Jersey Posted August 30, 2003 Share Posted August 30, 2003 I am completely out of ideas guys. I really think i'm missing something logical and simple but i just can't figure out my Z's problem. I think it's been three weeks of troubleshooting now and i just can't find it. Here's the symptoms and what i've found: - No timing advance. Just sits @ 20BTDC. Looks like it slightly retards about 2 degrees when bringing up R's but that's it. VERY slight movement. - Runs very rich @ idle - Green LED on ECM does not flash, ever. Only time i see it lit is when key is in "run" position Any idea what could possibly have an effect on all these things to just happen all at once? It's an '82 L28ET in a '73 240, NPR I.C., Walbro Pump, 1G DSM BOV. Everything else on the motor is stock. No POV, EGR or AAC. Before whatever it is causing all these things to happen, the car ran perfect. Nothing was changed, i just noticed one day that she didn't want to basically hold an idle and was running real rich. Shoot any ideas that you may have, as simple or as weird as they may be. I am at a complete loss here and am open to ANY ideas. Thanks guys. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted August 30, 2003 Share Posted August 30, 2003 hmm okay shooting ideas... probably nothing helpful, but here... Have you hooked up the timing gun to all the other spark plug wires to see how they are sparking? Look for consistency in the rythm of the spark, and also see if/how any of them respond when you rev the engine up. I forget if you've mentioned this, but have you verified the dizzy is good? Have you tried the dizzy out of the other '83zxt? I dont know if this would matter, but if you try the other dizzy, you may want to try the other dizzies shaft too. It may be something wrong with the wiring harness itself. Can you or have you tested all the wiring? Not sure how to put it more technically, but, is there a way you can hook one end of the voltmeter to one wires end, at the ecu side, then the other contact of the voltmeter at that same wires end, at the sensor? I know this would probably be a pain in the ass, but shorts do occur in the wiring harness sometimes, and I assume it could keep signal from the CAS from getting to the ECU, or who knows... but you DO know that information is getting dropped somewhere, info that the dizzy needs to adjust timing. I dont know if it would be any easier... neither idea is gonna be easy, but alternately, you could use the wiring harness from the other '83 zxt. But with everythign else tested, there's really not anything else... it's almost GOTTA be the wiring. Wiring harnesses aren't THAT hard to change, once you already know where everything goes. Isn't only like 6 or 8 wires that actually need to be cut and spliced? I dunno Jersey you know I feel your pain, on chasing gremlins that seem like they can never be found... this is all I can think of. Quote Link to comment Share on other sites More sharing options...
Guest Cusp Posted August 30, 2003 Share Posted August 30, 2003 One thought that you haven't listed is the AFM flapper door. Moisture may have affected it's travel or tension, might be worth a look. If the door was too stiff, low RPM airflow would be sporadic or nearly non-existent. Only other idea is your BOV is stuck open, though that's a longshot. Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 30, 2003 Author Share Posted August 30, 2003 Hooked up light to different wires, all firing consistantly, timing doesn't change. Swapped out the dizzy with internal CAS, no advance Ohmd just about every single wire in the harness, end to end, all tested good. Also checked the values of all the sensors, at the sensor and then back at the ECM, all good. Swapped out AFM last night, no change. Eliminated I.C. and all pipe, including BOV, by re-installing stock J-pipe last night, no help. Also, all the parts that i'm swapping out are known good because i have another ZXT side by side with my Z and it runs perfect. I just keep taking parts off of it, installing them on my Z, watching it fail, then swapping them back. Keep shooting ideas at me guys, it's got to be here somewhere!!! THANKS. Quote Link to comment Share on other sites More sharing options...
DatsunBoy77 Posted August 30, 2003 Share Posted August 30, 2003 i had a coolant temp sensor unplugged once and it did that. I think you already checked that i think i read, but thats all i can think of. Quote Link to comment Share on other sites More sharing options...
