Acceleration Hesitates

[cmedrift240]

When accelerating quickly the motor seems to hesitate and sometimes backfire. Its around 3200 to 4500 rpms. The car will accelerate then when it hits those certain rpms the car seems to to backfire some and hestitae after each backfire; then when i reach past 4500 rpms the car is fine. Im thinking my injectors cant handle my Walboro Fuel Pump.

[Matt Cramer]

What kind of mods do you have? Sounds like your tuning is way off in that particular area. It's probably going too rich and not igniting in the cylinders, then the unburned mixture lights off in the exhaust.

It's very rare for a too large fuel pump to cause trouble, unless you are powering it with a wire too small or have a fuel pressure regulator so restrictive that the fuel pressure goes up. And in that case, you'd have the problems show up mostly at very low RPM.

[Slidin240Wayz]

Vaccuum Leak possibly. I would not push the car past the hesitation point because something can break.

Check- timing- fuel pressure- spark plugs- etc...

Carlos

[ledzeppelin240]

Throttle Position Sensor has a open or short???

[S14monkey]

Hi, I am having this same problem with my car. I was just wondering if this problem was solved.

Setup:
S14 w/ s14 sr20
walboro fuel pump
FMIC
Blitz bov
safc
apexi filter
z32 maf
along with a couple other things like down pipe and exaust.

I was driving the car, car was running fine, and then I let off the gas for a second. When I step on the gas again the car is hesitating. Car doesnt have as much power and has a lot of backfire. Hesitation occurs past 3k rpm.
I completed the swap less than a year ago and the car ran fine, a little rich but without any problems other than that.

I have already checked for boost leaks, and I was able to fix a couple. Now when I boost leak test i dont hear any leaks. I changed the oxygen sensor, I checked the resistance through all of the coils and all of them are good. I looked at the cas because I read the a dirty cas could cause hesitation, but mine looks clean...I am stumped. I want my car to run the way it was but I dont know where to go from here. What else should i look into?

[backroadtouge]

look at the spray you injector is shooting, might have a faulty one.

[Canpablo123]

I hava almost the same problem but my once it passed 3000rpm it hesita all the gears what can it be

[stevejames3]

yet another sr240 with the same problem.

as i was searching, i found this. its the same problem im having with mine. if i acelerate slowly and slowly go up in the r's its usually okay till about 4k. after that it stutters and makes a sounds like a muffled automatic gun out the exhaust, once past that it wound boost and kick some ass . but i was only pissed off enough to do it once. i have an oddesy bettery from HT.com or enjuku, and im only getting 12.1-12.3 volts on my SAFC2. im kinda wondering if its not enough or maybe grounds could be an issue. the hard part for me is not much on the motor(besides block and head) is stock. my setup is, gt2510,running 15-16lbs. 480cc(s15 blacktop inj) W255, z23maf, FMIC, z32 fuel filter. also my zietronix wideband doesnt fluctuate as much as my buddie aem, it seems hard to find it out of the 10.2 range(AT ANY TIME). sorry to hijack the thread but i think if one of us gets this problem it will help us all out.

heres what i think needs checked first(IMO):
1. check a dif. wideband on my car to see if mine is even reading properly
2. grounds
3. battery. (12.1-12.3 enought to run the ecu and everything under load?)
4. sparkplugs(did tonight, seemed fine, replaced anyways. gapped to 29)
5. coilpacks
6. boost/vacume leaks
7. bov. greddy sure messed up on those purple type s's. i dont know if im getting compressor surge or its the sound of the bov.

[S14monkey]

Hey,
I finally figured out what was wrong with my car. I pretty much read every single thread on zilvia that was related to my problem and tried every single solution on my car. It turns out that the very last one i tried was the one that solved my problem. Things that I tried:

Boost leak
O2 sensor
Timing
Sparkplugs
coilpacks- found #2 was cracked, swapped it, no change in hesitation
tps
cleaned cas
maf
grounded wire somewhere
battery
loose plugs

I even took every coupler off my car and spent time hunting for even the tiniest crack on one of them. Found nothing.

And then I found my solution:

I saw a thread that your coilpacks could crap out and not give any real indication that they are dead. Meaning, the car runs on all four cylinders and idles normally, but when accelerating the car backfires and stumbles under boost. So I started to swap out my coil packs one by one and it turns out that the very first coil pack that I swapped out was the one that was dead. Now the car runs like a champ!

sorry for the long winded post, but I have been dealing with this problem for months and I am unbelievably happy it works properly again.

Thanks to Luke for taking the time to try and help me diagnose my car on not one, but two different occasions.

[steve shadows]

to the original poster what is the condition of fuel and maf? stock or larger?

It sounds like some sort of issue with improper seen voltage from MAF, ie you wired up a Z maf and a AFC and did not select the right IN and OUT value in the MISC menu for sensor selection. should be 2 and 6 for Z maf iirc.

[MELLO*SOS]

Originally Posted by cmedrift240

When accelerating quickly the motor seems to hesitate and sometimes backfire. Its around 3200 to 4500 rpms. The car will accelerate then when it hits those certain rpms the car seems to to backfire some and hestitae after each backfire; then when i reach past 4500 rpms the car is fine. Im thinking my injectors cant handle my Walboro Fuel Pump.

Originally Posted by me in every other vague thread like this

What codes are stored in the ECU? If you have a code 34 for a knock sensor wiring problem it will pull spark timing from 3000 through 5000ish and run like shit.

You could start by pulling the codes off the ECU, that might point you in the right direction.

And yes your walbro could be overpowering your stock FPR causing some backfire, but probably not as bad as you're explaining it. To find out you would install a fuel pressure gauge in the fuel hose between the fuel filter and the fuel rail. You should have 43.5psi without the vac/boost line hooked up to the FPR.

Have you checked for vac/boost leaks?