Quick ?? on voltage drop - 14.2 v <> 13.2 v

90topdown · Nov 12, 2008

I have a 3G alternator and I am trying to chase some possible electrical gremlins.

With engine running at idle I have:

14.28 volts at the battery

13.23 volts at Pin 19 of the EEC with direct ground to battery

13.18 volts at Pin 19 of the EEC using body ground

I re-did all the grounds and added the extra one for the 3G. I also ran the 4 ga power wire w/ circuit breaker from alternator to solenoid.

I have a 1 volt drop between the battery and the EEC. Is this ok or should it be < .5 volts?? In which case I should have 13.8 volts at the EEC??

stang&2Birds · Nov 13, 2008

For all of your voltage readings, you must use the same exact ground point and connect to that point in the same exact way. Otherwise, you may be chasing something that is a result of your measurement connections and procedure.

So, get a 12 foot piece if wire. Use that to connect your ground probe to the neg battery post. LEAVE that connection always on and don't move it or take it off. THEN, do all of your voltage measurements.

Otherwise, yes, 1V is too much of a drop between the battery and EEC. To double check, put the negative probe on the battery positive post, and the positive probe on the EEC power pin. That measures the voltage difference between those 2 points. If you see 1V, that's not good. Another thing to try is that same measurement, but with the car not running.

90topdown · Nov 14, 2008

Ok, here are some more readings:

Key off, pos meter lead on pos batt post

neg post- 11.98v
radiator support ground point- 11.98v
alternator case- 11.98v
ground point next to starter solenoid- 11.98v
driver side firewall gound point- 11.98v

Key on, engine off, pos meter lead on pos batt post

neg post- 11.55v
radiator support ground point- 11.55v
alternator case- 11.55v
ground point next to starter solenoid- 11.55v
driver side firewall gound point- 11.55v

Engine running, pos meter lead on pos batt post

neg post- 14.22v
radiator support ground point- 14.22v
alternator case- 14.22v
ground point next to starter solenoid- 14.22v
driver side firewall gound point- 14.22v

Key on, engine off, neg meter lead hardwire to neg batt post

Pin 1 - EEC power input - 12.5v

Engine running, neg meter lead hardwire to neg batt post

Pin 1- (EEC power input) 13.85v
Pin 19 - (fuel pump) 13.03v
Pin 57- ( EEC relay) 13.80v
Pin 59- ( #2 inj) 12.02v

Engine running, neg meter lead hardwire to pos batt post

Pin 1 - -.04
Pin 57 - -.11

Engine off, key on, neg meter lead hardwire to pos batt post

Pin 1 - -.02
Pin 57- -.05

1. Is it normal to have a .44 ( 11.98 - 11.55) voltage drop from just turning the key on??

2. I assume that the voltage is low at Pin 59 since it is an injector the voltage will rise as the rpm rises

3 .If I have 13.85 volts coming into the EEC (Pin 1), why do I only have 13.03 volts going out at Pin 19 ( fuel pump)?? How is the EEC sucking up .82 volts??

How do I fix this??

HISSIN50 · Nov 15, 2008

The injectors receive VPWR when the key is on. The ground to the injectors is what is modulated to excite the injectors and control PW.

FWIW, your battery is severely discharged (assuming 12.0 V, which yours is below).

It's super late but your drop values didnt look horrid to me. In case I misread your readings, I start to worry if I see more than a 500 mV drop personally (others will probably freak at a lesser drop). You are dropping voltage in the wiring but I'm not sure the amount you're dropping would lead to meaningful issues (it hasn't in my experience).

The FPM circuit is dropping a lot, but it has a decent length of wiring. I'd do a drop test between the normally-open FP relay terminal and the FPM pin on the EEC (pin 19).

Just MHO. The opinion of S&2B's might differ.

RumbleFox · Nov 15, 2008

Yeah what he said. Remember theres a certain % of voltage loss for every extra foot of wire.

90topdown · Nov 17, 2008

Took it for a long ride and had no issues so I guess that it is fixed. Voltage must be ok.

Thanks for the help, guys!!!

Quick ?? on voltage drop - 14.2 v <> 13.2 v

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