Afshin Posted August 31, 2003 Share Posted August 31, 2003 Wow! I can't believe how difficult this problem has been to solve. At this point you have checked every sensor at the sensor and at the ECU, you have swapped all the major EFI and ignition components and also checked for broken wire to ECU, ruled out vacuun leaks, checked fuel delivery and all is still negative. Considering this and that both your timing advance and fuel mixture are off my best guess is a short which is throwing off the ECU which would acount for both fuel and ignition problems. Since you already swapped ECU's, dizzy and AFM, it seems most likely that the short is in the harness itself. Checking resistance in each wire end to end obviously won't let you know about any shorts. You could check resistance between each wire/pin at the ECU end and the body for a ground short, since they are the most common type (on non ground pins off course). If all is OK you could then check for resistance from pin to pin, but that is a pain in the ass specially since some of them (i.e. comming from the same sensor) should have some continuity. At this point I would check for a ground short first, if negative I would call every nissan dealership in NJ and find one that has the factory ECCS analyzer which can check for proper input to the ECU as well as proper output from the ECU. Of course you could also try to locate another zxt harness, it would be relatively easy to install. I just can't think of anything else since you have been so thorough in checking all individual systems components. The only thing left is a short Quote Link to comment Share on other sites More sharing options...
Guest szlash280z Posted August 31, 2003 Share Posted August 31, 2003 what about your oxygen sensor? mine would idle weird whenever it would warm up and get out of the cold running mode. I knew my oxy sensor was bad anyway (I jacked it up when I was removing it for DP cleaning) but I had it plugged in anyway. my idle would flutter and the car ran like crap. I noticed an immediate change when I unplugged it. I am still running without the sensor hooked up and it hasn't done the idle flutter thing since. So the Question is: Have you checked to make sure the Oxy Sensor is in perfect working order? A faulty one caused me problems, it can be causing you problems too. If you remove the wire, don't let it ground itself to anything, it will make the car run like crap again. Try running it without the sensor, if it improves, you might want to check into getting a new sensor. Quote Link to comment Share on other sites More sharing options...
Bernardd Posted August 31, 2003 Share Posted August 31, 2003 I've been fooling around with my timing the last few days and have noticed that the only time my advance doesn't activate is when the tps is disconnected. Have you checked btwn pins 18 and 25? The harness could be shorted together. Or grounded together. Tps opens up at 900rpm or so? The only other thing I can think of is the transistor or capacitor at the coil may be having some effect. There's a small tab on the bottom of the dizzy beside the harness plug with a grounding tab. Is it grounded? Doubt that will have anything to do with it. When you tried the other cas and stuff did you try your stuff on the other car as well? Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 31, 2003 Author Share Posted August 31, 2003 I've checked/ohmed and even swapped the Head Temp Sensor out today which made no change. Afshin, this has been unreal. I'm now thinking exactly how you are that it HAS TO BE in the harness somewhere, even though i checked all grounds, powers, sensor inputs....basically everything. I will check for shorts to ground at the ECM side of the harness on every pin. Great idea. I haven't tried that one yet. I think i'm really in need of the ECCS Analyzer as you mentioned. I've been through every sensor and just about replaced (substituted with known good sensors) every one including the ECM and i still am having the problem. I will check for shorts. O2 sensor is good. I replaced it anyway, because i wasn't getting a flashing green LED on the ECM like it's suppose to but, still no LED flashing, still rich, still no timing advance. What bugs me is, if the O2 is sending the correct signal and climbs when running her @ 2k rpm, say starting around .4v and continues to climb, the ECM LED never flashes and the O2 voltage just continues to climb. It gets to a bit above .9v and then fluctuates there. I watched the other '83ZXT's LED and right around .630v, the LED flashes, the voltage drops to around .3v then jumps around between .3 - .6volts, all the while the LED flashes as it adjusts injector pulse. I understand that this is the correct function on the O2 and ECM but, i just cant understand why with either ECM plugged into my Z, they dont adjust for the O2 value? BTW, i put my ECM in the known working '83ZXT and it flashes away when the O2 reaches a certain voltage so, i know my ECM is good. Doesn't the ECM LED react solely on the voltage reading from the O2 or does something else effect this LED? Guys thanks. Any further ideas/suggestions...please. Near wits end with it. Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 31, 2003 Author Share Posted August 31, 2003 Hey Bernarrd. Just got your post, ran out to the garage and triple checked TPS - not grounded to each other, insulation test is good and it does work properly because i can hear injector pulse slow down after she warms up at idle. Injector pulse increases as soon as the R's are bumped up a little, like you say 900rpm. I also swapped out the coil and transistor which didn't help. I did not swap out the cap because i would think that it would have no efect on timing advance but, i'm all out of ideas so i will go out and try it now. What the heck, can't hurt to try...i'm all out of logic! Thanks. Quote Link to comment Share on other sites More sharing options...
