Jersey Posted August 16, 2003 Share Posted August 16, 2003 How does timing advance work on the '82 L28ET? I understand the CAS inside the dizzy and i know it has 4 wires going to it, two of which are power and ground. The others go back to the ECU. The problem i'm having is that i cannot get the timing to move off of 20deg BTDC. What i mean by this is, i know can physically adjust the dizzy and set the initial timing to whatever but, when i bring the R's up or down or wherever, it shows 20deg ALL the time. Never moves, never advances or retards, ever. I've been having a rich at idle problem for the last week if anyone hasn't read my recent babbling posts. Is there a certain wire from the CAS to the ECM to tell it to advance? In closed loop mode (or open loop, the one when it's not up to normal operating temp) does the timing just get a default value and stay there until the HTS gets to certain value? Doesn't sound right but who knows. I'm shooting in the dark at anything lately but i do know my advance was working, and no it's not. I did read about how the CAS works in the FSM but it's a little too vauge in which wires actually do what and if there's a way to test them, or the CAS itself. It also says the CAS can be adjusted in the FSM but for the life of me, i couldn't find the "how to" anywhere! Can you tell i'm frustrated Anyway, any help in advance is appreciated. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted August 16, 2003 Share Posted August 16, 2003 ECU advances the timing, you can take the dizzy out (still plugged to the ECU) turn the shaft with the ignition on and see if you are getting signal or not. It'll click once for rev. (twice on Z31 CAS) other then that I would suspect the ECU not working properly Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 16, 2003 Author Share Posted August 16, 2003 Yo - not exactly sure what you mean. Take the dizzy completely out, keep it still plugged into the ECM, rotate the shaft and what will click per revolution? Sorry, just not following you - cob webs in brain @ 35 I know i'm geting signal (i think that's what your having me test) because the car does run, it just doesn't advance. You say the ECM advances the timing...so i'm assuming it sends a certain voltage down one of these 4 wires going to it to make it advance/retard? If so, do you know which one and what i should see on a meter? Boy my L28 w/SU's was so easy Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted August 16, 2003 Share Posted August 16, 2003 If your TPS is closed, it will not advance timing off initial. If you know TPS is open, you got a strange problem - the ECU will change timing, even if it's just going from a closed TPS to open, you should see timing change. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted August 16, 2003 Share Posted August 16, 2003 What else does the ECU use the reading from the CAS for, other than to control timing? Just curious. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted August 17, 2003 Share Posted August 17, 2003 dizzy will click once per revolution to give the ECU 1 rev. signal. I guess it's hard to explain. I'm an alien Just take the dizzy out with it still plugged up to the ECU, with key on, turn the dizzy. you hear what I'm talking about Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 18, 2003 Author Share Posted August 18, 2003 Got it Yo/Sleeper. Thanks. Yeah, the CAS & TPS are working correctly. I don't know. Guess i'm at a brick wall now with this thing. I swear i've gone over everything...twice! Only thing left is ECM. My cousin's buying a '83ZXT this week. I'll steal his brain and try it. 99% sure the '82 and '83 ECM's are the same. Should be plug and play, right? We'll see. Thanks again guys. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted August 18, 2003 Share Posted August 18, 2003 I got a 82 turbo ECU if your brother's doesn't work Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 18, 2003 Author Share Posted August 18, 2003 You are the man Yo. I'll keep you posted. Thanks. Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 19, 2003 Author Share Posted August 19, 2003 Yo, picked up my cousins '83ZXT last night ($800, been sitting in driveway since 1995, 80k miles) did all the usual to bring it back to life and had it running perfect by 11pm! Anyway, this morning i robbed his ECM, popped it my Z and NOPE, NO HELP! Damn. As much as i didn't want my ECM to be bad, at this point i just wanted it to be. So as of right now, i wont be needing yours. Thanks. Oh yeah, with his ECM plugged in, i figured i'd check timing just to see if it was advancing, and it wasn't...still rock solid on 20btdc. So, i think i'll start a new post about timing. Maybe someone else has had this problem and found it to be the power transistor or coil....SOMETHING. haha. Thanks again Yo. Quote Link to comment Share on other sites More sharing options...
fl327 Posted August 19, 2003 Share Posted August 19, 2003 CAS?? if so, that means distributor basically. Try swapping AFMs? Figure its cheaper than dist. stuck at 20 degrees, hmmmmm Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted August 19, 2003 Share Posted August 19, 2003 CAS?? if so' date=' that means distributor basically.Try swapping AFMs? Figure its cheaper than dist. stuck at 20 degrees, hmmmmm[/quote'] Can't be CAS. It is not responsible for timing advance. All it can do is tell the ECU what the engine position is; there is no advance mechanism inside it. The ECU controls the timing advance, so it must be missing a sensor input, hearing as how ECUs have been swapped. Sorry Jersey, I'm out of ideas. Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 19, 2003 Author Share Posted August 19, 2003 Thanks 327, Sleeper. Do either of you, or anyone else that reads this, know what sensors would tell the ECM not to advance timing because it's possibly sending a lean condition? Maybe all of them combined or, maybe if only one of them is out of spec, it would disregard all the rest? I'm not even sure if any of the sensors where sending a lean condition that it would stop the ECM from advancing the timing. Just guessing away now. I do know that the knock sensor will retard it. Maybe the knock sensor wires and picking up some kind of noise in the car and sending a signal to the ECM like it's knocking, even when the wires are unplugged from it? I thought all the sensors below send signals to the ECM so it can determine how much and how often to through fuel at the system, not mess with ignition timing, no? O2 HTS AFM ATS TPS Only thing left sensor wise on my Z is the knock, which is the only thing that i know controls ignition...in a retarded type of way Sorry. Well, at least i have my cousins '83 ZXT in my drive for a couple of days and can get some time to do some comparisons. Thanks again guys. Quote Link to comment Share on other sites More sharing options...
BayAreaZT Posted August 19, 2003 Share Posted August 19, 2003 Maybe the ecu is not reading rpm. It may not be getting the signal from the CAS because it doesn't advance or retard. Quote Link to comment Share on other sites More sharing options...
fl327 Posted August 20, 2003 Share Posted August 20, 2003 I cant think of a dang thing man, I can see myself repeating things in posts and starting to throw some weird ones atcha Quote Link to comment Share on other sites More sharing options...
Afshin Posted August 21, 2003 Share Posted August 21, 2003 The crank angle sensor has two diodes one which reads rpm (diode 1) and tells the ECu about RPM and is used to set timing. The second diode is used to signal TDC. I think it may be possible that the first diode has failed and timimg does not respond to RPM and that the second diode is still providing info for TDC and setting the fixed timing of 20. I don't know if this could happen for sure (i'm making a guess) but I would strongly consider swaping the whole ditributor with your cousin's and see if any thing changes. If this does not work another guess would be a short causing errors in the ECU reading or output. You should also swap the AFM if you already haven't since it could cause your rich mixture and maybee a short in the unit is throwing off the ECU and timing. Quote Link to comment Share on other sites More sharing options...
Afshin Posted August 25, 2003 Share Posted August 25, 2003 Hi Jersey, have you had the chance to do any more diagnostic work on the car? I'm really curious as to your progress and finding what is causing all of your problems. Also did you say that after resetting the timing it always goes back to 20 after you run the car ? Quote Link to comment Share on other sites More sharing options...
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