99 tahoe wont start


tyflesh
05-21-2011, 03:19 PM
This is the deal with this tahoe, sometimes it would start sometimes it wouldnt, I have read all the threads on these trucks that wont start, I changed out the fuel pump 2years ago, changed plugs, rotor and cap, wires, fuel pressure regulator, crankshaft sensor, took it to the shop they replaced the ecm, then it was sending a code on the cranksensor, the shop told me the crankshaft sensor had to relearn itself, ok took the truck on a 300 mile trip ran great, got back home the next day it wouldnt start again, checked the fuel pressure with key to the on position, it hit 66 then immediatly fell to 60 and dropped to about 58 soon after and continued to fall off slowly for the next 20 mins down to 52, between 58 and 60 PSI during cranking, Im starting to believe maybe my fuel pump and maybe the injector is bad.... Thanks for any help...

inafogg
05-21-2011, 03:54 PM
This is the deal with this tahoe, sometimes it would start sometimes it wouldnt, I have read all the threads on these trucks that wont start, I changed out the fuel pump 2years ago, changed plugs, rotor and cap, wires, fuel pressure regulator, crankshaft sensor, took it to the shop they replaced the ecm, then it was sending a code on the cranksensor, the shop told me the crankshaft sensor had to relearn itself, ok took the truck on a 300 mile trip ran great, got back home the next day it wouldnt start again, checked the fuel pressure with key to the on position, it hit 66 then immediatly fell to 60 and dropped to about 58 soon after and continued to fall off slowly for the next 20 mins down to 52, between 58 and 60 PSI during cranking, Im starting to believe maybe my fuel pump and maybe the injector is bad.... Thanks for any help...

soungs like it could be the pump,do you know what brand name it was??
they rec to use the delco/delphi units

tyflesh
05-21-2011, 04:09 PM
I know it was from autozone, but not sure what brand it was and it was a 150 bucks and if im right it was the cheaper one at that.....

jrsmail
05-21-2011, 04:14 PM
It is funny this thread is here, I went out to start my 99 2 dr tahoe and the same thing. I can hear the fuel pump running, but will not go. I'm going to pull of the line and see if get and fuel pumping though line. I parked it last week and worked great.

jrsmail
05-21-2011, 07:20 PM
It is funny this thread is here, I went out to start my 99 2 dr tahoe and the same thing. I can hear the fuel pump running, but will not go. I'm going to pull of the line and see if get and fuel pumping though line. I parked it last week and worked great.

Here is what I got
99 tahoe 5.7 no start. Fuel pressure is 60 psi at pump start and the off to 52 and drops 4 psi over 3 minutes. Fuel pump issue????

j cAT
05-21-2011, 08:24 PM
This is the deal with this tahoe, sometimes it would start sometimes it wouldnt, I have read all the threads on these trucks that wont start, I changed out the fuel pump 2years ago, changed plugs, rotor and cap, wires, fuel pressure regulator, crankshaft sensor, took it to the shop they replaced the ecm, then it was sending a code on the cranksensor, the shop told me the crankshaft sensor had to relearn itself, ok took the truck on a 300 mile trip ran great, got back home the next day it wouldnt start again, checked the fuel pressure with key to the on position, it hit 66 then immediatly fell to 60 and dropped to about 58 soon after and continued to fall off slowly for the next 20 mins down to 52, between 58 and 60 PSI during cranking, Im starting to believe maybe my fuel pump and maybe the injector is bad.... Thanks for any help...

GET DTC codes...if none and your fuel pressure is good...could be the ECT ...or the connector to it etc....

how many miles on engine ?

tyflesh
05-21-2011, 09:31 PM
the engine has 128,000,n theres 1 code says the crank position sensor is not learned, mechanic at the shop said that by putting the new ecm in that it had to relearn it's self and it should go off on its own, but never did, truck ran fine for a few days took it on a trip didn't start acting up till I came back...

j cAT
05-22-2011, 10:11 AM
the engine has 128,000,n theres 1 code says the crank position sensor is not learned, mechanic at the shop said that by putting the new ecm in that it had to relearn it's self and it should go off on its own, but never did, truck ran fine for a few days took it on a trip didn't start acting up till I came back...

post what the codes are ...mechanic explainations usually don't help !

AUTO ZONE PART STORES CAN READ CODES FOR YOU !

or you can purchase a code reader. buy one that can be updated for newer vehicles..this is a good investment IF YOU are planning on repairing or making sure whats going on with your vehicles before the repair shop works it..

after the code issues are displayed then proper troubleshooting can occur.. also you should have a manual if YOU are working on your vehicle...................

danielsatur
05-22-2011, 10:22 AM
Swap fuel pump fuse + relay with another in the fuse box.
Check the fuse rating, and relay #'s for same type.

tyflesh
05-24-2011, 11:46 PM
That actual code number was cleared, but what it said was ( crankshaft position sensor not learned).....and that sensor was replaced back in march.

tyflesh
05-24-2011, 11:49 PM
@ Daniel the fuel pump hit 66 on test gauge then immediately fell to 60 and proceeded to drop drown to 52 within 20 minutes ...As if the injector was leaking...

MT-2500
05-29-2011, 06:19 AM
@ Daniel the fuel pump hit 66 on test gauge then immediately fell to 60 and proceeded to drop drown to 52 within 20 minutes ...As if the injector was leaking...

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.

Hard to start cold.
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.
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.
Post-back fuel pressure readings.

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