4krpm loss of IDC under boost

[SoCoNoHa]

I've read tons of threads, haven't seen anyone with this issue. As I pass 4krpm in boost, my IDC cuts to nearly zero for a moment then back to normal. If i pass 4k in vacuum, there is no issue, it's only with positive manifold pressure.

It's blowing my mind because the ecu shouldn't have a clue whether I'm in boost or not. I have a greddy emanage ultimate in a 97 LGT, stock ecu. I have tried a couple other ecus I have for the EJ25D, they do the same thing, so I'm thinking it's not the ecu but of course it still could be.

For the record, this isn't the emanage cutting IDC, I'm losing the IDC INPUT to the emanage, FROM the ecu. Naturally, since the piggyback is reducing the injector signal to manage larger injectors, if it sees near zero IDC then that's about what it puts out. This happens for as brief a period as my logs can measure. 20ms to go from normal down to nothing, then another 20ms back to normal.

Oddly, it's more severe at partial throttle, less severe at full throttle, but certainly still there, as long as there's at least some boost. I'll try to get a pic of my log posted.

I'm hoping some ecu guru could suggest why the ecu would do that, or perhaps someone with emanage ultimate experience (no694terry?) has seen this before.... Thanks for any and all help.

* Registered users of the site do not see these ads.

[benflynn]

Megasquirt friend

[that11guy]

Are you maxing out the maf? Sounds like your hitting the limit of something.

[SoCoNoHa]

Technically yes, but the ecu shouldn't know that as I have a variable voltage clamp on it. IDc's have just gone to 100 when I've given the ecu max MAF voltage before. I'll set a reminder to post some logs tonight. I'm convinced it's got to do with the closed loop transition, but I have the o2 connected and get no codes for it. I do have injector low voltage codes though. Expected since I'm cutting half the signal or so.

[wtdash]

Hi, I have '98 Foz running NA-T, but stock ECU only - no other EM. I know on mine if I run over 7 PSI I get a MAP sensor code (the one by the pass. strut tower).

I fixed that by putting a one-way valve inline w/the MAP so it doesn't 'see' boost (although I now get an EGR code after a few drive cycles).

Edit 4/12/25
CEL info:
-I've had a recurring P0400 EGR code, that's due to the one-way valve I have on the vacuum line going to the MAP/pressure sensor.
-If remove the one-way valve I get the P0108 Subaru Manifold Absolute Pressure Sensor Circuit High Voltage due to the (relatively) high boost - 10 PSI.
-Since the P0400 code pops about every 3rd drive cycle, vs every drive cycle w/the P0108, I just live with it and reset it as needed.>>This is not my DD. I drive it about 1-2 x a week.
-If I run stock TD04 @ 7PSI wastegate boost I get no codes. But I like that extra boost.
-Installed the Zener diode and the code hasn't come back after multiple 10 PSI runs.
-The diode limits the max voltage the ECU 'sees'. When the voltage gets to 5.1V (when in boost) it 'clamps it' / stops it from going any higher to the Sensor's Signal, which would trigger the P0108 Code.

Install
-I removed the one-way valve to the MAP (that caused the P0400 EGR code), which brought back the P0108 (high input in the manifold absolute pressure (MAP) sensor circuit).
-Probed the unplugged plug and initially got the same voltage on both the Signal and the Sensor 5V (?), plugged it in and was able to figure out the middle 'green/yellow' wire as the Signal (?!) - used Key On-Engine Off is 3.9-4.1V.
-Red/Green is Ground (?!).
-Installed the 5.1V 5W diode between Signal and Ground wires.
-This works 95% of the time - meaning I still get a P0108 code occasionally, so either need a different diode or 'it is what it is'.


Thanks to @kay95 over on the RS25 forum, I learned about using a Zener diode: Zener diode can be used to fix voltage in a circuit by acting as a voltage regulator or reference

[SoCoNoHa]

So you're running 7+psi without pulling any timing?

[wtdash]

Originally Posted by SoCoNoHa

So you're running 7+psi without pulling any timing?

Correct. Totally stock ECU, injectors, etc.
10 PSI for the last year+. I updated my post above to my latest 'fix'.
I'm NOT saying this is a good idea, but it just keeps running- no issues.


I had a Greddy EMU installed on this same car - with an EJ22T/EJ25D setup- and might still have a Greddy EMU tune if you want it for reference. I got it and a bunch of parts from Morrocco88 back a LONG time ago. Here's his original thread: https://forums.nasioc.com/forums/sho....php?t=1792564
Edit: I see you posted in that thread - 3 years back. :-) Not sure what happened to him...probably moved on to other projects>life.

My setup:
'96 EJ22 block with EJ25D heads.
TD04
Head Gasket: EJ25D Fel-Pro HG.
Intercooler: '07 FXT TMIC
Hood Scoop - Impreza RS: Cut hood (!)
EJ22T water pipe- moves the temp sensors out of the way
Fuel Pump: Walbro GSs342
Down pipe: Aftermarket 3" - Installed 12/21 (?)
Exhaust: 2008 Forester XT - mid-pipe + axle-back + muffler - Installed 12/21