94 Caravan - fuel pump won't run

The van has been sitting for a while, but started fine 2 weeks ago. A
few days ago it cranked fine, but the fuel pump didn't do the normal
2-second pressure up when the key was first turned on.

I can get the fuel pump to run if I jumper the fuel pump relay, so the
wiring to the pump and the pump itself seem to be OK. I tried swapping
the ASD relay with others (they all have the same PN, and all show the
same resistance between the coil terminals), but nothing. I tried
jumpering from B+ to the coil +, still nothing.

What else can I try? Is there a fuel pressure sensor that thinks the
pressure is up, so doesn't tell the pump to run? I don't think it's
the Hall effect, since it doesn't come into play until it starts
cranking.

Thanks
KC

 

I forgot to specify engine - it's the 3.0 V6.
KC

 

Remove the 60-pin connector from the SBEC and inspect the pins and sockets
for corrosion; clean the pins by pushing a pencil eraser straight down
onto each pin, and packing the sockets full of Ox-Gard or Noalox.

Check all of the fusible links carefully; it sounds like one or more of
them may have popped. Of course if this is the case you'll have to find
the cause or the new link will pop, too.

I don't think it's the Hall Effect Pickup, since the 3.0 doesn't use one.
The 3.0 does tend to develop problems with the *optical* pickup in the
distributor, and with the wiring between the distributor and the SBEC, so
you can check for that by disconnecting the battery negative cable for a
few minutes, reconnecting it, cranking the engine and then checking the
flash codes. However, that probably isn't the problem since you say the
fuel pump isn't energized with initial key-on.

To check the computer codes:

With the engine off, switch the ignition key on-off-on-off-on,
leaving it "ON". Do not
go to "start", just "on" during this procedure.

Watch the "Check Engine" or "Power Loss" light. It will turn on, then go
off, then will begin to flash-out any trouble codes that have been stored.
For instance, if it flashes:

flash <pause> flash flash
<long pause>
flash flash flash <pause> flash flash flash flash flash
<long pause>
flash flash flash flash flash <pause> flash flash flash flash flash

Then you have a 12 (one flash followed by two) a 35 (three and five) and a
55 (five and five). 55 means "end of codes" or, if by itself, "No codes
stored. Check the codes and report what you find.

 

Thanks for the tips, Daniel. I'll try these tonight and hopefully get
it going. I wanted to donate it to my church (they in turn donate it
to those who need cars but can't afford them), but they won't take it
if it isn't running. And since I can't sell it (tried twice, can't
even get an offer at $800, and it's in pretty good shape), and it's not
doing me any good sitting in my driveway, this seemed like a good
option.

Just curious - what is it that tells the fuel pump to quit pumping
before the engine starts? The pressure regulator only holds the
pressure at a certain level and returns the excess back to the tank,
right? But that's with the pump running continuously. Something tells
it to stop when the key is on but the engine's not running.

KC

 

The initial "Bzhhhhht!" that you get from the pump when you turn on the
key is just a timed pump pulse of (nominally) 1 second. The purpose is to
pressurize the system for engine startup. It's not necessary to monitor
the pressure, because as you know, the pressure regulator makes sure
there's no overpressure.

DS

 

stored.

Update: removed the SBEC connector and cleaned it, didn't see any
signs of corrosion. While I had access, I unplugged and replugged all
the electrical connectors under the battery. Then put everything back
together. Still no fuel pump. Tried to get the codes to flash.
Several times. Nothing. Jumpered the fuel pump relay so the pump runs
whenever the key is on. Won't start. That indicates to me that
there's no spark. Verified that with a timing light. So am I down to
fusible links? The only one I saw was one to the alternator, so I must
not know where to look. Seems strange that the computer won't blink,
though - it should at least give the 55=end of codes, right? I'll go
back at it tomorrow, check any fusible links and the wiring to the
distributor.

KC

 

Excellent indication that you've got a blown fusible link upstream of the
SBEC. Common causes of this include (but are not limited to):

-Oxygen sensor wires shorts to one another or to ground (can happen if
they fall on the hot exhaust manifold)

-Radiator or condenser fan motor seizes

Not if it's not getting power, which it evidently is not!

Let's make sure we're not jumping the gun, though -- check the pull-apart
main disconnect in the positive battery cable about 5 inches down from the
battery terminal. It feeds everything *except* the starter. Lift its
locking tab and pull it apart. If it is internally broken and/or corroded,
clean it up or replace the battery cable assembly.

