Fuel cuts when in boost

[2.2TLegacy]

Here is the deal, the other night, drove the car home from work and everything was fine. Went back out in the morning to start and the check engine light was on. Car runs fine, EXCEPT FOR

Have to blip the throttle at idle before engaging the clutch otherwise it will die

-and-

Cannot go into boost with out massive fuel cuts.

If i stay out of boost the car runs fine, any rpm.

I am going to tear into it today but I just wanted to see if you all had some ideas where i could start.

Car is a built 2.2t:

ej22t
DOHC head from the ej20g
Weisco forged internals for ej22 stroker (part number K602M975)
Phase 1 EJ25 crank
2007 sti vf-39 turbo
Sti 550cc injectors
2004 WRX intercooler (only one that fits without modification to the firewall)
Full 3" custom stainless steel exhaust
5sp transmission from a 1996 STI (Japan spec, crated from Subaru in Japan)

[Legacy777]

Check the codes before you do anything else. I've learned that the hard way. Instructions on how to pull the codes can be found on my site.

www.surrealmirage.com/subaru/engine.html

[2.2TLegacy]

"scanned" the codes, got codes 13, 14, 23 and 45.

13 - No signal entered from cam angle sensor, but signal (corresponding to at least two rotations of cam) entered from crank angle sensor

14 - Fuel injector #1 inoperative (Abnormal signal emitted from monitor circuit)

23 - Abnormal voltage input entered from air flow sensor

45 - Atmospheric pressure sensor (faulty sensor)


I believe that 13, 23 and 45 are related to my build and that the inoperative injector is my problem. Seems to be an intermittent issue though because like i said if i stay out of boost, the car runs fine.

Any other inputs would be awesome.

[Legacy777]

Try clearing the codes and then see which ones come back. Use the method described on my site with both the green & black connectors. Also, you can try just the green connectors for "active" codes at that moment. That may also narrow things down for you.

[2.2TLegacy]

Did the active codes by using the green connectors. The only active code is 45, which after noticing there was a turbo and N/A column is:

Faulty sensor or pressure exchange solenoid valve inoperative

Still confused as to why I only have issues at idle when first hitting the throttle after coming to a stop and when i am in boost (which is like clockwork, as soon as it hits 0psi on my boost gauge the car bucks violently and cuts power)

[Alphius]

An undocumented behavior that I found is that when Code 44 is active for the boost control solenoid, any positive pressure causes fuel cut. I wonder if it is the same for Code 45? If the car cannot reliably measure boost pressure, I would bet it just cuts fuel to keep the engine safe.

The pressure exchange solenoid is the solenoid on the passenger side of the engine bay attached to the strut tower that the vacuum line from the front runner of the intake goes to. The Subaru system only has one pressure sensor. The ECU uses the solenoid (which is separate) to periodically switch that sensor to measuring atmospheric pressure instead of manifold pressure. If the vacuum lines are hooked up wrong or the solenoid is bad you will get that code.

As far as the idle problem, I would bet that since it doesn't know what atmospheric or manifold pressure is that some part of the ECU off-idle programming is dependent on that information.

I bet if you fix that code your car will run fine.

[Legacy777]

I agree with Alphius, check the vacuum lines, pressure exchange solenoid, and the MAP sensor to make sure they're all good. Once you've fixed the problem there, clear the codes and see what symptoms, if any are still present.

[2.2TLegacy]

That is what i am figuring the issue is, is there anyway to test if the solenoid is functioning properly or if it is a wiring issue instead? Don't want to throw $100 at a new sensor and find that's not the issue. All the vacuum and boost lines are OK so i am almost certain the issue is the sensor or the wiring to the sensor.

[Legacy777]

You can apply 12v to the solenoid and if it clicks it should be ok. Also you can measure the resistance across the solenoid, it should be 48 ohms.

Check out this scan
http://www.main.experiencetherave.com/s ... sensor.jpg

Also, the engine & electrical manual has a little more info on the next page if you want. You can d/l it here.

http://www.main.experiencetherave.com/s ... lectrical)

[2.2TLegacy]

Thanks for the help guys, I'll go test that solenoid to see if its working properly and then hopefully be back to running at 100%

[Alphius]

If you go into D-Check mode with Key On Engine Off the ECU will cycle every relay and solenoid attached to it. I forgot which pair, green or black is used to activate this mode but you can figure it out because with one of those connected all relays will click on and off, including the engine fans. It's easy to tell when you have the right mode.

