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Fuel pump problem-no three second prime or purge
11-16-2018, 02:23 PM
Post: #1
Fuel pump problem-no three second prime or purge
Hello
I have a 96 geo tracker 4door m/t.
I took off very quickly from a stop. Car stalled. No lights del or otherwise.

Checked fuses. Sign/coil fuse was blown. Relays chattering. Replaced fuse. Fuel pump would not energize. I ran a switched and fused wire from battery+ to pink+ black wire to get me home (way out in the woods off road )

Now, that i'm home I'm trying to diagnose the problem. my fuel pump will not run(or prime), suspecting ecm or wiring problem.

Steps taken.
Main relay check. -good
12v at blue/ black wire
12v at black/white
ECM triggers main at key on and sends power to fuel pump relay and ecm on blue black wire.

Fuel pump relay test
12v at blue/ black wire
12v at black/ white wire
12v power applied to pink black starts fuel pump
*Pink wire at fp relay*
**This is where I found confusion and need help

When testing the pink wire, it goes to 12v at key on, but does not close the relay. 0v to pink/black.

When the fuel pump relay is disconnected the pink wire shows 4.65v for three seconds then goes back to 0v.
****
Further tests
continuity good between ecm and relay on pink wire.
5v reference on tps wire.
12v at MAF sensor.
12v at distributor.
All fuses good and 12v on both sides of fuses and 12v back probing wires at fuse box.
Cel light is on with key.
Starts and runs good with fuel pump directly supplied 12v with fuse and switch. No hesitation or miss.
I also Grounded ecm case with copper stranded wires and loop connectors.
Pulled ecm and inspected for damage-none seen obvious to the eye. No heat, water, corrosion evidence obvious.

My questions.
I see several posts saying that the pink wire is supposed to supply a ground for three seconds at key on. How to test this ? Can I back probe the pink wire with the negative side of my metre and put the (red)+ side of my meter to 12v positive.

With relay removed pink wire shows 4.65v for three seconds at key on. (Positive of meter to pink wire, negative to body ground) Is this correct? If not what should the reading be?

If the results of these tests is showing the ECM is cutting fuel, what faults can cause this condition?

Anyone with more experience is welcome to ignore my questions and provide further diagnosis procedures. Sorry for the lengthy post I wanted to provide as much information as possible.
Thank you,
Sky
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11-16-2018, 05:25 PM
Post: #2
RE: Fuel pump problem-no three second prime or purge
No takers yet eh?
If I get this resolved I will return to share the cause. Smile
Short version

FP not priming for three seconds, or at key on.
Main relay good .
Power to do relay where it should be.
Continuity on pink wire from ecm to FP relay
FP relay not closing.
Seeing 4.65v at ecm pin for three sec at key on the 0v with relay disconnected.




Possible causes (educated guesses).
12v at key on (all times with relay connected) tells me that the ecm is commanding the relay open(no power to fp) I've read that it should read 0v to trigger the fuel pump and then float to 12v when commanded off. Why would the ecm cut fuel at prime, before start?


Bad input or short in ecm harness.(no idea where)
Stuck in unflood mode(does this kill 3 second fp at key on?)
Bad ecm.
Bad component shorting ecm.
No how to diagnose from here.
96 are slightly different animals than most.

Thanks again.
Sky
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11-16-2018, 08:24 PM (This post was last modified: 11-17-2018 01:59 AM by fixkick.)
Post: #3
RE: Fuel pump problem-no three second prime or purge
some of old dogs sleep.
I guess the car does not start and run , right? (cranks ok)
this is real easy , basic, electrics.
that Pink wire. must go to at least 11vdc key on for 3 seconds, or the wire is shorted. (or bad relay)
wires can open, or short.
pumps can go open or short
or the relay is bad,
I use amp meter to read pump current 4 amps good 10 bad. 15 bat, more than that the fuse blows.
no the 96 is same as 91, to 98 generations in how it works.
96 they moved the fuel pump relay to heater box, and you can swap relays there, seen with same P/N sure can.

