I am still hunting for my hard start solution and I noticed that the fuel
pump relay in the glove boax runs very hot. I assume one of two things...
A partial short in the wiring harness or a pump that's running too hard due
to a failing motor or similar... Here's my question...
Can I test amp draw for the pump from the relay socket or computer
connection or similar?? Do I have to test the draw right at the pump
connector? It is VERY tricky to access without dropping the tank. It
doesn't seem impossible but it is the next closest thing to impossible..
The relay gets hot when? You can check the current anywhere between the
relay and the pump, not at the computer connection. If the pump was drawing
too much current the fuse, if it's the correct one, should blow.
If it helps any... When the pump in my suburban went it was drawing 18amps.
After the pump was replace the new pump was drawing 2amps peak. I have
heard of times were the wiring to the top of the tank corroded and in cases
I just tested the amp draw on my pump from the test connector under the hood
and I saw a fairly steady 8.6A (I checked for glitch capturing within 1A and
nothing turned up). I scoped it while I was as it and it had a very steady
wave with no real drops or rounded edges so either it's in fine shape or
it's worn to a point that it doesn't fluctuate. I read somewhere that these
high output fuel systems will have a draw up to 10A on a good pump. Can
anyone verify this? I still think it's a nasty electrical issue with supply
to the relay but I just wanted to update anyone who's helped out this far.
in article 45d9db88$0$9861$ firstname.lastname@example.org, r_d at
rock email@example.com wrote on 2/19/07 12:19 PM:
Have you ever replaced the fuel pump relay? If the points get bad, the
heat and resistance will increase. A badly worn relay can actually
cause the pump to burn-out due to low voltage to pump motor.
I have replaced the EFI relay 3x to be sure that's not my problem. I don't
think the issue is with the relay unless it's a bad/cold solder joint in the
actual socket itself.
in article firstname.lastname@example.org, James1549
at email@example.com wrote on 2/19/07 7:09 PM:
If anyone knows the flow rate...I could calculate an estimated value based
on the pressure, flow, efficiency and voltage.
Also, you might measure the resistance through the load side of the fuse to
ground and compare that to a new pump.
wrote on 2/19/07 12:19 PM:
I have a Tech2Tech article that suggests 28mmils at 60psi. I have a
# of cylxMax Duty Cycle
-------- = ------- = 20lb/hr??
but I didn't look at it very hard. Do you know exactly whre the fuel pump
is grounded at? I still suspect a ground differential.
in article 5vrCh.59379$ firstname.lastname@example.org, News Skimmer at
email@example.com wrote on 2/19/07 7:36 PM:
WTF is all that? Not sure what your formula is for. What unit is your flow
rate in? not sure what mmils are...please spell out. also does that rate
include the recycle...recycle must be included in the horsepower calc.
On the c/k's, the ground peels out of the harness / plug near the pump and
bolts to the frame. If it is a ground problem, I don't think that would
lead to excess amps.
wrote on 2/19/07 7:36 PM:
Sorry - I was just pluging in some numbers based on a formula I have seen
used. The formula is for flow rate based on Lbs/hr. I believe that it's
used to determine injector sizing with modified motors. BSFC (Brake Specific
Fuel Consumption as a calculation of lbs per horsepower-hour) , Max Duty
Cycle set at .80 b/c most injectors would burn up b/w 90-100 I would think).
Mils (volumetric 1000th of an inch) 'mmils' was a typo.
Anyway, forget the formula - I was just playing with a formula I had seen
used - as for recycle rate - I don't know.
Thanks for the feedback. As for the grounding issue - I'm not so concerned
with high amps now that I know 8-9A is on the normal side for these fuel
systems - the pump will run intermittently at startup meaning that sometimes
turning the key won't engage the pump motor. I thought maybe a bad ground
could be to blame...
in article DlOCh.47984$ firstname.lastname@example.org, News Skimmer at
email@example.com wrote on 2/20/07 9:43 PM:
Maybe this weekend I'll measure the amp draw on my 99 5.7r
My 93 4.3z TBI with a new bosch pump pulls less than 2.
