Is it my fuel pump?

[99gs420a]

Ok so i have tryed searching on here but i cant find anything that is close to my problem. I have a 95 gst six bolt swap, 560cc injectors, evo 9 fuel pump, 16g, running on dsmlink speed density. My problem is when i go WOT at around 5100- red line the car makes this sputter likes its bogging out. it will be going just fine from 1000 rpm to 4900 rmp and then it starts, it looses most of its power after 5000, the car will just start to buck and sputter, i don't know any better way of describing it. I was thinking its my fuel pump cause this problem just started happening. any insight would be GREATLY appreciated .

 

[mondale]

Do you have a log that you can attach? What is the WB reading when this issue happens?
Wade

 

[ChiTownHussla]

Is it fuel cut maybe? Look it up

 

[jmye86]

I had a similar problem in my car, I did not have the same mods as you but my car would shutter and buck around 4500 - 5500 rpm. It ended up being my fpr, my car ended up throwing a cel but I would check your fpr. If you still have the stock fpr you will need to upgrade because of your bigger fuel pump and injectors.

 

[dsmgreddy]

Check the gap on those plus too,that very well could be your problem. We need more info...
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[99gs420a]

I will attach a log. im am using a 1g regulator and 1g rail, spark plugs are fine brand newish. This problem just started happening not to long ago. its also struggling to make boost, before all this the car would make boost right away and very strong but now it takes awhile and the boost gauge just rises very slowly.

 

[dsmgreddy]

Do a BLT, but very possible it's a problem with the pump. I had a similar problem with a fuel pump around that same rev range, tossed a new 255 in and the difference was night and day, might as well replace the fuel filter too since you'll already be playing with fuel.

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[97gst_spyder]

Did you ever re-wire the fp? That made a world of difference with my Evo 9 pump.

 

[dsmgreddy]

True, loss of voltage on the higher end could easily contribute to your problem.

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[gofer]

I can't look at your logs from work but has your car been tuned on your Speed Density setup, specifically your VE table?

When it starts bucking/misfiring are your AFR's going extremely rich?

If your AFR's peg rich its not a problem with your fuel system, odds are you've got a boost leak and hitting different VE cells on your SD map. Also go through the motions and replace your spark plugs making sure they're properly gapped for your setup once you fix the issue.

 

[lag monster]

i say start by doing a boost leak test.

 

[99gs420a]

First of all thanks for all the input. I did preform a blt last night it turns out my j pipe has a semi small hole in it so i made a new j pipe. my compressor broke on me last night so im wait to run over to a friends house and do some more investing. just to be on the safe side tho im also gonna order a 255 and rewire kit ( been wanting one anyways ). Gofer, my ve table has been tuned by RRE nothing crazy just a little street tune, It doesnt seem to be going really rich when the problem happens it just seems cut out, one thing i did notice when i looked at the log i posted and an old log is that around the same rpm the fuel flow is alot less, the old log showed 1090cc/min and when i had the new log it was something like 600cc/min. Also i have my mbc maxed out and its barley making any boost. but im gonna keep going at the boost leak test. Ill post results as soon as i find out.

 

[99gs420a]

Ok guys so i figured out what was wrong with the boost issue my wastegate control arm broke . but the bucking and stuttering problem still remains and is now happening at 4000. I ordered a walbro 255 with instal kit and rewire kit. So im pretty sure its the fuel pump. fpr is new and working fine