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Urgent help needed!!! Voltage problem


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#21 MaygZ

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Posted 25 October 2010 - 11:07 AM

(with battery in the car and pos terminal on the battery, touching neg terminal on to the battery gives a big spark


You have something getting power.  I'm sure that you have checked the key position ... so if it's a BIG spark, then it's drawing a lot of current so look at those things (Starter, alternator, sub-woofer?, HID lights etc)  If it's a smaller spark then look at smaller items.

It is true that if nothing is turned on at the time, you shouldn't get a spark by connecting the battery up.

By running a test light between the block and the -ve terminal, the light should only shine if something is 'turned on' or has shorted out.  With everything turned off, the circuit souldn't be completing and therefore no light.

If a battery terminal is getting hot, that confirms, for me, that there is a short in the system.  (don't discount a short in the battery its self).

I would look at a trial and error system.  You said that there are no pinched wires, and you've tried other starters, so disconnect the electrical supply of the alternator and try again, if no good then try other components.  Are you carby or EFI?  Don't forget the EFI system and all it's components.

The lack of ignition spark could be as a result of too much loss of current either before or during engine crank to create a spark OR maybe the problem is in your coil?

Chasing electrical problems is the bane of any mechanics life.  Good Luck and be methodical.  You will find the problem.

#22 Bigworm

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Posted 25 October 2010 - 05:09 PM

ok got it all sorted, basically i cooked the wire that went into the back of the negative battery terminal so when i was cranking it over it wasnt making a solid connection and just burning itself making it get hot. so thats that and the reversed polarity was just my LED light from the immobiliser feeding power through the body (nothing to worry about though).
So thats fixed and i have good spark, now the next problem im getting is it kicks over but runs very lumpy and i found that it must be flooding with fuel because if i clamp down on the fuel line with some multi-grips when the engine is running, it runs perfect but when u release the multi's it get lumpy again. Im thinking i might need to replace the fuel pressuer regulater on the injection rail but i think i replaced tha not long ago aswell. any other idaes why this would be happening????

Well at least its no longer an electrical problem its mechanical so thats half the battle.


#23 Scoota G

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Posted 25 October 2010 - 07:42 PM

Maybe you have to reset the ECU if it's got one.

#24 Bigworm

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Posted 25 October 2010 - 10:46 PM

this might seem like a stupid question but how do i reset the ecu??

#25 PZG302

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Posted 26 October 2010 - 08:02 AM

If it's the standard L28 computer, to the best of my knowledge you can't. it was a very basic Bosch computer from the late '70's early 80's so basically bugger all you can do with it or to it.

#26 Scoota G

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Posted 26 October 2010 - 08:09 AM

Oh i though you just diconnnect the battery and drain all the power from the electrical system, or leave it unhooked for a period of time.

#27 PZG302

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Posted 26 October 2010 - 11:04 AM

Later computers that self learn, like the Ford EECIV and EECV computers will reset themselves and self learn, but the L28 computer was very basic and didn't really do much in the way of adjustments on the fly

#28 Bigworm

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Posted 27 October 2010 - 11:14 AM

ok i tried re-setting the computer by draining it but that didnt seem to work, then i managed to grab another one the same and put that in and still no difference so i think that there may be an issue with the actuater thing near the fuel pump letting too much pressure through the line to the front. maybe i can find some sort of aftermarket fuel line regulator to fix the issue??? it seems like my fuel pump is contantly cranking when ignition is on and someone told me that it should only run for about 5 seconds then cut out so maybe thats a part of the problem with mine?? any thoughts on this theory guys???
thanks

#29 Six_Shooter

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Posted 27 October 2010 - 03:14 PM

Going back to the battery connection/test light discussion.

There doesn't necessarily need to be something turned "on" to have a draw. Many items will have a draw when turned "off", to keep any volatile memories alive. Things such as radios (with clocks and electronic presets) have volatile memories that will draw a small amount of current. Clocks, especially mechanical clocks, will draw current, security systems will also draw a small amount of current when turned "off".

Moving up to the current discussion...

Before replacing anything, I would look at the AFM. From what I read, these can go out of adjusment and because of thier switch design, if it doesn't close almost fully at idle, this can cause problems. Also check your Throttle Position Switch. There are two switch points, not a range of voltage in the L28 EFI system. Closed throttle and Wide open throttle. If the closed throttle switch side is not adjusted properly or your throttle linkage is binding up and not allowing the throttle to close fully, that can also cause idle issues.
One other thing that seems to be common is the flexible tube between the AFM and the throttle body can tear and this will cause inaccurate readings of the AFM, since unmetered air is allowed to enter the engine this way.

#30 MaygZ

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Posted 27 October 2010 - 03:48 PM

Going back to the battery connection/test light discussion.

There doesn't necessarily need to be something turned "on" to have a draw. Many items will have a draw when turned "off", to keep any volatile memories alive. Things such as radios (with clocks and electronic presets) have volatile memories that will draw a small amount of current. Clocks, especially mechanical clocks, will draw current, security systems will also draw a small amount of current when turned "off".


The current draw of things like a radio memory, alarm sensors and a clock would produce only the tiniest of sparks.

