Author Topic: P8 ECU Help and Need To Buy One  (Read 1682 times)

Offline Tom H

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P8 ECU Help and Need To Buy One
« on: January 13, 2022, 07:55:19 PM »
Let's start with the need to buy: I would like to buy 1 or 2 P8 ECU for the '98ish EV at a reasonable price.

Why: Somehow I fried two of them while trying to tune an EV while "trying" to help Mark at Guzzi Classics. I don't know what "I" did wrong. I would like to replace them or at least one.

The issue: Somehow that I am not sure of, while hooking up my cables for Guzzidiag (that have no problem with a 15M) the ECU lost signal from the TPS and could not get it back.

I had previously checked TPS voltage with a multimeter, withing spec. Hooked up my cables for Guzzidiag (which would not connect to the ECU even with the correct model and P8 listed), then the bike ran like crud. After trying to figure out if I knocked a wire loose, I found the TPS had at idle aprox. .001V, at W/O throttle about .100V.

A NOTE: A Senior moment here. THIS time while moving the wires around on the bike to connect to the diagnostic cable, I noticed a spark at the positive battery terminal. The Senior Moment: I don't remember if it was before or while I was connecting my cable to the diag. cable?????

Installed another P8 and now had the correct TPS voltage and the bike ran fine.

So if I fried something in the ECU, can it be easily replaced without being an electronics wizard?????

I feel like crud over this. Hopefully someone has an answer for repairing the ECU or can sell me one or two that they don't need!!!!!!

THANK YOU!!
Tom
2004 Cali EV Touring
1972 Eldo
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1973 R75/5 SWB with Toaster
2007 HD Street Bob
1953 Triumph 6T (one day it will be on the road!)

Offline Kiwi_Roy

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Re: P8 ECU Help and Need To Buy One
« Reply #1 on: January 13, 2022, 08:48:47 PM »
The first thing you need when troubleshooting a P8 is a copy of this document
http://www.dpguzzi.com/efiman.pdf

A couple of questions.
Does the pump prime when you turn the key On? That tells me if the brain is powered up and working. See below.
You can remove the cover off the large edge connector to give you access to the connections for checking the Voltage.
Looking at the schematic on page 26 they show the TPS as item (6) Dont take too much notice of the pencil marks on the drawing, I think
terminal 30 is positive, terminal 11 is negative, you should see a Voltage across those either 5 or 10 Volts. There is several different ways Guzzi wired the
Measuring the Voltage from 11 to 17 you should see a DC Voltage that goes up scale as you open the throttle.
There are a couple of different ways Guzzi wired the TPS but they all rely on a reference Voltage across the ends and a Variable Voltage coming back from the TPS to indicate how far open the throttle is.
Of course if we don't see these Voltages it may mean that the reference Voltage is missing, Let us know what you see.

Below
If the fuel pump doesn't prime chances are the safety diode inside the ECU is blown, its in there to protect the ECU from accidental battery reversal.
This was the problem on 2 P8s I have fixed.
The Safety diode grounds the ECU Pump relay coil so if it's open the relay will not pull in.
The diode doesn't need to be buried inside the ECU connected to pin 28 it will work just as well if you clip the wire adjacent to the relay's 85 pin and just run it to chassis through a small diode, this is how they did it on later versions.
« Last Edit: January 13, 2022, 09:40:05 PM by Kiwi_Roy »
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Offline lucky phil

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Re: P8 ECU Help and Need To Buy One
« Reply #2 on: January 13, 2022, 09:24:34 PM »
Well the advantage with the P7/8 and 16M ecu's is they are old school and the boards are easily accessible for component replacement. I would track down a repairer( they do exist) and explain the issue with regards to the TPS supply voltage so he's not troubleshooting everything and see what the repair cost is. I don't see a ton of these around anymore and SH electronic units of this age come with a risk.
Were you measuring the TPS voltage with a fly lead or spiking the loom/plug.

