Bucking and Hesitation

[mayhem]

My tercel has, for a while, had a problem with some slight bucking under load. Lately it has progressively gotten worse. Any hints or ideas?

Other than this the car seems to run fine. Occasionaly it idles rough when first started. This problem can occur rather the motor is warm or cold. It has about 120K miles on it.

I love the car because it gets good gas mileage, is reliable and very cheap to work on.

[Phi]

When was the last time you did a general tune up? What was done to it?

-maybe warn ignition wires causing misfire?

[mayhem]

Sorry for the lack of maintenance info.

This summer I put in new plugs/wires/distributor cap. I was hoping this would solve the problem but it didn't change anything. I had a dealership put on a new timing belt about 2 years ago. Would have done it myself but they had a special for $50 and that was worth my time.

[Nick]

fuel pump... if it only does it under heavy acceleration, your pump isn't putting out enough pressure

happened to my camry, got a pump from a tercel (same part)

[deizel295]

Bucking under load? that is not usually fuel issues. I am in an advanced engine performance class at college right now, check your MAP (manifold absolute pressure) sensor.
1st try disconnecting it electrically, the ECU will revert to using the tps and ckp sensors, if the car runs better then you found it. OR use a digital volt ohm meter (DVOM) to look at the signal at different vacuum readings.
these are just general numbers but they should look somthing like this (SOMETHING)

Volts VS Vacuum
4.5V 0" hg (inches of mercury)
3.5V 5" hg
2.5V 10"hg
1.5V 15"hg
1.0V 20"hg
Test this between the signal wire and ground. use only a high impedence DVOM or you'll destroy the ECU and the DVOM
your higher "hg readings will be at less throttle positions (toward idle or on decel - obviously you can't do this while in motion)
This may sound far fetched but it worked on shop vehicles.

Also check your MAF (mass air flow) sensor, a good check of this is to disconnect it electrically, like before if it runs better you got it! also try spraying the wire inside the air flow area with brakleen ( DO NOT USE CARB CLEANER!! TRUST ME DO NOT!! ) and it sometimes cleans it up, carbon builds up on the wire and the ECU cannot sense the air flowing past it. MAF's work by heating up a wire (hot wire MAF) and looking at the voltage drop across it to keep it at a constant temp, as the voltage drop changes the ECU computes this to a different air flow number. so try those, they may be the issue. always do the tune up stuff first, but don't throw a high priced pump at it unless you diagnos it. If you think it is the pump, do a fuel pressure gauge on the fuel rail, the try a fuel volume test, it should put out at least 1 pint in 30 seconds and have at least 40psi running pressure. hope all goes well.

TOYS RULE BABY!

[piggyfinndude]

Where is the MAF sensor on our tercels? Specifically my 91' Tercel DX??

Thanks!!!

[kene]

on the distributor there is are 2 wires that run into a rubber semi circle grommet on the distributor.(there are 6 wires total that run to your dist....one group has 4 wires the other grpoup has2...u want to follow the 2 wires.) inside that rubber grommet the 2 wires may be separated..i had this problem happen to me 2 years ago and it just happened again..it a common occurence in the tercel. just go to a junk yard and take one off urself and then pay 1$ for it...to take it off you musy open the dist.., the 2 nuts holding the wires to the coil are 6mm i believe... be very tender when taking the nuts off, cause u can tear the wires from the ring terminals they are connected to very easily.(i did this the first time)


you will end up replacing the wires and the plug they connect to..its not a hard job..

a good way to tes this is make sure ur engine is running and have someone rev the motoro up and hold it at around 3500rpms(safe level..not too high) and then go to the 2 wires(they will be wrapped in heat shrink) and move them around, side to side ect.



hopefully this is it. other thing could be ur throttle position sensor..if its not bolted up properly(very loose and flimsily connected to the intake manifold) or the wires on the plug that goes to the TPS are worn or have corrosion build up in them.( i was told this happend every now and then...words of a toyota technician. chekc this too

[piggyfinndude]

Is this a seperate problem you know of...or this is directly related to the MAF sensor?

[kene]

its a separate problem that happened to me

[jeffs94]

Originally posted by deizel295
Bucking under load? that is not usually fuel issues. I am in an advanced engine performance class at college right now, check your MAP (manifold absolute pressure) sensor.
1st try disconnecting it electrically, the ECU will revert to using the tps and ckp sensors, if the car runs better then you found it. OR use a digital volt ohm meter (DVOM) to look at the signal at different vacuum readings.
these are just general numbers but they should look somthing like this (SOMETHING)

Volts VS Vacuum
4.5V 0" hg (inches of mercury)
3.5V 5" hg
2.5V 10"hg
1.5V 15"hg
1.0V 20"hg
Test this between the signal wire and ground. use only a high impedence DVOM or you'll destroy the ECU and the DVOM
your higher "hg readings will be at less throttle positions (toward idle or on decel - obviously you can't do this while in motion)
This may sound far fetched but it worked on shop vehicles.

Also check your MAF (mass air flow) sensor, a good check of this is to disconnect it electrically, like before if it runs better you got it! also try spraying the wire inside the air flow area with brakleen ( DO NOT USE CARB CLEANER!! TRUST ME DO NOT!! ) and it sometimes cleans it up, carbon builds up on the wire and the ECU cannot sense the air flowing past it. MAF's work by heating up a wire (hot wire MAF) and looking at the voltage drop across it to keep it at a constant temp, as the voltage drop changes the ECU computes this to a different air flow number. so try those, they may be the issue. always do the tune up stuff first, but don't throw a high priced pump at it unless you diagnos it. If you think it is the pump, do a fuel pressure gauge on the fuel rail, the try a fuel volume test, it should put out at least 1 pint in 30 seconds and have at least 40psi running pressure. hope all goes well.

TOYS RULE BABY!

I know what your saying as im in an advanced course at a particular school and own a 94 tercel. These cars, 91-94 ,use a MAP sensor setup. Ive had similar problems and after replacing the fuel filter the problem was gone. Toyota says they're a lifetime filter but those in the know know thats bulls**t.

[piggyfinndude]

So the 91-94's don't have a MAF sensor? I see in my Hayne's manual that there is something called an air intake temp. sensor, but from the pic it looks like it's only on the carb. models of ther tercel....true??

Thanks!

[piggyfinndude]

oh yeah and would a bad fuel filter cause an interrmitent bad idle problem or would that be a constant?

I've got to check into that wire that Kene was talking about...it seems to make sense.

[kene]

also the air intake temp sensor is also on the tercel/paseos from 91+...i haven't looked into the carbed models.

[piggyfinndude]

Do you know the exact location of this sensor? I can only see where it is located on the carbed. models of the tercels....Where would it be located on the intake of the EFI models?

Thanks so much!!

[kene]

on the EFI model it is plugged into the air filter box. its black plastic about 2.5 inches long and has 2 wires running from it.