#31 Bigworm

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Posted 27 October 2010 - 09:53 PM

well i have replaced the AFM yesterday (before i swapped the computer) to see if there was any difference but it did nothing, so maybe it could be the TPS, i will have a look when i get a chance. and from knowledge the air hoses on my car seem in good condition but ill check them out aswel.
cheers

#32 Zedman240®

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Posted 28 October 2010 - 09:08 AM

Try unpluging the cold start fuel injector; it may be stuck open. From memory its located near the throttle body.

#33 Six_Shooter

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Posted 28 October 2010 - 01:39 PM

The current draw of things like a radio memory, alarm sensors and a clock would produce only the tiniest of sparks.


:facepalm:

I never mentioned anything about sparks, besides "tiniest" is relative.

The current draw form those items is more than enough to cause a test light to turn on, used as a ground connection.

#34 kolonelklink

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Posted 28 October 2010 - 09:05 PM

+1 on cold start injector... I hear they a frequently dysfunctional in zx's... Clamp off the fuel if you have to (jammed open?)
Test all injectors are firing? place a flathead screwdriver against the body of the injector and hold your ear to it.. listen for the "click click"...
Check your plugs (are they black and wet?)
Another thought: check your coolant temp sensor. A faulty sensor or bad connection will read VERY cold to the ECU which will rich-out to compensate.

Good luck.
-pete

#35 MaygZ

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Posted 28 October 2010 - 09:32 PM

Is it just me, or do old fashioned carbies sound really good about now?

#36 kolonelklink

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Posted 28 October 2010 - 10:39 PM

Is it just me, or do old fashioned carbies sound really good about now?

No way... you couldn't pay me to take my MS off me. EFI is far superior to carbs in almost every aspect except simplicity for troubleshooting. Carbs are a metered leak, EFI gives superior atomization without the need for comprises in manifold air temperature, flow and port design required to maintain atomization in carburated systems.

Don't blame EFI... the zx ecu is 30 years old and not built for user interface. That said, I don't think it sounds likely that the ecu is the source of failure, it would just be nicer if you could plug the laptop in and see the ECU readouts for troubleshooting like in a aftermarket system but that's how it goes.

Keep us posted on progress... there are lots of simple tests you can use to track down the problem if you think about it logically. I also have HEAPS of zx efi spares that may help if you need.

-Pete

#37 Bigworm

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Posted 29 October 2010 - 08:31 AM

thanks pete, i think when i get over there today im gonna get the multimeter out and test all the electrics on the wiring harness and the component switches and relays just to eliminate it being an electrical fault (thus eliminating a faulty ecu) and also i have tried running it without the cold start valve plugged in to no effect, but i might have to pull it out completly and have a look if its jammed or something.Also i did adjust the TPS yesterday but that didnt seem to do anything really either.



#38 kolonelklink

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Posted 29 October 2010 - 12:18 PM

nws.
If you're not sure about reading plugs swap in some brand new ones, run them for a bit (10 mins+?) and then pull them out and take a photo straight away, also note if they are wet (is it thick grimey wet with oil, liquidy and smells strongly of octane, or watery with a bit of green... dab it on paper if you have to) ... It will really help with troubleshooting if you know exactly what the problem is. Fuel plus spark plus air = bang... one of those is the problem so work out exactly which first then we can work backwards through EFI if nessecary.

Although the normal instinct is to change things untill you find the problem it can stuff with you ability to locate problems by adding complexity... think about it like this:
1. If it was working and now isnt, something has changed.
2. It is probable that there is only one point of error
3. The probable source or error is the last thing that changed (what have you changed recently?)


If you started fidling with wires and changing things stuff without following a logical process you may be introducing new errors - cables can come loose, short etc.
The probability of finding two errors is exponentially greater than finding one because you only have one source of information output (does it work? - yes/no)

I cannot recall the number of times i've changed a relay or wire and then had to adjust it afterwards because i'd let somehting sit loose or connected incorrectly. Without knowing is you've made a mistake you could potentially introduce a plethora of new problems :(
Start from basics would be my strongest advice.



-pete

#39 Six_Shooter

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Posted 29 October 2010 - 12:39 PM

I find EFI to be more simple than carbs.

Just FYI, there are a number of OEM EFI systems that have datalogging capabilities, the Z and ZX ECMs are not able to though. The GM ECM I use in my 240Z has an ALDL (Assembly Line Diagnostic Link) connector that has all sorts of info sent through it. :D

#40 Bigworm

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Posted 29 October 2010 - 04:20 PM

ok an update on whats goin on. I have sorted out the problem with the excess fuel pressure (seems my uncle who was helping me with the car had unplugged the sensor on the block next to the oil filter for some reason and forgot to plug it back in :-[)but as soon as i plugged it in all was well with the fuel system it builds up pressure and then shuts off after a few seconds and keeps it at the correct pressure so the fuel system is fine! :D Now the car kicks over and idles but it is still lumpy and blows a bit of smoke, i took the rear cover off the afm so i could monitor it and the potentiometer thing is flapping a bit and if i gently hold it shut it runs nearly perfect, making me think there is some kind of airflow or vacum problem. also what is the easiest way to tune these systems to get them running nice?? i have tried a combo of timing/idle speed adjuster/AFM bypass screw but it doesnt seem to do much (maybe it has something to do with the air problem??)
thanks

Jesse




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