DS

 

I don't find that on mine. The clamp has 2 cables - one goes to the
starter, the other to the fuse block, with a junction there to another
large wire that goes to the alternator. So everything but the starter
must be fed from the fuse block. Sounds like I should look between the
fuse block and the SBEC for a fusible link, somewhere inside that wire
bundle. Or does it run to the fuse block under the dash before it
comes back to the SBEC? Seems like a bit of a mess until I look under
the dash of my 95 Isuzu Trooper, then it seems like a model of
simplicity by comparison!

KC

 

It's possible someone replaced the cable in the past with a non-factory
item. The factory cable assembly has the plastic pull-apart disconnect.

Check for power at the fuse block!

Yep. Probably orange or white.

DS

 

Might be faster to first use a multimeter to check for voltage on the
supply pin to the computer. That is faster than tearing into a bundle
of wires.


Matt

 

(((Just curious - what is it that tells the fuel pump to quit pumping
before the engine starts?))) If the PCM doesnt see that the engine is
running after 3 seconds, it shuts down fuel and spark thru the ASD relay,
You know that you are getting fuel but possibly loosin spark, go to the
windshiled wiper resorvoir and under neath it is where you will locate the
fusible links, look at them and gently pull on each one to see if any are
broken/burnt.If all ok
Check b+ to PCM with a test light for voltage.If ok Check the 5 volt power
supply to the sensors for a short to ground. A short to ground on the 5 volt
power supply to sensors such as: MAP, TPS, A/C PRESSURE TRANSDUCER, EGR
POSITION, etc. will cause the vehicle to die out and may cause the PCM to be
a no response. All this of course would be easier using a scan tool to see
acuall values and be able to acuate spark and fuel systems, so taking it to
a repair facility may be the next option. Good Luck
Glenn Beasley
Chrysler Tech

 

Good idea, Matt. There's power to the fuse block, all the lights and
gauges and everything else works fine. With the key on, there's power
to 4 pins of the SBEC connector - 3 on the left side bottom row, 1 just
above them on the middle row. So there's power to the SBEC, but it
won't flash codes and won't turn on the fuel pump or spark. Sounds to
me like it's time for a different SBEC. Opinions?

KC

 

First you need to check the schematic in the FSM to ensure that the 4
pins that have power are the only ones that should have power. If the
SBEC needs power at 5 pins, then it may not be the SBEC.


Matt

 

Looking at the 60-socket connector with the wires facing away from you,
the cavities are numbered thus:

Top row (all the way across, disregarding the central bolt post):
1 (left) through 20 (right)

Middle row (all the way across): 21 through 40

Bottom row (all the way across: 41 through 60


Cavity 3 (top row, 3rd from left): Direct battery voltage

Cavity 11 (top row, immediately to right of central bolt post)
AND
Cavity 12 (immediately to right of cavity 11) are the grounds. Check for
continuity between them and battery negative.

DS

 

Grounds are good, but no power on pin 3 with key on. Also, found a
little corrsion on 2 pins at the firewall connector, and more when I
pulled the boot back. Cleaned them up, but made no difference. Where
does the red and white wire for pin 3 go? I expected to see it coming
through the firewall connector, but didn't. Is it time to rip the
bundle apart? Are there fusible links in there?

KC

 

The "engine" fuse IIRC.

A 94 Caravan has but one fuse link; the one between the
alternator output stud and the battery.
Everything that -was- protected by fuse links the year before is
protected by fuses in 94.

You -did- check all the fuses didn't you?

 

Bingo. No power to the SBEC. (Did you check your O2 sensor wires for
shorting?)

Oof. I don't have '94 minivan wiring diagrams. Start a-followin' it back
until you come to the problem (probably a burnt fuselink)

Unfortunately, the fuselinks are within the bundle.

 

That explains why I am talking about fuselinks, my newest minivan
electrical repair was to a '92. Thanks for clearing that up.

DS

 

Yep, checked em. I expected the SBEC to be powered by the "ignition"
fuse under the dash, but that one has power and a good fuse. But pin 3
isn't connected to any of the pins in the firewall connector, that's
why I'm confused. There aren't any matching red with white stripe
wires in that connector, so if it's supposed to be connected, it isn't.
I guess I can pull apart the wire bundle and track it down.

KC

 

You may want to jump battery + to pin 3 and see if the SBEC will power up.