Thread: Sensors

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Have a 1999 Pontiac Sunfire. 2,2 4ci. Evey so offten the car will want to bod down on take off. will not stall, but will act like it,s runining out of gas. You can stop. Cut engine off. Let it rest a few minints. And it will run alright again. It could go another 1000 miles or so and do it again. The engine light does not come on. Have had it in the shop a couple of times. They can't find anything wrong. Have supected the tranmission may not downshift some times. My question is this. Can a sensor stop working some times and then work again? Have ofcourse changed the gas filter, air filter. Put new plugs in. Kind of runing out of ideas, What would be some good advice? Thanks, John.

Update. Had a shop clean the throttle body and injectors. Drove again for aboyt 40 miles. And it did it again. Only this time it stalled. Never did that before. So far I,ve had the car in 4 shops, Have spent about 400 dollars. And still the proplem remians. I guess I,ll have to figure it out myseft. Need to learn about sensors and fuel injectors and the like. I,m an old chevy short block man. Can work on them okay. But anything after 1990 I,m lost. I guess I,ll go ahead and replace the catalytic converter and oxygen sensor. And then every week replace the other sensors. If that don,t work, I.ll replace the injectors. Rebuild the throttle body. I would have thought a dealer and some of these shops could have at least told me what the issue could be. With all the money I,ve paid to other people. I,ve could have done all these things already. I,ll never take a car to a shop again. If I can,t fix it myseft. I,ll junk it.

Does the motor have a crank sensor. The can sometimes cause an intermittent issue like that. I had a similar issue with a 97 Explorer. It did the same thing a couple of times and then quit altogether. Replaced the crank sensor and she fired right up. And has ran great since.

Just a thought for you to consider.

C

Update: Went ahead and took the 99 Sunfire to another shop. As before, they could not find anything wrong with it. Kept the the car for 3 days. He did not charge me any fee. But he did have an idea. My gas hand in the car does not work. Has'nt worked for a long time. He said that perhaps at times the car was low on gas. And that the pump may have issue with a low gas level. And or this may also be allowing some dirt in settell in in the tank. And this dirt may find it's way to the fuel injectors. He recomended to keep the tank almost full at all times and also to put some fuel injection cleaner in the tank when I got gas. So I,ve been making sure the tank level is high. And also I've been useing the high test gas, 93, instead of the 87. And I put some STP fuel injection cleaner in. I've run it about a 150 miles so far. And it has run fine. So maybe that's it. We'll see. Buy the way. On top of my engine it saids SFI. Does this mean Single Fuel Injection? My repair book saids all these cars come with MFI. So I was just wondering about that.

SFI=sequential fuel injection, the injectors fire in order, not all at the same time.

Ther is a sensor. Not sure at the moment what it,s call. It tells the fuel injectors when and much gas to put in the intake according to how far open the flap in the thotle body is. Could this sensor malfunton at times giving a fause reading. But not puting the engine light on. Maybe not telling the fuel injectors the right thing? Thanks, John

the sensor you are thinking of is the TPS = Throttle Position Sensor, which works together with the MAP sensor = Manifold Absolute Pressure... to check the TPS, there should be 3 wires, tpin and connect a scopemeter to the middle and top or bottom sensor and set it to check resistance, resitance should change in a constant sweep as you move the gas pedal, if there is any break in the resistance it means that there is a worn spot in sensor..... the MAP sensor could also be dirty, it will be on the intake piping, a rectangular box with i believe 6 wires on that car, take it out and clean the sensor tip with electronic cleaner, be sure to be careful the little wire in there is very fragile.... i really doubt it would be transmission related.... but also to clean those injectors better you can take them out and hold them upside down and lightly tap them on a bench, they have little screens to catch particles..... make sure to replace the o rings if you do take the injectors out.... another thing could be fuel pressure, the regulator could be going out.... to find the regulator trace down the fuel rail and fuel line to find a little device with a vaccum hookup... you can disconnect the vaccum line and plug it to give full fuel pressure all the time... its not so much pressure it will damage anything and it might even give you a little bit more pep

The regulator. Might have somthing there. I don,t think anybody at these auto repair shops have thought of that. Just disconnect and plug up the vacum. Might do just that. Also, If I happen to be out and the car acts up again. What might be some quick fix things I can try just to get the car home. Or at lease out of the road. Thanks John. Also, I.m still perflex about the issue of a sensor working sometimes and not working sometimes. Also does anyone have a time machine so I can go back to 1970? LOL. Thanks, John.

nope no time machine sorry..... ussually an intermittent sensor would be caused by an exposed wire that shorts sometimes or a loose connection.... or maybe a resistor that is heating up and shorting out when it gets hot.... the pressure regulator was a trick that gm was telling mechanics to modify if experiencing problems similar to yours, they told us to tap an indentation into the regulator with an 11/16 socket to crush the spring a bit and keep the regulator open just a little more..... its not in any books, but mr goodrich gave us a memo about it