Engine not compensating for accessory power loss

grippingdrifting · Post by **grippingdrifting** » Wed May 16, 2007 10:59 pm

When ever I turn on an accessory like the headlights, rear defogger, AC, etc. the RPMs drop. I know this is normal but the problem is when the AC plus other accessories are turned on and the radiator fans engage. The RPMS drop by 300-500 so sometimes the engine will stall if I let off the gas too quickly. It doesn't matter if it's cold, warm, parked, or driving. I checked under the hood after the car was warmed up and turned on everything with AC. Everything was fine until the fans turned on at the same time causing the RPMs to drop greatly.

I have replaced the spark plugs & wires, cleaned all the ground contacts & added grounding wires, checked all the fuses, replaced the fan relays, checked alternator & battery, and replaced the coolant temp sensor.

Is there a part that is responsible for compensating the loss of engine power when accessories are turned on? I remember seeing something along those lines in a wiring diagram for an older model engine but I can't recall the name. I don't have them on me right now so will have to check later.

Post by **Legacy777** » Thu May 17, 2007 5:37 pm

The ECU does monitor voltage drop, and will kick the idle up if the battery needs charging. I'd check all your battery/alternator connections. Clean them if necessary. Also, you may want to clean/check the IAC valve.

grippingdrifting · Post by **grippingdrifting** » Sat May 19, 2007 12:25 am

I was thinking of replacing the entire battery cable. I cleaned the IAC valve several months ago with seafoam but that didn't get rid of the code. I put in a used IAC but that still didn't work and when I went to start checking the electrical, my multimeter wasn't working cause its fuse was blown. I'm waiting for a replacement fuse to be mailed so I was looking over how to check the IAC. Where are the ECU conections F47, B56, B58, & B48? The ECU is usually grey and is behind the gold-colored TCU, correct?

Post by **Legacy777** » Mon May 21, 2007 5:37 pm

The ECU connectors are right on the ECU. If you look at the ECU I/O page from the manual, it tells you what is what.
http://www.main.experiencetherave.com:8 ... _page1.jpg
http://www.main.experiencetherave.com:8 ... _page2.jpg
http://www.main.experiencetherave.com:8 ... _page3.jpg

The ECU is located off to the left of the TCU. Here's a pic
http://www.main.experiencetherave.com:8 ... cuhide.jpg

grippingdrifting · Post by **grippingdrifting** » Tue May 22, 2007 3:35 am

Thanks for the picture. I found the ECU and now it is only a matter of getting to the connectors. It's been raining here so I've only gotten to the first connector B48. I was comparing the pinouts from the manual scans to mine and I noticed that there is no wire in pin 20, the AT/MT identification. There is however a wire in pin 19 on my connector but I couldn't find anything to correspond to pin 19. Is it possible that some of the wires are not going to the proper ECU connections and this is causing problems?

Post by **Legacy777** » Tue May 22, 2007 5:52 pm

I'm not sure what pin 19 is for. If there's not a wire at pin 20 for the AT/MT ident pin, that means the ECU sees 5v. If you need to ground that pin, you'll need to put a wire in there, or take a pin from another ECU connector.

grippingdrifting · Post by **grippingdrifting** » Wed May 23, 2007 5:41 am

I added a ground wire that attaches to the chasis and then into pin 20. Everything is working except for the lights on the gear selector...I must have loosened a wire. I also measured the voltage on each wire and I got a couple volts on pin 21 which is supposed to be sensor ground. What sensors ground through pin 21?

Post by **Legacy777** » Wed May 23, 2007 6:07 pm

Not sure.....You'd have to scan through the wiring diagrams. I have some diagrams on my server. Info can be found in the stuff you need to know forum.

grippingdrifting · Post by **grippingdrifting** » Wed May 23, 2007 11:35 pm

Thanks for all your help. I won't have much time to work on my car until this weekend but ideally I want all the ECU wires to match the specifications on the ECU I/O manual scans. However, the car runs fine (for the most part) and I don't want to mess things up so I probably should just leave things be.

grippingdrifting · Post by **grippingdrifting** » Fri Jun 01, 2007 12:04 am

The other night I was coming up to a corner behind some slowpoke so I gave them some distance becuase I like cornering fast. Well, I was going a little too fast and came up and the car's tail quickly so I let off the gas and hit the brake. I go to turn the wheel and there was no power-steering so I look down at the dash and notice the engine stalled. I started the car back up and the power light flashed 7 or 8 times. The power light hasn't flashed since then but I tried to pull the transmission codes anyway and wasn't able to. The power light never blinked, it just stayed on. I used the instructions from here http://www.surrealmirage.com/subaru/trans.html

Post by **Legacy777** » Fri Jun 01, 2007 5:53 pm

Those instructions are good. Are you getting any blinking at all when trying to pull the codes?

grippingdrifting · Post by **grippingdrifting** » Fri Jun 01, 2007 11:46 pm

Nope, no blinking. The light stays on constantly.

grippingdrifting · Post by **grippingdrifting** » Sat Jun 02, 2007 12:10 pm

So I was able to pull previous problems and the light blinked steadily. Still unable to pull existing codes but since there are no previous problems, does this mean everything is fine with the tranny? I'm pretty positive my main issue is electrical so I was thinking of getting a new ECU. However, I don't know what year I should get because I don't know the engine year.

Post by **Legacy777** » Mon Jun 04, 2007 6:18 pm

Just for my clarification. The ECU and TCU are separate. I gave you a link to the TCU. Are you checking the TCU or ECU for codes?

grippingdrifting · Post by **grippingdrifting** » Tue Jun 05, 2007 3:20 am

I'm checking the TCU. Sorry about the confusion, I was thinking out loud about the ECU.

terranaj98 · Post by **terranaj98** » Wed Jun 06, 2007 4:36 am

i got rid of my "surge/flux" of power during startup with a TB clean and idle adjustment (which i shouldnt have touched)
ive resetted the ECU and closed the idle screw
right now it seems fine..

i think part of the problem is the air way to your tb or.. something clogged.. we did a through job of cleaning the tb

Post by **Legacy777** » Wed Jun 06, 2007 5:03 pm

Don't clean your TB!!!!!!!

grippingdrifting · Post by **grippingdrifting** » Fri Jun 15, 2007 11:09 pm

I ended up solving my problem: replaced the ECU. I had an ECU from a 90-91 MT N/A so I bought one from a 94 AT N/A to match my car.

All I had to adjust was the TPS because the idle switch was throwing a CEL. Now everything seems to be more responsive and smooth.

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Engine not compensating for accessory power loss

Engine not compensating for accessory power loss