Interesting backfires: No throttle = boom?

[DreadedFist]

I've noticed in the last few months, that if I'm beating on my car during a cruise (since I drive like a granny any other time), I get backfires, but not inbetween shifts. I get them if I'm coasting in gear and touch the throttle. If I've done a particularly long pull in a higher gear, and let off, and begin coasting, if I just barely stab the throttle, enough to register maybe 3% throttle application, I get a huge backfire. It sounds like a gunshot, too.

If the pull was a very long fourth and fifth gear kind of pull (in a controlled race track enviornment, of course), as I'm slowing down afterwards just coasting, I can get 5 or 6 huge backfires and assosciated gunshot sounds by just barely touching the go pedal. One bang per stab of the pedal, not one touch of the pedal and then a bunch of bangs.

Is this a lean missfire, or something else? I can't imagine much fuel is getting injected when you are coasting.

I find this also happens on the highway if I'm cruising in 5th gear at a constant speed for a significant amount of time. If I let off and then touch the throttle a bit, I get a pop. Not a huge one, but a pop none the less.

Halp

edit: plugs are fine. They look brand new. Gapped to 0.8mm if that makes a difference. I'm also getting horribly fuel mileage. If i drive to the fuel light (which I never do) I'll get 300-320km to a tank, driving like a grandmother. I have a mines chipped ECU. I would suspect that the afr's would be a bit leaner compared to stock. Usually aftermarket tunes result in better gas mileage... Or so I've been told. 02 sensor was replaced about 2,500km's ago.

[Skym]

Only time my car did something similar was when 02 sensor, TPS were stuffed (ECU was in limp home mode due to I gather was faulty TPS). Used to pop flames from exhaust (running very rich) on motorway, street, etc when backing off throttle.

It's normal for stock ECU to add fuel around 1300rpm, then cuts fuel around 1000rpm.

Also could be that ECU is running on knock fuel map that's very rich at 4000rpm+ due to running on low octane gas.

Running rich can clog / stuff o2 sensor.

[DreadedFist]

Only time my car did something similar was when 02 sensor, TPS were stuffed (ECU was in limp home mode due to I gather was faulty TPS). Used to pop flames from exhaust (running very rich) on motorway, street, etc when backing off throttle.

It's normal for stock ECU to add fuel around 1300rpm, then cuts fuel around 1000rpm.

Also could be that ECU is running on knock fuel map that's very rich at 4000rpm+ due to running on low octane gas.

Running rich can clog / stuff o2 sensor.

the weird thing is that it doesnt happen when I back off the throttle. If i coast for 10 or 15 seconds and then touch the gas pedal, it does it. It's like it's been waiting for me to unleash it, I'm always filling up with 94 octane since I have a mines chipped ecu

[Skym]

Then it's related to TPS (check ECU for TPS error code or check voltages at TPS plug). TPS makes ECU add fuel when suddenly accelerating (throttle body suddenly opens and why TPS is connected to throttlebody) to prevent engine going suddenly lean that makes engine hesitate.

Usually when you replace o2 sensor, TPS should be replaced at same time as part of routine maintenance (every 40,000km-60,000km).

[love_boost]

i think it is normal. when you appply light throttle while coasting you are sending a little more fuel through your injectors, right blip of the throttle at the right time can make a bang.

[Shadao]

my car does this as well, but its not super super loud, it sounds like lil booms goin off, some friends of mine who i drove by said it sounds awesome...

as far as i know i have stock ECU, and i run only 94...

since i generally take it easy im not too worried about it... when i have the coin i will be upgrading some things and maybe then i will fix this if it is a huge issue... but until then im not worried.... unless of course i should be

[DreadedFist]

Then it's related to TPS (check ECU for TPS error code or check voltages at TPS plug). TPS makes ECU add fuel when suddenly accelerating (throttle body suddenly opens and why TPS is connected to throttlebody) to prevent engine going suddenly lean that makes engine hesitate.

Usually when you replace o2 sensor, TPS should be replaced at same time as part of routine maintenance (every 40,000km-60,000km).

ahhhh so it thinks that I'm giving it more throttle than I am, perhaps? That would explain the big kaboom with nearly 0 throttle application. I wonder if any CDN market vehicles share a TPS...

[M13]

How about before you consider the TPS to be broken, check its voltage first?


~0.48 V at zero throttle.

[RSi]

Yeah come and use my consult cable like you were supposed to.

It could be your mines ecu too

[DreadedFist]

I checked for codes today, none.

M13, I don't have a multimeter. Are they expensive?

edit: Rich you live in Surrey, right?

[archaeic_bloke]

i get the exact same thing, checked ECU.. no codes, tested TPS and it showing a low voltage for WOT... proceeded to check O2 sensors... one of them is completely dead...lol

like everyone is saying, change your O2's and your TPS. TPS is only like $45... O2's are a bit more pricey.

[DreadedFist]

i get the exact same thing, checked ECU.. no codes, tested TPS and it showing a low voltage for WOT... proceeded to check O2 sensors... one of them is completely dead...lol

like everyone is saying, change your O2's and your TPS. TPS is only like $45... O2's are a bit more pricey.

Do you know if a TPS sensor is available on a Canadian car that will work with an rb20? I figure if it's only 40 or 50 bucks I might as well replace it anyway. It's always better to have brand new stuff, as opposed to 18 year old stuff

Mines a 5 speed, if that makes a difference...

[RSi]

How do you test an O2 sensor?

[Skym]

TPS is like a electronic version (TPS tells ECU where throttle is and ECU via looking at tables adds fuel via injectors) of a accelerator pump on carb engine (does a similar job) if your used to working on carb engines.

I've been through 2x TPS on my car. Unfortunately TPS is Skyline specific and TPS design changed around when R33 was made, where I think they removed the idle, WOT pins inside and relied on voltage to set TPS correctly.

I was looking into a Toyota version of TPS that that I hear is optical (no circuit board with track inside that wears out or pins that bend when throttle is released or floored), but haven't a clue which Toyota has a optical TPS that stock R32 ECU can read from. I thought it might have been a fly by wire sensor, as that is what it sounded like, so didn't bother investigating it anymore, as stock R32 ECU wasn't capable of running a fly by wire setup. But Motec M600 ECU was.

From what I can remember, to test o2 sensor, hold engine at around 2000rpm and count how long it takes to go from lean to rich triggers. If voltage fluctuates slower, means 02 sensor is stuffed.

[M13]

w/ NISTUNE, you can watch the voltage reading of TPS on a laptop live, which makes life super awesome.

I'd just ask vendors or hit up NISSAN FAST and get the part number and have a trip down to a NISSAN dealership.


Check the voltage first though.

ZERO throttle should be around 0.48V and full throttle should be ~5.0V

Adjust the base and open throttle slowly to see if it jumps to 5.0 If it doesn't, then it's time for replacement.