QuestionThe problem could have occurred before, but there was other problems, code PO171 too lean Bank 1 and code PO720 output speed sensor.The would go in third and stay there.They also changed another sensor it was about 2" wide with a cluster of holes and a slotted adjustment bolt hole and wires.The check engine light was on all the time. The last time it came on showed too lean. Let me say once the engine warms up there is very little problem.If I press hard on the gas when it hesitates the light will come on if i baby it and wait for the engine to rev the light stays off. When you let off the gas it is very jerky rather than the normal smooth.They also replaced the crank sensor but this was damaged by teeth coming of the timing belt.( did not skip)a new timing belt was installed.Could the sensor with all the holes be adjusted wrong since a new timing belt was installed.Before the Transmission issue it was fine.Also had the trans. flushed.Thank-you
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I believe he was getting the signal from the sensor that is in the exhaust manifold,the mechanic do nothing it was switching back and forth on it's own.-------------------------------------------
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I have had recent maintenance done to my Sanota timing belt,plugs,two plug wires,two sensors for the trans.
The problem is sometimes when you try to accurate it is if you are running out of gas then it will surge and accurate.
The mechanic's tester showed that the fuel went from a reading of about 180 then jumped to 800 then back down again then up again he said most cars don't jump that far apart the readings are closer together. This would explain no fuel then lots of fuel.My question is what could be the cause and how do i correct this problem? Thank-you Dave
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Let's start with the fuel pressure readings. What are the units for the numbers 180 and 800? And what did the mechanic do to make the number change?
The fuel pressure specification is approximately 255kPa or 37PSI. A high fuel pressure would be caused by a faulty fuel pressure regulator or a blockage in the return line. A low fuel pressure is most often caused by a worn fuel pump, but could also be caused by a restriction in the delivery line.
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Gotcha. That would be the oxygen sensor. The upstream oxygen sensor should switch back and forth from a value over 500mV to a value under 500mV. 180mV and 800mV are typical values and do not indicate a problem.
I suppose this would be a good time to back up a bit and get some more background information. Let's not jump into checking the fuel pressure right away. I had thought that's what the mechanic was checking.
1. Did this problem occur before the work, after the work, or both?
2. If both, was there any change in the problem after the work was completed?
3. Is/was your check engine lamp illuminated?
4. What sensors were replaced on the transmission?
5. Do you think you'd be able to tell the difference between a transmission issue and an engine issue, each of which would cause the vehicle to accelerate poorly?
AnswerAdditional follow-up:
After doing some more thinking about this, I recalled some instances where I've seen the surging you're describing by a loose or broken air intake bellows. That could also be a cause of the P0171 code. You should make sure the bellows between the mass air flow sensor and throttle body is securely clamped onto the throttle body and air flow sensor and has no breaks or rips in it. In fact, it'll be best to take it off the car and inspect it carefully and reinstall if it's okay.
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It sounds like the sensor you're describing may be the throttle position sensor. It's approximately square in shape (I think about 1.5 inches on a side), about 1/2 inch thick, and has two slotted screw holes where it attaches to the throttle body. The connector that attaches to the sensor has four wires.
A poorly adjusted throttle position sensor can cause some odd driving issues, including the surging your are talking about. Part of the throttle position sensor is a component called the idle switch. The throttle position sensor should be adjusted so that the switch is closed when the accelerator is not applied the switch opens with just a small amount of accelerator input.
I also don't see anything in the repairs that would address a P0171 issue. This is typically caused either by a vacuum leak (especially at the PCV hose) or a faulty air flow sensor. A vacuum leak could also cause the surging you describe, but a faulty air flow sensor would tend to only cause a hesitation, and only in some instances.
