 subaru Loyale that has an EJ22t swap. Cone filter, silicone intake tubes, wrx factory intercooler with the recirc valve, stock turbo, cat delete and exhaust. everything else is stock subaru, just as it was intended to be in a Legacy SS

Engine was rebuilt and installed into the car 4 years ago and has since seen 70k miles of nothing but fun. Always ran great, no issues, 10psi. everything right as rain, not a single thing has been changed other than regular maintenance.

A few days ago i go to get into the throttle and notice im stuck on 5psi. Everything feels normal, no weird issues, just wont boost past 5psi.

First thing i do is check for engine codes, not a single issue reported. I then proceed to clear the memory from the ECU per shop manual instructions.

Car now boosts up to 10psi perfectly no issues. This is where the headache begins. The ecu falls back into limp mode (5psi) with just a few minutes of driving. Regular driving or hammering on it, the condition always comes back after clearing the ECU.

-I always use 92 octane gas (from the same gas station i fill up my 500hp honda civic) so i know thats not the issue.
-I checked all my obvious connections (vac and electrical)
-Spark plug wires are fairly new so ive ruled that out
-I replaced the spark plugs
-I replaced the MAF (tried cleaning the old one, nothing changed)


I plan on replacing the knock sensor tomorrow (i removed and inspected the one on the engine, no cracks)


Im really at a loss here as to why the limp mode condition keeps coming back but is not providing a code for reference. I keep this car in tip top shape, the engine and bay is sparkly clean. it has no leaks of any kind, doesn't burn oil, none of that. For the last 70k miles its been free of any issues until a few days ago and ive been reading and trying all kinds of stuff without an answer. Shop manual hasnt given me much to work with other than running the self diagnostics and memory clear functions. If someone on here could point me in the right direction it would be greatly appreciated.

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Sun Sep 22, 2019 9:18 pm

Replaced the knock sensor, cleared the ECU. issues comes back after 5 minutes of driving. Still no codes.

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Mon Sep 23, 2019 12:11 am

Replaced the Ignition Control Module, cleared the ECU, it switched back to limp mode in several minutes worth of driving. No codes.

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Mon Sep 23, 2019 3:44 am

Replaced the O2 sensor and verified mechanical timing, cleared ECU, switched back to limp mode in several minutes of driving. No codes

Something i tried later in the day was resetting the ecu and driving the car super easy for about 15-20 minutes, no boost, no more than a 1/4 throttle or so. I tried that and was able to boost around on 10 psi for almost 30 minutes before the ECU kicked me back down to 5psi. It would seem the ECU has some time to build up a known history of running conditions thus allowing me a longer period of time to drive around hard without it kicking me out of normal mode. Still doesn't address the original issue but a different result.

Legacy777
Site Admin
Site Admin
Posts: 27536
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Re: The infamous limp mode!!!(5psi)

Post by Legacy777 » Mon Sep 23, 2019 6:15 pm

Welcome to the BBS.

This thread points to a MAF sensor.

viewtopic.php?f=2&t=54081

Do you have a spare or have you tried cleaning the MAF?

I would also suggest checking/testing all the vacuum/boost lines. Also check the MAP and PES.

These diagrams are helpful.

https://www.surrealmirage.com/vrg3/vacuum/
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Mon Sep 23, 2019 7:44 pm

I already tried cleaning my original MAF, with MAF cleaner, reset ecu, limp mode came back within 5 minutes of driving. No codes

I replaced the MAF, reset ecu, limp mode came back within 5 minutes of driving. No codes


I will recheck all of my vacuum lines again.

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Tue Sep 24, 2019 5:18 pm

Pulled the fuel filter this morning and cut it open to see what was inside, it was super dirty. Decided to pull the injectors to check the screens and they were real nasty as well. Dropped them off to get cleaned/flow matched with new screens. Will report back at the end of the week when I get them back.

Legacy777
Site Admin
Site Admin
Posts: 27536
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Re: The infamous limp mode!!!(5psi)

Post by Legacy777 » Wed Sep 25, 2019 5:36 pm

Thanks for the update and let us know how things go with the injectors.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Thu Sep 26, 2019 12:03 am

Well, the injectors were down 10 percent on flow. Got them cleaned so now they are good to go, new screens installed as well as O rings.


Got everything back in, reset the ECU, car was running fantastic on 10lbs of boost, everything feels great, unfortunately the ECU kicked me back down to 5psi in about 10 minutes of driving.

