'98 Prizm stumble on acceleration
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From: Travis on 7 Oct 2007 12:11 '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
From: Ph on 7 Oct 2007 13:36 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.
From: Travis on 7 Oct 2007 15:56 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(a)Boy" <user(a)example.net> wrote in message news:rsOdnfp1ItiyhJTanZ2dnUVZ_r7inZ2d(a)trueband.net... > 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.
From: Jeff Strickland on 7 Oct 2007 16:20 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" <travis4(a)adelphia.net> wrote in message news:470939d3$0$32484$4c368faf(a)roadrunner.com... > No MAF can be found. I looked through the factory manual set and there is > no > mention of it. There is a MAP sensor on top of the throttle body, what I > think is the IAC idle air control, below that. In the air filter box the > only sensor is for air temperature. A small probe above the filter > element. > > > "Ph(a)Boy" <user(a)example.net> wrote in message > news:rsOdnfp1ItiyhJTanZ2dnUVZ_r7inZ2d(a)trueband.net... >> Travis wrote: >> > '98 Prizm, 5spd, 100K. Pretty bad stumble whenever I try to >> > accelerate, >> > regardless of initial speed. Idles fine, Runs fine at speed, throws no >> > codes. Replaced spark plugs, PCV valve, no change. Connected to OBD > computer >> > and data, like MAP, spark advance -- changes as you would expect under >> > acceleration. I have put some injector cleaner in the gas now but that > is a >> > stab in the dark. This is my daughters car so I only have a few days to >> > figure this out so I would appreciate some suggestions to pursue. I > can't >> > find an EGR valve on this vehicle, otherwise I would look there. >> > >> > Seems to me that when the vacuum drops, the problems begin, then > recovers as >> > load is reduced. >> > >> > Thank you in advance.... >> > >> > Travis >> > >> > >> If you did not already, try cleaning the mass airflow sensor (hotwire). >> Use a spray contact/brake cleaner that does not leave any residue. Do >> not touch the sensor with your hands or use swabs, just spray it clean. >> That may help. > >
From: Travis on 7 Oct 2007 18:38
Jeff, I think that makes a lot of sense except on this model the pressure regulator is part of the pump assembly in the tank and there is only one line out to the fuel rail. There is no connection to engine vacuum as near as I can tell. The pressure is not monitored by OBD and I do not have a mechanical gauge to verify that the PSI is being maintained. Thanks, Travis "Jeff Strickland" <crwlr(a)verizon.net> wrote in message news:hcbOi.2317$ln.544(a)trnddc07... > 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" <travis4(a)adelphia.net> wrote in message > news:470939d3$0$32484$4c368faf(a)roadrunner.com... > > 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(a)Boy" <user(a)example.net> wrote in message > > news:rsOdnfp1ItiyhJTanZ2dnUVZ_r7inZ2d(a)trueband.net... > >> 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. > > > > > |