'98 Prizm stumble on acceleration

No MAF can be found. I looked through the factory manual set and there is no
mention of it. There is a MAP sensor on top of the throttle body, what I
think is the IAC idle air control, below that. In the air filter box the
only sensor is for air temperature. A small probe above the filter element.


"Ph@Boy" wrote in message

> Travis wrote:
> > '98 Prizm, 5spd, 100K. Pretty bad stumble whenever I try to accelerate,
> > regardless of initial speed. Idles fine, Runs fine at speed, throws no
> > codes. Replaced spark plugs, PCV valve, no change. Connected to OBD
computer
> > and data, like MAP, spark advance -- changes as you would expect under
> > acceleration. I have put some injector cleaner in the gas now but that
is a
> > stab in the dark. This is my daughters car so I only have a few days to
> > figure this out so I would appreciate some suggestions to pursue. I
can't
> > find an EGR valve on this vehicle, otherwise I would look there.
> >
> > Seems to me that when the vacuum drops, the problems begin, then
recovers as
> > load is reduced.
> >
> > Thank you in advance....
> >
> > Travis
> >
> >
> If you did not already, try cleaning the mass airflow sensor (hotwire).
> Use a spray contact/brake cleaner that does not leave any residue. Do
> not touch the sensor with your hands or use swabs, just spray it clean.
> That may help.
 >> Stay informed about: '98 Prizm stumble on acceleration 

"Travis" wrote in message

> '98 Prizm, 5spd, 100K. Pretty bad stumble whenever I try to accelerate,
> regardless of initial speed. Idles fine, Runs fine at speed, throws no
> codes. Replaced spark plugs, PCV valve, no change. Connected to OBD
> computer
> and data, like MAP, spark advance -- changes as you would expect under
> acceleration. I have put some injector cleaner in the gas now but that is
> a
> stab in the dark. This is my daughters car so I only have a few days to
> figure this out so I would appreciate some suggestions to pursue. I can't
> find an EGR valve on this vehicle, otherwise I would look there.
>
> Seems to me that when the vacuum drops, the problems begin, then recovers
> as
> load is reduced.
>
> Thank you in advance....
>
> Travis
>

Start with the basics.

Check the condition of the air filter.

Check to make sure there are no cracks, gaps, holes, etc. in the black
plastic snorkel between the air filter housing and the throttle body.

Check manifold vacuum to make sure there are not vacuum leaks.

Check the condition of the ignition wires.

--

Ray O
(correct punctuation to reply)
 >> Stay informed about: '98 Prizm stumble on acceleration 

I'm wondering if the Fuel Pressure Regulator is giving you fits. The
regulator is vacuum controlled, and when the vac drops (as when opening the
throttle) the fuel pressure should rise to support the rising demand of the
injectors. If the fuel pressure was slow to rise at the same time that the
injectors were calling for more fuel, the result would be a hesitation that
would go away when the demand was removed, and if the gas pedal was
depressed slowly, there may not be any hesitation at all.

What the regulator does is sends excess fuel back to the gas tank. The fuel
pump delivers a fixed amount of gas, but at low speeds (low demand) there is
extra fuel that goes back to the tank. When there is a sudden increase in
fuel demand, there is a resulting loss in vacuum -- an open throttle plate
will drop the vacuum -- which should close the regulator so that more fuel
is delivered to to the injectors to support the longer duty cycle that the
open throttle is going to create. If the regulator was slow to respond to
the change in vacuum, the result would be a momentary low fuel supply and
lots of air. After the regulator finally responds, the engine speed will
rise according to the throttle position and adequate fuel supply but in th
emean time, you will notice a hesitation that is not likely monitored by the
computer. You would have a hesitation and no code ...





