Jump to content
SAU Community

Recommended Posts

With a doubt every single time I go to the petrol station and fill up with whatever amount I always get rough idling and my car backfires like crazy when I'm off the throttle.

I get rough idling from time to time but when I really notice it is on humid days. Sometimes my car just will not idle after I let go of the throttle, I would have to gently bring it to idle.

It is driving me nuts!!!

Belive me I have been under the hood checking for leaks, testing the electronics pulling apart and cleaning.. Im missing something...

But there is one thing I noticed. On my safc I noticed when my idle plays around my airflow readings is different instead of idling at 750 rpm with afm reading of 0.9 it would be 1.1-1.4 ... Im thinking maybe my afm is effected some how by humidity but if does not explain the filling up problem. My guess atm is maybe the fuel regulator or pump but I'm not going to spend $$$ on a hunch. Has anyone go any ideas...

btw my safc is tuned for 4500 revs and above so this has no effect.

set the throttle position screw a little more in,so it lets a little more air in the motor.

in other words the butterfly might not be letting enuf air into your motor when the throttle is shut.

you will more than likely have a higher idle speed though.but let the engine get the air it needs

Just open it up slightly and check it out it's an easy fix to just in case it has to be set back to stock.All you need to do is mark it's origional location with a marker of some sort.

Try it and see what happens.:rofl:

It is hard to see but the orange writing in the pic says this is the screw and the blue arrow points to it..

It wont fix the back fire problem though.

Is it possible that when you fill up it stirs up crap sitting in the bottom of your tank and gets sucked through the filter. Check your fuel filter and remove the pump and inspect the bottom of the tank. Won't cost you anything.

  • 1 month later...

Trust33 : thanks. I have increased my idle to sit ~ 850. It is better now. But idle still stuffs around when I fill the tank - everytime. :( The car came out of the factory idling at 650 so this is a nice patch for now until I find the real problem.

3LIT3 FORS3: I have changed the filter not that long ago. It made no difference :D

I tried getting the pump out. My good the screw tight!!!! So I gave up.. Any suggestions on getting the pump out?

tikki169 Told me one of his friends has the some problem, but I dont kow how it was fixed yet. So there must be someone else out there that has had this problem and is now solved.

On the weekend I went for a cruise to see a few mechanics to ask their option on my idle problem.. One worth mentioning is the guy from bayside performance. Nice guy seems honest and did not cost a thing - just good old aussie advice. Here is what he said.

Raf: I have a idling problem every single time I fill up my tank with petrol.

BP: Is it worse in hot weather

Raf: Yeap

BP: Does it happen any other time

Raf: no not really

BP: mmmm I reckon it is the fuel cap not releasing enough pressure...

Raf: Why?

Bp: you fill up the tank, when you run the car the pressure builds up in the tank thus increasing the pressure going to the fuel rails. Then when you release the cap fill up with petrol the pressure has dropped and you computer has to re-adjust itself to correct idling.

Raf: Sound logical... cool

So I went out an bought a new fuel cap. No problems so far - see how it goes.

Anyone have any though comments? think what he was saying is crap?

If this is true and it works it can possible save you crap idlers hundreds of $$$$ .. Cap cost me $20.. Well if if turns out good or bad I will let you all know.

Filled up first time with $20. I noticed when I let the cap off less pressure escaped :( Good sign so far.... Filled her up, paid for it, and gave her a start. Woohoo idle was fine :( not a problem there and then.. But driving down the road letting the gas off I still got the backfire - not as bad though. Then on the odd case when I let the car warm down for ~20 mins and give her a start the idle would be hunting again :rofl:.

I need to fill up again today, so I wil check if the idle problem after filling has vanished.

I also notice that my fuel pressure drops to 10 from 34 psi within 2 hours or so. I was told by the same mechanic that my one way valve in the pump could be stuffed - this could also cause problems. I should check this..

I have now filled up three times since my new fuel cap.. So this is what I have noticed so far.

First time fill with new cap (optimax): Idle was fine bit of back fire when off idle.

Second time(optimax): did not notice any difference. Idle was perfect and no backfire

Third time(optimax): Again idle spot on and no back fire.

mmmmm why did I have backfire the first time. My guess is that the fuel I had in the tank before was of a lower octance, it was premium star fuel I think. So my computer would have been running richer as soon as I put the higher octane in and thus causing the backfire..

As I fill up for the next month I will add more notes on my success or failure with the fuel cap.

