Previa Fuel Problem?

September 15, 2008

I have a 91 previa 2.4L alltrac w/ 260k miles, and up until about 6 months ago it ran sweet!

It started out in the late winter, it would have a hard time starting on cold mornings, and when it did start (after almost draining the Battery from cranking it over) it would run rough for about a minute, and then clear up. This went on for awhile until it warmed up outside. In April I went through the whole rig and tuned it up rather well, new filters, cap, wires and plugs. About two weeks after the tune up, the so called cold start problem came back, and did it every time I started the vehicle. It would always clear up and drive smooth. Two weeks ago it started to do it all the time. When i drive it, it has no power, the whole engine vibrates, and you can smell fuel, or well......rich smelling exhaust. I have had over a dozen people telling me what the problem is, but I kind of don't like taking advice from people who think they know what they are talking about, but don't.

I am short of cash, and cannot afford a diagnostic test, so I was wondering if anyone knows what the situation might be, and then I can spend the cash I DO have on the problem itself. I am somewhat mechanically inclined and enjoy working on my Toyotas, so please if anyone knows about this issue, or a simple home test i can perform to locate the problem that would be freakin' sweet!!!

josh

September 15, 2008

So the real question is will you view the advice given here with the same skepticism as you have that given to you by the other 12 people :huh:

With any petrol engine you a require a mix of air/fuel in the right mix for any given load, a spark delivered at the correct time and of course compression. If you are looking for a quick cheap twist this, tap that and all will be ok answer you are not going to get it. Trying to diagnose a problem sight unseen is nigh on impossible one can only work from the symptoms.

As you seem to be running rich AND you claim to have done a "tune up" there are a few things to check.

1. Most importantly have the compressions checked. This at the outset will give an indication of the condition of the vehicle. It must be done on a hot engine and a compression tester can be bought from any auto spares shop. Use the screw in type.

2. There are a number of causes of an over rich mixture.

a. The computer is getting an overlean message from the lamda/oxygen sensor and is over compensating.

b. The cold start injector is leaking

c. The fuel rail pressure bypass is not working.

d. The breather in your fuel filler cap is blocked.

e. Leaking fuel injectors

f. Your throttle body is horribly carboned up (the most likely cause on these cars)

g. Your plugs are incorrectly gapped.

h. You ignition timing is way out (but you say you have done a tune up)

Not a cause but perhaps will produce similar symptoms

a. Your head gasket is starting to go. This will also be shown up from the compression test. a low reading between two adjacent cylinders is a good indication of this as too is loss of coolant and the car starting to run a bit hotter than normal.

One thing you can try (and this will only work if the fault is due to the computer having learned an erroneous profile) is to disconnect the EFI fuse for 20mins. This resets the ECU memory and allows it to relearn. A long shot but worth a try.

September 16, 2008

With any petrol engine you a require a mix of air/fuel in the right mix for any given load, a spark delivered at the correct time and of course compression. If you are looking for a quick cheap twist this, tap that and all will be ok answer you are not going to get it. Trying to diagnose a problem sight unseen is nigh on impossible one can only work from the symptoms.
As you seem to be running rich AND you claim to have done a "tune up" there are a few things to check.
1. Most importantly have the compressions checked. This at the outset will give an indication of the condition of the vehicle. It must be done on a hot engine and a compression tester can be bought from any auto spares shop. Use the screw in type.
2. There are a number of causes of an over rich mixture.
a. The computer is getting an overlean message from the lamda/oxygen sensor and is over compensating.
b. The cold start injector is leaking
c. The fuel rail pressure bypass is not working.
d. The breather in your fuel filler cap is blocked.
e. Leaking fuel injectors
f. Your throttle body is horribly carboned up (the most likely cause on these cars)
g. Your plugs are incorrectly gapped.
h. You ignition timing is way out (but you say you have done a tune up)

Could also have a problem with the coolant temperature sensor.

What you really need to do is see if the ECU has recorded any fault codes. If you open up the diagnostic socket cover (should be under the front passenger seat), join the Te (may be Te1) and E1 terminals together with a thin piece if wire (being careful to not damage the terminals), turn the key to the ignition position, and see what the check engine light flashes. It should either flash continually with no intermittant gaps, which indicates no fault found, or it should flash two digit codes.

These are for example, flashes 2x, short gap, 3x. Code 23. There should be a longer gap, then the same code flashes again, in which case, there is only one code, or it will flash a different code. Take note of all the codes, they will start repeating from the beginning of the code list.

Some of the codes might be from ages ago, and have nothing to do with the current problem. Clear the codes by disconnecting the Battery for a minute. Check the codes again before starting, to make sure the codes are clear, then start up a few times with the problem occuring and recheck the codes. That will bring up any codes that are currently present.

I'll find out what the code means for you, then see where we go from there...

September 16, 2008

Interestingly enough an error in the ECU is 99.9999% of the time coupled with an MIL illuminating. These cars are not like Nissan's that have a 50 start reset of an error code and as such once on the light will remain on until the problem is rectified. What's more the error codes on these cars can be erased by simply removing the EFI fuse for a minute, much easier than disconnecting the Battery and doesn't cause the alarm to go off unnecessarily or cause you to have to reset the clock :rolleyes: