Tbi swap build thread

[rfmaster]

Originally Posted by manimal

OK, here are my findings......
Key off; .01 dcv between dark green/white and black/white
Key in run; 12 dcv, does not go off after 2sec
engine cranking/running; .66 dcv
* accidentally touched the tan/white wire instead of dark green w/DVM engine stalled
I cannot find a fuse link-also my FSM says that is only for the "CK" and not the "RV" vehicles. I am confused.....
I then followed the FSM for the test...
I hooked up 12v power to the FP test wire and pump runs.
disconnected the fuel module and removed the 12v to the test wire..key to run, pump does not run.
key on;checked the orange wire to ground I have 12v, then dark green/white to battery -, I have 12v,but when I use a test light between the two I get nothing????(test light is good) NOW I am really confused!
using the test light proceedure, my manual says there would be an open or short in the dark green/white wire or faulty ECM.
SO I continued on based on the DVM reading of 12v @ the dark green/white wire......
again key in run still no FP running.
Reconnected the fuel module engine running,disconnected the FP relay, engine still ran.
Key off, I probed the FP test socket, no power....Factory Service Manual says-NO TROUBLE FOUND.
Does any of this make sense? Cause I am REALLY confused.
Thank You

Ok lets take it step by step.

1) Take a look at a circuit attached. The RV section is top of the page.
The only major difference between the two is that RV has prime terminal hanging at the end of red wire (under FP relay) and CK have that end terminated at ALDL connector. Otherwise functionally and electrically they are the same.

2) Theory of operation.
Re-install FP relay. Disconnect oil pressure switch connector.
At the oil pressure switch locate orange wire terminal - it must have 12 volts at all times. The fuel pump side may have either tan/white or gray color wire - this is a switched side of FP relay. During POST ECM applies 12 volts at Pin A1 (dark green/wht) energizing FP relay for about 2 seconds. Also at the same time it monitors voltage on pin B2 (Fuel pump signal). FP power-up FP circuit for about 2 seconds and shuts off. This is a normal operation without fuel module.
When you removed FP relay ECM will not see 12 volts pin B2 (Fuel pump signal) which will set DTC 54 (FP voltage low). With DTC 54 set ECM goes into limp mode and depending on calibration it may not apply control signal (A1) during cranking - I simply do not know why, but I have seen this before. What is important is that ECM is able to supply +12 volts to FP relay from pin A1 dark green/wht wire.

Now, with FP relay re-installed connect DVM to measure DC voltage from gray pin of the oil pressure connector to ground. Oil pressure switch is a fail safe mechanism if FP relay fails with engine running. With ign off you should see 0 Vdc, ign into run - you should see 2 sec (with Fuel module disconnected) or 20+ seconds with fuel module connected. During cranking there must be +12 volts.

3) dark green/wht is a low current switched source - supplied by ECM (pin A1). It should not be shorted to ground as it will blow switching transistor inside ECM! Use DVM - do not use test light since you do not know how much current your test light is pulling. Typical FP relay has a coil resistance between 200 and 300 Ohms and pulls less than 100 mA of current from 12V.

4) Take a look at FP test connector (490 red on attached schematic). It is connected to NC contact of FP relay. Under normal conditions, FP relay is powered moving center contact from NC to NO position and with engine running you should 0 volts. If and only if FP relay failed to close and engine is running you will see +12 volts as fuel module or oil pressure switch are supplying power to FP. This way you can establish if you have a flaky FP relay coil or control circuit.

//RF