ASenna Posted May 21, 2009 Share Posted May 21, 2009 I have a thread for my car's issues, but this one is dedicated specifically to the electrical system which has new developments. Bought the car needing a fuel pump. Replaced the fuel pump. Found out the car doesn't recharge the battery. -Battery's GOOD. -Alternator's GOOD. ( on my 3rd alt now! First one tested good, then bad. 2nd was from a parts car, good then bad. 3rd is definitely GOOD ) -Wiring going to L and S connections ( exciter and sense ) for the alt input is GOOD ( checked this myself and had this checked by an alternator shop...which told me the alt I had in the car was bad and that my wiring was GOOD ). So by the guy's recommendation, In had the alt swapped for a known GOOD unit. Throw the thing in the car, and what do you know, no dice. Runs around 12.1V across the battery. Car doesn't charge sitting at idle. Will charge around 13.0V around 3000RPM, far lower than the 14.45V that the sense connection aims for out of the alternator. Fuel pressure should be 40psi at idle. I get 36psi. Upon increasing RPM, the fuel pressure increases to about 40psi ( it should increase ), and then drops down to about 33psi. I'm thinking low voltage across the pump is causing it to lose fuel pressure. I'm going to tear my hair out trying to figure out what's wrong! Any ideas??? I've been at this for a MONTH. OH YEAH. Doesn't like to start. At all. Will start and die. Takes about 5 start and dies before it will start and run, and will run very low at 500RPM. Quote Link to comment Share on other sites More sharing options...
dhp123166 Posted May 21, 2009 Share Posted May 21, 2009 Voltage regulator? Quote Link to comment Share on other sites More sharing options...
ASenna Posted May 21, 2009 Author Share Posted May 21, 2009 WHOOPS Forgot to mention that the alt was converted over to an internally regulated alt via this thread here: http://www.atlanticz.ca/zclub/techtips/alternatorswap/index.html All the wiring and connections are confirmed good ( I've redone them just to make sure ). Also, the car has been running like this for well over a year, so the connections had BETTER BE good ha. Problems resulted from the last alternator blowing out and then the fuel pump starting to make a horrendous whine. New alt. New fuel pump. No fix. Quote Link to comment Share on other sites More sharing options...
dhp123166 Posted May 21, 2009 Share Posted May 21, 2009 Electromagnetic pulse from your exploding alternator wiping out your on board electronics? Quote Link to comment Share on other sites More sharing options...
FlatBlack Posted May 21, 2009 Share Posted May 21, 2009 Fusible links were giving me lots of trouble, I was in the same boat with a new battery and alternator. I converted to the Scoche fuse block and have had no problems. I would recommend it. Quote Link to comment Share on other sites More sharing options...
ASenna Posted May 23, 2009 Author Share Posted May 23, 2009 The fusible link connections in my car are good. I'm taking the car to a mechanic on Tuesday. A few of the guys there have Z's, one's building an '83 turbo and knew what I was talking about when I said Megasquirt, so we'll see how this goes. Cross your fingers! Quote Link to comment Share on other sites More sharing options...
dhp123166 Posted May 23, 2009 Share Posted May 23, 2009 By a used core and slap it on. If that is not the problem you still have a used core to replace yours when it does break... Quote Link to comment Share on other sites More sharing options...
ASenna Posted May 30, 2009 Author Share Posted May 30, 2009 I'm running megasquirt, so another ecu wouldn't help me, but it wouldn't hurt for a suggestion for a car with a stock ecu Apparently, the shop thinks the problem lies in the ground cable from the alternator. The rest of the wiring looks good, but there's a breakage somewhere in the line and they're just trying to find it. Quote Link to comment Share on other sites More sharing options...
ktm Posted May 30, 2009 Share Posted May 30, 2009 The folks over at Classiczcars.com diagnosed a floating ground as well. It is easily tested by running a ground directly from the alternator to the chassis/battery. Quote Link to comment Share on other sites More sharing options...
ASenna Posted June 1, 2009 Author Share Posted June 1, 2009 The folks over at Classiczcars.com diagnosed a floating ground as well. It is easily tested by running a ground directly from the alternator to the chassis/battery. Thanks. I wish I had the car in my possession or I'd try that myself! I'll call the shop tomorrow and see if they can just run a ground to the chassis and confirm that that's in fact what's wrong. Apparently this is a classic problem for old Zs? Where does the ground from the alternator run? All that wiring is covered in piping ( or electrical tape for an OEM harness ) just out of the alternator, so I haven't been able to really see where it runs. I've got a rear mounted battery. Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted June 3, 2009 Share Posted June 3, 2009 Since the alternator ground should be just a ring terminal bolted to the body of the alternator, then it should be the same as engine ground. I believe the ground lift referenced at the other site has to do with grounding between body and engine. I always keep a set of jumper cables handy and clamp one to a bolt on the body and one to the engine and check if symptoms change or go away. While being a diagnostic specialist, I found at least 4 per week with a bad body ground out of 15 or so calls per day average. Quote Link to comment Share on other sites More sharing options...
