Bogging and detonation issues!

[spooled240]

I was driving home last night and I noticed a weird noise coming from under my hood at 13 psi of boost. It sounded like a heat shield or something rattling loudly. And this only happened at 13 psi of boost, at 10 psi and under, it was smooth and silent. At high rpms and full boost(10 psi) the car doesn't pull as hard as it used and and feels weird as if something is holding it back.

I've had some bogging issues under high/moderate load prior to this for about a few weeks now. Lately, it seems to have gone away but now it seems to be coming back. The car is fine during daily driving in vacuum but when I'm at full boost or high rpms, the engine seems to be experiencing a fuel starvation.

I just installed a brand new Walbro Fuel Pump a month ago and it seemed to have worked perfect before this whole problem came up. So I think it has something to do with the MAFS or a bad 02 sensor(s). I have the mafs on my cold-pipe for the blow-through setup for about 2 years now. My question is, could a bad mafs or a bad 02 sensor cause a lean condition?

[480sx]

A bad maf i dont think would cause this situation. If your maf is on the way out, you may notice a stumbling at around 2500-3000, or a CEL heh. You can still do a simple maf voltage check to rule it out, a FSM has the directions. Heck you dont really even need a FSM you can just bust out a multi meter and use your head to figure out if its working right, real easy to do solo.

The o2 sensor, not a chance. Under moderate or heavy load, the ECU is in open loop and ignoring the O2 sensor data.

Did you note any significant temperature changes when you were having the problem Vs when you wernt?

The fact that its happening under moderate load too leads me to believe its a fueling issue. As far as testing that, well, its not the easiest thing to set up to diagnose your issue.

Rule out all other culprits first. Good plugs, good wires? Rotor, cap, fuel filter? Check your spark plugs and read them, see if you find any differences from cylinder to cylinder. What about your injectors? Sure its not just a bad batch of gas?

Do you have a WBO2? :/ That would really be some good info to have. You might want to invest in a dyno session. What you need to do, is rig up a fuel pressure gauge to your fueling system. Have the dyno operator run the dyno and watch your fuel pressure as he does. That will let you know if your pump is doing what its supposed to, and what your AFR's are.

I wouldnt boost more than 10 until you figure this out. Wouldnt boost much at all really.

[spooled240]

trust me, boost is strictly off-limits until i get this figured out.

The things that sort of rule out the possibility of a bad mafs or a bad O2 sensor is that DD is perfect/normal still. Just when I floor it at low rpms or boost is when the problems arise.

My ignition is stock but I don't think that is the problem because my engine runs fine under normal driving and low boost. I am 90% sure it is fuel related =/

My injectors are nismo's i bought brand new, I changed my fuel filter about year and a half ago and I always use Shell (sometimes chevron)

I dyno'd my car not too long ago but it was before I had these issues. AFR's stayed around 13 on boost. No wideband at the moment tho =/

I'm starting to think this has something to do with this Walbro pump I just installed about 1 month ago. Just driving home right now on 1/8th tank of gas I can hear my fuel pump speed up and whine whenever I brake as if the gas is sloshing around in my tank and the pump is running dry with no load and speeds up. Maybe the pump is smoked, who knows?

[240sxvaj]

I dyno'd my car not too long ago but it was before I had these issues. AFR's stayed around 13 on boost. No wideband at the moment tho =/

I'm starting to think this has something to do with this Walbro pump I just installed about 1 month ago. Just driving home right now on 1/8th tank of gas I can hear my fuel pump speed up and whine whenever I brake as if the gas is sloshing around in my tank and the pump is running dry with no load and speeds up. Maybe the pump is smoked, who knows?

isnt boost afr should be high 11's to low 12's to be safe? well if you can hear the pump prime then most likely you have a bad pump or a fuelpressure regulator. have you ever upgraded your fpr? my stock fpr lasted me about 2 weeks after i installed walbro fuel pump, the car would stall out once in a while and started gettting worse every week until it died on me leaving me stranded on side of freeway. i would hear the fuel pump prime right after the car stalls out.

get a fuel pressure gauge and check for readings, while on idle and look at it after your shut off the car and see if it dropps down really fast.

So first thing is if you havent upgraded fpr then get that first and you can move on to the next thing. GL

[spooled240]

i have the stock FPR. Wouldn't a bad regulator fail to keep the fuel pressure under control though? A bad regulator would probably allow the fuel pressure to increase and flood/stall your engine. I'm having the exact opposite, not enough fuel.

