When I leave my 97 Chevy 1/2 ton for a few days
the damn thing don't want to start. Cranks like all get out. No starty.
Eventually, after 5 or 10 minutes of crankin and waitin, it will start.
After that, starts fine all day long.
Today when I tired to start it, nothing for maybe 5 minutes. So I pulled
the intake off and poured a little fuel into the throttle bore and it
fired and died. Poured a little more in and it fired right up and ran
great all day.
I checked the fuel pump pressure and that's fine. Put a new filter on a
few months back.
Is there some kind of one way valve that might be bad, allowing fuuel to
bleed back down? Or something else I'm not looking at? It must be a fuel
delivery problem, but only on the first start after sitting a couple of
days. I'm stumped.
350 5.7 auto 4x4
When you first turn the key (ON not to start) do you hear the fuel pump
turn on? It should turn on for a couple seconds and then turn off.
If it isn't then check the fuel pump relay.
What normally happens is you turn on the key, the pump turns on for a
couple seconds to pressurize the fuel system. The engine then starts and
the computer then looks at the oil pressure sensor to see if the engine
has pressure. If it does(takes about 5-10 psi) it turns the pump back on
and keeps it on until you either turn off the key, the oil pressure
drops to zero, or the fuel line/pump system fails.
The back-up to this system (in case the relay fails for some reason) is
that the oil pressure sensor also supplies power to the pump.
Wiring colors at the relay-
Red - Pump prime (connect 12V here to bypass the relay and test the pump)
Orange - Power into relay
Gray - Wire to pump
Dark green/white stripe - Relay control from ECM
Black/white stripe - Ground for relay.
Wiring at oil pressure switch -
Body - Grounded to engine
Tan - Pressure signal to ECM/Gauge
Orange - Power into switch
Gray - Power out to pump
Wiring at pump -
Gray - power into pump and sender
Dark Blue/white stripe (or purple on later trucks)
Black/white stripe - ground to vehicle frame
Yes, pump is turning on, then off after a couple of seconds.
Oil pressure reads OK.
Pulled out the relay today, then plugged it back in. Turned on the ign
switch, could hear fuel pump cycle, then turn off. Pulled out relay
again with switch still on. Plugged it back in. Heard and felt nothing
inside the relay. Also, fuel pump didn't cycle again. Could the relay be
Still no start until I pour a little gas into the throttle body. Then it
fires right up and runs/starts fine all day long.
Weird. This thing is driving me crazy
The timing is controlled by the ECM, It will only cycle the relay when
the key is turned off/on. That starts the timer.
What I would probably do is let it set a couple days, till it won't
start. Hook a fuel pressure gauge on it then turn on the key. See what
you get for pressure. If you have good pressure then BUT no still no
start then I would check the connection to the injector harness and
stick a couple noid lights on there to see if the injectors are firing.
Is there a pressure regulator or one way valve in the fuel line that
might be leaking fuel back into the tank after sitting overnight? What I
can't figure out is, why will it start if I dribble fuel into the
throttle body, and will start fine once it's been running for a few
minutes and start fine the rest of the day, but only on the first start
from sitting will it not start. I hate having to take it to a shop to
figure it out.
Thanks to everyone for all the help and suggestions so far.
There is a pressure regulator on the line. However if it is leaking down
like that it likely wouldn't hold pressure any other time. So you would
have to keep starting it with extra fuel each time. There is also a one
way valve on the pump itself. It is easy to test.
See what the pump is doing. If it comes up to pressure fast and the
system test for the regulator is OK, run the leak down test (basically
you get the engine running, then shut it down and watch the fuel
pressure) There is also a check like that for the pump.
Re tested the pump this morning.
48PSI with key on, no crank
40PSI during cranking.
Book says should be 55-60.
Would that slight amount of lower pressure result in a no start?
I'd hate to have to drop the tank and throw in a $300 fuel pump over a
10-15 PSI differential if that's not the problem, but nothing else is
Yep, That is enough to cause a problem.
I would test the regulator and test the pressure against a dead end
first though. It is possible that the regulator is faulty and letting
the pressure drop off early.
There are a list of tests in the book. Easiest way on the pump is to
pull the line from the pump and see what it reads with a gauge on it.
When was the filter changed last?
Or you can shotgun it with a new pump and regulator.
Replaced the filter 2 months ago, so that's not it.
Since the pressure regulator is attached to the pump, that means I gotta
drop the tank anyway I look at it, and with the tank down, I might as
well just replace the entire assembly. The truck has 304k miles on it
and I'm not sure if it is the OE pump or not, but it doesn't make sense
to take chances. The 1 chance I am going to take is with an aftermarket
pump. My parts guy says he hasn't seen much of a difference in bad
replacements between Delco and the aftermarket in tank pumps, but there
is a huge difference in price. I can get an aftermarket (Carter) pump
off Ebay for $75, while a new Delco is almost $400. Even Autozone wants
almost $300 for their aftermarket pump (airtek), so for the $75, I
figured I'd take a flyer.
Of course, it never fails. I just filled the tank day before yesterday,
so now I gotta borrow a few 5 gal jerry cans and pump all 20 gals fuel
out before dropping the tank.
Thanks to everyone so far for all the help and direction. I'll let you
know how it works out.
Pressure regulator is on the fuel injector assembly inside the intake
plenum. There is a prescribed way to test it.
I would run the tests first. It will show you if it is the pump module
or the regulator.
As for a new pump, I would try RockAuto.com
They show a Delphi pump ONLY for 74.00. That doesn't include a sender or
the filter sock.
I already ordered the fuel pump assembly off EBay, but looked at the
Rockauto site you mentioned. They don't show a fuel pump only, or I'm
not looking in the right place. I bought the entire assembly for the
same price as the pump alone. Hope it works.
When we tested the pump pressure this morning, I believe the pressure
test point is before the regulator in the plenum, so the 48/40psi we got
means the pump is weak anyway. In the event the new pump doesn't sure
the problem, I'll replace the regulator too, but I'm hoping the pump
does the job. Now I just have to go to the neighbors house and borrow a
couple of jerry cans.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.