The Rodding Roundtable
Motorhead Message Central => Rodder's Roundtable => Topic started by: mrloboy on February 01, 2016, 09:45:21 PM
I just did an engine swap in my daily driver. 1993 GMC 2500 with 5.7 engine. It will spin over , but not fire. Pour a bit of gas into the throttle body and it will fire up and continue to run. I'm an old school guy and understand carbs and points ignition. Don't know where to go from here! Help!
My guess is low fuel pressure. It cannot get quite rich enough to start.
Have you replaced the fuel filter? Start there.
If that is done, you may have a weak pump, or the hose in the tank between the pump and the mount mah have a problem.
I had an 89 k1500 with a 350 that did what you are describing, and the short piece of hose had a plastic band clamp on it which slipped off of the pump, so the hose was "against the pump", but not slipped over it. It ran decent like this, but would not start.
Btw, if you have to service the pump, just pull off the box instead of dropping the tank, it is easier.
Good luck!
fuel delivery , make sure the pump is running. Mine in my 92 Silverado just died with no prior warning .
I found a blown fuse on mine when it did this. Not sure what the fuse was actually for any more but I went threw everything before I found it. I had fuel pressure all the way to the * carb no power at the injectors.
I would be checking grounds. When doing an engine change it's easy to miss one. as I recall there is one on the right rear that is important, and hard to reach.
I have had a few of these electric pumps cars run by cycling the key a few times to build pressure in the fuel rail or by hitting it with starting fluid. They will run, not well, but will fail to start after you shut it off. Weak fuel pumps were the problem.
Don
i borrowed a Snap-on scanner from a friend and will check it out this weekend hen I am home. We'll see what that brings forth. I'll let you all know what I find as long as I can figure that dang machine out!
Have someone listen near the fuel tank & turn the ignition key to "on" ... You should hear a "whirring" noise at the tank that will last for about 3 seconds & then go away until the key is turned off for about 15 seconds & then turned to "on" again ... If you do not hear this noise , use a rubber mallet to "smack" the bottom of the fuel tank as the key is turned to "on" .. This should jar the pump & sometimes get it to run ... If this does not work , follow the same procedure as above with a test light on the power wire to the fuel pump.( The gray wire should be the power wire to the pump) .. This should prove out the power to the fuel pump ... Don't forget...If the PCM does not see the engine turning over after 3 seconds, it shuts the power to the pump off & you need to turn the key off for 15 seconds & start over ...
IIRC, there is a fuel pump relay on the passengers side of the firewall , ( Under the hood) , that also can fail & give you the same symptoms ... If the relay fails , you will get NO power to the pump...
See the photo below ...
#1 is the fuel pump fuse nobody knows about ...
#3 is the fuel pump relay .....
Hope this helps ....
Bob.. :wink:
with the image that ugly olds posted..
i vote to replace the 15 to 20 buck fuel pump relay... do not throw out the old one..
WHY and how it all works..
GM trucks from the mid 80s thru 2003... have both a fuel pump relay and a oil pressure switch that are in parallel..
when you turn the key on.. the computer commands the fuel pump relay closed for 2 seconds.. when you start to crank the motor.. the computer commands the fuel pump relay closed again.
once the engine starts.. there is a either ONE 3 wire oil pressure switch or 2 oil pressure switches.. the oil pressure switch powers the fuel pump when the oil pressure is up.
i normally pull the fuel pump relay.. gently pry the guts out of the fuel pump relay. most will come apart with a little effort without damage to the cover.
inspect the fuel pump relay contacts.. use can wear the contacts far enough back that the relay cannot close.. i usually plug the bare relay back in without touching it to anything. the frame is powered
squeeze the relay... this turns on the fuel pump.. does the pump run.. you should hear fuel surging thru the fuel lines.. you do not need the key on for this test..
if you have help.. you can have somebody turn the key on.. do the relay contacts close for 2 seconds. then close again while cranking. this indicates the relay is connected to the computer.
PLEASE DO NOT probe the relay socket.. the green wire with the white stripe is SWITCHED POSITIVE from the ECM/PCM.. it will burn out if you touch it with almost any test light. the circuit driver is rated at 1.0 amps.
HOW to test the OIL pressure SWITCH, fuel pump power contacts..
with the engine running, unplug the fuel pump relay.. if the engine continues to run.. the fuel pump contacts in the oil pressure switch are probably OK. if it dies when you remove the fuel pump relay.. then you know the oil pressure switch is not working.
if the fuel pump relay does NOT close as the key turns on.. or while cranking.. please check the fuse Marked CRANK or Cranking.
i am going to link this voltage drop test to make it easier to print a copy of
http://i.imgur.com/WMDprhm.jpg
test 5 on your 93 goes to the rack of power distribution studs on the firewall
this test only takes a few minutes and will save you grief later on.
"use a rubber mallet to SMACK the bottom of the fuel tank". My story , on roadside fuel pump repair .Used a snow scraper /brush combo to smack the tank . I may add , "repeat as necessary" as the pump gave out on a trip to pick up an already ordered pizza . After wearing out my good arm smacking while kneeling in the snow at a busy intersection I proceeded to " violently hurl the snow brush back into the vehicle through the still open door" . NOTE " be sure to bank the brush off the side of the passenger seat in order to ensure a deflection toward the front windshield. Just a comment , did you know that a wood handled , plastic snow brush can shatter a front windshield ? I try to learn something every day.
Quote from: "chimp koose""use a rubber mallet to SMACK the bottom of the fuel tank". My story , on roadside fuel pump repair .Used a snow scraper /brush combo to smack the tank . I may add , "repeat as necessary" as the pump gave out on a trip to pick up an already ordered pizza . After wearing out my good arm smacking while kneeling in the snow at a busy intersection I proceeded to " violently hurl the snow brush back into the vehicle through the still open door" . NOTE " be sure to bank the brush off the side of the passenger seat in order to ensure a deflection toward the front windshield. Just a comment , did you know that a wood handled , plastic snow brush can shatter a front windshield ? I try to learn something every day.
:lol: I had a good laugh Thanks..so did my g/f..
Last summer I used a wood handled plastic snow brush to to sort of give a little push to a snapping turtle on the highway..tp hurry him across..he was stopped. Just did not go that well :idea: :lol: for me
This was a good size and he charged at me..I had no idea they could move that fast..
So I went home and got a long handled metal snow pusher :idea:
That was a really bright idea..it climbed over the shovel and tried to climb the handle to get me..when It could not do that it just laid in the shovel and I picked it up..
Quote from: "chimp koose""use a rubber mallet to SMACK the bottom of the fuel tank". My story , on roadside fuel pump repair .Used a snow scraper /brush combo to smack the tank . I may add , "repeat as necessary" as the pump gave out on a trip to pick up an already ordered pizza . After wearing out my good arm smacking while kneeling in the snow at a busy intersection I proceeded to " violently hurl the snow brush back into the vehicle through the still open door" . NOTE " be sure to bank the brush off the side of the passenger seat in order to ensure a deflection toward the front windshield. Just a comment , did you know that a wood handled , plastic snow brush can shatter a front windshield ? I try to learn something every day.
Since we're off the tracks here while we wait for the answer to the original post, did you know that you can crack a windshield in a Ford pickup in the Winter with a shell ejecting from a 30-06 when fired from inside the truck?
[quote="phat46"Since we're off the tracks here while we wait for the answer to the original post, did you know that you can crack a windshield in a Ford pickup in the Winter with a shell ejecting from a 30-06 when fired from inside the truck?[/quote]
It wouldn't surprise me. Can you hear again, yet?
Quote from: "enjenjo"I would be checking grounds. When doing an engine change it's easy to miss one. as I recall there is one on the right rear that is important, and hard to reach.
The fuel pump ground on my 94 c1500 was on top the frame rail just to the front of wheel well. 6ft bed, drivers side.
Update. Truck runs great. Discovered the problem. After adding a couple gallons of gas in the tank, she fired right up! Boy do I feel stupid!😳
Been there done that. Bought a car from a guy once that wouldn't run, gave him $50, put gas in it and sold it for $200. If you have ever seen the movie Slingblade, you have to look at it and say..."hmmm, ain't got no gas in it" in Carl's voice! 😜 Glad to hear it was something easy.