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What's Causing '97 Acura to 'Hesitate?'Posted 8/8/2007
By Todd Erickson
Customer's complaint: The car "hesitates." "Ever since it got an oil change and injector cleaning, it has been running like this," said the owner. A more technical description would be that the car hesitates under hard acceleration. It was also noted that the malfunction indicator lamp (MIL) is not on, and it has set no codes.
The first thing tested was spark strength at the spark plug wire. Weak spark is a common cause of driveability problems on these vehicles. But be careful; we have all been fooled by a spark tester. Spark looked good, and all the secondary ignition components had been replaced with genuine Honda parts.
With the common spark problem ruled out, we had to rethink. The car doesn't like anything more than light cruising and goes flat above 2000 rpm. When you let off the throttle, it recovers and the spark isn't weak, so it must be a fuel problem. Fuel pressure was tested and was about 45 psi when the problem occurred.
Next, we needed to determine if the vehicle liked added fuel when the problem occurred. There are various methods of adding fuel ... most commonly a can of carburetor cleaner (B-12 is my favorite) or a good source of propane such as a gas grill size propane tank (a small torch bottle will not flow enough to perform a good test). I have heard of a setup that uses a regulator, hose, tube and valve from a gas grill.
We found it liked added fuel. But why was it lean? It has good fuel pressure.
The amount of fuel delivered by an injector is equal to injector command, fuel pressure and the ability of the injector to flow. Translation: we needed to check the injector pulse width next to determine if the electronic control module (ECM) was commanding the fuel injectors to open. The injector pulse was going greater than 25 milliseconds under hard acceleration so it didn't appear to have an ECM-related problem.
Even though fuel pressure was good, the fuel pump was noisy, so it was replaced to be sure there wasn't a fuel volume problem. The fuel pump sounded better, but now it developed a lack of power over 4000 rpm instead. What was left besides the fuel injectors being plugged? The injectors were sent out for cleaning using a reverse ultrasonic method. There was little improvement.
Why is it still so lean? The tech took it on yet another test drive but this time with a different fuel pressure gauge attached directly at the fuel filter. It ran great, power all the way to redline. What was the difference in this test drive versus all the others? The banjo bolt. The fuel gauge kit replaced the banjo bolt on the fuel filter with a banjo bolt that had a fitting on top for the gauge to attach to. As the technician took the original bolt out of his pocket and inspected it carefully, he found a tiny piece of rubber in the center hole of the bolt. He picked the rubber piece out and reinstalled it. A test drive confirmed the problem was fixed.
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