"Travis" wrote in message

> No MAF can be found. I looked through the factory manual set and there is
> no
> mention of it. There is a MAP sensor on top of the throttle body, what I
> think is the IAC idle air control, below that. In the air filter box the
> only sensor is for air temperature. A small probe above the filter
> element.
>
>
> "Ph@Boy" wrote in message
>
>> Travis wrote:
>> > '98 Prizm, 5spd, 100K. Pretty bad stumble whenever I try to
>> > accelerate,
>> > regardless of initial speed. Idles fine, Runs fine at speed, throws no
>> > codes. Replaced spark plugs, PCV valve, no change. Connected to OBD
> computer
>> > and data, like MAP, spark advance -- changes as you would expect under
>> > acceleration. I have put some injector cleaner in the gas now but that
> is a
>> > stab in the dark. This is my daughters car so I only have a few days to
>> > figure this out so I would appreciate some suggestions to pursue. I
> can't
>> > find an EGR valve on this vehicle, otherwise I would look there.
>> >
>> > Seems to me that when the vacuum drops, the problems begin, then
> recovers as
>> > load is reduced.
>> >
>> > Thank you in advance....
>> >
>> > Travis
>> >
>> >
>> If you did not already, try cleaning the mass airflow sensor (hotwire).
>> Use a spray contact/brake cleaner that does not leave any residue. Do
>> not touch the sensor with your hands or use swabs, just spray it clean.
>> That may help.
>
>
 >> Stay informed about: '98 Prizm stumble on acceleration 

Jeff,
I think that makes a lot of sense except on this model the pressure
regulator is part of the pump assembly in the tank and there is only one
line out to the fuel rail. There is no connection to engine vacuum as near
as I can tell. The pressure is not monitored by OBD and I do not have a
mechanical gauge to verify that the PSI is being maintained.

Thanks, Travis

"Jeff Strickland" wrote in message

> I'm wondering if the Fuel Pressure Regulator is giving you fits. The
> regulator is vacuum controlled, and when the vac drops (as when opening
the
> throttle) the fuel pressure should rise to support the rising demand of
the
> injectors. If the fuel pressure was slow to rise at the same time that the
> injectors were calling for more fuel, the result would be a hesitation
that
> would go away when the demand was removed, and if the gas pedal was
> depressed slowly, there may not be any hesitation at all.
>
> What the regulator does is sends excess fuel back to the gas tank. The
fuel
> pump delivers a fixed amount of gas, but at low speeds (low demand) there
is
> extra fuel that goes back to the tank. When there is a sudden increase in
> fuel demand, there is a resulting loss in vacuum -- an open throttle plate
> will drop the vacuum -- which should close the regulator so that more fuel
> is delivered to to the injectors to support the longer duty cycle that the
> open throttle is going to create. If the regulator was slow to respond to
> the change in vacuum, the result would be a momentary low fuel supply and
> lots of air. After the regulator finally responds, the engine speed will
> rise according to the throttle position and adequate fuel supply but in th
> emean time, you will notice a hesitation that is not likely monitored by
the
> computer. You would have a hesitation and no code ...
>
>
>
>
>
> "Travis" wrote in message
>
> > No MAF can be found. I looked through the factory manual set and there
is
> > no
> > mention of it. There is a MAP sensor on top of the throttle body, what I
> > think is the IAC idle air control, below that. In the air filter box the
> > only sensor is for air temperature. A small probe above the filter
> > element.
> >
> >
> > "Ph@Boy" wrote in message
> >
> >> Travis wrote:
> >> > '98 Prizm, 5spd, 100K. Pretty bad stumble whenever I try to
> >> > accelerate,
> >> > regardless of initial speed. Idles fine, Runs fine at speed, throws
no
> >> > codes. Replaced spark plugs, PCV valve, no change. Connected to OBD
> > computer
> >> > and data, like MAP, spark advance -- changes as you would expect
under
> >> > acceleration. I have put some injector cleaner in the gas now but
that
> > is a
> >> > stab in the dark. This is my daughters car so I only have a few days
to
> >> > figure this out so I would appreciate some suggestions to pursue. I
> > can't
> >> > find an EGR valve on this vehicle, otherwise I would look there.
> >> >
> >> > Seems to me that when the vacuum drops, the problems begin, then
> > recovers as
> >> > load is reduced.
> >> >
> >> > Thank you in advance....
> >> >
> >> > Travis
> >> >
> >> >
> >> If you did not already, try cleaning the mass airflow sensor (hotwire).
> >> Use a spray contact/brake cleaner that does not leave any residue. Do
> >> not touch the sensor with your hands or use swabs, just spray it clean.
> >> That may help.
> >
> >
>
 >> Stay informed about: '98 Prizm stumble on acceleration 

OK, Basics -- spark plugs -- I had the old NGK originals that I replaced
several years ago with Autolite "equivalents". The stumble seems much
reduced after regapping the old NGK's and putting them back in. I think I
will go to the local parts store tomorrow to find Denso or NGK's.

