99 yukon denali bad cold start

[Erab81]

Ok i bought this truck about 5 months ago and ever since its had a hard time starting when its cold, not cold like outside temp but anytime its sits overnight, no matter what the temp is, its hard starting. so ive already put new plugs, wires, dist. cap & rotor, fuel filter, fuel pump relay, and cleaned injectors, dealer says its fuel pump and that the pressure tests at 44lbs and is supposed to be 66-70. funny, everytime i check the pressure its between 66 & 70 with the lowest being 60lbs when its 10 degrees out and sat all night, anyone had this problem? PLEASE help i dont wanna change this $230 pump if its not the problem

[2000CAYukon]

Since you have a fuel pressure gauge, do the following tests:

1) Engine Running with Pressure gauge attached. Turn off the engine and watch the pressure. It will lose a little pressure over time but should hold. Note how long to get to 50 PSI, 40 PSI, etc and if it gets to zero noting how long it took.

2) Let engine sit overnight (might as well leave gauge attached). Might need a friend for this one. Watch the gauge while someone turns on the ignition but does not try to start the engine. Note the pressure and any changes (like it went to 40 when the key was on then went to 60 after 30 seconds).

Once the pressure is 60 (or higher), try to start it and watch what the pressure does. Does it drop while the engine tries to start?

Post back with the results.

//2000CAYukon

[reekor]

I have the same problem with my 96 5.7L yukon. Fuel pump is a year old, changed the plugs, cap & rotor, ign coil and module. still no luck.

Originally Posted by Erab81

Ok i bought this truck about 5 months ago and ever since its had a hard time starting when its cold, not cold like outside temp but anytime its sits overnight, no matter what the temp is, its hard starting. so ive already put new plugs, wires, dist. cap & rotor, fuel filter, fuel pump relay, and cleaned injectors, dealer says its fuel pump and that the pressure tests at 44lbs and is supposed to be 66-70. funny, everytime i check the pressure its between 66 & 70 with the lowest being 60lbs when its 10 degrees out and sat all night, anyone had this problem? PLEASE help i dont wanna change this $230 pump if its not the problem

[Erab81]

im thinking about trying a fuel pressure regulator anyone ever change one of these on the 5.7 vortec??

[2000CAYukon]

Test #1 in my first post will tell you if the FPR is bad.

Look at my 3rd post in this thread: http://www.automotiveforums.com/vbul...30#post3874530 it has a link to some instructions for taking off the upper intake manifold. This needs to come off to get at the regulator.

//2000CAYukon

[Erab81]

Its been awhile since i've posted about my truck due to some long 13-14 hour days of work for the past couple weeks, finally i got a day off and was able to do the 2 tests 2000CAYukon told me to in his previous post. my first test was after the truck had run for only a couple of minutes to pull it into the garage. i shut it off, and hooked up the pressure tester. when i turned the key the pressure shot right up to 68-70psi after about 15 - 20 seconds it dropped to 62-64psi. I then started it, cranked for maybe 2 seconds and fired right up and ran at 61-62psi. after shutting it off i left the key in the off position and watched the pressure, it remained at 68-70 for over an hour. My second test was a little later in the day after it had sat for a couple hours. With the garage at 70 degrees i turned the key and the pressure went to 65psi i left the key on and watched the pressure slowly drop. 60psi after one minute, 30 seconds later 58psi, 1 minute later 50 psi, 30 seconds later im at 45 psi, 10 seconds later im at 40psi, and 30 seconds later im at 37 psi. after this i tried to start the truck it was very hard maybe 6-7 seconds of cranking before it finally fired. pulled it out of the garage shut it off and let it sit for about 2 minutes, and started it again, it fired right up. dunno what the hell it could be. 2000CAYukon if you can help me it would be appreciated.

[2000CAYukon]

Originally Posted by Erab81

Its been awhile since i've posted about my truck due to some long 13-14 hour days of work for the past couple weeks, finally i got a day off and was able to do the 2 tests 2000CAYukon told me to in his previous post. my first test was after the truck had run for only a couple of minutes to pull it into the garage. i shut it off, and hooked up the pressure tester. when i turned the key the pressure shot right up to 68-70psi after about 15 - 20 seconds it dropped to 62-64psi. I then started it, cranked for maybe 2 seconds and fired right up and ran at 61-62psi. after shutting it off i left the key in the off position and watched the pressure, it remained at 68-70 for over an hour. My second test was a little later in the day after it had sat for a couple hours. With the garage at 70 degrees i turned the key and the pressure went to 65psi i left the key on and watched the pressure slowly drop. 60psi after one minute, 30 seconds later 58psi, 1 minute later 50 psi, 30 seconds later im at 45 psi, 10 seconds later im at 40psi, and 30 seconds later im at 37 psi. after this i tried to start the truck it was very hard maybe 6-7 seconds of cranking before it finally fired. pulled it out of the garage shut it off and let it sit for about 2 minutes, and started it again, it fired right up. dunno what the hell it could be. 2000CAYukon if you can help me it would be appreciated.