Ciao 
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Offline Tom H

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Re: P8 ECU Help and Need To Buy One
« Reply #3 on: January 13, 2022, 10:09:48 PM »
Let's see if I can answer so far.

With the ECU that is having the TPS voltage issue. The bike will run on the center stand, it will not idle. It will run on open throttle above idle. I do not think it will run down the road. So everything SEEMS to be working except TPS voltage. As in the ECU is not getting the throttle position value.

TPS was tested with a Caspers break out cable. Unplug the bike cable to TPS, plug into Casper cable, plug Casper cable into TPS. Casper cable has an extra set of wires to connect a multi meter to.

Kiwi: To be clear, are you saying that you can pull the rubber cover back from the ECU main connector to measure the voltage? As in, pull boot, turn key on with ECU connected to cable, measure from the pins??

Tom
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1972 Eldo
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1973 R75/5 SWB with Toaster
2007 HD Street Bob
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Re: P8 ECU Help and Need To Buy One
« Reply #3 on: January 13, 2022, 10:09:48 PM »

Offline fotoguzzi

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Re: P8 ECU Help and Need To Buy One
« Reply #4 on: January 13, 2022, 10:24:29 PM »
Here is the piece that fries, I had one fixed by my electronic guru.



I forgot where in this pic the part was from, I will try to find a better pic of the fried part insitu

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Offline Tom H

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Re: P8 ECU Help and Need To Buy One
« Reply #5 on: January 13, 2022, 10:39:15 PM »
foto, to be clear. You had the same issue and the little part is was fried that kept the ECU from getting the TPS voltage??

If so, that could/should be an easy fix.

I also wanted to add that when I tested the TPS with the break out cable installed I'm 99.9% sure that no cable touched each other or the bike while the key was in the ON position. The issue SEEMS to have come from when I was messing with the wires to get to and connect the diag. cable.

I also wanted/NEED to know: The 15m I believe has a ground wire from the ECU chassis (connected to a cover screw) to either frame or to battery ground. Should the P8 have the same ground wire?

THANK YOU!!!!!
Tom
« Last Edit: January 13, 2022, 11:20:39 PM by Tom H »
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Offline lucky phil

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Re: P8 ECU Help and Need To Buy One
« Reply #6 on: January 13, 2022, 11:20:59 PM »
Here is the piece that fries, I had one fixed by my electronic guru.



I forgot where in this pic the part was from, I will try to find a better pic of the fried part insitu



It looks like the component directly above the sticker lower right. Looks like a rectifier diode but full disclosure, I'm an electronics muppet.

Ciao
« Last Edit: January 13, 2022, 11:26:59 PM by lucky phil »
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Offline Kiwi_Roy

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Re: P8 ECU Help and Need To Buy One
« Reply #7 on: January 14, 2022, 12:13:30 AM »
Let's see if I can answer so far.

With the ECU that is having the TPS voltage issue. The bike will run on the center stand, it will not idle. It will run on open throttle above idle. I do not think it will run down the road. So everything SEEMS to be working except TPS voltage. As in the ECU is not getting the throttle position value.
Yes, that sounds to me like the TPS reference Voltage might not be there, as you open the throttle you don't get more Voltage so of course you don't get any more fuel
Measure the Voltage across the TPS I think it will be 5 Volts, if your other one works compare the two.
Print out page 26 of the document I sent it shows where the Voltage originates, if you have a Guzzi schematic it might show you a little different.

 
TPS was tested with a Caspers break out cable. Unplug the bike cable to TPS, plug into Casper cable, plug Casper cable into TPS. Casper cable has an extra set of wires to connect a multi meter to.

Kiwi: To be clear, are you saying that you can pull the rubber cover back from the ECU main connector to measure the voltage? As in, pull boot, turn key on with ECU connected to cable, measure from the pins??  Yes, you should be able to slide the cover off the ECU plug, I mean the one attached to the loom at least I could on my 98 EV (may have to remove a couple of screws) then its really easy to touch your meter on the different connections (Loom side, not ECU side) I think your Casper cable does the same thing.

