So I tried to search for some info on these items but archive searching is currently disabled (?) and none of the recent posts held any answers for me...

Anyway, I finally got my car up and running with VAFC and DSM 450's (long story), and I'm now experiencing some of the problems that others have mentioned in relation to running such large injectors and tuning them down with the VAFC.

1. Timing advanced into the stratosphere under boost. Is there anything that can be done about this other than just retarding the static timing way back? I'm pondering buying an MSD 6btm to maybe help with this, but it doesn't seem like it would do much good. Any other options in this case?

2. Part throttle bucking... way annoying in parking lots... sometimes it even manifests itself while cruising... I'll be driving along with my foot steady on the gas and the car will just buck a little and lose power. Is this what everyone is referring to when they talk about "part throttle bucking"? I suppose tuning should fix this somewhat, since it seems like there's a very defined line there where the fuel curve changes.

3. Hard starts... hard starts... hard starts... the car starts hard and idles incredibly low and rumbly for about 1 second then pops up to where it should be. Is there anything that can be done about this, or do I just live with it? What causes this? It seems almost like the injectors just take time to start pumping the correct amount of fuel in... I've tried a few things, including waiting until my fuel pump is completely primed, and waiting until my VAFC is completely initialized to start, but it still starts hard and idles the same for a short period until it becomes normal.

So, what do ya guys say? Are these things just things that I have to live with being that this is a "Hack"? Or are there some things that can be done to minimize them or aleviate them altogether?

Hopefully we can get some good knowledge flowing in here related to these things and figure out some work-arounds.

 

the ONLY way to get proper timing is to reburn the chip with corrected ign maps. BTM's and hsi just wont cut it.

 

Uber, is this because the BTM just doesn't retard enough to do the job, or is there some other reason? I guess with the BTM, the ECU still does it's thing with the timing advance, the BTM just cuts in after the ECU and before the distributor to tell it to back off a little when there's boost. What's the advantage going with remapped timing in the ECU over just cutting in like the BTM does and pulling the timing back when in boost?

I'm just trying to figure out the best route to take in my situation here. A BTM is tempting and I can get a good deal, but if it's not going to work at all for me with the VAFC hack, then it's not worth it.

 

2 main reasons. Your ecu's timign curve isnt linear, the btm is. The other big reason is the btm only BEGINS to advance when u enter boost. when i saw begin, i mean it wont reach full effect til you reach peak boost and even then it may nto be enuf. meanwhile u may be detonating on the highway while out of boost.

 

how bout apexi's ITC? will it help?

 

so will the itc cut it?

 

Ok, so now that we've covered timing... does anyone else have any comments regarding the other two issues I posted about?

In other words... BUMP.

 

for the hard starting problem..some people have it some people don't. most of the guys who use the 1g (blue top) injector doesn't have peoblems with it. it's not known why some behave like **** and some don't but age may be a factor. some switched to rc injetors and solved the problem with hard starting.

as for the part throttle bucking..i think it's inherent for the vafc hack. unless someone here has already solved it. hope they share it with us.

 

I am currently using the V-AFC hack. It idles pretty good. It is a bit jerky in Parking lots. And it seems to bog out a bit sometimes when i get on it. I have my FPR set at 40psi and my V-afc at -40 all the way across. It seems to idle best at that point. Timing is at -5 of stock. And i am running 8-9psi of boost.

Also, Sometimes when i drive my car for awhile then i stop it and start it back up after 10 minutes my idle will drop all the way down so that it almost dies. I think sometimes it does actually die.


[Modified by 95c1v1cs1, 1:52 PM 4/4/2003]