I have a strange one I am hoping someone has dealt with before. 97 4 cyl. quit running the other day. trailered it home and started looking for the problem. The fuel pump relay is chattering badly (it is not the relay I replaced it and same thing happens) it clicks on and off probably 10 times a second. there is fuel pressure at the Schrader valve and I removed the relay and jumped the terminals to supply the pump power and I hear it run (I do not know what the pressure is I just stopped and got a pressure gage today) truck won't start. Spray ether and it does fire but not very strong. it seems like there is a ground issue on the fuse box/relays but I wouldn't know where to even start. seems like it is an electrical issue cause the pump sounds good when I jump it. anyone got an idea??
thanks

 

Power for the Fuel Pump Relay runs like this:

Battery--------30amp Fuse------EEC Relay---------Fuel Pump Relay----computer----Ground

This is NOT the fuel pump power, it is the relay power.

The Computer controls the fuel pump relay by grounding it.
The fuel pump relay gets 12v battery power when key is on via the EEC relay which closes when key is turn on.

Then the fuel pump relay "waits" open until computer Grounds it to close it and then it passes power from the battery to the fuel pump.

So a clicking relay means either the 12volts is not 12volts, or the computer has a problem.

Get a voltage meter and test relays base, so remove fuel pump relay.
With key off there should be one socket with 12volts, that is for the Fuel Pump power, it has 12v all the time.

Turn on the key, there should now be another socket with 12volts, this 12v is from the EEC relay, if it is onlt 1 or 2 volts then wire is probably corroded

 

RonD, thanks for the reply, yes you are in the right direction. I did not get a chance to update this morning but I found this our last nite. I checked the voltage at the relay base and there was 12.2 vdc with the relay out (the circuit that energizes the relay 85,86) I made some jumpers so I could test when the relay was plugged in, with the relay plugged in I was only getting about 3.2 vdc so definitely I have a connection problem somewhere. The issue is effecting spark also (I can jump the fuel pump and I get 38 psi at the Schrader valve but it still won't run) so maybe something at the computer. any idea after that input??

 

pins 85 and 86 are connected inside a relay by a coil of wire so some resistance but should show 12v at both when power is applied.

So I would go to the EEC relay It is set up the same way, 85/86 is the coil but one is always a ground, the other gets power when key is turn on, so this relay is closed with key on.
Pins 30 and 87(the contacts) pass power from a fuse to the computer, coil and fuel pump relay.

With key on the center wire on each coil should have 12v coming from the EEC relay.

Could be EEC relay "contacts" are corroded, so limited voltage is seen.

 

Ok I will start at the EEC relay and see what I have. Thanks I will report back what I find hopefully I can work on it tonite

 

RonD,

i finally got time to work on truck again, I removed the ECC relay and plugged a jumper wire into the socket at 30 and 87 to simulate the relay coil energizing and making the contact closure. the FPR clicked on/off repeatedly again - no change. so i think i have proved the FPR is ok and the ECC relay is ok. I have checked and added jumper wires to all the grounds from battery to body and engine i have verified 12v + at the relay panel i am out of ideas could it be the computer has failed?? i have never had one fail, but there is always a first. anything else you can think of to check?

 

FPR relay shouldn't click on and off 'repeatedly'
With EEC relay socket pins 30 and 87 jumped FPR should click closed for 2 seconds then click open and stay open until engine is running OR you remove jumper and hook it up again.

With EEC relay pins 30 and 87 jumped check voltage at FPR 85 or 86, one should have battery voltage, if voltage is low then the wire of something on the EEC relay circuit is drawing too much power.

EEC relay powers FPR, Computer, fuel injectors and Coil.
Check voltage at Coil and fuel injectors with EEC jumper in place, should get battery voltage.

 

Ron i jumped the EEc 30 and 87 and checked FPR and the voltage is 12 v with no load (relay pulled) plug in the relay and voltage drops to 3.8 and relay pulls in adn drops out repeatedly. i checked voltage at coil pack on the 2 outside wires and got no voltage with key in the on position. is that correct the 2 outside wires ??
Voltage on EEC with the 30 and 87 jumped is 12 v with or without FPR plugged in

 

The center wire on the 2.3l coils is the 12volt(key on) wires, from EEC relay

Get a new relay or swap relay and retest.
The 3 relays, EEC, FP, and WOT are the same

EEC pins 30/87 pass voltage to FP relay(not fuel pump itself), computer, coils and sensors.
If voltage drops to 4v only with FP relay plugged in then that relay is bad or wiring to/from FP relay pins 85/86 are

 

Ron,

i have verified that the relays are ok and that there is 12v to the center wire on the coil pack. if i understand it correctly the FPR energizes by the ECM completing the ground. if i have the keyswitch on the FPR constantly clicks i checked the voltage and it is 3.5v. if i jumper wire the ground side of the relay to the - battery post the relay pulls in constant. i believe i have something going on in the ECM or the ground wire that is supplied to the ECM for use. If i jump the ground i have 38 psi at the rail but it still won't start. if i spray ether it will act like it wants to try but still not strong spark i believe cause it just sputters more than fires.
i have checked (removed wire emery cloth shiny) every ground wire that i can find. unless you have any other test taht i could try i think i am leaning towards the computer is failing.

 

The EEC(ECU/PCM) relay should be next to the FPR(fuel pump relay) in the power box.
When key is turned on the EEC relay closes this sends 12v(battery voltage) to the FPR, if you are only getting 3.5v at the FPR then yes it would click open and closed since that is not enough voltage to hold it open.
I would check the voltage at the EEC relays load pins, 30 and 87.
Or the under side of the power box may have some corroded wires.

Check the voltage at the Fuel injectors as well, should be 12v with key on, these get 12v from the same EEC relay as the FPR

Yes the ECU(EEC/PCM) Grounds the FPR to close it which sends power to the fuel pump.
ECU also uses Grounds to open fuel injectors

 

Was this issue ever sloved? I have the exact same problem. THANKS