Tom

I think we are getting a bit confused by the different symptoms depending what board you have plugged in
Could you plug each board in and see if the pump primes for 2 seconds when you turn the key On then we can rule out the safety diodes.
You could also measure the Voltage across the TPS on each one so you know what to expect.

The two P8s I have fixed had an open Safety diode but if the bike even tries to start I think you can rule that out, a pity because its really easy to fix.

If you have a bad Safety Diode its easy to find, just measure with the Ohmmeter from pin 28 to one end of the different diodes in the board, zero Ohms will indicate you have found the right one, the other end of the diode (with band) will go to chassis or pin 1. replace with any low current silicon diode.

Sorry I don't have a bike with the P8 or I would be able to trace out the reference Voltage, they are quite a simple device.
« Last Edit: January 14, 2022, 02:24:53 AM by Kiwi_Roy »
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Offline Kiwi_Roy

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Re: P8 ECU Help and Need To Buy One
« Reply #8 on: January 14, 2022, 01:11:13 AM »
Here is the piece that fries, I had one fixed by my electronic guru.
 
Fotoguzzi yes that looks like the one I found too, both the cards I fixed had a blown diode, I'm not sure why it blows perhaps far too much current.
I'm not sure its the one on lower right though, that looks more like the coil driver area.
I think Tom might have blown the Voltage reference on his
« Last Edit: January 14, 2022, 02:28:09 AM by Kiwi_Roy »
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Offline yogidozer

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Re: P8 ECU Help and Need To Buy One
« Reply #9 on: January 14, 2022, 05:25:07 AM »
Anyone replace the P8 with a 15M?
Those dang points and condensers were SO much trouble. Thank God for computers  :rolleyes:

Offline fotoguzzi

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Re: P8 ECU Help and Need To Buy One
« Reply #10 on: January 14, 2022, 07:27:17 AM »
I did not cause the fault, I got the bike that way so not sure what caused the rectifier to burn. When I worked at the TV station we had a few genius electrical minds there, it was an easy fix for my friend Tom Z.. we identified the fried part by a little burn /black area around it on the board.
« Last Edit: January 14, 2022, 07:28:39 AM by fotoguzzi »
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Offline Kiwi_Roy

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Re: P8 ECU Help and Need To Buy One
« Reply #11 on: January 14, 2022, 08:24:35 AM »
I did not cause the fault, I got the bike that way so not sure what caused the rectifier to burn. When I worked at the TV station we had a few genius electrical minds there, it was an easy fix for my friend Tom Z.. we identified the fried part by a little burn /black area around it on the board.
I never thought you caused it to burn out.
When I had an EV the  diode went poof one day, I must have shorted the battery onto it for a nanosecond somehow because its effectively wired from the pump relay coil to chassis therefore limited to about 100 mA by the coil resistance but it blew anyway, I call that a design fault.
« Last Edit: January 14, 2022, 08:30:09 AM by Kiwi_Roy »
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Offline PeteS

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Re: P8 ECU Help and Need To Buy One
« Reply #12 on: January 14, 2022, 08:47:23 AM »
Looks like a 1N4003 which is a common rectifier diode.





https://www.digikey.com/en/products/detail/diodes-incorporated/1N4003-T/603

You can get them on Amazon too………of course, what can’t you get there.

Pete
« Last Edit: January 14, 2022, 08:49:48 AM by PeteS »

Offline John A

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Re: P8 ECU Help and Need To Buy One
« Reply #13 on: January 14, 2022, 10:14:01 AM »
I fixed one for a guy and it was not too troublesome. A local guy had reversed polarity when connecting his battery, one of the things that may fry them. I read over it from instructions on here on WG and went to radio shack and got a diode. It was obvious visually when I opened the case which one it was. The hard part was that I didn’t have a good soldering iron for small work which I didn’t realize until I  tried my small iron so used what I had and was careful not to desolder everything around the diode as I got the old one out and the new one in. The good part is that it is under a cover so the thing was not visible when I was done and it worked, surprisingly. I’ve not heard from the guy in years so I assume it still works
John
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Offline Tom H

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Re: P8 ECU Help and Need To Buy One
« Reply #14 on: January 14, 2022, 10:37:38 AM »
I plan to go and see if I can find a bad diode. If so, I'll find a way to get a new one soldered in. Thanks for the link on where to get them.

