4k problem 1 more time

[davidgt97]

Ok I'm still trying to diagnose my horrible 4k stutter problem. When I bought the car it was bone stock w/ a dejon intake. It had a stutter/miss when you hit 4k. I went ahead and bought it anyway thinking that it must be something minor and I would have it going in a couple of weeks. Long story short it's about 6 months later and the car has thousands of dollars in new parts and still runs like crap. When you drive the car it seems to drive fine up until you hit 4k rpms. It doesn't matter what gear you're in. I have also tried very lightly running the car up to 4k in 2nd and 3rd gear to see if it had the same issue w/ no boost. It does. At WOT the hesitation is more violent than if you run it up softly but never the less it won't hardly rev past 4500 rpms. The car gets 15 mpg and my less than 200 mile exhaust has black soot all around it (I'm guessing it is running rich.) Below is a list of new parts and everything I can think of that I've changed.

Kar King 6 bolt long block
MHI 16g evo3
stainless header and o2 housing
walbro 255
new o2 sensor
560 cc injectors (yeah I know bad idea w/ untuned car)
2 sets of plugs gapped at 28 and 2 sets of wires
swapped out coil pack
tried a Motoguy ECU and sent it back

I have a logger w/ MMCD. If anyone has any ideas PLEASE let me know. I'm stumped.

 

[absolute_DSM]

Youre tryin to run the wrong sized injectors on an 450cc size programmed ECU. Try throwing in 450s, get an AFPR on that rail, and go from there.

 

[davidgt97]

Oh yeah, I have done boost leak test after boost leak test. I get the same results whether I test at the turbo outlet hose or at the TB. It takes a little less than 2 min for the boost to leak from 20 psi to 0. I am thinking this problem is not boost related as it happens at 4k even under no boost.

 

[davidgt97]

I have a buddy at work making me a line for my afpr. When he gets it done I'll swap out the 560's and go from there. Thanks for the quick response.

 

[absolute_DSM]

Check your plugs now too. Running rich like that causes some issues.

 

[CHEVYTECH21]

sounds like running rich, smaller injectors and a tune couldnt hurt.

 

[kenamond]

If you have an automatic and auto-ECU, you'll need 390cc/min injectors. 1g guys correct me if I'm wrong.

 

[absolute_DSM]

If you have an automatic and auto-ECU, you'll need 390cc/min injectors. 1g guys correct me if I'm wrong.

Unless I misread his profile, hes a 5 speed. He lists a clutch as an upgrade.

 

[->PrOjEcTGS<-]

Definitely get an AFPR on that thing with the 255 pump. Also you need some sort of tuning device for those 560's. Looks like you already know that tho.

 

[davidgt97]

This morning I pulled the 560's and reinstalled the 450's. Who!! what a difference. It pulls smooth to about 4800 - 5k then has a little hesitation but pulls like a rocket from 6k to 7200(when I let off). I am still getting the line made today for the afpr. I might also get a new set of plugs as those are probably gummed up from running so rich. I didn't think going from 450's to 560's was going to be such a big deal. Shows what I know. I'll get the afpr on and come back w/ my results. Any ideas on the slight hesitation from 5k to 6k?

 

[davidgt97]

I put the afpr on this morning. I tried to adjust it to 37psi w/ the vac line off but it bounces around w/ the line off. W/ the line on at 37psi it make too much fuel. I drove it down the road and it felt like I had the 560's back in. Right now the fuel pressure is about 23 w/ the line on. Is this too low? The car seems to run pretty well although it's getting a little boost creep at about 5500. It holds a good 10 - 11psi until then and slowly spikes to 14.