hesitation when pressing gas pedal

[THE NEW GUY]

Hi everybody. My SVX shows some hesitation when I press the gas pedal to change lane and pass somebody. This hesitation last 2 or 3 secs, after that, car pushes hard and show all the torque. Do yo think temperature going down may affect? Any ideas anybody? No CL. New air filter (K&N): no change.

[michael]

Try cleaning the mass airflow sensor and getting on oem air filter.

[THE NEW GUY]

news about this issue:
I´ve just verify that the hesitation is just until rpm´s get 2500rpm. from that point, the car push really hard. I suspect this is because of the firing advance.

[Sean486]

news about this issue:
I´ve just verify that the hesitation is just until rpm´s get 2500rpm. from that point, the car push really hard. I suspect this is because of the firing advance.

IS it a 92? It could be that it needs the old bead crush mode.

http://www.subaru-svx.net/forum/showthread.php?t=12740&highlight=bead+crush

[michael]

Check for ECU Codes too.

http://www.svx-iw.com/svxiw/article/print.php?article=78

btw: did anyone notice the first sentence in this doc? hint, transmission.

[THE NEW GUY]

I have no CEL on.
What is it "the old bead crush mode"?

[Crazy_pilot]

There is a noise suppression bead on the ECU circuit board. The SVX had a hesitation issue when it was first sold, and the factory fix was to take a pair of pliers and crush that little bead. There's a thread on it, and a How-To page.

[michael]

Sean posted a link ^^^^

[Sean486]

I have no CEL on.
What is it "the old bead crush mode"?

Sorry that was supposed to read "mod" not mode. Damn smart phone.

[david_12121]

it doesn't seem a problem they way you say it...mine is kinda the same
when you step on it in 4th, it can't push that hard so it waits to make sure you wanna go fast then downshifts and you'll be gone...process takes 1-2 secs!
it's just the way most automatics are...
again it might not be this but mine "hesitates" too!

[THE NEW GUY]

to David 12121: theres no kick down in the process... I´m in Power mode all the time. This hesitation is present in every gear but its more noticeable at 3rd or 4th or when cold, when you can feel almost three steps of torque improve before reaching the 2500rpm point, where it really pulls. When hot, only the 2500rpm piont is really noticeable. I would say its mapped on the chip...
to crazy pilot: so I have to remove the ECU, identify one resistor and crush it with a plier? is it the bead crush about? So I dont need to change the chip?

[michael]

Did you check to see if you have old codes stored? Sounds like you may have a sensor on it's way out.

[THE NEW GUY]

Did you check to see if you have old codes stored? Sounds like you may have a sensor on it's way out.

I did not have time to check stored codes but I did remove the throtle body and clean it deeply. bypass valve too. Control of iddle speed is way better now... but still hesitate. I've discard relations between hesitation and induction valve by confirming the operation of the induction valve in different moments of the hesitation. (vacuum meter connected to the induction solenoid). By the way, I've got to say that the induction valve does not activate the iris at speeds over 4200rpm's. As a matter of fact, the induction solenoid was activated only when the torque of the engine is very required at low rpms and stay on until you release the gas pedal or the engine reaches the exigency level demanded by the gas pedal. Tomorrow, I'll read stored codes and try to replace the O2 sensors.

[oab_au]

I did not have time to check stored codes but I did remove the throtle body and clean it deeply. bypass valve too. Control of iddle speed is way better now... but still hesitate. I've discard relations between hesitation and induction valve by confirming the operation of the induction valve in different moments of the hesitation. (vacuum meter connected to the induction solenoid). By the way, I've got to say that the induction valve does not activate the iris at speeds over 4200rpm's. As a matter of fact, the induction solenoid was activated only when the torque of the engine is very required at low rpms and stay on until you release the gas pedal or the engine reaches the exigency level demanded by the gas pedal. Tomorrow, I'll read stored codes and try to replace the O2 sensors.

The valve between the two halves is normally open, to close at 2200 rpms to form the Inertia system. This systems torque peaks at 3200 till at 4200 the valve opens to join the two halves together, to allow the Resonate system to take over, peaking the torque at 4800.

This system won't cause your problem.

Harvey.

[THE NEW GUY]

Ok guys. I should check stored codes before posting this.
I have the following codes:
32: copilot's O2 sensor
37: pilot's O2 sensor
28: pilot's knock sensor (but is new, bought in amazon))
14: injector 1
56: EGR valve (but I just replace the EGR plastic pneumatic valve and disassemble and clean all the system, and replace all the vacuum hoses)
23: MAF abnormal voltage

I'll change the O2 sensors this week... then I'll let you know.

[Tapani]

Check that the ECU connectors are fully pressed in. If that's not the problem, thoroughly check you wiring harness.

A bad MAF can do weird things.

Again, a diagnostic tool is your window to see what's really going on.

Tapani

[THE NEW GUY]

Looks like you was right again: When I install the MAF from my outback in the SVX , the SVX becomes furious again!