Thanks, Travis

"Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message

>
> "Travis" wrote in message
>
> > '98 Prizm, 5spd, 100K. Pretty bad stumble whenever I try to accelerate,
> > regardless of initial speed. Idles fine, Runs fine at speed, throws no
> > codes. Replaced spark plugs, PCV valve, no change. Connected to OBD
> > computer
> > and data, like MAP, spark advance -- changes as you would expect under
> > acceleration. I have put some injector cleaner in the gas now but that
is
> > a
> > stab in the dark. This is my daughters car so I only have a few days to
> > figure this out so I would appreciate some suggestions to pursue. I
can't
> > find an EGR valve on this vehicle, otherwise I would look there.
> >
> > Seems to me that when the vacuum drops, the problems begin, then
recovers
> > as
> > load is reduced.
> >
> > Thank you in advance....
> >
> > Travis
> >
>
> Start with the basics.
>
> Check the condition of the air filter.
>
> Check to make sure there are no cracks, gaps, holes, etc. in the black
> plastic snorkel between the air filter housing and the throttle body.
>
> Check manifold vacuum to make sure there are not vacuum leaks.
>
> Check the condition of the ignition wires.
>
> --
>
> Ray O
> (correct punctuation to reply)
>
>
 >> Stay informed about: '98 Prizm stumble on acceleration 

"Travis" wrote in message

> OK, Basics -- spark plugs -- I had the old NGK originals that I replaced
> several years ago with Autolite "equivalents". The stumble seems much
> reduced after regapping the old NGK's and putting them back in. I think I
> will go to the local parts store tomorrow to find Denso or NGK's.
>
> Thanks, Travis

Let us know how you make out!

--

Ray O
(correct punctuation to reply)
 >> Stay informed about: '98 Prizm stumble on acceleration 

On Sun, 07 Oct 2007 18:38:37 -0400, Travis wrote:

> Jeff,
> I think that makes a lot of sense except on this model the pressure
> regulator is part of the pump assembly in the tank and there is only one
> line out to the fuel rail. There is no connection to engine vacuum as near
> as I can tell. The pressure is not monitored by OBD and I do not have a
> mechanical gauge to verify that the PSI is being maintained.
>
> Thanks, Travis

Take the cheap way out. On an '85 Toyota truck and a '90 240SX that had
this problem I found the fuel filters were full of mud. Low speed
acceleration was OK on the 240 SX, but low speed and high speed
acceleration on the truck was horrible, and high speed acceleration on the
SX was pretty bad.




