Hi, I'm new to Subarus and was hoping for some insight on a flashing CEL... 

 

I have a 94 Impreza with a 96 Legacy 2.5 motor in it.  This is the high compression one with HLA DOHC heads.

 

In order to run the motor in my OBD1 car, I used an OBD1 JDM 1995 Legacy 2.5 ECU and rewired the harness for it.  Everything seems to work, I added a knock sensor on the appropriate pin.

 

However, I can reset the ECU, turn the ignition on without starting the car, and the CEL starts flashing continuously.  The test connectors are not connected.  I thought that the steady flashing is supposed to mean a misfire is occuring, which is detected using the cam and/or crank sensors.  Since the engine is not running, I don't see how the ECU detects a misfire...  is there any other cause for this flashing??  I have swapped out both the cam and crank sensors, and no change.

 

The other thing that happens is that the motor runs perfectly when cold, then starts running rich and misfiring a bit when it's warmed up, and it's cutting out at exactly 5000 rpm in every gear.  I've swapped out the MAF sensor twice, bought a new O2 sensor, ECT, and all the emissions stuff is disabled because the JDM ECU isn't programmed for it.  Fuel system is all new w/rebuilt injectors, same with ignition, exhaust is all new/copper gaskets, no leaks in the intake.

 

I'm thinking that the running issues are caused by the CEL flashing, but I don't know what the problem is.  I thought maybe there are some OBD1 gurus on here, any insights would be appreciated?

Running good when cold would make sense if running rich. Then again, if it should be in a closed-loop operation using generic tune, and sounds like when it's going to read the sensors after warming up, it's running into an issue(s).

Do you  know enough on how to pull the codes, it would be a start to see whats upsetting it, and yes, just as you thought its cutting at 5k to limp mode. 

Check codes. Sounds and seems like the wiring isn't happy.

 

How positive are you had wiring is up to snuff?

Hi,

This doesn't help...now...but did you look @ swapping the throttle body from your '94 1.8 and running it w/the stock ECU on the 2.5? It should've been good to go....but I've not had the pleasure of working on the 1.8  so may not swap.....?

 

Google this: OBD1 JDM 1995 Legacy 2.5 ECU

 

And look under the Rs25.com results. There are others that have done this.....and this one: http://www.rs25.com/forums/f72/t69103-1995-jdm-n-2-5-ecu-into-1995-usdm-n-1-8-car.html

 

GL,

TD

Edited April 5, 20169 yr by wtdash

Sorry, wasn't getting notifications...

 

Bushwick - I think you are correct, and I just put a wideband on the car and it's very rich at idle after it warms up.  14s when it's cold, 10s after it warms up.

 

nipper - the only code I'm getting is for knock sensor.  I have one on order arriving tomorrow.  The wideband shows a huge lean spike at 5000 rpm, so I guess either it's cutting fuel because it's in limp mode, or something else is causing the lean spike and it's pulling timing due to knock.

 

grossgary - not 100% confident of the wiring, but no codes other than knock sensor and misfire flashing, which happens at key on engine off.  Running issues existed before the knock sensor code, also.

 

wtdash - yes, I'm familiar with 2slo4u's car, he actually helped me a lot in getting mine running.  I used the same jdm ecu and followed what he did... problem is, his swap was 7 or 8 years ago, and he doesn't remember much about the wiring issues he had.  

 

So now that I have the wideband, I know it's a fueling problem, but cause is unknown.  Symptoms are, runs nice, almost perfect when cold, when warmed up, super rich idle with misfires, cruise is OK, but AFR is all over the place between 13 and 15,  acceleration gets richer, but AFR still fluctuates, more like 12 to 14, and when I nail the throttle, it spikes lean at 5000 rpm in every gear, even neutral.

It's surprising what the knock sensor can do. It can do all sorts of weird things.

I will be overjoyed if replacing the knock sensor fixes it.  We shall see.

It's surprising what the knock sensor can do. It can do all sorts of weird things.

+1

 

Limp mode 

CEL flashing with engine off is pretty interesting.  

 

in the end:  what wiring is there: 

 

all EJ25 intake, body side, and ECU wiring?  

94 EJ18 body side wiring, 1996 EJ25 engine side wiring, no emissions in the 95 JDM ECU, not even EGR.  Just MAF, crank, cam, ECT, TPS, IAC, O2, oil pressure sender, knock sensor.  

Installed new knock sensor. No codes now, flashing CEL still comes on with ignition, and fueling/misfire issues persist.  At least I know my engine is protected from detonation.

 

Going to look at my ECU documentation again and see if anything jumps out at me.

So right now it has no codes? 

 

i would google search "check engine light flashing but no codes" - but you'll have to sift through miles of them because of the "check engine light flashing" part will bring up a bunch that happen while driving.  or creatively filter. 

 

EJ18's don't have a knock sensor - so the body side may not have a knock sensor wire - but since it did respond to the new sensor you added it or i'm wrong and it does have the wire?

 

 

How about check for continuity from every sensor to the ECU....although that should give codes if that was the issue

Yep, no codes.  I added a new shielded wire to the correct pin for the knock sensor, and I'm pretty confident that it's OK now that it has a new sensor.

 

Continuity check is a good idea, I'll do that when I have time to dig out the ECU.