Yukon Won't Start - Help!

[ncmoore4]

Hello all-

I've been a member for a long time but have never posted a topic. My wife has a 2003 Yukon with 73K miles. Two years ago at 53K miles it would not start after sitting in the garage for the weekend. Had it towed to dealer and they replaced the throttle body. It happened again about a month ago. Parked it Friday in garage, go to start Monday and won't start. It turns over but then stops and sounds like its choked or the TB won't open up, etc...just like the first time it happened. I disconnected the battery and had it cheked at Auto Zone. A couple of hours later I hooked it back up and after trying it a few times it started and has been fine every day for a month. We parked it agian this weekend and then the same problem on Monday. This time the battery disconnect will not fix it. The battery is a couple of years old and checked out fine at Auto Zone a month ago. I disconnected both cables for about 4 hours and went ahead and replaced the throttle body myself today (reman from O-Reilly). It still will not start! I do not want to tow to dealer and pay $800 again so PLEASE help if you can. I have replaced the fuel filter but it's been a while. We ordered and bought it new and it's basiclly still brand new except for the mileage. This has to be some "computer" problem since I fixed it so easily last time. Any ideas? Anyone heard of this before?

[bigredmariner]

Can't help you brother, but welcome to the board. Bump.

Might also try posting in the Ask The Technician area for more response on the subject, maybe have a mod move this thread.

[Draenor]

May not be getting enough fuel. Do you hear the fuel pump turning on?

 

I'd go back to Auto zone and see if they do a loaner tool for a fuel pressure gauge. Check the pressure at the rails. Should be about 55-60 psi when the pump is on and no more than a 2-3 psi drop once it has been turned off for anout 15 min.

[bill190]

...This has to be some "computer" problem since I fixed it so easily last time. Any ideas? Anyone heard of this before?

 

As to "computer" problems, which basically means most engine problems, you need a factory service manual set for your specific vehicle (order from GM dealer), and then would need to test various sensors to find the trouble. Mostly you would use a multimeter for testing.

 

Most factory service manuals have a section on how to use multimeters to test for voltage or resistance (ohms). Also there is a ton of instruction on the internet.

 

The factory manuals give detailed troubleshooting instructions based on the problem you are having. You go through a flow chart for the specific problem and test various components, then if each is ok, proceed to check additional components until you find the problem.

 

As they say, you need the right tools to do the job, with electronically controlled engines, one essential tool is documentation which gives instructions for troubleshooting. And also tells you what various sensors *should* be doing when you test them.

[brims]

If it turns out that the computer is shot, one of the tuners should be able to sell you a new computer with stock configuration for your truck for a good deal. Just throwing it out there, I recommend this only if you determine with some good testing to be the problem.

[bill190]

The factory service manuals also tell you how to check the engine computer to be sure it is working.

 

But basically you start out in the books with the problem you are having, then it would lead you to testing that if it could be a cause of the symptoms.

 

These are "flow charts". You look in the index for a certain engine problem, then turn to that page, then it will tell you to check this and that. Then if OK, measure this and that wire with a voltmeter (multimeter) and see what you get, then if a certain reading, check another thing, etc.

 

Basically the charts lead you to the problem depending on the results of testing various things.

[TexasAl]

OK. First check to see if your hear the fuel pump. Turn the ignition key to the on position (do not crank). See if you hear the pump priming the lines (small whine). If you hear it, then it should be okay. Also, do you have any dummy lights on( Check engine) ? If so, go to autozone, and rent the scan tool (free, but you need to leave a deposit). See if you find any codes. Let us know what you find.

[TexasAl]

The factory service manuals also tell you how to check the engine computer to be sure it is working.

 

But basically you start out in the books with the problem you are having, then it would lead you to testing that if it could be a cause of the symptoms.

 

These are "flow charts". You look in the index for a certain engine problem, then turn to that page, then it will tell you to check this and that. Then if OK, measure this and that wire with a voltmeter (multimeter) and see what you get, then if a certain reading, check another thing, etc.

 

Basically the charts lead you to the problem depending on the results of testing various things.

 

You can also go to alldata.com and get a subscription for the same materials. The books are better, but the subscription is cheaper.