>
> "Jeff Strickland" wrote in message
>
>> I'm wondering if the Fuel Pressure Regulator is giving you fits. The
>> regulator is vacuum controlled, and when the vac drops (as when opening
> the
>> throttle) the fuel pressure should rise to support the rising demand of
> the
>> injectors. If the fuel pressure was slow to rise at the same time that
>> the injectors were calling for more fuel, the result would be a
>> hesitation
> that
>> would go away when the demand was removed, and if the gas pedal was
>> depressed slowly, there may not be any hesitation at all.
>>
>> What the regulator does is sends excess fuel back to the gas tank. The
> fuel
>> pump delivers a fixed amount of gas, but at low speeds (low demand)
>> there
> is
>> extra fuel that goes back to the tank. When there is a sudden increase
>> in fuel demand, there is a resulting loss in vacuum -- an open throttle
>> plate will drop the vacuum -- which should close the regulator so that
>> more fuel is delivered to to the injectors to support the longer duty
>> cycle that the open throttle is going to create. If the regulator was
>> slow to respond to the change in vacuum, the result would be a momentary
>> low fuel supply and lots of air. After the regulator finally responds,
>> the engine speed will rise according to the throttle position and
>> adequate fuel supply but in th emean time, you will notice a hesitation
>> that is not likely monitored by
> the
>> computer. You would have a hesitation and no code ...
>>
>>
>>
>>
>>
>> "Travis" wrote in message
>>
>> > No MAF can be found. I looked through the factory manual set and there
> is
>> > no
>> > mention of it. There is a MAP sensor on top of the throttle body, what
>> > I think is the IAC idle air control, below that. In the air filter box
>> > the only sensor is for air temperature. A small probe above the filter
>> > element.
>> >
>> >
>> > "Ph@Boy" wrote in message
>> >
>> >> Travis wrote:
>> >> > '98 Prizm, 5spd, 100K. Pretty bad stumble whenever I try to
>> >> > accelerate,
>> >> > regardless of initial speed. Idles fine, Runs fine at speed, throws
> no
>> >> > codes. Replaced spark plugs, PCV valve, no change. Connected to OBD
>> > computer
>> >> > and data, like MAP, spark advance -- changes as you would expect
> under
>> >> > acceleration. I have put some injector cleaner in the gas now but
> that
>> > is a
>> >> > stab in the dark. This is my daughters car so I only have a few
>> >> > days
> to
>> >> > figure this out so I would appreciate some suggestions to pursue. I
>> > can't
>> >> > find an EGR valve on this vehicle, otherwise I would look there.
>> >> >
>> >> > Seems to me that when the vacuum drops, the problems begin, then
>> > recovers as
>> >> > load is reduced.
>> >> >
>> >> > Thank you in advance....
>> >> >
>> >> > Travis
>> >> >
>> >> >
>> >> If you did not already, try cleaning the mass airflow sensor
>> >> (hotwire). Use a spray contact/brake cleaner that does not leave any
>> >> residue. Do not touch the sensor with your hands or use swabs, just
>> >> spray it clean. That may help.
>> >
>> >
>> >
>>
 >> Stay informed about: '98 Prizm stumble on acceleration 

Well, I was disapointed this morning that the stumble was back and almost as
bad as ever. After thinking about this for awhile I worked out the problem.
It seemed to be related to the spark plugs but both sets perform about the
same. One of the plugs (#4) that I first removed had a curious black track
down the side of it. This plug was also a bit carbon fouled where the other
3 were lean-white. I looked hard at the plug wire connector that goes over
the #4 plug and there was a carbon arc line straight down the inside that
hugs the plug insulator. I scraped it with a pocket knife and the stumble is
gone. I will order a new wire set for good measure.

Thanks to all, for all the help and encouragement!
"Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message

>
> "Travis" wrote in message
>
> > OK, Basics -- spark plugs -- I had the old NGK originals that I replaced
> > several years ago with Autolite "equivalents". The stumble seems much
> > reduced after regapping the old NGK's and putting them back in. I think
I
> > will go to the local parts store tomorrow to find Denso or NGK's.
> >
> > Thanks, Travis
>
> Let us know how you make out!
>
> --
>
> Ray O
> (correct punctuation to reply)
>
>
 >> Stay informed about: '98 Prizm stumble on acceleration 

"Travis" wrote in message

> Well, I was disapointed this morning that the stumble was back and almost
> as
> bad as ever. After thinking about this for awhile I worked out the
> problem.
> It seemed to be related to the spark plugs but both sets perform about the
> same. One of the plugs (#4) that I first removed had a curious black
> track
> down the side of it. This plug was also a bit carbon fouled where the
> other
> 3 were lean-white. I looked hard at the plug wire connector that goes over
> the #4 plug and there was a carbon arc line straight down the inside that
> hugs the plug insulator. I scraped it with a pocket knife and the stumble
> is
> gone. I will order a new wire set for good measure.
>
> Thanks to all, for all the help and encouragement!

Thanks for the update! Stick to Denso ignition wires
--

Ray O
(correct punctuation to reply)
 >> Stay informed about: '98 Prizm stumble on acceleration