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Vengeance is mine
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907 Posts
Discussion Starter #1
Well here goes..before i get flamed I DID do a search and came up with nothing on this problem. I installed a vpc and safc2 today, my car is running stock twins, bpu with a 3row and about 20psi. The problem I'm having is that the car runs great through first and second gear, as soon as I try to boost in third it feels like the car is being "held" back, where second feels nice and crisp, third still pulls but feels like it is bogging down somewhat. I have tried leaning it out up to -8% on the afc with all the vpc knobs 12 o'clocked and it didn't really help. If i stay on the throttle the car sometimes will make a little "pop" (almost like a very weak backfire) if I keep the gas on after this as the rpms rise it will generally clear up a little as i get to around 6k+ rpm's. Anyone have any ideas about what it could be? I have tried all different settings on the afc from leaning out to rich (all adjustments made above 4k) and very small change between the two. The afc IS wired correctly and I have gone over all connections on the afc and vpc very carefully. The vpc map also is run to it's own vacuum source. Anyone have any ideas? In my opinion it almost feels as if the car is loading up between 4k and 6k in 3rd gear and above. I replaced the plugs with denso's gapped to .032 not very long ago, and also tried resetting the ecu this evening but it didnt help at all. Any help would be appreciated thanks.
 

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1,009 Posts
I suggest that you should not adjust the afc settings without having a wideband 02 in your car or unless you are on a dyno. Try to stay off the gas until you get it tuned on a dyno or you pick up a wideband kit so that you see how your afr is and tune from there.

carlo
 

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Vengeance is mine
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907 Posts
Discussion Starter #3
Well I based those settings off similar cars...I know it needs to be tuned with a wideband but it shouldn't stumble like that. And it doenst seem like a common problem people are having when first installing vpc's.
 

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boost is good
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772 Posts
what kinda denso's are you using? whenever you change plugs again, ide just swap them out for some ngk 3330's...they are cheap and work awsome..i used iridiums at one point and so did a friend of mine with a mr2 turbo and neither of us had any luck with them.

but anyways, ide also say you need to get on the car on a wideband to see whats going on...have you looked at the plugs since installing the vpc/afc? they might be getting fouled if you car is running really rich, which the vpc will do...also, you have the right chip in the vpc i assume? the stock one? (chip A i think)...ide suggest looking at your plugs, maybe try gapping them down a little but either way you need to get the car tuned with a wideband
 

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Vengeance is mine
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907 Posts
Discussion Starter #5
I have them gapped to .032 which worked fine at bpu. The plugs have less than 8k on them. But that is just a guess it is probably much less than that. I will try some 3330's but those plugs always gave me a rough idle and lasted only about 2k mi, I got then denso's hoping they would last longer. If it was the plugs wouldnt I have had that problem before the vpc? I'm running the same amount of boost and before the vc I had no trouble at all, the car ran perfectly fine.
 

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HKS T04Z & Vpro Equipped
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3,149 Posts
I had the same problem and then I switched plugs. I don't know how to describe it but my car would bogg out when I would get on it. Defintley change the spark plugs.
 

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boost is good
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772 Posts
macd7919 said:
I have them gapped to .032 which worked fine at bpu. The plugs have less than 8k on them. But that is just a guess it is probably much less than that. I will try some 3330's but those plugs always gave me a rough idle and lasted only about 2k mi, I got then denso's hoping they would last longer. If it was the plugs wouldnt I have had that problem before the vpc? I'm running the same amount of boost and before the vc I had no trouble at all, the car ran perfectly fine.
like i said before the vpc will tend to make the car run rich..which in turn builds up carbon on the plugs..and causes missing out...just take out your plugs and look at them.
 

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DONT HASSLE THE HOFF
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893 Posts
No doubt. I used to have to change my plugs twice as often as my oil.

A couple things to check, make sure the pressure sensor for the VPC nipple is facing down and make sure there are no kinks in the vacuum line connected to it (mine had a kink and caused some problems). It's most likely the plugs though so change them and see what happens.

gritsak said:
like i said before the vpc will tend to make the car run rich..which in turn builds up carbon on the plugs..and causes missing out...just take out your plugs and look at them.
 

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Vengeance is mine
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907 Posts
Discussion Starter #9
I took the plugs out and they looked fine, no carbon build up and not white either. Looked to be a nice clean burn. I tried to get some 3330's but no one had them in stock....I guess it could be the plugs but the one's I have are relatively new. I beleive they are denso double platinums, they were listed as a recommended plug for the supra and again I swapped from 3330's to these because the car went through 3330's quickly and these plugs idle much smoother and seem to last much better.( i had a set before trying 3330's) Thanks for the feedback guy's , any other help is welcome also.
 
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