Ljet

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sgkent
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Re: Ljet

Post by sgkent » Tue Apr 25, 2017 7:27 am

#15 on the coil gets 12 volts. #1 goes to the distributor. When pin #1 is momentarily grounded by the points current flows from #15 thru the coil to #1 then onto the distributor and ground. As soon as the points open the current stops causing the magnetism in the coil to collapse and trigger higher voltage in the secondary winding of the coil which in turn causes the spark plug to fire. Think of the 12V like water pressure. The 12V pressure is always at both sides of the coil when it is connected but the electricity only flows when #1 has a path to ground. If you put 70 PSI pressure into one end of a water pipe, the other end will also have 70 PSI even though the faucet is closed. When the faucet is opened the water will flow out of it, and the pressure at the faucet end may fall quite a bit more than the other end hooked up to the water main. The electric pressure is voltage and it is always present in the coil when #15 is hooked up and power applied to it. As soon as #1 is grounded it will read a lower voltage because of the resistance in the coil. You need to have the distributor hooked up and working for the ECU to get a signal that causes the injectors to work.
TBone208 wrote: "You ppl are such windbags. Go use your crystal ball to get rich & predict something meaningful. Nobody knows what's going to happen. How are we supposed to take ppl who don't know the definition of a recession & "woman" seriously?"

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dingo
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Re: Ljet

Post by dingo » Tue Apr 25, 2017 3:47 pm

Thanks for that very clear explanation. makes sense.

The 50k ohms i measured at each inj plug (to ground)..i traced thru the harness,ecu, and out to the resistor pack..

i opened the ECU and it looks parkling clean...no corrosion. Part # is correct for the year. Is there any procedure for testing this thing of analog beauty ??
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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dingo
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Re: Ljet

Post by dingo » Wed Apr 26, 2017 1:26 pm

TO TEST GROUND SIDE - you need to put your test light alligator clip to the (+) #15 on the coil, the probe on the ground side of the injector plug and crank engine. This is where you should see pulsing.
Colin

test light between Coil+ and Inj.plug ground terminal...i get nothin ( i tried on more than one plug)

also i got a full ignition jolt thru my left hand which was holding the clip on coil+
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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sgkent
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Re: Ljet

Post by sgkent » Thu Apr 27, 2017 12:10 pm

the pulse is across the injector plug, preferably using a NOID light. Flip the light over if it doesn't work one way. We are talking small current so don't be using a big honky light bulb. A digital meter may not be fast enough to see the individual pulses. I have no idea where cinpuerter is. FYI - if you put a lead to pin 15 of the coil and the other side to ground you better be 100% sure there is a VOLT meter between the two. You do not want much current flowing from 15 thru the ECU or you will burn up the components in the ECU. They were designed to handle the limited current thru an injector not a heavy load. Do not read amps or you will burn up the ECU and maybe your meter too. Just get a NOID light.
TBone208 wrote: "You ppl are such windbags. Go use your crystal ball to get rich & predict something meaningful. Nobody knows what's going to happen. How are we supposed to take ppl who don't know the definition of a recession & "woman" seriously?"

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dingo
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Re: Ljet

Post by dingo » Thu Apr 27, 2017 5:14 pm

Ok Thanks. It is getting clearer by the day. I have verified that the pos. terminals have voltage during cranking, but the gnd terminals on the injector plugs are not getting grounded. verified by noid light.
I verified coil- to #1 is good and clean...so the ecu is receiving the trigger. I verified that the ecu grounds to engine are good at 5,16,17...and also verified that 14,15,32,33 from ecu out to inj plug gnds are all good clean connections.

I prodded gently around the ecu and found that the big power transistor mounted on the side is doing the switching. One terminal goes to the grounds at 16,17. Another terminal goes to inj gnds at 14,15,32,33
ON503 7703 no other markings..so not sure yet if it is NPN or PNP in order to test it.

Also verified from old samba thread that yes, all 4 inj plugs have to be removed, or you will see 12v on both terminals...so that is no longer an issue.
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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dingo
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Re: Ljet

Post by dingo » Fri Apr 28, 2017 11:27 pm

Ok, removed the big pwer transistor, and according to my multimeter tests, it is DEAD.
so far havent found any info on the possible replacements....or specs ? Does anyone rebuild these ecus out there?
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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sgkent
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Re: Ljet

Post by sgkent » Sat Apr 29, 2017 1:20 pm

Not that I am aware of. FIC sells rebuilt ones but a discussion with them many years ago they basically resolder the connections then test and toss if bad.

The ECU gets the trigger from #1 . That wire breaks sometime at the connector.

