usc iroc

Alright while data logging my fuel pump voltage dropped to 6-9 v and the car goes to crap. It may run fine for a few miles then drop again.

Battery voltage is around 13-14 at idle. I replaced the relay but didn't help. At the relay I have around 13-14 v at the orange, green/white, and tan/white wires. Red and black have 0. I have good oil pressure.

Any ideas?

usc iroc

Come on guys....I know this isn't something new. Someone on here has had this problem

vetteoz

iTrader: (13)

Double post

vetteoz

iTrader: (13)

But what volts do you have on the tan wire when the log indicates V to pump is dropping?
What V on the incoming Org wire under same situation?


ECM monitors Volts on the output side of the relay and switch and as the OP switch and relay are wired in parallel that would rule out a problem with either (the ECM and pump would still see the higher batt voltage if one item dropped out or failed)
so problem must be the incoming supply.

TBI shown but circuity similar

usc iroc

At the relay I have around 13-14 v at the orange, green w/white strip, and tan w/white strip wires. Red and black have 0.

These readings were taken when the ECM was reading low voltage at the fuel pump.

I don't have a solid tan wire...it has a white strip on it and it reads whatever the alternator is charging

usc iroc

the voltage is .087 at terminal G on the ALDL

vetteoz

iTrader: (13)

Look at the circuit diagram ;
the ECM does not read voltage " at the pump" ; it reads the voltage on the tan / wht wire out of the pump relay

If you are showing the same voltage into and out of the relay then you only have a problem with the wire
that indicates the pump voltage to the ECM ; not with the actual voltage going to the pump


Irrelevant
That is a input to supply power direct to the pump for testing purposes

usc iroc

ok...I will start tracing out the tan wire and see what I can find. So just to make sure I got this....the fuel pump is running at the proper voltage but the voltage the ECM is reading is low for whatever the reason may be, corrosion, bad terminal, etc... Since the ECM is getting a bad reading it is making adjustments that are unneeded to compensate for something that really isn't happening.

ASE doc

I'm not aware of any compensation for low voltage to the fuel pump in GM's programming. More likely the low voltage you're seeing is indicative of a problem in the ECM circuits, maybe poor connection at the ECM itself, that is affecting more than just the fuel pump voltage PID. Always a good idea to verify clean tight ground connections at the rear of the cylinder heads. Also be sure that both ECM connectors are fully inserted and locked in place. Check for any damaged or backed out terminals

The ECM can compensate for a low battery voltage reading by adding fuel and increasing ignition dwell.

vetteoz

iTrader: (13)

Think again

https://www.thirdgen.org/forums/diy-...orrection.html

ASE doc

Thank you for that link. I have been aware for years of the battery voltage correction. Wasn't aware of the FP voltage correction. Makes sense though. Voltage affects pump output and thus pressure. Definitely need to look at ECM connections and voltage drop across the tan/wht wire between the relay and ECM.

usc iroc

OK...I traced the tan/white wire and it reads the same voltage that the car is putting out at idle. 13-14volts. I checked it at the ECM and it shows 13 - 14v but the data is showing 5-6volts at the pump and the exhaust fumes will water the eyes and drain the sinuses. Any ideas?

usc iroc

OK...I traced the tan/white wire and it reads the same voltage that the car is putting out at idle. 13-14volts. I checked it at the ECM and it shows 13 - 14v but the data is showing 5-6volts at the pump and the exhaust fumes will water the eyes and drain the sinuses. Any ideas?

vetteoz

iTrader: (13)

Gotta ask , is the ECM tuned for your mods?
Is the over fueling / low indicated voltage a recent problem?
Got another ECM to try ; yours may have a internal fault ( intermittent bad connection ?) that is not delivering the correct voltage

usc iroc

ECM is tuned; it is a new problem that I have been struggling with for a few weeks; im going to try a new ecm tomorrow.