the 4 pins are here.
http://www.fixkick.com/ECU/1996/EFI2.jpg
blk/wht = IG-coil fuse 12vdc, all the time. key on, power.
pink- ecu control line, 12vd key on, and 0v for 3seconds key just turned on and 0v cranking it relay energizes , CLICK
blu/blk= main relay out, 12vdc keyon, all the time key on, if not ECU goes dead. this is FI fuse. if 0v. FI blew, or main relay bad.
pink-bk - runs the pump that is all it does and gets its power from main out. 12vdc.
http://www.fixkick.com/ECU/1996/EFI1.jpg

i do not understand these 2 links (heard? is what you meant, closing?)
FP relay not closing.
Seeing 4.65v at ecm pin for three sec at key on the 0v with relay disconnected. (what Pin what color wire) my wild guess, is the solid pink wire, relay to ECU?

i do not have enough data from you,. on pump relaypin volages, for 3 second key on, all 4 pins matter for that 3 second, test.

4.6v is bad, for any key on event.
what do all pins read when you saw, 4.6v, key on for 3 seconds.
we already know 2 things on this car
1: the pumps can and do short.
2: when 1 happens and say 14amps flow, (partial shorts happen or say OVERLOAD inside pump) this overloads the ECU power feed, causing ECU go nuts. 4.6v = NUTS.


why would ECU cut the prime, answer it never does unless
you overload the blu/blk= main relay out wire.

when any FP relay fails, measure all 4 FP relay pins key for 3 seconds then after.
if you see main voltage drop, that is pump short or battery dread or cracked FI fuse.

which I had the basics first.
does car start and run, my guess n0.
does the starter crank fast and rubustly and normally, Y/n?
IF no those, then the battery is dead. (or bad wiring to fuse boxes, need details not stated here, )

if how ever cranking is ok, (100 amps the starter uses ) so that is more that enough to run any 4 amp fuel pump, for sure.
next is the 4 pins on the FR relay
if the pump shorts it will overload the ECU power feed wires called MAIN. we know it does that on 1/2 the pump failures ( open pump and shorted pump are both common failure mode)
this is because the wires used are tiny.
The ECU can even chatter relays like mad with near shorted fuel pump.


blk/wht = 12vdc keyon, full time key on,IG-coil line it is. (power pin)
pink- 0v or 12v are only valid here, never 5v ever. if you see 5v (4.64 = 5v) then below is wrong volts.
blu/blk= 12vdc key on, or for 3second or full time key on, and cranked. if you read 5vdc here the pump is short. (this is power pin)_
pink-blk = pump wire, 0v key off , then 12vdc (11v is common) key on for 3 seconds, then falls to 0v, but not if cranked if cranked 12vdc (11 or as slow as 10v cranked)

i can get by just knowing 4 voltages above, key on 3 second long time. just at prime time, what do you read for 3 seconds.
those 4 voltages are prime data.

if the pump shorts (or near) the main power relay output overloads. (pump shorts or the wires to it short)

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11-16-2018, 08:28 PM (This post was last modified: 11-17-2018 02:02 AM by fixkick.)
Post: #4
RE: Fuel pump problem-no three second prime or purge
a bad shorted pump
can in fact cause main to overload and not blow fuse (hint a nice nasty 14amp short)
and the ECU goes nuts (chatters relays) ecu goes dead, 5vdc will never run any ECU made ever.

first test the 2 power pins, seen here, for 10v to 12vdc, (10 cranked ,12v key on)
ok? if test 1 fails the pump is shorted, if the battery reads 10v cranked.
the ECU goes nuts below 10, ,9v is my guess,



[Image: 3_16_11_18_9_45_09.jpeg]

never ever jumper (hotwire) ECU driver pin #3 to anything, or ECU blows up Q106 transistor, instantly,
use a dmm meter, for all tests.
measure all 4 pins on the relay , only. and record them ,
during the 3 second period of key just turned off to on.
this is the best way to find the cause, bar none.
if pump volts is weak. (5v?)
check pin 2 above, if that is weak too (5v) and same voltage, weak, the PUMP is shorted or wires to it are.