I just wanted to say again. The bike will run with the bad ECU. It will not idle. It will only run if you hold the throttle open. The TPS is giving a voltage reading with my break out cable, but no where near what it should be.

I'll let you know what I find.

THANK YOU!!!
Tom

2004 Cali EV Touring
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Offline yogidozer

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Re: P8 ECU Help and Need To Buy One
« Reply #15 on: January 14, 2022, 10:52:17 AM »
Could it be a bad TPS? Kiwi_Roy, you seem to know a lot about electric stuff, any guesses?

Offline Kiwi_Roy

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Re: P8 ECU Help and Need To Buy One
« Reply #16 on: January 14, 2022, 11:10:58 AM »
Could it be a bad TPS? Kiwi_Roy, you seem to know a lot about electric stuff, any guesses?
My guess is the TPS reference Voltage +5 shorted to chassis, it shouldn't be too difficult to re-build it.
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Offline Tom H

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Re: P8 ECU Help and Need To Buy One
« Reply #17 on: January 14, 2022, 11:14:32 AM »
I do not think the TPS is bad. It was fine when I originally checked the voltage.

This all started when I tried to connect my cables for Guzzidiag. As mentioned previously, at some point while moving the wiring around I saw a spark. I don't know what wire sparked to the positive terminal of the battery. OR, if it was while I connected the Guzzidiag cable to the diag. cable on the bike. I wish I could remember which it was.

Tom
« Last Edit: January 14, 2022, 11:15:16 AM by Tom H »
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Offline guzzisteve

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Re: P8 ECU Help and Need To Buy One
« Reply #18 on: January 14, 2022, 01:49:21 PM »
There are 2 of them on ebay, $270 & $400 take your pick. I'm sure you saw these.
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Offline Tom H

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Re: P8 ECU Help and Need To Buy One
« Reply #19 on: January 14, 2022, 02:48:06 PM »
Here is where I'm at.

Connecting from pin 30 28 and touching just about everything, I could not get continuity or resistance. Meter always showed O/L.

When I connected to pin 1 or the chassis I could get the meter to show continuity showing 0.000 on one side some items. I can get a resistance reading x.xyz on the other end.

I believe that the items that gave me any readings were the diodes?

I tested 3 ecu's. All gave me the same results.

2 of them have the tps issue.  1 has no fuel pump issue.  All tested the same as far as I can tell.

In the pictures I think I found 4 diodes. Tested with continuity and diode function. Of the 4....the top one in the pics gave me a resistance reading on both legs. On the third from top, just under the bar had no resistance on one leg 0.000 and O/L on the other.

what else can I try?
Posted from my phone,
Tom




« Last Edit: January 14, 2022, 05:05:19 PM by Tom H »
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Offline Kiwi_Roy

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Re: P8 ECU Help and Need To Buy One
« Reply #20 on: January 14, 2022, 04:42:49 PM »
I do not think the TPS is bad. It was fine when I originally checked the voltage.

This all started when I tried to connect my cables for Guzzidiag. As mentioned previously, at some point while moving the wiring around I saw a spark. I don't know what wire sparked to the positive terminal of the battery. OR, if it was while I connected the Guzzidiag cable to the diag. cable on the bike. I wish I could remember which it was.