Probably going to getting gas at a different station than i normally do to see if its not happy with whats in the tank right now.

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Thu Sep 26, 2019 5:09 am

Okay so running 93 octane fuel didn't change anything

I did try something a little different for diagnosis purposes, first i tried moving the knock sensor to a new location on the engine (to desensitize any knock readings going to the ECU). Reset ecu, limp mode came back within 5 minutes of driving. No codes

I then grounded the knock sensor and removed it from the engine and let it hang in the engine bay. reset ecu, limp mode came back within 5 minutes of driving. No codes


So at this point im fairly certain im not getting any type of knock or false knock readings. Im now thinking maybe the TPS needs re-calibrated or something else. Any input would be appreciated.

Legacy777
Site Admin
Site Admin
Posts: 27536
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Re: The infamous limp mode!!!(5psi)

Post by Legacy777 » Thu Sep 26, 2019 5:29 pm

I would tend to agree with you that knock sensor is not causing your issues. I don't think the TPS is the issue either, however calibrating the TPS is easy and quick.

My suggestion would be to with the MAP sensor, pressure exchange solenoid, and all the vacuum lines. For testing purposes, if you have a manual boost controller try using that and see if you get the same limp mode or fuel cut. With the MBC the ECU won't be able to lower boost, it'll just cut fuel.

Check all the wiring from the sensors to the ECU for good continuity as well as the vacuum lines for leaks. If you have a vacuum/pressure pump use that to test the hoses.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Thu Sep 26, 2019 10:02 pm

Well i think i have a spare map sensor and pressure exchange solenoid, i will also do some electrical testing today and see what i can figure out.

something else to be considered is i might have electrical interference/bad knock sensor wiring, i may end up running a new shielded wire to see if anything changes.

The problem with using a manual boost controller is that i can force it to run 10psi but the underlying issue will still be there. When it goes into that mode it not only cuts boost down to wastegate pressure but it pulls a lot of timing out. Running it on 10psi forcebly wouldnt give me the performance or efficiency from the engine.

Where is the subaru select monitor connector on the factory harness for a Legacy SS? i might try and see if a subaru shop can plug into it.

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Fri Sep 27, 2019 12:40 am

replaced the pressure exchange solenoid, didnt change anything.

I ended up buying an AEM wideband kit, gonna install that tonight and take a look at the fuel air ratios and make sure its running safe

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Fri Sep 27, 2019 6:25 am

AEM wideband installed, manual boost controller installed, for the most part seems to be okay under full throttle air fuel ratio wise, everything feels okay as well.

I do need to relearn the idle as it hasn't been that great with multiple ECU resets. idles low and irregular with very lean readings.

I will probably just run the setup this way after i address the idling issue. I really wanted it to be back to oem running condition as it should be but it was becoming an expensive headache for no reason and i just couldn't justify doing more to it.

wtdash
Fifth Gear
Posts: 2283
Joined: Fri May 04, 2007 4:09 pm
Location: N. ID

Re: The infamous limp mode!!!(5psi)

Post by wtdash » Sat Sep 28, 2019 9:11 pm

Where is the subaru select monitor connector on the factory harness for a Legacy SS? i might try and see if a subaru shop can plug into it.
Not sure on your swap, but it's the YELLOW connector near the driver's right knee on the stock SS.

If you build a cable (search on here) you can use some of the online diagnostic tools, but since it's not OBD2 may be just the Evoscan ($$) and Revtronix.

There is/was a VW guy that made SSM scantool for his EJ20G-swapped Vanagon, but can't recall the name....been 10 years ago.

Edit: easier than i thought: http://www.vwrx.com/index.php?pg=selectmonitor

Free but donation requested.
Turbo Subies:
'87 GL-10 Turbo 4WD Wagon (pre-Loyale) - SOLD
'90 BJ, EJ22T/DOHC and 5-speed swap - SOLD
'04 FXT, Forged internals, VF39, STI TMIC, Cobb AP- SOLD
'93 Legacy SS - 5-speed, SOLD :-(
'02 WRX GG-SOLD
'96 BD - turbo'd-SOLD

dankberries
Second Gear
Posts: 482
Joined: Thu Oct 27, 2011 5:09 am
Location: Dirt Roads, Colorado

Re: The infamous limp mode!!!(5psi)

Post by dankberries » Mon Sep 30, 2019 3:08 am

Do you have the factory ej22t wastegate solenoid hooked up?
93 impreza rally muffin
93 legacy ss Tarmac Terminator
89 Nissan 240sx sr20
90 Nissan 240sx 2jz
killajamal wrote:Dank is actually German for "silly term which the kids have come up with to describe exceptionally choice marijuana.''

