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| low_ryda |
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trying to diagnose an electrical demon within my falcon.. (ea mpfi)
anyone able to help? just died on the move one day,now the ecu just doesn't want to push fuel through. when tracing back the power supply system of the ecu i've discovered that pin 57 lacks voltage, reading around 3v as oposed to 12. on standby the main yellow power wire (pin1) picks up 12v untill you turn the ignition on and then drops to bout 2-3v i can't see that being normal. i've checked both relays (fuel & ecu)and both function as required out of the car.in the car i appear to have the ecu relay kick in on key turn but not the fuel pump relay. i've checked the harness all round the battery area and furthur up towards the firewall and can't find a problem. checked the pump, tried spare ecu,checked the fusible links and hardwired suspect plugs etc.(only checked the links for voltage drop & resistance not current) i've investigated far too much to note here so if replies could be specific as possible i can return pin voltages etc.
_________________ Not to get technical, but according to chemistry alcohol is a solution. |
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| alfy12 |
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Well all the pins you've checked should be 12v at koeo and 12-14.5 with engine running. I thought a relay problem but I don't think the 12v from pin1 of the ecu goes thru any relays.
Also the fusible links from the positive battery terminal (2 of them) are known to cause trouble under load. They will measure ok with the ignition off but as soon as current flows (ign on), they will have a large voltage drop. Turn you igntion on and measure between the positive battery terminal and the back of the fusible link plugs (within 6 inchs from the battery terminal. 2 large black plugs with spade connections. Usually corroded from battery electrolyte spillage). I've edited this response in light of what you said about pin1 of the ecu.
_________________ NF Fairlane: Non Factory Dual Fuel - New coolant tank, New fuel injectors, New fuel pump, New earth cable, ECU capacitors replaced, New O2 sensor, leads and plugs, New Radiator/Condensor cleaned. 483,000kms. AU I6 Powered. Struts, Shockies, Tie rods and ball joints replaced. Last edited by alfy12 on Mon May 25, 2009 9:39 am, edited 2 times in total. |
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| alfy12 |
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If Pin1 of the ecu is dropping down to 2-3 volts, then you have a voltage drop of 9-10 volts elsewhere in the system. I don't think the keep alive memory goes thru a relay as it is required all the time regardless of key position. Sounds like it could still be a bad connection around the battery/fusible link area or a connector. Trace that large yellow wire back towards the battery (from pin1)and measure with a multimeter at each connection with the ignition on. Where you have 9-10 volts across a connection/fuse/fusible link that will be the culprit. When I say measure across, I mean positive lead on one side of the fuse/link/connector and negative lead on the other side. Don't measure between connection and chassis. You could even jump a little further initially to prove the theory. Say measure between pin1 of the ecu and the positive battery terminal (may need an extension wire) with ignition on. Should definately have 9-10 volts on the multimeter. If not you battery is stuffed. Once you have you 9-10 volts, half split the wire run and attempt to gain access at a connector. Do the same check again half splitting until you have the culprit.
Good Luck.
_________________ NF Fairlane: Non Factory Dual Fuel - New coolant tank, New fuel injectors, New fuel pump, New earth cable, ECU capacitors replaced, New O2 sensor, leads and plugs, New Radiator/Condensor cleaned. 483,000kms. AU I6 Powered. Struts, Shockies, Tie rods and ball joints replaced. |
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| low_ryda |
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thanks alfy i'll try what you've mentioned.
what amp wire is used for the fusible links so i can replace them ? or at least close to for diagnostic purposes. could you still even buy new spares ? what do people normally do with them ?
_________________ Not to get technical, but according to chemistry alcohol is a solution. |
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| alfy12 |
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I downloaded an EA factory diagram and it suggest that the main links are 1.25mm. It showed 6 fusible links in total with 4 black wire ones 1.25 mm, red one was only 0.85 mm and the green was only 0.5 mm. The fusible link is special wire which are not rated like normal copper wire. I would ask a local auto electrician what they use. Fusible wire is generally a lot thinner than its equivalent copper conductor for the same current rating. You could try Ford.
 Be careful replacing the links with conventional wire as you remove the week link in the system. This means if you have a short in a system, the wiring could melt anywhere in that system. Can be a mess if other conductors melt as well. You could try normal wire just to get the car going and fit a fusible link later. Just look below the link at the connector (where the link connects to the normal vehicle wiring). The wiring on the far side of the link would be the appropriate size.