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11-17-2018, 02:05 AM
Post: #5
RE: Fuel pump problem-no three second prime or purge
The driver pin 3 is
0v key off
the same pin goes to 0v key on and sustains for 3seconds then goes to 12vdc after 3 second timer expires.(inside ECU)
if you crank the engine, pin 3 goes to 0v full time cranking, so the engine can inject full.
at no time must power pins drop below 10v. ( and there are surely lots of ways to cause this, huge, and ask if true)
battery cranking voltage is near that, 10v to 11, if not fix bad power first.

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11-17-2018, 05:01 AM
Post: #6
RE: Fuel pump problem-no three second prime or purge
Car runs good only witg test fuel. Also runs good with fuel pump relay (pink black) directly wired to battery+ with FP relay removed.

Car cranks and turns over good. 12.6v at battery +

Quote:i do not understand these 2 links (heard? is what you meant, closing?)
FP relay not closing.
Seeing 4.65v at ecm pin for three sec at key on the 0v with relay disconnected. (what Pin what color wire) my wild guess, is the solid pink wire, relay to ECU?

FP relay not closing.
Means relay is not working, or passing power to fuel pump. No click felt it heard. No fuel pump prime.

Quote:Seeing 4.65v at ecm pin for three sec at key on the 0v with relay disconnected. (what Pin what color wire) my wild guess, is the solid pink wire, relay to ECU?

Because the relay was not working, I removed the relay and tested continuity on the pink wire(pin) from ECM to Fuel pump relay. Meter shows good continuity.

While i was AT THE ECM I tested pink wire with Fuel pump relay removed from its socket. Results-pink wire showed 4.65v for three second key on....I Expected 0v at key on, then a float to 12v

I will go to the car now and test Fuel pump Relay voltages with key off, key on for three seconds, and after.

Thank you for your knowledge, experience and willingness to share. I have used your site, schematics, and forum advice to others for years. Fixed many cars with help from your pages and posts.

Checking now
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11-17-2018, 05:57 AM
Post: #7
RE: Fuel pump problem-no three second prime or purge
Key on Blue black 12.45 turning starter 11.01
Key on Black white 12.21: turning starter10.7
Key on Pink 12.07 key on never changes: turning starter 10.7
Pink black 0v key on, let off, or start 0v

Fwiw
I have swapped relays, main and FP. Fuel pump relay works correctly in main relay socket. I have also swapped for another good relay. Relay seems good.

Why 12v at pink ECM wire, but no power to pink/black.
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11-17-2018, 08:45 PM (This post was last modified: 11-17-2018 09:04 PM by fixkick.)
Post: #8
RE: Fuel pump problem-no three second prime or purge
Quote:RE: Fuel pump problem-no three second prime or purge
Key on Blue black 12.45 turning starter 11.01 (GOOD)
Key on Black white 12.21: turning starter10.7 (GOOD)
Key on Pink 12.07 key on never changes: turning starter 10.7 (dead)
Pink black 0v key on, let off, or start 0v
(if Pink is dead, so will be pink/blk so will be pump dead. the above PINK not keying the relay means, ECU is failing. only why remains.

The ECU is failing. ,
quesiton1:
ECU tests, (key on CEL must GLOW Does it?) if not ECU is dead or power pins to ECU are dead. The CEL = cluster check engine lamp MUST GLOW KEY ON, does it.? if not power to ECU is missing.
question 2, Are the wires in the car, to ECU or EFI hacked ? (see wires cut or transgressed upon ? from stock)? inspections are very easy and effective if ECU malfs.


seen this yet.
http://www.fixkick.com/ECU/1996/96ECU.html
your ECU, is there.
i annotated each pin, to show what voltage are there.

C2 , see power and ground here?
connect meter minus black lead, to battery negative LUG (jumper test lead wire,), for best readings.
then probe with red meter probe (20vdc range) to the ECU pins key on.
did you connect your OBD2 scanner first thing?, see if the ECU connects and communicates and shows all sensor readings? if ECU is dead now , above pins are wrong voltage (power pins)

inspect ECU yet, lid off,
sniff sniff for smells of burned things. look at Q106 , is it burned or cracked? Q106 is FP relay driver transistor on board.
look next for bulging or cracked/leaking, large (can shaped) CAPS. in the HTML link above i have photo of ECU PCB, see Red X on top of 3 caps that like to leak, top left is prime suspect.


http://www.fixkick.com/ECU/1996/Full96%2...volts1.pdf


Quote:Fwiw
I have swapped relays, main and FP. Fuel pump relay works correctly in main relay socket. I have also swapped for another good relay. Relay seems good.