[Tapani]

There's link in this thread to "how to resolder the MAF".....

http://www.subaru-svx.net/forum/showthread.php?p=686756#post686756

Cured all my driveability problems..... and is an interesting exercise - and it's completely free !

If you swap a MAF from another vehicle be sure it is exactly the same type.

Tapani

[icingdeath88]

Looks like you was right again: When I install the MAF from my outback in the SVX , the SVX becomes furious again!

The outback MAF will function, meaning it will make the car driveable again, but you will lose a significant amount of power at higher RPMS, due to the MAF maxing out. You should try soldering the MAF, and if that doesn't work get another SVX MAF.

[Tapani]

If the MAF maxes out at a lower mass air flow (than expected) it will also make the car run pig rich - except maybe while in closed loop .... if the fuel trim can compensate. Right?

The ECU will see a higher than actual air flow under all conditions and will look for fuelling data at all wrong places :).

Get the right one or repair the one you have.

Tapani

[icingdeath88]

I think it will run lean at higher RPMs because it's getting more air than it's able to read?? I think it reads correctly, but it just can't read above a certain flow rate of air. But I'm not sure.

Closed loop might be alright.

[Tapani]

When I saturated mine (stock sensor) @ 5000 rpm I hit the fuel cut off.

If a non-original sensor saturates let's say at 4000 rpm, it will read 5V .... the ECU will think you're gulping air worth 250 hp and will fuel accordingly, eh :eek: ? I'd say rich.

Tapani

[icingdeath88]

When I saturated mine (stock sensor) @ 5000 rpm I hit the fuel cut off.

If a non-original sensor saturates let's say at 4000 rpm, it will read 5V .... the ECU will think you're gulping air worth 250 hp and will fuel accordingly, eh :eek: ? I'd say rich.

Tapani

Hmm, makes sense. I was thinking it wouldn't be able to make it read 5V, only like 4V for example, even if there's more air than that. Lean.

Sounds like you might be right though, that makes more sense.

[Tapani]

Well - dunno really, but I was able to see 4,8V with the ECUtuner just before the fuel cut off hit - and the serial link is not very fast.... thanks,

Tapani

[THE NEW GUY]

I can still feel some hesitation but I think it's the original performace of this engine with stock ecu chip and 87 octanes gasoline.
You all are rigth about the MAF readings: The outback MAF have a diameter reducer on the plastic mold right before the sensor. It speeds up the air flow so it is reading more air than before; but I think the O2 sensors are doing their work by reducing injection duty time. At high rpms, performance is noticeable poorer than before. I've never reach fuel cut off point with my SVX, so I don't know how the reading are but I can try reading voltage and check what rpms correspond to 5v with this outback MAF.
I insist: even if I make the mix richer wit the outback MAF the O2 sensors will tell the ecu to reduce the duty of the injectors and will compensate to keep stechiometry, rigth? Is this correction fast enought?
I'll resolder the SVX MAF tonight. Let see if I can post some pics.

[Tapani]

Fuelling is controlled by the O2 sensors while in closed loop, i.e. idle, cruise and low load acceleration. Stoichiometric AFR (14.7) is maintained to let the catalytic converters do their job, but are too lean under higher loads. This done by fixed maps and the O2 information is ignored.

Fix the MAF or get a correct replacement.

Tapani

[THE NEW GUY]

Tell me one thing: when in desaceleration, above the 1200rpm the injection is cutted. Does it happen when the transmission is in power mode or manual mode? or when the gear is located on any other position different than D?

[THE NEW GUY]

news on this case. on my way back home from work, in the middle of that rush hour trafic 5km/hr; hessitation came back very bad. Theres no stored codes on the ecu. Solder and clean the stock MAF, replace it and measure it: 1,204vdc at iddle and 4.943vdc maximum. Repeat the same with the outback MAF, install it on the SVX, repeat measures: exactly the same. I leave the original one on the SVX... Lets see tomorrow how it work at 24F in the morning.

[THE NEW GUY]

The way to my work this morning was OK but I can still feel like the engine were choking when traveling around 10mph and press the gas suddentlly and slightly. This hesitation last only 1 or 2 secs, enougth to loose the change to pass another car on the rush hour trafic. Once this happen, the car is ok for a while. No stored codes, no CEL, but the auto climate on. Any ideas?

[THE NEW GUY]

Ok fellows. I recently realize that this hesitations happens only when I'm stuck in traffic for more than 20 min. It was like if I were using the car in normal transmission mode, not in POWER. It was like if the transmission were taking too long to decide lower one gear. Then I remember that I never change the AT oil in this 6 months and I doubth that the girl before me where took that care to the car. So I decided to change the AT oil. I bought Mobil one syntetic ATF oil. I also prepared an "after cooler" for this oil and installed it between the water radiator and the AC condenser. (right were the power wheel coller is). The car is amazing now. I've never feel it like this. Very responsive and fast on the gear designation. No more hesitation.
So I think I had both, problems with the MAF (re-welding mod) and a very weared oil on the tranny.
I change the O2 sensors also in the process without any change. But you have to start somewhere!
I hope this experience wuold help someone.