If my math is correct, you went from 65 to 37 psi is about 5 minutes. This means that the fuel pressure regulator is leaking, or an injector is leaking or the check ball in the pump is bad.

The regulator would be the first place to look since they are known to go bad on the Vortec. My guess is that as the regulator warms up, it starts to leak; however, it could still be in injector. If an injector was leaking, the plug would be wet with fuel (if you let it sit for 5 minutes with the fuel pump on).

The reason is was hard to start after the pressure went from 65 to 37 is that the engine was flooded. If you only let it sit for 2 minutes, it will not get flooded and will start right up.

My neighbor has a 97 Yukon that would backfire when it sat for an hour or two. When I hooked up the gauge, the engine was hot. It went from 65 to 10 in about 3 or 4 minutes.

My money is on that your regulator is bad.

//2000CAYukon

[Erab81]

Thanks for the advice i will start there and post back to let you know how it goes

[Erab81]

i bought a new regulator and am in the process of installing it. there are 2 metal fuel lines that run into the top of the upper intake manifold right next to the injector electrical plug, how the hell do you get these out there is little to no play with them, and unless they can be moved i cant get the upper intake off

[2000CAYukon]

Originally Posted by Erab81

i bought a new regulator and am in the process of installing it. there are 2 metal fuel lines that run into the top of the upper intake manifold right next to the injector electrical plug, how the hell do you get these out there is little to no play with them, and unless they can be moved i cant get the upper intake off

You need to use a quick disconnect tool. Looks something like: http://www.lislecorp.com/tool_detail.cfm?detail=570

Most auto parts store will carry them (maybe not the same brand).

//2000CAYukon

[Erab81]

OK so it took me 3 and a half hours (includeing a mcdonalds run and a couple smoke breaks) but the new FPR is in, ran a little rough at idle last night but took it for a drive and got on it, and it runs great. started it this morning and it fired RIGHT up, didnt even have to crank twice. Just want to say thanks for all the help, i thought for sure i was going to be putting a fuel pump in this thing Thanks agian

[2000CAYukon]

Originally Posted by Erab81

OK so it took me 3 and a half hours (includeing a mcdonalds run and a couple smoke breaks) but the new FPR is in, ran a little rough at idle last night but took it for a drive and got on it, and it runs great. started it this morning and it fired RIGHT up, didnt even have to crank twice. Just want to say thanks for all the help, i thought for sure i was going to be putting a fuel pump in this thing Thanks agian

Glad to hear that it fixed your problem!!!

//2000CAYukon

[Erab81]

allrite, i was a little depressed and a little upset to hear this morning when i tryed to start my truck the excessive cranking and hard starting is back....
Well i was also off today so i pulled it into the garage to repeat the tests i had already done, with the key in the on position the pressure still drops however very slowly, now after about 8 minutes it goes from 65 to 45 where as before it dropped almost 5lbs per 15-20 seconds. Also when you first turn the key it only hits 65lbs. Now assuming it was a leaky injector, i started it (rough start) and let it run for about 1 minute to burn out any excess fuel potentially from a leaking injector. shut it off and restarted, not AS hard to start but pretty much the same. after running for about 10 min, i shut it off and it will fire right up. im starting to assume that the dealer is right and it might be the fuel pump

[2000CAYukon]

Originally Posted by Erab81

allrite, i was a little depressed and a little upset to hear this morning when i tryed to start my truck the excessive cranking and hard starting is back....
Well i was also off today so i pulled it into the garage to repeat the tests i had already done, with the key in the on position the pressure still drops however very slowly, now after about 8 minutes it goes from 65 to 45 where as before it dropped almost 5lbs per 15-20 seconds. Also when you first turn the key it only hits 65lbs. Now assuming it was a leaky injector, i started it (rough start) and let it run for about 1 minute to burn out any excess fuel potentially from a leaking injector. shut it off and restarted, not AS hard to start but pretty much the same. after running for about 10 min, i shut it off and it will fire right up. im starting to assume that the dealer is right and it might be the fuel pump

It it went from 65 - 45, you don't have a leaking injector. Have you look at the pressure while you are trying to start the engine? It needs to 60-65 or it will be hard to start.

//2000CAYukon