| Author |
Message |
Vanagon Nut
Samba Member
Joined: February 08, 2008
Posts: 10365
Location: Sunshine Coast B.C.
|
 Posted: Sun Jun 21, 2020 2:40 pm Post subject: Fuel pump relay coil circuit fault = bad input to ECU? |
 |
|
hi folks.
Under Vanagon Digifant, if the fuel pump relay 85/86 coil circuit had an intermittent break or constant voltage drop, since the ECU supplies (my term) a ground to energize that relay coil, could the ECU see that as a "bad" input then possibly adversely affect other engine management component(s)?
Neil.
_________________
1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN |
|
| Back to top |
|
 |
jlrftype7
Samba Member
Joined: July 24, 2018
Posts: 3574
Location: Chicago
|
| Posted: Sun Jun 21, 2020 2:52 pm Post subject: Re: Fuel pump relay coil circuit fault = bad input to ECU? |
|
|
Not perceived perhaps, but definitely affecting, since a fuel pump going in and out could affect O2 sensors values due to fuel trim and regulated pressure getting wonky. I would be surprised with our simple systems if anything much is perceived by the ECU.
Later engine management systems have so much more in the way of feedback circuits to give an ECU info.
_________________
'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto |
|
| Back to top |
|
|
RawUmber
Samba Member
Joined: June 23, 2019
Posts: 223
|
| Posted: Sun Jun 21, 2020 6:30 pm Post subject: Re: Fuel pump relay coil circuit fault = bad input to ECU? |
|
|
The ECU sees the Fuel Pump relay coil as an output and doesn't 'know' whether it is working or not (ie, not an input).
Low fuel pressure's effect on engine performance could possibly be measured on the O2 sensor, Air Flow Meter, and Coolant Temp sensor, which could cause the ECU to adjust the fuel injection quantity given the parameters of the moment. However, once your relay is repaired/replaced, everything is back to normal the next time you start your van.
An intermittent relay coil can cause intermittent relay switching, which may add a little wear/tear to the fuel pump, relay contacts, and ECU fuel pump driver transistor, but to what degree would depend upon the circumstance. |
|
| Back to top |
|
|
Vanagon Nut
Samba Member
Joined: February 08, 2008
Posts: 10365
Location: Sunshine Coast B.C.
|
| Posted: Sun Jun 21, 2020 7:30 pm Post subject: Re: Fuel pump relay coil circuit fault = bad input to ECU? |
|
|
| RawUmber wrote: |
The ECU sees the Fuel Pump relay coil as an output and doesn't 'know' whether it is working or not (ie, not an input).
Low fuel pressure's effect on engine performance could possibly be measured on the O2 sensor, Air Flow Meter, and Coolant Temp sensor, which could cause the ECU to adjust the fuel injection quantity given the parameters of the moment. However, once your relay is repaired/replaced, everything is back to normal the next time you start your van.
An intermittent relay coil can cause intermittent relay switching, which may add a little wear/tear to the fuel pump, relay contacts, and ECU fuel pump driver transistor, but to what degree would depend upon the circumstance. |
| jlrftype7 wrote: |
Not perceived perhaps, but definitely affecting, since a fuel pump going in and out could affect O2 sensors values due to fuel trim and regulated pressure getting wonky. I would be surprised with our simple systems if anything much is perceived by the ECU.
Later engine management systems have so much more in the way of feedback circuits to give an ECU info. |
Very helpful information. Thanks very much!
I'd always thought of this type of relay as behaving in an "on or off" manner; it would work "100%" or fail "100%" Today I wondered if a voltage drop on the coil side could cause the relay switch to sporadically open/close but still work well enough to allow the engine to run. I also wondered that if the 86 leg join to coil was broken, current might instead try to pass through the suppression resistor to the coil.
The relay in question is a "WBX 53" on my Jetta conversion which has Motronic 2.9 but figured asking after Vanagon Digifant would help regardless.
After replacing this fuel pump relay, it feels like starting, running are consistently better and I'm hopeful I've solved the random stall and/or dip in idle when coming to a stop issue.
If the other 53 relay (ECU etc. power) is the same make (design) I'll pull it and see what it looks like inside.
Neil.
_________________
1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN |
|
| Back to top |
|
|
|
