Hesitation, MAF, AC, etc.

[McVeigh]

ok guys,
so i know that there is a lot of discussion on the SVX problem of hesitating when accelerating, then kicking in. people have reported that it happens when it is cold, too hot, from a stop or when the air conditioner is on. I was/am having this problem as well and suspect that it is the result of a few different things. I replaced the MAF a while ago and that nearly corrected the problem entirely, i would recomend it to everyone having those symptoms.

However, now i am having similar issues, but only when the air conditioner is on. can someone point me in the right direction on this one? i've searched the site and i know that the information is probably somewhere but can't seem to track it down.

so, once again does anyone have an answer to this problem or can give me some advice.

gotta love SVX quirks!!

[n00b on demand]

Sounds like the same problem ive been having although since my a/c got recharged and i put a K&N filter in the problem hasnt come back. http://www.subaru-svx.net/forum/show...ation+problems

[longassname]

The intermittent hessitation found in a non-broken SVX: Mass air flow meters are a little bit slow to register an inrush of air. This is just the nature of how they work (unless someone invents a better one) so engine management systems which use mass air meters also use throttle position sensors to overcome this shortcoming of the technology. The way it works is the ECU, the computer, measures if the throttle is pushed with the throttle position sensor and has a fuel enrichment table it uses with the voltage from the throttle position sensor to throw in extra fuel as soon as the pedal is pushed untill the mass air meter has time to register the air flow. The values in the table defining how much fuel to put in are averages of all conditions and sometimes will result in a lean condition and sometimes in a rich condition. When they result in a rich condition the ECU is able to detect that it can throw in more ignition advance and does so giving more torque, power, and all that good stuff that makes the car fast. When they result in a lean condition the ecu detects the precursors to detonation, pullls out a bunch of timing, and the car hessitates until everything gets worked out again and the car taks off like it should have to begin with.

If your are now suffering only from the typical intermittent hessitation that all drivers of stock SVXn suffer with then I suggest you get our ECUtune SVX Stage Iv4 package which will fix that and improve your acceleration. I say our because I'm the developer of the system and president of the company. There's a lot of information on our website www.ecutune.com and there is lot of information and are happy customers on these forums; poke around and see what they have to say. You seem interested in the workings and will probably enjoy the time spent.

Other things that might contribute to worsening the intermittent hessitation: An all too common worsening of the lean condition comes from leaks in the air hosing. That big, molded air hose isn't the easiest thing to work with and it has lots of hoses connecting to it. If it's not on right or there are any disconnected or broken hoses the engine will be able to injest air which hasn't been measured by the mass air meter. The resulting leaner condition will worsen the hessitation. I noticed you said your problem is worst with the ac on. The ac puts a load on the engine and the ecu uses another enrichment table whenever the ac is on. This table, like all enrichment tables, is a table of the best values for an average of all conditions and sometimes adds just the right amound of fuel, sometimes a little too much, and sometimes not quite enough. If you are dependably running not quite enough then there is something wrong. Possible causes would be a leak in the intake hose or broken vacuum line, coolant temperature sensor is incorrect, fuel pressure is low.

Originally Posted by McVeigh

ok guys,
so i know that there is a lot of discussion on the SVX problem of hesitating when accelerating, then kicking in. people have reported that it happens when it is cold, too hot, from a stop or when the air conditioner is on. I was/am having this problem as well and suspect that it is the result of a few different things. I replaced the MAF a while ago and that nearly corrected the problem entirely, i would recomend it to everyone having those symptoms.

However, now i am having similar issues, but only when the air conditioner is on. can someone point me in the right direction on this one? i've searched the site and i know that the information is probably somewhere but can't seem to track it down.

so, once again does anyone have an answer to this problem or can give me some advice.

gotta love SVX quirks!!

As i was reading your post, even before i saw Michael's reply, i was thinking "He needs ECUtune". I've recently installed it and it totally eliminates the low end hesitation. There is a chart on their website which makes it real easy to understand; the stock SVX is pretty much flat at the low end(Air/Fuel ratio) and the ECUtune solves the problem. An interesting side note: before i installed the ECUtune, i was getting 21.5 to 22.5 MPG; after installation the first two tanks were down to 19.5, then the next one was 23.7, and the most recent 23.4. Don't know if there's any correlation but i remember reading that the module continues to 'learn' for a while after it's been installed. Altogether a wonderful accessory, every SVX should have one. Marc

[ssnsltd]

The ECUTune Stage one took care of my 95' issues. It is a great product.
I just wish I could figure out a how to stop the hesitation in my 96'. I have already cleaned and or replaced the MAF and vacuum lines. It made some difference, but nothing like the ECUTune.

[McVeigh]

very interesting michael. the product looks solid and has gotten some good reviews. do i need to purchase the v4 update, or does it come with the unit? also how difficult is it to install? i do most all my SVX maintinance, but am not expecially great with electrical, but i can get by.

i'll start by checking all the vacuum lines etc. . . but i think i'll install the ECUtune product anyway.

thanks again everyone. i love this site.

[longassname]

Originally Posted by McVeigh

very interesting michael. the product looks solid and has gotten some good reviews. do i need to purchase the v4 update, or does it come with the unit? also how difficult is it to install? i do most all my SVX maintinance, but am not expecially great with electrical, but i can get by.

i'll start by checking all the vacuum lines etc. . . but i think i'll install the ECUtune product anyway.

thanks again everyone. i love this site.

No, v4 is our current revision and that is what all orders have been shipping with since we came out with it. The installation instructions are on our website and are very detailed; if you look those over you'll know exactly what you are looking at--it's easy.

[svxcuseme]

Could this fix my problem?

I'm suffering from similar hesitation with RPM's lower then 2000, under load, uphil, etc. I've tried replacing many parts to remedy this situation but I'm leaning now towards air/fuel mixture. The car even occasionally bucks. I'm also annoyed by the rev limiter that kicks in around 5000 rpms, sometimes 4500.

Can you describe the behavior of the hesitation the chip addresses? Will it remove the rev limiter?