ASenna Posted June 3, 2009 Author Share Posted June 3, 2009 UPDATE: Alright, so I got the car back from the shop. They put in a new ground from the alt to the body. It seemed to run better, so they checked the voltages. Apparently the alt is putting out 15V, but it's only getting 13V across the battery, so, due to liability reasons, they recommend ME to put in a cable that goes directly from the BAT connection on the alt to the positive side of the battery. A hotwire if you will. I get home and do it. Big 4 AWG cable from the alt to the battery. Start it up. I get 11.9V across the battery, give it a rev or two, and it settles around 12.5V at idle. I wasn't happy since I'm supposed to be seeing 14.5ish. So I think, "OK well I've driven on less voltage and the alt seems to charge a little while moving" so I take it out. Car runs fantastic. Fuel pressure's all there matching the manifold pressure increase I'm seeing. Get to the end of my road ( about a mile away ) and she dies, never to start again. Had a buddy bring me another battery and I get her home. OK so I've got a direct connection from the alt to the battery and the correct voltages in all the wires going to the alt. What am I missing here? Cleaning up the battery to body ground here in a bit. Quote Link to comment Share on other sites More sharing options...
ASenna Posted June 9, 2009 Author Share Posted June 9, 2009 OK, so today I made sure it wasn't my battery terminals by cutting off the cables just before the terminal ( they were one piece ) and putting fresh cable into new terminals. The negative side looked a little corroded so I had big hopes. Had the battery charged up to 12.8V and chucked it into the car to try it out. Started it up. Had really good fuel pressure. Idle bobbed around from 750RPM down to 500RPM. After 10 SECONDS, the car shuts off. I turn the key to start her back up ( standard procedure with the car by now ) and *CLICK*. Nothing. Check the voltage across the battery. It's 12.25V. Pulled it out of the car and set it on the floor. Between yanking it out of the car, setting it on the floor, and grabbing my multimeter again, the potential had dropped to 12.05V, in about a 10 second span. An hour later I check it and it reads 11.6V. Time for a new battery? Quote Link to comment Share on other sites More sharing options...
ktm Posted June 9, 2009 Share Posted June 9, 2009 Sounds like some cells are dead. Also, you will not see 14.4 v across the battery terminals using a stock 280z internally regulated alternator at idle. You will only see the 14.4 v at RPMs over approximately 1500 - 2000. I mentioned your battery VERY early on as well. You've drained it but good. I went through the same issue with my battery when hunting down an alternator problem. All the start ups without sufficient charging, etc. really drains a battery. Quote Link to comment Share on other sites More sharing options...
ASenna Posted June 9, 2009 Author Share Posted June 9, 2009 Sounds like some cells are dead. Also, you will not see 14.4 v across the battery terminals using a stock 280z internally regulated alternator at idle. You will only see the 14.4 v at RPMs over approximately 1500 - 2000. I mentioned your battery VERY early on as well. You've drained it but good. I went through the same issue with my battery when hunting down an alternator problem. All the start ups without sufficient charging, etc. really drains a battery. Hm that's interesting. I am using a reman ZX alt if that makes any difference. I could probably throw on a smaller pulley and that might do the job ( assuming I can fix this issue ). The battery's drained for sure, but it wasn't always that way. This isn't my problem correct? It's just an unfortunate side effect. Any suggestions on tracing down the real culprit? Quote Link to comment Share on other sites More sharing options...
woldson Posted June 9, 2009 Share Posted June 9, 2009 Get yourself one of those obital batts and don't look back. (six pack looking guy) You can even get remans. Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted June 9, 2009 Share Posted June 9, 2009 I actually had a battery that worked great and suddenly, when I came back out of a video store, it did the click thingy like it had a bad terminal. I got out and found the terminal hot so I removed it and cleaned it to make good contact. Same issue so I held the key turned to see if the load would give me indication of where the trouble was by smoking. Terminal was hot again. It turned out the terminal had broken through almost all the way inside the battery case and I was lucky to not have it blow up. Bizarre. Quote Link to comment Share on other sites More sharing options...
ASenna Posted June 10, 2009 Author Share Posted June 10, 2009 YES! So I got a new battery, free since it was less than 2 years since it was bought. I found the firewall ground, but mysteriously one wire went down to my MS relay box and the other went in an enormous cable that was cut at the end. Oh well, decided to clean it up anyway. After fixing the battery terminals and cables, cleaning the firewall ground, and chucking in a new battery, I now get about 14.1V around 2000RPM. I ran her for about 5 minutes and went and checked the battery potential again. Hadn't changed so I was thrilled. Took her down the driveway to go down the road and back and my gauge lights go out before I even hit the road! Looks like I messed with one too many grounds... Anyone have the location for the gauge lights ground? Quote Link to comment Share on other sites More sharing options...
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