Based on the 2 at 10-12 psi, 60 psi would raise the amps for the same flow
wrote on 2/20/07 9:43 PM:
Once again - I appreciate the help. I was able to confirm that 8-10A is
acceptable for a 60psi Vortec fuel system so you needn't worry about
metering your trucks for me. I will post again if I solve the intermittent
no start issue. As a gesture of good faith, I pulled almost every harness
on the truck and packed them with dielectric grease. I sanded and refitted
all the engine grounds also. I didn't put any grease in the computer molex
connectors because I was a little leary about that even though it's likey to
be fine. I have yet to remove and sand down the fuel pump ground but it's
next on my list. Failing all of this, I will replace the entire relay
'convenience center' in the glovebox and then start metering outputs on the
in article PZQCh.31049$ firstname.lastname@example.org, News Skimmer at
email@example.com wrote on 2/21/07 12:43 AM:
Intermittent no starts (no fire/no fuel) can be caused be a bad ignition
On the fuel pump relay...you might consider removing it and powering the
pump directly with a fused jumper through the load side of the fuse.
On my 93 c1500, you can power the pump through one of the OBD1 connector
pins which then passes through the fuse. You might need to check your wiring
diagrams because that pin might not work if the relay is pulled out or arc'd
close (welded closed in run position). I think my test connection opens when
the relay closes. Make sense? probably not but study your schematics.
wrote on 2/21/07 12:43 AM:
Thanks again. Are you saying that I should run a jumper from the relay
socket to the fuse panel? I assume you mean strictly for testing purposes?
If I were to leave that connected, it ranks up there with dumnping fuel into
the carb with the wiper pump... Your thoughts on the ignition module may be
a good place to look. My only concern about that is if I power the pump via
the test connector under the hood, she fire right away. I've never had such
a battle with an electical gremlin to date - I'm almost ready to take it to
a tech even though that's against my religion (with the exception of
I'm still not sold on the fact that the ignition sewitch might be causing
these issues... At $200 for a replacement I'm not ready to gamble on it yet
though. The reason I suspect maybe the ign switch might be to blame is that
I can turn the key to ACC several times before the pump engages. Once the
pump engages, it starts right up. Some day I will figure this one out. I'm
still secretly hoping that someone with the same issue will reply with a
in article JLaDh.130$ firstname.lastname@example.org, News Skimmer at
email@example.com wrote on 2/22/07 1:28 AM:
Ok I finally got it! I tested the GRN/WHT continuity from the steering
column to the relay harness and it was fine. I tested the continuity from
the ECU to the relay and it also checked out. I then verified trigger at
the relay and also was able to run the pump with a jumper on the load side
of the socket. I verified 2 relays to be working flawlessly and had the
same intermittent results with both of them. The problem?? The connector
on the pump side of the socket was loose internally (hence it tested ok when
pressed with my probes on both sides but was intermittent when standing
alone. Some **very** carefull bending with a pick on that damn terminal
seemed to lock it in place and solve my problem. It starts every time now.
Vvrrooommmmmm... Case closed!
Thanks for all your help! To think I was about to throw an ignition switch
and crank sensor at this problem...
I am glad to see you found your problem. I'm going to just bullet some
thoughts so you'll know for next time.
*You should find and study a wiring diagram and locate each connection on
the vehicle...then you will figure out the shortest/direct path to the load.
On my c/k, a good place is through the fuse on the engine side of the
firewall by the evaporator. I don't know where your fuse is located or where
it compares to the socket on the relay...but either report to the pump. If
you bypass the fuse...provide a fuse in your jumper....or else $%&#$
*Testing (the pump) through the relay can go crazy if the contacts have
arc'd or something weird has happened.
*Testing through the OBD connector is okay if it has one.....although that
circuit opens when the relay closes.....at least on mine.
*Not sure what you mean on the fire and dumping fuel, etc. When the fuel
pump is hot-wired, fuel will only recycle to the tank unless something is
pulsing the injectors.....like cranking or the engine running...i.e.
reference pulses being received from the distributor. If you are dumping
fuel, your injectors are leaking.
I hope you read this and it helps.
wrote on 2/22/07 1:28 AM:
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