Dear Auto Advisor,
Every Saturday I look forward to the automotive question and answer article you write in the paper. It is a lot of good advice and seems based on automotive common sense. I have been working on cars for years and normally I can get figure out what is wrong with them. I am writing you because I am stumped on this vehicle!
The vehicle that is killing me is a 2001 GMC Blazer with a 4.3 Liter, code W with 101,000 miles. The symptoms are as follows:
1) When driving down the road the car will loose power and barely run.
2) Shut the car off for a few seconds and it runs okay for another 10 to 15 minutes.
3) I have gotten it to act up in my shop and if I spray carburetor cleaner down the throttle body it runs great
I know it is starving for gas and I have changed the fuel pump and filter, the Mass Air Flow sensor, the O2 sensors (both of them) changed the cam and crank sensor. (I was able to take all these parts off another car and try them without having to charge the customer for them). Still this problem persists and after 40 hours of work on this car it still has me baffled.
Jay in Panama
Dear Panama Jay,
I too have been where you are and it is not a pleasant sight! We technicians can get cantankerous at our employees and family because these problems go home with us at night. It just really bugs problem solvers like you and I. So let’s step back and look at this problem with a fresh set of eyes.
You said the symptoms are that it acts like it is running lean. And if you shut it off for a few seconds and turn it back on it runs fine for a few more minutes. You said it ran better if you sprayed carburetor cleaner down the throttle body when it was acting up. So let’s look at the fuel delivery system!
1) Hook up a fuel pressure tester to the fuel rail and drive it. At the same time have your scanner hooked up and watch the short term and long term fuel trim.
2) If the fuel trim is running plus or minus 10 all is well. I suspect after a few minutes it will be inching towards the + 15 to +25 on your short term fuel trim.
3) Watch the fuel pump pressure gauge, if it drops at the same time then the fuel pump pick up screen is clogging up and/or the fuel pump is overheating and slowing down.
If the Short term fuel trim does go to +15 to +25 then I suspect that the NEW Fuel pump is the problem, or the fuel tank is contaminated with water. Either one of these variables can and will cause the symptoms you are describing. Just because a part is new does not mean it will work properly. Some new electrical parts have a 10 to 20% failure rate, no matter if they came from the dealer or the local parts store. As you and I have found out over the years N.E.W. means, NEVER .EVER .WORKS! Let me know what you find.
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