It is very possible that the vacuum from your engine was drawing fuel from the tank and up to the purge canister. This would have been caused by the lack of pressure hold in your fuel tank. Good work for solving your problem. I apologise for not getting back to you sooner as I saw you were getting on top of it and I got very tied up with my turbo conversion.

  • 7 years later...

Record thread revival?

I have a similar issue with backfire on decel that is worse after fill up.

I see a new fuel cap helped this in this thread. I assume that the cap has been replaced with a vented instead of non vented?

Stock should be non vented with the charcoal canister used to release excess pressure and recirculate fuel vapours.

I think at some point the charcoal canister on mine has been replaced and only one line to it. Maybe it's not working properly?

Is best thing to do drive it without fuel cap and see if that fixes issue.

If it does fix it the

1. either reinstate all the fuel vapor lines. Or

2. block it off and use a vented fuel cap

Any ideas?

Thanks

Ben just make sure your fuel breather to charcoal canister is fine. Then vent charcoal canister to atmosphere. (block off vacuum lines at engine of course)

See if that fixes it temporarily.

That's what I did as I was interstate when I had issues. Had plans to fix it but still venting to atmo.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • Good tips, will get on those tomorrow. When doing the maintenance I did move a few of those connectors around, and things that are old tend to not like moving around. (Like me).
    • Don't try it. It will be shit. Better chance of damaging the engine than gaining any knowledge about the old one. Maybe, but unlikely, especially if the O2 sensor is working. You can use NissDataScan to look at the stock ECU.   Cleaning the AFM is seldom necessary and seldom helps. The R35 coil & loom conversion should eliminate dud coils or plugs. But as you still have misses - look to the plug where the coil loom connects to the engine loom, and the CAS plug. Need quality connections there. Also look to injector plugs. And the AFM plug while you're at it. Also look to whether your injectors are clean and flowing evenly. Get them out and onto a testbench.
    • Good to know, I feel like I am in for a rollercoaster ride that looks like a sine wave. 
    • You'll fit right in. Acceptance is the first step.
    • Hey folks. I've been lurking and browsing the forum for a while, since I got into my head that I wanted a skyline. Having purchased an overpriced completely stock GTT, (only "mods" it has is HKS pod filter and catback) now that it became legal in the US, it was all glorious and sututu noises here and there. But then I wanted to do things right and went to do basic maintenance. After all the fluids, filters done, I did the spark plugs, that's when the problems started.. First the car started spluttering at around 4.5k RPM. Which I gapped down the new plugs and that solved the sputter there, but the car now always misfires at idle with pops when lifting off and shifting 2nd to 3rd. Similar to the issues in this recent thread. I've been banging my head against the wall, reading the threads here and trying suggestions for a couple months now, so decided to start this one to explain exactly what I tried and what is going on. The symptoms of the issue: Idle and low revs misfiring intermittently. You can hear the exhaust tone change and the shakes on the shifter knob. It happens frequently, but doesn't seem to have a rhythm to it. Pops when backing off throttle. It pops and or burbles almost feels like it spits fire when it pops. (Happens mostly in 3rd gear at around 2k RPM). When under load and after 6k RPM, it also pops when shifting from 2nd to 3rd. There's a ticking noise at around 2k RPM in 2nd gear going downhill, seems unrelated though but I am out of educated and downright dumb guesses. Not noticeable lack of power when putting the car into load. The attempted diagnosis and solutions: Unplugging coils when the car is running This did nothing to change the idling and tone shift for every cylinder. Checking the exhaust headers with thermometer They all are within what I'd say it is margin of error of the laser thermometer New spark plugs Tossed two new sets, copper, iridium and using the old ones, still misfiring, even re gapped to 0.8mm, still same thing. MAF cleaned with the "specific" spray cleaner No changes in the issues what so ever. Brand new loom and r35 coil conversion (was going to add the r35 coils anyway) car runs arguably better, still misfires, but seems like does less frequently. Placebo? Code 21 now being thrown, thanks nissan gods. Removed the CAS to check the shaft for play or anything. CAS seems all fine, nothing that indicates any issue, visually speaking. Things to attempted next: Ordered a new MAF (chinesium from Amazon, to be able to return regardless of result). Fuel with proper gas, maybe it is this California water that they sell as gas that is to blame? Plugin the link ECU and check the info using the built in base map. Go back to BMW and eat my rob bearing breakfast without milky oil mixture.   Do any of you have experienced anything like this or have any suggestion?
×
×
  • Create New...