Idnevno Posted August 31, 2003 Share Posted August 31, 2003 couple obvious ideas not sure if you checked yet.... what is your fuel pressure at the rail??? and are all of the injectors firing equally?? all sound the same with same intensity of click as well consistent firing pattern of sound? what is the injector voltage? also have you checked to see if the cold start injector is hanging up (stuck open)? back to the fuel pressure thing is it a consistent fuel pressure at the rail or does it spike up and down alot? bout all the ideas i can come up with right now... Dave Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 31, 2003 Author Share Posted August 31, 2003 Have a gauge setup between fuel filter and fuel rail. Pressure is about 36psi at idle (a litle high because of high flow pump) I used a vac pump on the FPR to bring it down to 30psi and it made no difference. Rich an no timing advance. Fuel pressure stays steady until i hit the throttle, which increases it to 42psi or so then levels back down a bit. Last night, i pulled the complete fuel rail off with injectors attached to make sure i didn't have a leaky or bad injector. Turned an extra valve cover over and cranked it to watch them fire and they all shot a nice continuous spray pattern. One thing to note if anyone tries this - be smarter than i was and unplug the 2 prong connector from the coil transistor. Yup, you got it...i was cranking it for a little bit, watching the spray patterns and the vapor was greater than i thought and it ignited. YES, a large flash fire that ignited the fuel laying in the valve cover from the injector spray. Lots of flame. I was careless, it was late and it could have been bad. Funny now, not so funny at the moment! Anyway, haven't checked the injector voltage. They seen to all be firing good and clean. No cold start injector on the '82 L28ET's. Thanks. Any other thoughts, run 'em by me. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted August 31, 2003 Share Posted August 31, 2003 I"m still thinking wiring harness itself. Afshin thinking the same as me on this one... it's really not that hard to swap the whole thing once you already knwo where everything goes and your 240 is already set up for it. That's where I'd put my money. Interesting that you guys mentioned that the TPS opens at around 900rpm, and this is supposed to effect timing. When I was noticing my problem, about the timing suddenly dropping when revving, instead of advancing, it was right about when I'd hit about 1000rpm, and it was very sudden, like flipping a switch... would rev perfectly from idle to 1000rpm, then suddenly, timing drops 4* instead of advancing, and the car starts sputtering and missing and just generally running like crap. So that tells me that instead of a bad distributor, SOMETHING is happening when the TPS goes open. I'm not trying to hijack Jersey's topic or anything, but could anyone give me some ideas here? I'm thinking, just as a test, when I get the head rebuilt to fix the bent valve and get it running again, I'll disconnect the TPS and place a jumper in the wires end, basically 'tricking' the car into thinking the TPS is always closed, and see what happens when I rev it. Quote Link to comment Share on other sites More sharing options...
Bernardd Posted August 31, 2003 Share Posted August 31, 2003 Any chance you swapped out the fuel pressure modulator? It's tied into pin 18 at the ecu. Not sure how it works other than it controls the fuel pump in some fashion. I don't have many straws left to grasp anymore. Quote Link to comment Share on other sites More sharing options...
Afshin Posted August 31, 2003 Share Posted August 31, 2003 i just cant understand why with either ECM plugged into my Z, they dont adjust for the O2 value During start up, cold engine when O2 sensor not heated, during heavy load and when rpm is over 3600 the ECCS is in open loop mode and bypasses the O2 sensor input for fuel mixture. During this phase there is no oscillation of voltage. However, if the car is running rich for over 6.4 sec or lean over 10 sec the O2 sensor input will override the open loop and adjust mixture best it can (e.g. running lean under load) The voltage fluctuating between .3-.6 is because of the back and forth response in fuel mixture made by the ECU in response to the O2 sensor input, which happens during closed loop operation. My understanding is that in closed loop mode, the O2 sensor overrides most other info in determining fuel delivery (injector pulse..). The reason your voltage and led are not fluctuating is that the ECU is not able to get into closed loop mode. Faulty O2 sensor or circuit can cause this, but it should not cause the timing problem (by faulty I mean broken wire, not short, who knows what that can do). Timing, closed vs. open loop mode determination and fuel mixture all depend on input from engine temp (head temperature sensor) and engine load (determined mostly by AFM flap opening and RPM and vacuum). So perhaps you can check for shorts in these shared circuits while looking for an ECCS analyzer or other ZXT harness. You already checked all the actual components. Next I would check the head temp circuit for short, then the AFM circuit, then O2 sensor circuit and finally the dizzy circuit(since it provides RPM measurement to the ECU) . Best of luck Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 31, 2003 Author Share Posted August 31, 2003 Guys, thanks so much. I, actually WE figured it out. See my post HERE Thanks for all the time and knowledge. Quote Link to comment Share on other sites More sharing options...
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