[240sxvaj]

i have the stock FPR. Wouldn't a bad regulator fail to keep the fuel pressure under control though? A bad regulator would probably allow the fuel pressure to increase and flood/stall your engine. I'm having the exact opposite, not enough fuel.

Yes, a bad fpr will cause it to flood and stall out. it will cause your car to feel like you have a boost leak when you give it a certain amount of gas. i remember when i give it gas it started to feel like it was stumbling and then it stalls out. Also, how do you know if you dont have enough fuel when you dont have a fuel pressure gauge and wideband? when my fpr was bad i would hear my fuel pump prime a lot. stock fpr werent made to handle the extra fuel pressure so even if that wasnt your issue, i recommend you getting something like aeromotive.

[spooled240]

well my engine was pinging under boost so it's not getting enough gas. I had a kill switch to my fuel pump fuse before and the the switch started to go out, the fuel pump would cut out momentarily from time to time while driving. It felt like I was running out of gas, and this problem feels the same way.

It kinda weird, when it first happened, I could floor it at all even at 1500 rpms or it would hesitate and bog. It's gotten better but it seems like the problem is just kicking in at high loads (high rpm, high boost or both)

I think there is something stupid going on, maybe with a hose connection or how the walbro is mounted.

[480sx]

Well you really should have a 1:1 performance FPR for a high flow pump. Your fuel pressure is pretty inconsistent with a stock one and the Walbro, iv checked it it spikes and does all kinds of crap you dont want it to do. Never to LOW though, unless its failing. I have heard rumors that the 255 will kill a stock FPR given time, but you'v ran it for 2 years so.. idk.

As far as your 1/8th tank thing goes? Thats just how the walbro works. You really cant run your gas lower than 1/8th a tank or it sucks up air and will kill the pump given time.

[spooled240]

ive only had the pump for about a month. For the past two years I've been running the stock fuel pump. Since I have a shortage of fuel going into my engine, chances are it's not my fpr right?

[Razi]

My car used to freak out once in a while under boost, then I got my timing dialed in and got a new distributor cap and it helped a bit

Now it feels like it's holding back, and it happens randomly because sometimes it pulls just fine.Weird...

[spooled240]

did you change your wires? that may help a bit. I'm gonna check my walbro pump again, my timing and i might just change my dist cap, rotor, and wires. But I must find the problem to this fuel shortage, i can't even think at school

[Razi]

No, my wires are stock I think.Blah, don't feel like spending 60 bucks on wires.

Tell me if replacing all that fixes your problems.

[spooled240]

so i pulled the pump out and I noticed the strainer broke off. So I found it at the bottom of the tank, put it back on and threw the pump back in.

Took it for a test drive and I can't go WOT, boost or rev out the engine at half throttle without it bogging. The problem just got worse and the car is barely suitable for daily driving =/ i'm fckin pissed, idk what the hell is goin on.

[480sx]

Could have sucked crap up through the pump and roached it. Made sure you have a good strong flow of fuel coming from the filter?

Also, did you make sure the strainer was going to stay on this time? heh

[spooled240]

oh yeah i zip tied it on so it was going nowhere. Idk, maybe the pump got roasted.

I threw my stock pump back in and it runs good now. I did hear the "rattling" sound under my hood when the boost spiked to 13 psi again tho =/ idk maybe i need a new fuel filter or something

I decided to get some gauges next. AEM wideband, Oil pressure and Volts. The wideband will be really useful with these fuel problems.

Anyways, I get more boost when I drive down to school since the elevation is a lot lower and i'll see if I hear that sound again.

[kouki_hmongster]

oh yeah i zip tied it on so it was going nowhere. Idk, maybe the pump got roasted.

I threw my stock pump back in and it runs good now. I did hear the "rattling" sound under my hood when the boost spiked to 13 psi again tho =/ idk maybe i need a new fuel filter or something

I decided to get some gauges next. AEM wideband, Oil pressure and Volts. The wideband will be really useful with these fuel problems.

Anyways, I get more boost when I drive down to school since the elevation is a lot lower and i'll see if I hear that sound again.

yes a wideband is a must, also get a fuel pressure gauge. That sound could be detonation. Detonation sounds more like marbles in a can. Go z32 fuel filter and aftermarket fpr is a must. Installing the filter for walbro can be a bit tricky. Goooood luck

[D-UNIT]

A local shop over here got a bad batch of walbros three months ago. They sold like 12 of them and they all died within 2 months.

[spooled240]

how loud would pre-detonation be at 12-13 psi? The wierd "rattling metal" is still around when i'm boosting around 12-13 psi. But it's not really loud, just noticeable.

I'm wondering if my fuel filter got a little clogged with some garbage when the walbro was without the strainer.

