mass airflow meter wires melted
12-02-07, 10:20 PM
#1
mass airflow meter wires melted
well i start up my 88 TII for the first time tonight and the engine runs strong and is holding a good cold idle and i notice that it looked as if there were smoke coming form under my airbox. i immediatly shut the engine down and notice that the wires to the mass airflow meter had begun melting through the grey sleeve. i waited for everything to cool and stripped the sleeve down to the bare wires to view the damage. pics are to follow in this thread. now, the previous owner had an engine fire and burnt some wiring. he told me that he repaired the wiring that was burnt and after inspection of the wiring i was ok with it as i had no shorts or problems during the process of getting the car running. i know that i have a short somewhere and i need help tracing it. i would really love to know where the maf wiring goes to and what it ties into. i just need its complete path to save myself time in repairing the short and wasting time looking in the wrong places.
if someone else has any other ideas other than a short that would have caused this i'm 100% open to suggestions!
if someone else has any other ideas other than a short that would have caused this i'm 100% open to suggestions!
12-02-07, 10:30 PM
#2
honestly, if it were me, id pull the whole emissions harness out and re-do it with new wire, just cause tracking these things down can be a real PITA, and then you'll know that the repair was done right. There are a lot of things that could possibly cause that, but if it did it without blowing a fuse, especially after an engine fire, id be questioning the way it was repaired and rewired (unless it was somehow sitting on the turbo manifold or downpipe, but it doesnt look like thats the case here)
12-02-07, 10:36 PM
#3
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making a new harness is a pita. i believe aaron has done it i know its a ton of work. check for blown fuses. look at the wiring diagram found in the FAQ. find what wire is burnt what it goes to where it should go. looks like a few of those wires became fusable links.. now you have to repair the earlier repair good luck
12-02-07, 10:50 PM
#4
i'm not opposed to repairing the wiring, i just need to know the circuit so that i'm not wasting time trying to find the exact circuit. i'm not sure that the fsm has a detailed diagram for the afm wiring. i'll have to check again
12-02-07, 11:08 PM
#6
Ive re-done wiring harnesses in my 'vert, rewired a bunch of them for a megasquirt, and even made a harness from scratch (well, i had the plugs and connectors, but the rest was up to me). It really is not bad at all as long as you can follow lines on a piece of paper.
To the OP: You already have the harness in front of you, all you need to do is remove it from the car, completely unwrap it, and then one wire at a time replace them. Get a bunch of different colors of wire (same gauge as stock, dont remember OTTOMH), write down what colors you used for which things, and stay consistant with whatever color strategy you choose (black is ground, red is +12, orange is +5, everything else is other colors etc). Then just cut each wire one at a time (leaving room to strip and solder onto it at the plug), cut a new one to the same length as the old one, and re-solder to the bit of the old wire that you left. Just for peace of mind, check the continuity of each wire, then re-wrap in harness wrap (or a hell of a lot of electrical tape, as long as you do a thorough job).
To the OP: You already have the harness in front of you, all you need to do is remove it from the car, completely unwrap it, and then one wire at a time replace them. Get a bunch of different colors of wire (same gauge as stock, dont remember OTTOMH), write down what colors you used for which things, and stay consistant with whatever color strategy you choose (black is ground, red is +12, orange is +5, everything else is other colors etc). Then just cut each wire one at a time (leaving room to strip and solder onto it at the plug), cut a new one to the same length as the old one, and re-solder to the bit of the old wire that you left. Just for peace of mind, check the continuity of each wire, then re-wrap in harness wrap (or a hell of a lot of electrical tape, as long as you do a thorough job).
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12-03-07, 07:20 AM
#9
i also wouldnt mind repairing what i currently have to save some cash. i can see were the afm wiring goes into a larger loom by the air pump and from there where does it go and do the wire's colors remain the same throughout its path to the ecu without splitting off into a different pin'd connector? i would assume they do but i want to cover all of my bases.
12-03-07, 08:25 AM
#10
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It shows clearly in the FSM wiring schematics where the wiring goes.
The brown/white wire is the only one that should have had any power on it, and only 5vdc ref voltage at that. That wire comes of 2A and is also spliced to the other brown/white wires that feed ref voltage to the TPS, ATP, BOOST SENSOR, VARIABLE RESISTOR.
The two gnd wires are the black ones and are also spliced to the gnd wires for those other sensors.
The brown wire goes to the circuit opening relay and the fuel check connector.
The GL and GO go straight to the ECU.
I'd just cut off that plug from a wrecking yard harness along with at least a foot of the wiring and just splice that plug/wiring to the existing burnt wires (less the burnt part). Stagger the splices so they don't bunch up in one spot and put shrink tubing over it.
I have a problem with your prolem. Only one wire, the brown/white has 5vdc on it and it's ref voltage. I've a hard time believing that short didn't whack the voltage regulator inside the ECU.
There's no sense replacing a whole EM harness over this.
The brown/white wire is the only one that should have had any power on it, and only 5vdc ref voltage at that. That wire comes of 2A and is also spliced to the other brown/white wires that feed ref voltage to the TPS, ATP, BOOST SENSOR, VARIABLE RESISTOR.
The two gnd wires are the black ones and are also spliced to the gnd wires for those other sensors.
The brown wire goes to the circuit opening relay and the fuel check connector.
The GL and GO go straight to the ECU.