Tom
I didn't say the TPS is bad
I think it may be the Voltage the ECU is supposed to supply may be missing, Check this with your special cable.
You should see 5 Volts across 2 of the wires, this is supplied by the ECU
The third wire should change from near zero to about 4.5 Volts as you open the throttle, this is the Voltage coming back from the TPS to controls how much fuel is added (injector open time).

I didn't spell out exactly how much Voltage comes back, that is set when you align the TPS but its say 100 mV to 4.5 Volts (dont take that number literally)
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Offline Tom H

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Re: P8 ECU Help and Need To Buy One
« Reply #21 on: January 14, 2022, 05:01:34 PM »
Kiwi, that was a reply to Yogidozer. Sorry for the confusion.

I did not get to check if there was 5V at the TPS with the bad ECU today. He already had a spare from another bike installed and all was back together and running properly.

I still need to get the ones I had messed up fixed or replaced so that he again has spares.

I typed my post with the pics from my phone. Any clarification needed let me know. I was testing from pin 28, not pin 30 .

Thanks again.
Tom
« Last Edit: January 14, 2022, 05:06:15 PM by Tom H »
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Offline pauldaytona

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Re: P8 ECU Help and Need To Buy One
« Reply #22 on: January 14, 2022, 05:13:03 PM »
I suppose you switched the red and black connections to the battery. Happens more.
Paul

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Download Guzzidiag here: http://www.von-der-salierburg.de/download/GuzziDiag/

Offline Tom H

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Re: P8 ECU Help and Need To Buy One
« Reply #23 on: January 14, 2022, 08:27:24 PM »
I suppose you switched the red and black connections to the battery. Happens more.

Good thought but no. As mentioned, while suffering from CRS (can't remember sh..) there was a spark while either connecting the diag. cable or while moving wires to get the cable.

Thank you!
Tom
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Offline Kiwi_Roy

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Re: P8 ECU Help and Need To Buy One
« Reply #24 on: January 14, 2022, 10:02:02 PM »
We need you to give us feedback as to the Voltage you see on the 3 TPS wires with the key On
You can also check the TPS for continuity when the key is Off, all 3 wires should connect through to the main connector, less than 1000 Ohms between any two. There were a few different ways of connecting the early TPS to ECU, I don't want to confuse you by picking the wrong one.
They are really quite simple compared to modern ones and at least you have a fighting chance at finding a fault.
If you can trace the TPS wires back to the ECU terminals then you can open up the ECU and inspect the tracks for possible signs of overheating.

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Offline Tom H

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Re: P8 ECU Help and Need To Buy One
« Reply #25 on: January 15, 2022, 09:02:21 PM »
I can not do voltage testing right now. I can only do bench testing.

I have 3 ECU's to work with. 2 have the TPS issue and one has the no fuel pump issue.

I did some testing today with pin 10, the ground for the ECU relay. The results were confusing. The only thing I did find that was not confusing, was that on the ECU with no fuel pump, pin 10 is not connected to the diode. As in the circuit board has an issue. The other two both read continuity from pin 10 to the same leg of the diode.

I need to go back and test things again with another meter. I could swear that the meter is not reading at times, even though I remove the wires and test something else and it works. Yes, I'm doing my best to make sure I have good connections to make the reading.

Thank you,
Tom
2004 Cali EV Touring
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Offline Wayne Orwig

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Re: P8 ECU Help and Need To Buy One
« Reply #26 on: January 16, 2022, 08:15:52 AM »
I was once working on an EV, and when I connected the power wires to the diagnostic cable, I inadvertently connected the ground lead to the battery positive.

POOF!

I opened up the P8, and found that the power, coming in on the ground side, and burned a small bit of PC board track. I soldered a piece of wire over the burned-out track, all was well again.
Scientist have discovered that people will believe anything, if you first say "Scientists have discovered...."

