Hi Scotty,
My car is a Toyota Noah, 1998 model with an automatic gearbox.
A few months ago, we changed the fuel pump and soon after a whining or grinding sound could be heard below the hood when one starts the engine.
Certain times the temperature gauge rises and gets close to the halfway mark. If the vehicle is engine is stopped and restarted, the idling speed drops soon after engaging into reverse or drive gear. What could be source of this problem?
The current mileage is 160,000 km.
Many thanks.
Regards,
Todd
The most logical thought is that the new fuel pump is bad. "New does not equal known good." Is it an OEM pump or an aftermarket pump? Here in the U.S., it's not infrequent to hear that if money is an issue, and a new OEM pump is too expensive, it's a better bet to replace the unit with a used OEM pump from a salvage yard.
That's how bad Chinesium fuel pumps can be. So, if you have an aftermarket, non-OEM pump, start with that, since the problem, as you say, began with the pump replacement.
As for the temperature issues, this could be either a bad thermostat (is this the original, 24 year old thermostat) or a bad temperature sending unit. Not infrequently, if a coolant change has been done on a car with an old thermostat, problems with the old thermostat begin.
Idle drops when you move from an initial Open Loop state to a Closed Loop state, because the O2 sensors and the catalytic converters are warming up, and the initially high fuel trims are ratched down by the computer.
I'm not familiar with a Toyota Noah, per se. But this is, I think, reasonable generic advice.
Hi Geriscan,
Thanks for quick response.
I tend to agree with you when you say the "new pump" might bad. Does that mean the new pump can work but may give some warning such as the grinding sound if it is of poor quality (it is not an OEM pump but may be Chinesium like you say but shows "Made in Japan").
As for the thermostat, it was removed a few years ago. The Toyota Noah has a cooling fan that runs contiunuously. So most of the time the temperature is low. I only noticed this rising of temperature a few weeks ago because we now in summer. In addition, to the rising temperature, sometimes the idling speed goes down when the gear is engaged in reverse or certain times in drive mode. The idling can at times go below 500 rpm and there is a lot of shaking.
So, I do not what to do, whether to change the radiator or change the pump once again.
If the vehicle has an Idle Air Control Module, check that module. Clean it, if you can. (It's usually adjacent to the throttle body). A dirty or damaged IAC could be the cause of that. That's one possibility.
There are other possibilities: Fuel injectors that need cleaning, clogged air filters, bad spark plugs, and element of the exhaust. It would be easier to explore if you had a scan tool, and that scan tool listed some DTC (Diagnostic Trouble Codes). These DTCs don't necessarily lead directly to the problem, but they are a cue.
So, don't "fire the parts cannon." Have the vehicle scanned for trouble codes, and if available, for Mode 6 (manufacture specific tests).
Now that you have mentioned spark plugs, I did change the plugs a few weeks ago. I replaced the Denso ones with NGK but did not check whether they are all working correctly.
Thank you very much for your help.