I'd just cut off that plug from a wrecking yard harness along with at least a foot of the wiring and just splice that plug/wiring to the existing burnt wires (less the burnt part). Stagger the splices so they don't bunch up in one spot and put shrink tubing over it.
I have a problem with your prolem. Only one wire, the brown/white has 5vdc on it and it's ref voltage. I've a hard time believing that short didn't whack the voltage regulator inside the ECU.
There's no sense replacing a whole EM harness over this.
12-03-07, 05:05 PM
#12
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It's the approx five volts supplied to the pots in the items I listed for them to work. It comes from the ECU. Pin 2A.
Pull apart the wires in that plug and make sure they don't touch a gnd. Then key On and see if the brown/white wire has 4.5 to 5 vdc. If it does, all's well. If not and all the fuses are in, tough. No 5vdc means the coils/ignitors won't fire and the items listed won't work (not that it matters if the coils don't work).
I'd be worried about just how that harness got enough voltage to melt. Got me how.
Which wire is most melted????? Color or if not a color how about which pin in the plug is it attached to? How many pins from one end?
Pull apart the wires in that plug and make sure they don't touch a gnd. Then key On and see if the brown/white wire has 4.5 to 5 vdc. If it does, all's well. If not and all the fuses are in, tough. No 5vdc means the coils/ignitors won't fire and the items listed won't work (not that it matters if the coils don't work).
I'd be worried about just how that harness got enough voltage to melt. Got me how.
Which wire is most melted????? Color or if not a color how about which pin in the plug is it attached to? How many pins from one end?
12-03-07, 11:19 PM
#13
thak you for the help. i go tthe problem resolved and the engine running. i found the source of the problem. two connectors were plugged in together that should not have been, causing the short. the first pic is the male end 
that was plugged into another two pin connector with wire colors black with red dot and bown with blue dot, kind of shown here (sorry for the fuzzyness, i couldnt get it to focus) 
when those were plugged together and the engine was running (should have checked the previous owner's work on the wiring) the wires would quickly heat up and begin to smoke. i found this out after i repaired the harness. thus sourcing my problem. i unplugged those(which made no affect on the engine running) and no more melting wires. not sure what they are or what they should go to but i'm all ears on that.
that was plugged into another two pin connector with wire colors black with red dot and bown with blue dot, kind of shown here (sorry for the fuzzyness, i couldnt get it to focus) when those were plugged together and the engine was running (should have checked the previous owner's work on the wiring) the wires would quickly heat up and begin to smoke. i found this out after i repaired the harness. thus sourcing my problem. i unplugged those(which made no affect on the engine running) and no more melting wires. not sure what they are or what they should go to but i'm all ears on that.
12-04-07, 12:21 AM
#14
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Page 50-25 of the wiring diagrams in the free, online 88 FSM.
The fuel pump check connector has two wires. It's a yellow plug with two wires. One wire is black and the other brown. NOTHING gets pluged into this plug. You only Jumper these two sockets to get the fuel pump to work (key to ON) to check for leaks in the fuel system.
The other wire I'm not sure of, but the black/white wire is 12vdc when key is ON or better. So. You must remember, the brown wire in the fuel pump check connector also goes to the AFM (remember, on wire on the afm plug is brown). So it seems you put 12v on that wire. That brown wire is the ground wire for the micro switch in the afm. It all makes sense to me why the harness melted. Oh, the micro switch puts a gnd on the circuit opening relay to pull that relay in so the fuel pump will work.
I think the white, two wire plug is for a solenoid on the ACV, but the colors seem off a bit. Is that a green or blue wire with that black/white wire?
The fuel pump check connector has two wires. It's a yellow plug with two wires. One wire is black and the other brown. NOTHING gets pluged into this plug. You only Jumper these two sockets to get the fuel pump to work (key to ON) to check for leaks in the fuel system.
The other wire I'm not sure of, but the black/white wire is 12vdc when key is ON or better. So. You must remember, the brown wire in the fuel pump check connector also goes to the AFM (remember, on wire on the afm plug is brown). So it seems you put 12v on that wire. That brown wire is the ground wire for the micro switch in the afm. It all makes sense to me why the harness melted. Oh, the micro switch puts a gnd on the circuit opening relay to pull that relay in so the fuel pump will work.
I think the white, two wire plug is for a solenoid on the ACV, but the colors seem off a bit. Is that a green or blue wire with that black/white wire?
12-04-07, 12:31 AM
#16
this car was a mess of unconnected and burt wires and a completely removed emissions system from the previous owner. its been quite a task to sort everything out and make things work correctly. i installed every emissions component and have been dealing with the wiring ever since. at least the engine runs and holds a good idle. a little high but good.
12-07-07, 12:57 AM
#18
ok, here's the vid: http://www.youtube.com/watch?v=VmNZD37OVZ0
12-07-07, 01:25 AM
#20
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that vid made me miss my baby.hopefully by xmas she'll be running. BTW congrats on getting her running again.....now fix the air leak! (supposing that is what it is causing high idle :P )
12-07-07, 08:15 AM
#21
only when the engine is cold do i get a little backfire at 4K. once warm i dont get that. the idle stays around 1500rpm. so thats another gremlin to deal with. i also have to sort out why the oil pressure gauge does not work. the sender wire is snug on the sender. the oil needs changed anyways, smells like gas. the engine was pretty floded.
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