Offline Murray

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Re: P8 ECU Help and Need To Buy One
« Reply #27 on: January 17, 2022, 03:56:26 AM »
Fotoguzzi yes that looks like the one I found too, both the cards I fixed had a blown diode, I'm not sure why it blows perhaps far too much current.
I'm not sure its the one on lower right though, that looks more like the coil driver area.
I think Tom might have blown the Voltage reference on his
Typically "protection" diodes are zener diodes that will collapse if a certain voltage is applied to the cathode (non conducting stripe end) or short out and cook themselves if positive power is applied to the anode. They are typically placed across the +- of the power supply to protect upstream components and will draw enough current to pretty much instantly short them out if one of the two conditions is met.

Easy way to tell if you have  a dead short across the main power it is likely if you desolder the component at one end and the short goes away it was the diode, you can also test it with a diode tester on your multimeter although be aware that other components in the circuit may cause weirdness as opposed to the open circuit/0.7 volt of a diode you would normally expect. It is also possible that one of the voltage regulators in the power supply has let go 30 years old things don't last forever and the hardest working component in the system. Should be repairable by a competent shop that specializes in this kind of thing.

Offline Kiwi_Roy

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Re: P8 ECU Help and Need To Buy One
« Reply #28 on: January 17, 2022, 05:28:45 AM »
Typically "protection" diodes are zener diodes that will collapse if a certain voltage is applied to the cathode (non conducting stripe end) or short out and cook themselves if positive power is applied to the anode. They are typically placed across the +- of the power supply to protect upstream components and will draw enough current to pretty much instantly short them out if one of the two conditions is met.

Easy ----------------------------------
I'm very familiar with the protection diodes you are referring to but in this case it's just a simple Silicon Diode (as PeteS mentions in reply #12) in series with the ECU pump relay coil, all it does is block the relay from pulling in, I'm not sure how exactly it gets to blow but it happens very often on the EV.
It doesn't have to be any specific diode, any small signal diode will do.
I will attach a sketch of the EV relays where I show the diode inside the P8 (box at top of sketch), it could be located outside the P8 like they did on the later ECUs or if you were on the road you could just rum the relay coil direct to chassis.
All Fuel injected Guzzi's have this Safety Diode around 2000 for the 15M they put it under the relay base and modern ones have it inside the relay


Tom is almost there talking about the ECU with the fuel pump not priming (because the ECU relays not pulling in.
I can not do voltage testing right now. I can only do bench testing.

I have 3 ECU's to work with. 2 have the TPS issue and one has the no fuel pump issue.

I did some testing today with pin 10, the ground for the ECU relay. The results were confusing. The only thing I did find that was not confusing, was that on the ECU with no fuel pump, pin 10 is not connected to the diode. As in the circuit board has an issue. The other two both read continuity from pin 10 to the same leg of the diode.

I need to go back and test things again with another meter. I could swear that the meter is not reading at times, even though I remove the wires and test something else and it works. Yes, I'm doing my best to make sure I have good connections to make the reading.

Thank you,
Tom

The 2 ECUs with the TPS issue have a different fault, my guess is the reference Voltage has shorted out, again a simple fault
« Last Edit: January 17, 2022, 09:25:53 AM by Kiwi_Roy »
72 Eldorado
17 V7iii Special
76 Convert
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Moto Guzzi - making electricians out of riders since March 15 1921

Offline Tom H

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Re: P8 ECU Help and Need To Buy One
« Reply #29 on: January 17, 2022, 10:22:51 AM »
I decided to start with the ECU with the fuel pump issue because it seemed like the easiest to diagnose. Then having leaned how to diagnose the connections in the ECU for the relay ground, the TPS issue ones should be easier to figure out.

I'll be looking at them again today or tomorrow. Yesterday I decided to do something easy instead, striped and painted one of my old trucks white spoke wheels. One more and all 4 are done.

Thanks again!!!!!
Tom
« Last Edit: January 17, 2022, 10:32:38 AM by Tom H »
2004 Cali EV Touring
1972 Eldo
1970 Ambo V1000
1973 R75/5 SWB with Toaster
2007 HD Street Bob
1953 Triumph 6T (one day it will be on the road!)

 

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