I think my ignition may need some attention also. My car sounds a little like a suby when I take off but there's no hesitation or anything...it feels pretty smooth actually.

The world of ka-t, it's like having a high maintenance girlfriend. Oh what could be wrong THIS time lol

[kouki_hmongster]

SOunding like a suby? hummm... that reminds me the time when my bro installed new injectors and didnt plug one injector harness in. it was running on 3cylinders. sounded baD @SSS, like a hot rod. still drove strong. maybe there is something in the filter or maybe even the fuel line. get a pressure gauge asap, and new fuel filter. i dont want to see another blown ka-t. especially if it's your daily baby.

[480sx]

You shouldnt be getting predet at 13 psi on a JWT tune. Id just pull your fuel filter and check it out. Again, a dyno run + a fuel pressure gauge would tell you a lot.

[spooled240]

oh yeah that's what i say. I've ran 14 psi daily with no problems. I'm hoping it's just a bad fuel filter.

I know some engines have a little cap off the fuel rail for the gauge hook-up, but I don't see anything like that on the ka. Does anyone know of a good place to hook up the gauge?

[Razi]

My car sounded like a suby when my sparkplug wire was loose on cylinder #1.Check your wires for spark and injectors.

Hope your KA gets all fixed up.

[WDRacing]

So far we have a host of potential issues. Just so I'm up to speed lets go over them.

No idea where your fuel pressure is under load.Stock FPR + 255lph pump.Sounds from underhood when under heavy load on boost.Bogging sometimes, detonating others.Don't know your AFRs.

Anything else?

Does it bog and detonate (making metal noise) at the same time?Pull the plugs, take a pic, post it.Check the wires, see if they are shorted or grounding out. I had an issue with mine.

WD

[KFL]

Compression test motor, pic of plugsMetal noise, check loose bolts,turbo shaft play, detoation high possibility Hopefully its something not too bad.

[spooled240]

So far we have a host of potential issues. Just so I'm up to speed lets go over them.

No idea where your fuel pressure is under load.Stock FPR + 255lph pump.Sounds from underhood when under heavy load on boost.Bogging sometimes, detonating others.Don't know your AFRs.

Anything else?

Does it bog and detonate (making metal noise) at the same time?Pull the plugs, take a pic, post it.Check the wires, see if they are shorted or grounding out. I had an issue with mine.

WD

haven't checked my fuel pressure or my AFR's yet.

I'm back on the stock fuel pump, I think the walbro took a dump on me after the little strainer broke off =/

The car doesn't bog at all anymore, in fact it feels pretty strong and exactly how it drove before I even d!ck around with this walbro pump swap.

There is still that "rattling heat shield" sound coming from under my hood at around 11+ psi of boost, it seems to get worse in the upper rpm range. I'm guessing it's a problem with the fuel flow. I figured i'd change the fuel filter since that was only thing keeping all of the tank debris from entering my engine. I'm gonna throw that in and see if that solves the problem.

[a240sxpinoy]

sup josh

remember i was telling you about my rattlin at high rpms?

it happened to be my stock fan hitting the radiator hose clamp

im guessing the high reving would move the motor just a little bit and hit the clamp. i moved the clamp and now everything is cool lol

hope all is well. lets meet up sometime

[spooled240]

sup dude, yeah i remember you telling me about that good thing it was an easy fix

I threw in a new 300zx fuel filter and that noise is still there, time to check my fuel pressure and AFR's

I think my car has developed a knock, I'm not 100% sure but it doesn't sound like an exhaust leak...it's like a higher pitch ticking noise that i can only really hear when i take off.

[esahuque]

my friend had a similar problem with the sound and bogging and he thought it was the upper timing chain tensioner. After inspecting his turbo we found out it was the turbo blades hitting the housing, so at high RPM's the blade would hit the housing and make a noise and it would also cause it to bog because it would slow down spinning. Check your turbo for shaft play and signs of scraping on the housing

[spooled240]

^ checked my turbo and there's no shaft play.

I did a compression test and i got 150 on the first 3 cylinders and 95 on the last cylinder

I also noticed my little oil catch container filled up with a little more oil than usual so i'm pretty sure the rings are shot on #4. I'm gonna test my fuel pressure next and go from there to try and fix whatever effed my engine up.

[esahuque]

damn dude sorry to hear that. I've read that you running a blow through set up but you don't have a wide band to monitor your A\F and lots of people (including me) have noticed that running blow through makes you run leaner. maybe you where running lean the whole time and it just caught up with you.
Modified by esahuque at 7:49 PM 4/23/2009