Legacy777
Site Admin
Site Admin
Posts: 27536
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Re: The infamous limp mode!!!(5psi)

Post by Legacy777 » Mon Sep 30, 2019 5:34 pm

Here is another scan tool you can build.

https://surrealmirage.com/vrg3/b10scan

I agree with you that there may be an underlying issue, but at the end of the day if you can get it to run right with a MBC the result is what matters.

Unfortunately, these ECU's are pretty dumb in the grand scheme of things so they don't have very good diagnostic abilities and I've had people say they disconnected their knock sensor and didn't get any check engine light. When I put in my stand alone ECU I checked all the wiring and discovered my knock sensor wire was bad. I don't know how long it had been like that or if it got that way as a result of me messing with the wiring.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Fri Oct 04, 2019 12:39 am

So with the mbc hooked up on 10psi its okay but if i do an ecu reset its WAY faster on the same boost. Limp mode 10psi 10.0-10.5AFR wide open throttle. Normal mode 10psi 11.75-12.0 AFR wide open throttle. Whatever the ECU is doing in limp mode is more than just dropping the boost via the EBC, its pulling timing and adding fuel, way too much. Like i said it runs okay in limp mode with a MBC on 10psi but its a whole different animal when the ecu isnt in limp mode.

Still trying to figure out what i should do....

Legacy777
Site Admin
Site Admin
Posts: 27536
Joined: Tue Oct 15, 2002 11:37 am
Location: Houston, Tx
Contact:

Re: The infamous limp mode!!!(5psi)

Post by Legacy777 » Fri Oct 04, 2019 5:59 pm

I know it sounds tedious, but what I would do is check all the wiring going back to the ECU. Start with each sensor and check the resistance going back to the specific pin at the ECU. Also verify you have good voltage and ground. By doing that you should be able to at least eliminate wiring as an issue. Then I'd check every sensor to make sure it's in spec.

If you do all that and it doesn't change anything I would try a different ECU.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Sat Oct 05, 2019 1:09 am

So i decided to check the TPS calibration, it was slightly off 4.89v throttle closed so i adjusted it to 4.7v (manual states 4.8 is the upper limit)

Then some weird stuff started happening, the idle kept sticking on 2k rpms while driving around so i checked for codes, nothing showed up, so i did the ecu reset procedure and it wouldnt complete, kept pulling up a TPS code.

Checked the voltage again, still okay, checked a few other things and didnt get anywhere with it, so i dug around in my stuff and found another JECS TPS. The one that was on my car didnt show a brand just a part number.

Installed the JECS TPS i had, calibrated to 4.7v, disconnected battery terminal, let it sit for a bit. Reconnected the battery fired it up to do an idle re learn and shut it off when it was warmed up.

I got 30 minutes of hard driving at 10psi on the factory boost controller with no issues or limp mode. It might be okay now (fingers crossed) i drove it back home and parked it, gonna let it cool off and i will take it out for another rip later tonight.

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Sat Oct 05, 2019 6:46 pm

took it for a rip this morning, still running good, no codes no limp mode. guess we will see how long it lasts

SupaSubaru
In Neutral
Posts: 15
Joined: Sun Sep 22, 2019 4:41 am

Re: The infamous limp mode!!!(5psi)

Post by SupaSubaru » Tue Oct 08, 2019 6:31 am

So it finally came back.

There is something to note, im hoping someone will know what it means.

Normally after a memory clear/ecu reset, when everything checks out the check engine light will flash on and off consistently until i disconnect the green connectors.

This last few days when i was running good, everytime i checked the ecu for codes id get a solid check engine light. after limp mode and a reset im back to a constant blinking check engine light when i check for codes.

What does a blinking check engine light mean? (with the black plugs connected)
what does a solid check engine light mean? (with the black plugs connected)

mike-tracy
Moderator
Moderator
Posts: 4937
Joined: Tue Aug 25, 2009 7:52 am
Location: Des Moines, Wa

Re: The infamous limp mode!!!(5psi)

Post by mike-tracy » Tue Oct 08, 2019 5:59 pm

Constant blinking (code 11) means all clear, no saved or active codes. Solid light means a saved or active code.
1992 Legacy SS 5mt, build in progress
Josh Colombo wrote:
Mon Jan 14, 2002 10:23 am
Wait....I'm confused now.

Post Reply