Occasional High Idle Speed - $8D 383 fully modified TPI

[EagleMark]

I do have your pdf file and it is very nice work thank you! Just not sure where to put it right now since it covers Memcal type ECM/PCM...

Sure sounds like "IAC Command speed open loop offset" is an idle RPM setting for open loop. You can easily see if system is going Open Loop when the idle issue happens in data.

O2 sensors cooling off in headers is a common problem. Most narrow band O2 sesnors work the same whether heated or not, just the heating element is added. For GM a heated replacement can be from many vehicles, the only difference would be the connector. IIRC a 1995 Chevy truck and 1995 LT1 engine are the same and a good place to get one ordered from. Then add a rely and wiring for the heat circuit.

[zaut]

I did a little research an now know the difference between a wide band and narrow band O2 sensor. A wide band has a 0 - 5v output range, a narrow band has a 0 to 1 v output. My ECM uses a narrow band O2 sensor. What I need to know is what vehicles used a narrow band heated O2 sensor.

[zaut]

Thanks EagleMark. Do you know how many amps the heater circuit takes? If not I can bench test and measure the current.

The "IAC Command speed open loop offset" is set at 1000 RPM. I never changed it. I don't see where or what it affects. In open loop my idle (when working normal) follows the target idle rpm versus coolant temp table.

[RobertISaar]

I did a little research an now know the difference between a wide band and narrow band O2 sensor. A wide band has a 0 - 5v output range, a narrow band has a 0 to 1 v output. My ECM uses a narrow band O2 sensor. What I need to know is what vehicles used a narrow band heated O2 sensor.

actually, to get more in-depth the wideband controller outputs a 0-5 volt signal.... the wideband sensor itself is likely different.

your car uses a narrowband.

Thanks EagleMark. Do you know how many amps the heater circuit takes? If not I can bench test and measure the current.

most heater circuits i've seen peak at ~50 watts or so. at 12 volts, that's just over 4 amps. they quickly drop the amount of current used as it heats up though.

[EagleMark]

It may be for start up?

I don't know the amps of heated O2? For wiring I have used another fuel pump relay.

[zaut]

I think I found the root cause of my high idle. My Charcoal Canister Purge is on all the time. Unfortunately it appears that the ECM is at fault. The ECM turns the solenoid valve when it does not want to purge. The valve is normally open. I traced the circuits and I get 12 volts and continuity to pin F7 on the ECM. I never get a low resistance on that EMC circuit. It’s always about 12kohm. What my service manual says is that you will lose four outputs at a time. But that is for the original 85 ECM. This one is upgraded to a 1990 7730 ECM, which I do not have the service manual for. Does anyone know it I should have lost three other circuits and if this is repairable? Another thought I have is did GM change the logic of how the 90 canister purge worked? I was surprised to read that the valve was a normally open valve. Could by chance the 90 version use a normally closed valve and I am getting the purge at idle and not during driving? I will test this tomorrow.

[RobertISaar]

GM seemed to use normally open valves with setups that used ported vacuum, so that if the valve were stuck open, it wouldn't effect idle. when they transitioned to normally closed, they generally used a constant vacuum source. or at least this is what i've found to be true of most of the FWD GM stuff.

[zaut]

I hooked up a light to connector at the purge solenoid this morning. I went for a short drive, an behold, the light comes one when the laptop says it’s purging. This is the opposite logic used in the original 85 ECM. My original EMC was a 1985 165 1F$ mass air flow system. I converted to the 1227730 $8D system. So anyone else out there doing this change needs to know the purge system works differently. I am off the junk yard to get another valve/canister. No more high idle issues!!! I hope. Plugging the purge line is working until I get a new valve.

Does anyone have the wiring diagram for a three wire heated O2 sensor? I will be adding that soon.

[RobertISaar]

doesn't 8D have the option to use normally open or normally closed CCP solenoids? it should. if not, it would actually be a really easy patch.

[EagleMark]

Does anyone have the wiring diagram for a three wire heated O2 sensor? I will be adding that soon.

To easy, just a sensor wire and the other 2 are for heating element, pos and neg and you can reverse them.

[JeepsAndGuns]

doesn't 8D have the option to use normally open or normally closed CCP solenoids? it should. if not, it would actually be a really easy patch.

Just looked on my 8D xdf and there is a flag at 0x18 mask 80, thats called "canister purge when output energized" and then at 0x16 mask 2, there is a flag called "16 Hz ccp in use". Whatever that means. Either one of those flags anything usefull?
I'm thinking change the flag at 0x18 mask 80? On a stock AUJP bin, this flag is checked. So maybe try looking at your bin and see if its checked, if it is, try unchecking it and see if it works how you need it, going by the flag title alone, you would think its what you might be looking for. But I cant promise you anything, as know very little to nothing about most stock chevy vehicles.

[RobertISaar]

the 18, 80 sounds like the right one. the other option it what chooses the frequency at which it will drive the solenoid. generally, 16, 32 or 64Hz.

[zaut]

Yes, now that you mention it, I see a flag for it. It is called "canister purge when ouput energized". Thanks a lot.

[JeepsAndGuns]

Let us know if it fixes the problem.

[zaut]

Lol... I would, but you called me out. I already replaced the valve with a normally closed version before I read the post last night. After testing yesterday, I went junk yard hunting for that and some other misc parts. I feel foolish for not looking to see if the output was programmable. But the canister is much newer and the existing one had a problem of leaking charcoal. There is a filter media on the bottom that was deteriorated. So it worked out for the best anyways.


Eaglemark, I understood that the two extra wires are for the heater. What I am not sure of is which two of the three are for the heater and which is the O2 signal. I haven't got the senor yet, it is on its way. Maybe it will be evident with a meter once I get it. Thanks.