Pin 10 is where it gets 12V

Page 40 has the tests on each wire circuit. If the transistor is truly dead then it could have taken other components. https://www.thesamba.com/vw/archives/ma ... Manual.pdf

That said contact Telford, maybe he can look up the transistor for a substitute or suggest a repair for the ECU. Because they rarely die there are many out there for sale used. Don't let someone fool you into thinking they are rare and expensive.
TBone208 wrote: "You ppl are such windbags. Go use your crystal ball to get rich & predict something meaningful. Nobody knows what's going to happen. How are we supposed to take ppl who don't know the definition of a recession & "woman" seriously?"

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dingo
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Re: Ljet

Post by dingo » Sun Apr 30, 2017 12:07 pm

Thanks for the info ! Ill probably find a known working unit to compare with. yes the Xistor is truly dead, and maybe due to other component failure or perhaps other reasons. ..but these ecus are very easy to access and replace components, so my curiosity prevails...
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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dingo
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Re: Ljet

Post by dingo » Fri May 05, 2017 10:56 pm

Got a line of some calif ECUs....do you know if the cal vs federal is significantly different or negligible.??
I assume the connector pins are the same for all late 70s years and types.....so if i retain my harness, then should not be a problem ??
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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asiab3
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Re: Ljet

Post by asiab3 » Sun May 07, 2017 3:43 pm

The late Karl tested eleven or twelve different bus ECUs in his bus years ago, and said they all drove acceptably. He did not go into finer details of mixture/warmup differences, but I took that as a good word that any bus ECU will run for testing purposes. KentPS just passed CA smog with a 1700 engine and 2.0 ECU. I wouldn't worry about ECU differnces just yet.

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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sgkent
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Re: Ljet

Post by sgkent » Mon May 08, 2017 7:06 am

The California ECU 1975 - 1978 is likely to be a little leaner. The 1979 California ECU and FI is quite different and would not work well. Manual or automatic would be slightly different too however I suspect you could tune around it. Scott at German Supply also tested many different ECU and they all worked. 1975 and early 1976 had a slightly different FI system than late 1976 - 1978 and 1979 Federal. There is also this page, ECU numbers are near the bottom: http://www.ratwell.com/technical/FISwap.html
TBone208 wrote: "You ppl are such windbags. Go use your crystal ball to get rich & predict something meaningful. Nobody knows what's going to happen. How are we supposed to take ppl who don't know the definition of a recession & "woman" seriously?"

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dingo
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Re: Ljet

Post by dingo » Mon May 15, 2017 5:10 pm

I got the correct replacement ECU, but im still not getting any action at injector plug..no flickering of test light.
Just to rehash, i DO get 12V at one terminal of each injector plug with ign on
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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asiab3
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Re: Ljet

Post by asiab3 » Mon May 15, 2017 5:13 pm

Now is about the time I would look into the ECU plug for ANY wire pin connectors that may be backing out and not making good connection. Pay special attention to #5 and all the other ground pins.

Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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dingo
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Re: Ljet

Post by dingo » Mon May 15, 2017 6:25 pm

Yeah thanks will do. I did do that, but at this point...a re-do is all i got

I did notice that with harness plug removed pin10 get 12v with IGn ON...and Pin4 only get 4,5,6V as i crank....perhaps this is not enough
(i forget what site i got this testing protocol from..i just scribbled down 'pin 4 voltage while cranking')
'71 Kombi, 1600 dp

';78 Tranzporter 2L

" Fill what's empty, empty what's full, and scratch where it itches."

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Amskeptic
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Re: Ljet

Post by Amskeptic » Mon May 15, 2017 7:42 pm

dingo wrote:
Mon May 15, 2017 6:25 pm
Yeah thanks will do. I did do that, but at this point...a re-do is all i got

I did notice that with harness plug removed pin10 get 12v with IGn ON...and Pin4 only get 4,5,6V as i crank....perhaps this is not enough
(i forget what site i got this testing protocol from..i just scribbled down 'pin 4 voltage while cranking')


I just got a fuel-injected bus going after two years of every possible question and test, ohms, voltage, and fuel supply, regarding the fuel injection system. I did a lousy job of explaining my hunches, but we had two weird moments.

1) a test lamp showed voltage persisting at the series resistors even after the ignition was shut off until an eventual click from the double relay shut things down. I think it was a blown diode in the double relay.

2) Even though the injector plugs showed twelve volts at both sides, we concluded that the plugs had to be in the circuit with the solenoid coils accounted for for the ECU to give us proof of grounding. I forced the ECU to prove the grounds by having the injectors pulled, plugged in, charged with full fuel pressure, and I manually opened the breaker points with a screwdriver to watch the injectors actually spray at every other point opening. Thankfully the fuel was stale, so no explosions.

His bus drove well enough and started readily by the time I left. You should note that the basics were critical:
a) fresh battery charge and fresh gas
b) clean and gap the points and make sure the plugs are dry and clean and gapped
c) call out that Itinerant guy when he is in your neck of the woods, we're batting a thousand.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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