_________________ NF Fairlane: Non Factory Dual Fuel - New coolant tank, New fuel injectors, New fuel pump, New earth cable, ECU capacitors replaced, New O2 sensor, leads and plugs, New Radiator/Condensor cleaned. 483,000kms. AU I6 Powered. Struts, Shockies, Tie rods and ball joints replaced. |
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| low_ryda |
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yer i've gathered so much but have only replaced a couple at a time coz i'm worried bout burning something out but right now i'm pulling my hair out so i really dgaf. i'm figuring that if that it's not the fusible links then there has to be a harness problem somewhere and i'm guessing it's chaffed somewhere do to dodgey dealings with previous owner. so the links are my next focus.
i guess the most important thing i wanted to know was what the fusible links are made of. i'll have to consult an auto electrician, i've had bad history leaving my car in other peoples hands, particilarly frauds (read: wouldn't send my mother in law there) i've done alot of the labour intensive work i might just tow it to an auto sparky just to diagnose the problem. it's just finding one thats not out to rape me in this current economic climate will prove to be the challenge.
_________________ Not to get technical, but according to chemistry alcohol is a solution. |
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| alfy12 |
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Yeh, I know where you're coming from. Had to pay for mum's eb major service a couple of years ago which turned out to be $1000. Mum's a pensioner and didn't have the money. No phone calls to authorise anything. They just did the work and told her later.
Have you done any voltage drop checks at the links to confirm the fault? If you can confirm the fault, it's just a few phone calls to some auto elecs to see who is most co-operative. Ask them if they can supply the parts and how much. A good auto elec should have the problem diagnosed within 1 hour max. I guess you don't have too many options where you live. Always lots of horror stories in smaller towns. If you have a wrecker nearby, you could remove an EF/EL fusible link block and graft it into your ealier model. It should have the newer links (block type with clear window) in the same colours as your old links. Some soldering, heatshrinking and crimping and your in business. Just need to find somewhere next to the battery to mount it. Of course test the system first before hacking things to bits. Good Luck.
_________________ NF Fairlane: Non Factory Dual Fuel - New coolant tank, New fuel injectors, New fuel pump, New earth cable, ECU capacitors replaced, New O2 sensor, leads and plugs, New Radiator/Condensor cleaned. 483,000kms. AU I6 Powered. Struts, Shockies, Tie rods and ball joints replaced. |
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| low_ryda |
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ok awsome, i didn't know the later e's had a different system. i was almost thinking bout wiring in a mains box like the bf for reliability. nightmare at first but so is chasing elusive demons.
i've checked both voltage and resistance on each end of the plug and had no difference. but thats still not measuring current under load. i'm stll convinced it's near the battery somewhere. i know i have voltage drop at the ecu but thats the furthest point away from the source, current drop over distance would lead to voltage drop wouldn't it ?
_________________ Not to get technical, but according to chemistry alcohol is a solution. |
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| madeaspack |
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the wiring at the battery terminals can corrode causing the wires to all look ok but be in fact broken,this happened on my EA and guess which wire it was?fuel pump earth.
give all the wires on the battery terminals a good "tug" if any look dodgy at all replace the eye terminals of the individual wires
_________________ 97 el xr6,5 speed short shifter,sequential scoop,no arial,freshly resprayed,low on 17's,3 inch zorst,stainless hi flo cat,snort stage 3 stainless manifold,garrett t04e,front mount cooler,wolf 3d ecu,seimens 760cc injectors,walbro fuel pump |
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| alfy12 |
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Quote: i know i have voltage drop at the ecu but thats the furthest point away from the source, current drop over distance would lead to voltage drop wouldn't it ? Yes current flowing thru a circuit that has resistance will lead to a voltage drop but not of the order you're seeing. I would say that if you had a battery voltage of 12.6 volts then you would have about 12.5 at the ecu worst case. As madeaspack said, he had a problem with a resistive connection at the negative terminal. This voltage drop can occur anywhere in the circuit. The name circuit is just that, a complete path from voltage source (battery), thru the load and back to the battery. I'll give you an example using madeaspack fault and you're fault combined: You're battery is 12.6V and you're negative battery terminal to chassis (near the extractors) wire is stuffed. You're chassis of you're vehicle is +9.6v with respect to the negative battery terminal (remember the wire is stuffed). This means when you measure between pin 1 of the ecu and the chassis, you only get 3V. When you add the voltage drops together they are correct (3V + (9.6V across the stuffed chassis wire)=12.6V) Example 2: You're battery is 12.6V and you're fusible linkwire is stuffed. You're yellow wire from you're fusible link is 3V with respect to the negative battery terminal (remember the link wire is stuffed). This means when you measure between pin 1 of the ecu and the chassis, you only get 3V. When you add the voltage drops together they are correct (3V + (9.6Vacross the link)=12.6V) As you can see a few possibilities but its important to look for the voltage drop. It doesn't matter if its on the positive or negative side of the circuit, you need to measure between 2 points on the same circuit with power on to find it. A chassis to negative battery terminal wire or a fusible link shouldn't have any greater voltage drop across it than 200mV (probably a lot less) with the power on.
