How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Randall C Your Own Question
Randall C
Randall C, ASE Master Tech
Category: Cadillac
Satisfied Customers: 12894
Experience:  ASE Master Tech, 32 years exp,Cadillac 6 yrs
Type Your Cadillac Question Here...
Randall C is online now
A new question is answered every 9 seconds

98 deville fuel pump relay question. I have main power coming

This answer was rated:

98 deville fuel pump relay question. I have main power coming into the relay however when I turn on the ignition I do not get the 2 seconds on that energies the relay to give power to the fuel pump. What could be causing this and where do the wires go? One is black with white stripe and the other is green.

Hello, the blk/wht wire go to ground, the green goes to the PCM or computer which controls the fuel pump. You can try jumping across #30 and #87 relay terminals to see if pump works. There are several thing that must be check and tested. It could be crank sensor, PCM, etc.. You also need to know if you have spark and injector pulse. and the rest of the diagnosis is with scanner. I will not be able to walk you through everything in order to determine no run without a scanner hooked to car. here is the info you requested.



The ignition system uses a waste spark method of spark distribution. During cranking, the Ignition Control (IC) module monitors the crankshaft position sensor signals. The signals are used to determine the correct pair to spark first. After the crankshaft position signals have been processed by the IC module, it sends a fuel control reference pulse to the PCM. When the PCM receives this pulse it will command all eight injectors to open for a priming shot of fuel in all cylinders. After priming, the injectors are left OFF for the next eight fuel control reference pulses from the IC module (two crankshaft revolutions). This allows each cylinder a chance to use the fuel from the priming shot. During this waiting period, a cam pulse will have been received by the PCM. Now the PCM begins to operate the injectors sequentially based on true crankshaft position. However, if the cam signal is not present at start-up, DTC P0340 will set and the PCM will start fuel delivery in a random pattern with a 1 in 8 chance that fuel delivery is correct.

The crankshaft position sensor signals are used only by the IC module. It is used for spark synchronization and to initiate reference pulses only (not passed to the PCM).

Perform the Powertrain OBD System Check before performing this table to help prevent mis-diagnosis. See: Initial Inspection and Diagnostic Overview\On-Board Diagnostic (OBD) System Check


Customer: replied 8 years ago.
wow very informative. I will be accepting your answer I just wanted to see if this ingfo was useful in helping me or not when I jump the red and grey wire the fuel pump comes on and as long as they stay hooked the car runs. Also you wouldnt happen to have the pin out on the ecu so I could determine which wires do what in relation to this would you?
Just too many diagrams to send all. You have the basic one i sent earlier . You need to be sure you do not have a break in the green wire to PCM and check for no break in the gray wire to PCM. The wires will located in the "Blue" connector of the PCM. Be sure you have a check engine light coming on when you turn key on. You laso need to test termianl #85 of relay terminal for power when you crank the engine. If you do not have power on #85 when cranking, suspect PCM is bad. If you DO have power on #85, then your relay is bad
Randall C and 2 other Cadillac Specialists are ready to help you