Cold Start troubles

[squeasel]

I am having trouble starting my 1996 Tahoe (5.7L gas, 120,000 miles, original owner) when cold (first start of the day, not weather related). Car turns over fine but I don't get combustion. If I add a bit of fuel to the throttle body it starts right away. A little while ago I tried starting it without adding fuel and with the gas pedal down about 25% and it started to catch so I stopped, released the gas pedal and it started fine. Are there any next step ideas? I am not sure where to begin. I have a scanner with some live data features but I haven't found the proper value ranges for the various sensors.

BTW, there is no CEL.

This is currently an irritation but would like to stop the troubles before they get worse. Much thanks in advance.

 

[lesterl]

Check fuel pressure.

 

[hshark]

I agree fuel pressure, probably need a new fuel pump

 

[Slammed]

Yup fuel pump or blocked fuel filter

 

[hshark]

yeah start with the filter first, then move onto the pump these yukon/tahoe's are known for fuel pump failures after so many miles. Also if this doesnt fix the problem it might be your fuel pressure regulator this happend to a buddy of mine he thought it was the pump he changed it and nothing until we figured it was the regulator. A way to check to see the pressure manually if i remember correctly behind the intake or around there you should see a button type thing if you press it fuel should squirt up this would let you know if your getting enough fuel.

 

[squeasel]

Thanks to all. I will be performing fuel pressure and pressure regulator tests ... hopefully over the weekend. I will post results and any potentially valuable instructions. FYI since the first post the truck easily passed Calif. Smog test.

 

[lesterl]

Let us know....

 

[squeasel]

Greetings All! I need a bit of advice before running the fuel pressure test. The tester manual says that I should release fuel line pressure before attaching the test line. So I have been waiting on a Tahoe Manual to confirm. The manual has not come. My sense is that fuel pressure isn't so great (this is a Vortec engine and it seems a good reading should be 60-66 psi), but I have some experience with the FI on cars with real injector pumps and the pressures can be quite high and dangerous. So, should I attach the test equipment, as I suspect, or should I wait to find out how to release the pressure? Much thanks in advance.

 

[lesterl]

This isnt a diesel, just hook it up, be warned it may leak some, they are wooried about fire..... Fuel pressure should be something like 60 maybe? Could be like 47 IDK on the Vortec 350...... Check www.autozone.com they have repair manuals and specifications.

 

[squeasel]

@lesterl ... much thanks. I should have results tomorrow. And you're right about the high PSI experience ... Diesel.

 

[lesterl]

Yeah, Diesel injection isnt anything for the novice to screw with. These are pretty safe tho....

 

[squeasel]

Fuel pressure results ... 55 PSI with the ignition ON, slightly less when running cold and about 52 PSI on rev up. I will assume the gauge is right (got to trust something I suppose). The specs that I can find show that I should have 60-66 PSI and that a lesser amount will cause start troubles. I see no reason not to change the fuel filter since I can't find when it was last done, so I'll start with this as a first step. I will retest fuel pressure after the new filter is installed and post results.

 

[squeasel]

Fuel filter has been changed. New fuel pressure results ... 55 PSI with the ignition on, 55 PSI when started and 55 PSI on rev up to 3000 RPM. In general, not much change though the PSI's are more consistent with the new filter. I still have the cold start issue and have to put gas into the throttle body to start the car cold. It is fine once warm and runs well at all times.

So I am looking for more advice. I understand that the fuel pump replacement is a bit of a bear so are there any additional test to confirm it is the fuel pump? Any comments on pump replacement would be appreciated as well.

I did not test the pressure regulator. As mentioned in a prior post, the "fix-it" manual I ordered has yet to arrive (unsure if it is a vendor or postal problem).

 

[TCMERICK]

If you have to replace the fuel pump (which is and in tank unit) be prepared to replace the whole sending unit as well. The steel lines on the sending units (which have to be removed from the tank because the fuel pump is part of that entire unit) are very soft metal and will bend/kink easily when disconnecting. If the lines do come off without damage, be sure to use new rubber "O-rings" upon installation to prevent fuel leaks.

 

[squeasel]

@tcmerick ... thanks for the advice.

Unless I hear otherwise I will start to implement the replacement. Shop space won't open up until after the March LeMons Race @ Infineon so it will be TBI top-offs when I need the truck.

BTW @tcmerick, any chance you are an RROC member from Dallas?

 

[TCMERICK]

You are welcome and Nope, not from Dallas, from the Seattle area currently overseas.

I have replaced a couple of fuel pumps on a 93 Full Size Blazer and the biggest problem was having too much fuel in the tank, the lighter the better. The pump replacement basics are relatively straight forward. Hope this helps!!!!
AS A Safety precaution, disconnect the battery!!!!
1) Use a jack with a piece of wood or something under the tank for support ( have to figure out what works best for you)
2) loosen and remove the tank straps
3)Lower the tank a few inches and locate the sending unit wiring connector and disconnect it
4) Disconnect the fuel Supply/ Return Lines ( be careful if you intend on reusing the sending unit)
5) Lower the tank down and slide off from under the vehicle
6) CLean the dirt thoroughly off the top of the tank around the metal locking ring so that no dirt will fall into the tank when the locking ring and sendiing unit are removed)
7) Remove the sending unit locking ring by gently tapping it counter clockwise with a brass punch (brass does not cause sparks)
8) You can now remove the sending unit/fuel pump assembly from the fuel tank
9) To remove the fuel pump from the sending unit, remove the clamps on the rubber hose and remove the strainer from the bottom. you should now be able to remove the fuel pump itself.
NOTE: pay attention to the way the rubber gasket is positioned on the bottom of the pump.

Install is basically the opposite: you will want to buy a new fuel pump strainer (if replacing the pump only). sending units come with strainers as part of the package. Be sure to use new rubber "O"-rings on the fuel line connections too (if using old sending unit). Also, if you are using the old sending unit I recommend buying a new locking ring.

The procedure really is not that tuff, it just takes some time and patience.
Hope this helps!!!

 

[lesterl]

96 should have plastic lines comming off the tank, like my 95 I just did, found a Delphi pump assembly on Amazon.com for $139, whole unit, tank was a PITA to get down.

 

[lesterl]

Delphi FG0084 $148 for the one yours uses..........

 

[squeasel]

Well, the LeMons race is over so I can go back to the Cold Start Issue. Currently, the truck is starting when cold. Apparently the trip to Infineon did it some good. I have filled the tank, added FI cleaner and have been driving it daily. Cold start is about 5 seconds of cranking with no fire, stop, 2 seconds of cranking with a "mis-fire", stop, then another 2-3 seconds of cranking before high idle. Warm start is immediate. I believe I will drive around a bit more and check my fuel pressure gauge for accuracy, then go back to diagnostics.

 

[Gregski]

I am on my third fuel pump, 212,000 miles, and I will say this. To me the fuel pump is either working on this car or it is not. When you get in the car and turn the key to aux on you will hear the pump prime the system, vzzzzzz sound, if you hear that, the pump is working. (I know, I know, but it could be weak) well I don't think so.

So for $150 bucks I say you do a tune up. Plugs, wires, rotor, distributor cap. AC Delco OEM plugs for $3 bucks a pop, don't try to get all fancy. You can't make it any worse, but it could fix your problem, and you won't be replacing a working fuel pump, PIA job, with a working fuel pump.