When you're in that mode the solenoid should click. If it doesn't, then either the solenoid is dead or the wiring is broken to it. In my case, the ECU was bad because a wire had shorted to ground and toasted the driver for the BCS. After I fixed the wiring, it still wouldn't work so I had to replace the ECU. My issue was with the BCS instead of the pressure exchange solenoid, but similar troubleshooting for both.

[2.2TLegacy]

Measured the resistance of the solenoid, it was 40.7 which is low but still falls in the specified range of 37-48. Solenoid going bad or bad wiring.

Is there a way to test the connector to see if its getting power to the solenoid?

[Legacy777]

Yeah, you can do as Alphius suggested and put the ECU in d-check mode with the green connectors. The ECU will cycle the relays on and off. Check if the relay switches on and off.

The yellow wire with the red stripe is the 12v lead and should have a steady 12v on it with the ignition in the "ON" position. The other wire goes back to the ECU, and when you use your volt meter, it should have a cycling 12v when in d-check mode if you measure the voltage across the two pins.

[2.2TLegacy]

No power going to the solenoid. Any chance someone might have a wiring diagram for this?

[Legacy777]

Download the manual I linked in the preivous post. It has the wiring diagrams you need.

[Alphius]

Check each side of that wire for continuity to ground and continuity between the two. They should be open in both cases. If not, you have a broken wire somewhere. If they check out good, I would still run a new wire to the ECU at least for testing. If that still doesn't work, you may have a bad ECU or bad sensor. Try jumping 12v to the solenoid as Josh suggested and if it clicks, it is good.

[2.2TLegacy]

So im am pretty new to the whole wiring business and I am having a hard time trying to figure out where this connects to the ecu, any input would be very appreciated.

[Legacy777]

The first step is to download the factory manual I linked above. Have you done that?

In the manual it will have an ECU input/output diagram with diagrams of the plugs. You can use that to determine which plug & pin the wire is located at for the pressure exchange solenoid.

The easiest test is to just apply 12v to the solenoid to see if it actuates. That should tell you wether the solenoid works. From there, you can connect the green connectors under the dash to determine whether the solenoid still actuates or not. If not, you've got an issue with the wiring or the ECU.

[2.2TLegacy]

Yep, downloaded the manual. I found the page that shows the wiring for the solenoid itself so now i just need to fine the ecu input/output diagram.

I tested the solenoid, both resistance and with a 12V source, its resistance falls within spec and it actuated when power was applied to it.

So its narrowed down to a wiring/ecu issue, which is not my forte but I guess I gotta learn at some point haha.

[crisco]

subscribed - similar issues in mine.

[Legacy777]

The ECU I-O is in section 2.7, page 175 of 335 and is labeled on the bookmarks if you expand section 2.7

[Legacy777]

Keep in mind code 45 can also indicate an issue with the MAP sensor itself, so I'd suggest checking it as well.

The troubleshooting procedures in the factory manual are pretty good and give you step by step instructions on what to do. So you can find code 45 in section 2.7 and follow the troubleshooting procedures there.

[2.2TLegacy]

Another weird thing is that the Pressure Sensor connector is only reading at 4-5V with the key "ON" and spec is 10-13V. Yet the wastegate control connector is supplying 11-12V just fine. So in that area the Solenoid connector reads 0V, Pressure sensor connector reads 4-5V and the wastegate control (not in use, have boost controller) connector reads 11-12V.

[2.2TLegacy]

UPDATE: Who can explain this, the car runs completely fine now for about the first 2-3 minutes after i start it, then while im driving, the check engine light comes on and the problem surfaces again.

[Alphius]

The ECU doesn't check operation of the solenoid for a few minutes as you're driving. The only way it knows that it isn't working correctly is by trying to switch to measure atmospheric and not seeing a change in pressure readings. Your solenoid wiring is bad I am nearly certain.