ECM voltage ?

[driveshaft man]

Scanmaster is all over the place ,sometimes says 10.9 to 11.8 with an occasional 13.4 +/- . Battery voltage running is 14.2. 2 firewall grounds are good and clean; ground strap from batt to rt ft. fender and ground cable bolted direct to intake bolt. Is this correct for ECM ? Seems the ECM voltage should be constant and closer to batt voltage (13.8)

 

[49-blues]

The sensors work on only 5vdc

 

[driveshaft man]

Is it normal for the voltage readings to vary that much ?

 

[TurboBob]

I had a bad fuse holder in the fuse box do this once.

check and clean all the circuit paths to the ECM in the harness.

Make sure there is no water in the ECM and the connectors are not corroded.


Bob

 

[driveshaft man]

check and clean all the circuit paths to the ECM in the harness.

.


Bob[/QUOTE]

Sounds like a monumental undertaking to complete this task.
ECM is dry and clean but have not looked at fuses.I thought the
orange power feed at batt + terminal was the only 12v source for the ECM.From there it feeds various circuits thru ground signals was the reason I started looking/improving chassis ground points.Maybe I haven't found the right one yet.The wiring diagram I found online is missing a page .Is it available anywhere ??

 

[$1987 GN$]

Check the ECM power wire at the ECM see if it voltage is constant there. Use a voltmeter; car running.

I have seen that wire is damaged at the entry point in the firewall.
All kinds of strange things seem to happen.

It is actually wrapped at the point were the problem occurs sooo maybe when the harness were made they knew something is up. Not all the harness have this but a lot do.

Later AJ

 

[twodafloor]

ecm pin

recently heard a story of a pin at ecm connection being broken causing intermittent problems

 

[driveshaft man]

Thanks for the input....gives me more places to look.I'm still not sure what the ECM voltage is SUPPOSED to be.Maybe someone with a Scanmaster will chime in with some voltage readings.
Harold

 

[Jerryl]

Thanks for the input....gives me more places to look.I'm still not sure what the ECM voltage is SUPPOSED to be.Maybe someone with a Scanmaster will chime in with some voltage readings.
Harold

ECM voltage should = battery voltage.
You will see a voltage drop, but it should be minimal, AND, voltage should be stable.

 

[driveshaft man]

ECM voltage should = battery voltage.
You will see a voltage drop, but it should be minimal, AND, voltage should be stable.

This is how I perceived it should operate...with 14.2 at batt and maybe mid-low 13s at ECM.Agreed it only needs 5v to operate sensors but unless the voltage is reduced by design somewhere,the only loss should be due to wire size/distance from source .And it should be constant....therein lies my problem,why does it vary so much?
Does the ECM receive 12v from another source besides the orange wire hooked to + batt terminal?

 

[pajo]

drop

when the voltage drop occurs at ecm check to see if it drops at the alternator-battery which will kind of lead you to the fix ..If there is substantial drop at battery then it is probably alternator if there is no drop then your issues are ecm feed wire or ground to the ecm or fuse holder mentioned in the post above .

 

[driveshaft man]

Scanmaster will flash- ie 13.2 to 10.9 next flash,then maybe 11.5 .Stays in the 11s most of the time.All the while batt voltage remains constant at 14.2. I have not checked output at alternator but if the ECM 's sole source of power IS at the orange batt connection,alt output is not a factor.
I'm thinking the ECM has another 12v power-in wire but that info has not surfaced yet.

 

[Jerryl]

This is how I perceived it should operate...with 14.2 at batt and maybe mid-low 13s at ECM.Agreed it only needs 5v to operate sensors but unless the voltage is reduced by design somewhere,the only loss should be due to wire size/distance from source .And it should be constant....therein lies my problem,why does it vary so much?
Does the ECM receive 12v from another source besides the orange wire hooked to + batt terminal?

Your perception is correct.
ECM gets power from different sources as well, but really only one feed for your purpose.
Fuel Injection ECM Pinouts

Like some of the other post stated;
You have possibly a bad connection at the ecm, fuse box, etc.
Also verify the starter cable against the header ...........

Good luck with it. I HATE electrical problems!

 

[Eric Stage I]

The voltage reading on your scantool does not come from the orange wire (C16) to the battery. It comes from the ignition switch (A6). That is why Bob mentioned above that it could be a problem at the fuse box. It could simply be a bad fuse or corroded fuse terminals (ECM/IGN).

 

[Jerryl]

The voltage reading on your scantool does not come from the orange wire (C16) to the battery. It comes from the ignition switch (A6). That is why Bob mentioned above that it could be a problem at the fuse box. It could simply be a bad fuse or corroded fuse terminals (ECM/IGN).

Eric,
Every time I read your posts I learn something new.
Thanks for setting me straight ........ again!

Your perception is correct.
ECM gets power from different sources as well, but really only one feed for your purpose. ....

Driveshaft man,
I stand Corrected.
My appologies for the bad info.

 

[Eric Stage I]

I don't think you gave any bad info. I was just clarifying.:smile: The orange wire is important, but the actual reading comes from A6. The ECM needs that reading to know when the ignition key is on or off.

 

[driveshaft man]

Thanks guys! I think we have finally got to the bottom of this .Problem could be in ignition switch as well (that may be the A6 referenced) as the fuse box.With the pin-out link provided and this info I will attack this on the weekend when I have enough quiet time to keep focused.
hm