_________________ NF Fairlane: Non Factory Dual Fuel - New coolant tank, New fuel injectors, New fuel pump, New earth cable, ECU capacitors replaced, New O2 sensor, leads and plugs, New Radiator/Condensor cleaned. 483,000kms. AU I6 Powered. Struts, Shockies, Tie rods and ball joints replaced. Last edited by alfy12 on Thu May 28, 2009 9:13 am, edited 1 time in total. |
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| low_ryda |
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thanks alot alfy your heaps helpful
 thats deffinately given me a few things to think about. i noticed last weekend it's got (always had) a giant earth cable (bit bigger than the starter power wire) running from the bat- terminal to the block and only one midgey little earth comming from the harness near the extractors to the block and that was it. that can't be right can it ? i'll have another good crack this weekend or hopefully sooner if i find time with your advice in mind. cheers blokes, Chriso
_________________ Not to get technical, but according to chemistry alcohol is a solution. |
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| alfy12 |
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Sounds about right. The 2 thickest wires on the car are the positive battery term to starter solenoid wire and the negative battery to eng block wire. This is because your starter motor has the highest current draw (100's of amps) on startup. The remaining loads are everything else but they only draw a fraction of the current of the starter. The second highest would be your headlights. The current flow for your headlights, taillights, dash, ecu, a/c etc flow thru that thin wire you're refering to (near the extractors).
_________________ NF Fairlane: Non Factory Dual Fuel - New coolant tank, New fuel injectors, New fuel pump, New earth cable, ECU capacitors replaced, New O2 sensor, leads and plugs, New Radiator/Condensor cleaned. 483,000kms. AU I6 Powered. Struts, Shockies, Tie rods and ball joints replaced. |
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| low_ryda |
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and it's reasons like this that 12v electrics loose me lol.
_________________ Not to get technical, but according to chemistry alcohol is a solution. |
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| alfy12 |
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Quote: only one midgey little earth comming from the harness We don't want it to be to thin. Has to be able to handle 50-60 amps at least. Does it look like the original conductor?The general rule with copper wire is that the greater the current flow thru a circuit, the greater the cross sectional area of the wire needs to be. So if my starter was drawing 350amps when I turn the key, I need a nice thick cable or the conductor will overheat, resistance will increase which will ultimately limit the maximum current flow. Designers of these circuits have to ensure they use wire that is thick enough to meet all the demands but not too thick to cost more money and add extra weight. If I was to wire a vehicle with 1 gauge copper wire, I would add hundreds of kgs to the vehicle weight. If I was to wire the vehicle with 18 gauge wire, everything would overheat and the wiring insulation would melt/go open circuit. So I must wire each circuit with its maximum current flow in mind and choose the appropriate conductor size. The wiring gauge system works in reverse. The smaller the number, the larger the wire. Also a larger diameter wire has less resistance per foot than a thinner one. Cheers Alfy
_________________ NF Fairlane: Non Factory Dual Fuel - New coolant tank, New fuel injectors, New fuel pump, New earth cable, ECU capacitors replaced, New O2 sensor, leads and plugs, New Radiator/Condensor cleaned. 483,000kms. AU I6 Powered. Struts, Shockies, Tie rods and ball joints replaced. |
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| TickXR |
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Have you checked that the ECU relay is functioning correctly? I'm just looking at an EB MPFI diagram here and shows pin 57 going to a relay.
Sorry can't be much more of a help
_________________ If you don't do it whilst your livin, you aint got no bloody chance when your dead!!! |
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