"Dieseling" Concern- Carburetor knowledge required :)

Hi,

I've got a 90 Tercel that's got a severe "dieseling" problem (engine tries
to run despite the key being in the "engine off" position). The only thing
unique is the fact that it *only* occurs at normal operating temperature,
and the problem seems to be accompanied by acceleration-from-stop
problems, specifically, the car accelerates very slowly in the lower gears
and shakes like it's misfiring (again only at normal operating temp).

From what I understand, the usual suspects are:

*Carb choke/jet
*Fuel cut solenoid valve
*Incorrect ignition timing

I tried to perform a timing check, but I can't adjust the idling speed
down to 900 from 1100 (Toyota claims 900 is the maximum allowable speed
for a timing check). Other than that, all vacuum lines (and there are LOTS
of them) seem secure, the spark plugs are rich with fuel, the car gets
lower than expected mpg, and it's very difficult to get the engine to turn
over immediately after it diesels (though it will crank for a couple
minutes before it finally turns over, probably due to cooling down from
normal operating temp).

Any suggestions would be greatly appreciated, and I'll be watching this
topic with great interest. Thanks! :)

"Jemal" <Jemal@knowSpamn.com> wrote in message
news:d38c6afe19680ac5eca2e740aa9cd074@localhost.talkaboutautos.com...[color=blue]
> Hi,
>
> I've got a 90 Tercel that's got a severe "dieseling" problem (engine tries
> to run despite the key being in the "engine off" position). The only thing
> unique is the fact that it *only* occurs at normal operating temperature,
> and the problem seems to be accompanied by acceleration-from-stop
> problems, specifically, the car accelerates very slowly in the lower gears
> and shakes like it's misfiring (again only at normal operating temp).[/color]

Unfortunately, the carburetors on that vintage Tercel are a bear to work on.

It sound like the carb is running very rich. The misfire could be from
soaked spark plugs or cheap spark plugs. I recommend genuine Toyota
ignition parts.
[color=blue]
>
> From what I understand, the usual suspects are:
>
> *Carb choke/jet[/color]

See if the butterfly valve (choke) is in the open (mostly verticaly) or
closed (mostly horizontal) position when the problem is occuring. With the
engine warmed up, the butterfly valve should be open. If it it not, then
the choke pull-off might not be working or the linkage could be gummed up.

If the choke is open when this is happening then a jet may be leaking.

Check your air filter to make sure it is not clogged. To do this, shine a
light behind the filter element. If the light is dim when you look through
the paper, replace the air filter.
[color=blue]
> *Fuel cut solenoid valve[/color]

Since you have a problem when accelerating, I doubt if the fuel cut solenoid
is the main cause.
[color=blue]
> *Incorrect ignition timing[/color]

Incorrect ignition timing is not high on my list of suspect causes.
[color=blue]
>
> I tried to perform a timing check, but I can't adjust the idling speed
> down to 900 from 1100 (Toyota claims 900 is the maximum allowable speed
> for a timing check).[/color]

The idle speed is probably too high because there is too much fuel being
delivered to the engine.
--
Ray O
correct the return address punctuation to reply



Other than that, all vacuum lines (and there are LOTS[color=blue]
> of them) seem secure, the spark plugs are rich with fuel, the car gets
> lower than expected mpg, and it's very difficult to get the engine to turn
> over immediately after it diesels (though it will crank for a couple
> minutes before it finally turns over, probably due to cooling down from
> normal operating temp).
>
> Any suggestions would be greatly appreciated, and I'll be watching this
> topic with great interest. Thanks! :)
>[/color]

Thanks for your suggestions!

I think you're right about the carb running rich, but there doesn't seem
to be any obvious way to correct this problem. I can't adjust the mix
screw without drilling, and I'm having trouble with affecting the other
screws (perhaps the computer is countering my mods?).

I just put a new filter in a week ago, and the valves seem to be
operational, so a carb adjustment appears to be the solution. But like I
said, adjustments aren't working out for me. Do you have any suggestions?

THANKS ALOT!

"Jemal" <Jemal@knowSpamn.com> wrote in message
news:e887294cb9795ccc2e6f182c721caff8@localhost.talkaboutautos.com...[color=blue]
> Thanks for your suggestions!
>
> I think you're right about the carb running rich, but there doesn't seem
> to be any obvious way to correct this problem. I can't adjust the mix
> screw without drilling, and I'm having trouble with affecting the other
> screws (perhaps the computer is countering my mods?).
>
> I just put a new filter in a week ago, and the valves seem to be
> operational, so a carb adjustment appears to be the solution. But like I
> said, adjustments aren't working out for me. Do you have any suggestions?
>
> THANKS ALOT!
>[/color]
IIRC, you have an early 90's Tercel. If so, that car is a royal pain to
work on, and I do not recommend trying unless you have a factory repair
manual.

Use a vacuum gauge to check for vacuum leaks - you can rent one
inexpensively at an auto parts store.

You didn't mention whether the choke is open or closed. If it is stuck, use
some aerosol carb cleaner to free up the linkage. Also put in a can of fuel
injector cleaner in the tank and follow the directions.
--
Ray O
correct the return address punctuation to reply