earnman

crank engine does not start , spray starting fluid down intake and it fires and stays running???? new fuel pump last year.crank engine until oil pressure comes up and it still will not fire? any ideas?
thanks for any input

j cAT

this is the classic fuel pump failure....if you used a non oem pump this is what usually occurs...or operate vehicle on fuel level below 1/4 tank...


always verify your diagnosis WHAT IS THE FUEL PRESSURE!!!then go from there voltages/ ground at frame rail etc,etc....

earnman

did not check fuel pressure yet but will , by the way no DTC codes, do not think fuel pressure is a issue although it maybe ..but pulling a load and you mash the gas it goes like heck still??

j cAT

the fuel pressure is not a DTC this is why the gauges are required....It would be great if you could hook up a scanner on this vehicle and see that pressure...remember the fuel pump needs 12volts and a return to ground...make sure there is power to that pump....if it has power and its not running you need to remove pump....when checking pressures make sure the pressure does not drop off rapidly, it should hold pressure for a time after the pump shuts down....

earnman

OK i understand all that but why will it fire and stay running if i prime the system(spray starting fluid in the intake) this is the part i do not under stand

j cAT

this is where the volt meter is used....when cranking the fuel pump is not getting enough voltage.....or is it ???????what is the fuel pressure when cranking???????what is the fuel pressure when running??????what is the voltage to the fuel pump?????/this is how you troubleshoot to the componet ....most usually just keep changing parts....until they guess correctly......a bad ground or relay but what have you measured to have me or others help you...from where I'm sitting I cannot see exactly whats happening but you can ......If you lack the tools and knowledge have a repair shop make repairs ....

earnman

am a mechanic by trade (mainly diesel) 20 tears+ have$30,000 in tools. i have a solus snap on scanner. i thank you all for inputs just got home daughters vehicle
i know all the basics just looking for other possibilities or ideas that i may not think of. my first things are fuel pressure and voltage. hope to get vehicle tomorrow to check out. again thank you all for inputs!! anything more you can think of would be great!! will keep you posted and let you know if i fixed problem

earnman

forgot to say it does not do this all the time

earnman

found the problem!yeh!!

MT-2500

Earnman.
The injectors on that engine has to have full fuel pressure to squirt the injectors cold.
Even a couple of lbs low will give a hard start cold.
They will start and run all day after warmed up with lower than specs fuel pressure.
Also watch you scanner readings for high fuel trims and block learn readings.
They are a good sign of low fuel pressure.

And as Jcat said aftermarket fuel pumps are famous for low fuel pressure.
Repalce only with a AC-delco/delphi fuel pump.

Tips and guide lines on checking fuel pressure.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

MT

__________________
Remember proper testing gives us the answer to many problems.
MT

earnman

thanks for reply!! replaced fuel pump with delphi pump.. where i work delphi i get a discount!!! but as far as the problem that i solved!!yeh!! i for got to say i replace 2 brake lines ..which is next to fuse/ relay box... i found a broken wire off the main fuse/relay box right next to brake lines i replaced.. did not have problem going into my garage..so whats that tell you??? got to get schematic to see where this wire plays a roll ..it has got to do with bypass on start up...i think but all is well now

earnman

forgot will let you know all how i make out