This will probably be a long post- trying get as much info to you guys as I can- thanks!
I have an SR with a decent build
-gt28r
-big intercooler
- isis Intake
- 740cc injectors (red)
-SplitFire Coils w/ new plugs.
145+ psi in all cylinders
(Not sure of upgraded cams/pistons)
3in turbo back straight pipe.
Isis radiator W/ 2 fans
Electronics-- Apexi fc tuner w/ commander. Apexi electro boost solenoid. Running off a MAP system. Wide band + boost gauge.

I've done a lot of maintenance on this car since I purchased it. Fluids all round, gaskets from iaac to down pipe. Nothing within the engine though. New turbo and oil/fuel/ vac lines. (I like to maintain, especially a worked/beat vehicle)--enough ramble--

Car starts (cold start) and hovers around 2k then blips up and down until 1100 +- at operating temp. When I switch my fans on she's goes to 900-1000. Give her a tap of gas and she drops down around 700 rpm and then catches herself and goes back up.
-Gauges
-- 21~22 vacc
-- a/f 14.7~.8
--boost gauge works as it should
Now! While driving, she takes off fine minus the slight decline in rpm's at initial throttle. Goes through gears fine. My main issue is when I'm cruising at whatever boost I set, it will reach that number and I can hold it steady at 10-21 lbs and when I try and give it just a tad more gas she hits a wall, bucks sooo hard. It's like fuel cutoff cause there's power then absolutely nothing(extreme buck) then back to power. The power loss I'd say is about .5 of a second. Now with my A/F ratio it is ALWAYS at 14.7~.8 (at idle too full boost) it never changes. And after the bucking(granted- I DO NOT keep forcing my engine to go into that motion, just when I know when it's gonna happen and when I give a touch more gas) she's goes back down to idle fine.

After going through test drives and minor tweaks I have some important questions- I took out my o2 sensors one day and of course they were black, I cleaned them off with brake cleaner and through them back in, checked plugs and they burn PERFECT(gapped at .028) I turn the car back on and she fires right up (cold start) and stays strong at 2k with no blips at all, and then drops down at operating temp. Tap on the gas and she just goes up! No drop in rpm or stumble. BUT! Same issue happens when I hit my peak boost(extreme buck)

One more Q. Since I have an electro boost solenoid with mechanical waste gate. My theory is when the computer reads the pressure it's building (whatever the boost psi is set too) then it reaches that level it tells the solenoid to open and that goes straight to the waste gate and she fires right open- with this theory is that the reason I'm getting the extreme buck? I haven't determined what rpm it happens at because it only happens when it reaches the set boost pressure. Now I can drive the car fine when I pay attention to the boost gauge. Shifting right before the peak boost number. Decel situations are fine and normal- I do get a couple back fire pops/flames-- o2 sensor issue? But otherwise she drives awesome!! * apparently the car has been tuned from previous owner at AP tuning in PA. Rated too 313hp at 15.75 boost. I would LOVE to experience the car at it's full potential. In the coming months I'm saving g up to bring it to a tuner (Texas area- hour south Of Houston) to get her checked out. But I figured I'd drop some info at this forum too see if I can get some additional help. I've searched the internet and forums all over and I haven't found anything close to what I'm experiencing- things I've come across as possible issues from other ppls issues -- coil packs/plugs/ o2 sensors/timing/vacc leaks/etc etc. I've gone through the car a lot. I know my BEST bet is to bring it to a tuner and have them go through it
*ive brought it to a tuner back home in New York, but I had a horrible experience- wasted money with no results and a months worth of waiting for answers- wasn't impressed one damn bit!
-- told you it was gonna be a long one. Thanks for your time and I would appreciate some honest important advice/tips

This is my first turbo'd car, I wish it had a carburetor
Cheers
-Rusty

I have a Walbro 255 pump as well- forgot that
Cheers!

Sounds a lot like a boost leak. Whenever I see/hear "bucking" that is usually what it is.

Check your couplings and make sure your BOV is not leaking. It's usually the LAST coupling you check, the one you KNOW cannot possibly be bad. BAM! One inch tear right thru it, in my case.

i will re-check all my connections.
funny you should mention the bov-- my Tial setup does remain slightly open at idle- i believe i may need a stiffer spring according to my in. hg. reading. i may shim it with washers just to test it out, but I've read a lot on forums across the board about open or closed. once i do press the gas pedal it does shut quickly however.

do you or anyone else have an explanation for the a/f ratio staying the same from idle to full boost / buck? I've watched a good amount of videos and read on other forums that the mixture should become "richer" as you pick up speed, but like i mentioned in the previous post that it ALWAYS remains the same. 14.7 is good, but even at higher revs??

thanks for the reply again--
i noticed your from PK? i just moved from there down south to texas about 2+ months ago-- small world haha

I'm thinking of moving to TX too - screw NY with their useless new knee-jerk BS gun control laws that only penalize honest citizens.

I would definitely fix the BOV so it doesn't leak at idle. I've luckily never had to analyze AFR readings so I can't be much help there.

I do apologize for a late response- I've fixed a few more things with the car(bov opening, new vac line, and some electrical) but I wanted to bring up the boost leak theory-- I find it hard to believe that it is a boost leak, I've checked my connections again, but the fact I can set the peak boost to whatever I'd like-- say I set to 10lbs and it will buck/cut off then, BUT I can set to almost 20lbs and it will achieve that number(while passing 10) and then buck/cutoff. So I can still go over 10lbs- so wouldn't that rule out a boost leak? I've been doing research into the timing as well(retard/advanced) and that seems to be a "common" issue with a "fuel cut off/buck" scenario. I have to check my timing to make sure.

I'll chime in after working the car in the next couple days!

blkvrtswp wrote:I'm thinking of moving to TX too - screw NY with their useless new knee-jerk BS gun control laws that only penalize honest citizens.

I would definitely fix the BOV so it doesn't leak at idle. I've luckily never had to analyze AFR readings so I can't be much help there.

Last time a bought a case of ammo was before the new laws and went with cash and the horrible thought of Obama knocking on my door demanding my guns--haha