Why 12v at pink ECM wire, but no power to pink/black.
(the relay is doing its job, correctly , ECU Q106 is dead so will be the pump, and relay dead, that is its purpose to prevent as seen on TV
crash and burn. fuel fires.
basically your ECU is dead, but we test it first to see why ....
------------------------------------------------------------------------------------------------------------
back to square 1, no start car. cranks but no start
and that is step 1 on all cars is ..... , CEL lamp glows key on?????, it must
or if CEL dead, use the scan tool next, (lamps do burn out after 22 years, but no big deal)
the tool will show CEL status on or off, the lamp really is not important now, the scan tool answers that exhaustion, first.
if the scan tool shows comm failures, (no communications, that means the power pins on ECU are dead. (12vdc power or ground to C2 is wrong)

when did car fail driving down road?? or parked in drive way or garage or after rewiring things in car ECU died, history can help here.
or bought car dead.?
if car was molested, we inspect all wiring carefully for transgressions, (stock wiring good, not stock bad) splices, to wires? bad, see tape balls, or liquid tape balls on wires, bad.
22 year old cars can have things added to car, lots of things, remote start from h3ll is one big loser.(cruise, or other upgrades can be a horror)

make sure the TPS on the throttle body, see 4 wires to that sensor there make darn sure the wires are not cut, damaged, and the TPS is not cracked and damaged.
This ECU may cut the FP relay if TPS , TP pin is at 3.7vdc or able (called unflood mode to ECU)
http://www.fixkick.com/sensors/96TB-isc.JPG

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11-17-2018, 09:09 PM (This post was last modified: 11-17-2018 09:10 PM by fixkick.)
Post: #9
RE: Fuel pump problem-no three second prime or purge
never condemn any ECU/PCM.
until you check its wiring for damage.
and check power pins. (power and ground) power is12v ground is 0vdc.
and CEL lamp actions.
and scan it. never skip this critical step.,. if the ECU can talk it tells you things are wrong, listen to it. (TPS errors DTC )?
and TPS voltage on pin 3 seen here.
http://www.fixkick.com/IDLE-AIR/dutycycl...ml#16vduty

pin 3 is 1vdc. key on, not near 4v or 5.
1volt means throttle angle is zero .
pin 1 TPS, if that wire breaks, the ECU sees that as endless, unflood mode and injection stops and even the pump goes off line. but injections END NOW.

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11-17-2018, 09:18 PM (This post was last modified: 11-17-2018 09:21 PM by fixkick.)
Post: #10
RE: Fuel pump problem-no three second prime or purge
Quote:I took off very quickly from a stop. Car stalled. No lights Cel or otherwise.
(i edited DEL to CEL) sure CEL dead, the fuse blue, ecu is now dead.

Quote:Checked fuses. IG-coil fuse was blown.
Relays chattering.(that symptoms means ECU sees power feed overloaded in fact voltage power is below 9vdc. bad.
Quote: Replaced fuse.
Fuel pump would not energize.
I ran a switched and fused wire from battery+ to pink+ black wire to get me home (way out in the woods off road )
you hot wired pin 4 on FP relay
will if that action touched pin 3, the ECU is blown up, Q106 is not blown the kingdom come. easy as eating cherry pie, hot wiring the relay,
the battery has 500 amps on tap, so can blow .1amp transistor , 5000 times over. BOOM silicon is now carbon and air.

id test the pump FP relay removed, hot wire the pump and measure its current, if over 4 amps, the pump is bad and was the day one failure cause.
and blew the fuse.
hot wire the pump very carefully even pull the ECU connectors first, to protect the ECU. (all connectors on this car are lever locked, do not force connectors)

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