Bad Economy And Backfire

[chrissyo]

Hey this is my first post!

I recently bought a 1996 R33 GTS-T Series 2. Has done 94k and just recently had an engine rebuild.

Just wondering what i should look at firstly! im wanting to get abit better fuel economy as im only getting around 300k atm with mixed driving using boost rarely. I think its running around 8psi. Stock turbo and theres a really dodgy looking jaycar boost controller in the passenger footwell.

The car also is backfiring a bit and goes crazy if you rev over 4500rpm

What should i be looking at? ECU? Coil Packs? o2 sensor?

Thanks guys.

[NYTSKY]

Take it to your tuner,they will diagnose it very quickly.

[SDEWY5]

Take it to your tuner,they will diagnose it very quickly.

sounds like the crank angle sensor timing is retarded, may be for the run in as its only recently rebuilt

[H@ME]

clean amf with contact cleaner, have ecu reset, look at the crack angle sensor, change plugs, have coils checked and replace the 02 sensor then u should be right!

[series2r33]

If you have a aftermarket blow off valve that vents to atmosphere and doesnt plub back, try fitting the stock one or a plumb back one. The air that vents to atmosphere has already passed the o2 sensor therefore telling the computer that its getting that much air,.. in turn more fuel is added and the extra unburnt fuel can cause a backfire when backing of the accelator. Not a bad thing that it runs a little rich but just annoying having the backfire and maybe some black runoff on the back of your car yeah?!

A tune on the dyno will fix it up if its the air/fuel ratio but even still the plumb back item is much better for the car

[stolen_s15]

You just purchased the car and are boosting "rarely"??? That in itself is a mystery

[Godzilla32]

LOL at Nick

Could be alot of things. Goes crazy after 4500 rpm is a bit of a general statement. If its miss firing then look at coil packs for hairline craking (very common on RB25). Or check plug condition and gap. If its only running 8 psi then a gap of around 1.0-1.1mm should be fine without causing a miss.

If its running too rich then maybe check out your AFM, sometimes they will test out ok but can still be faulty, so on occassions its just easier to try another known working one. Cleaning the AFM shouldnt be necessary as Nissan's use a 'hot wire' AFM which as the name suggests uses a heated element to sense air flow. The more airflow, the less heated the element becomes resulting in less resistance. More heat, more resistance. Thats how the ECU reads what the AFM is passing. Anyway when they are turned on they heat up burning off most contaminants. They will commonly cause back firing from over fuelling and and misjudged mixture control if not operating correctly.

An O2 sensor is in the exhaust so anything running through the intake pipes has deffinetly not seen the O2 sensor. I think your thinking about the AFM. its true though that will cause the unmetered air effect and can screw up the mixture.

A tune on a dyno is useless unless you have some form of tuneability in the ECU whether its a piggy back system or a full computer swap, etc

Resetting the ECU will only wipe trouble codes that could help you fix the problem, it can temporarily fix the issue but its not normally a permanent fix. Theres no reason to run retarded ignition timing on a rebuilt engine. Should just be run at optimum settings.

So check all of the above:

Plug condition and gap (1.0-1.1mm)

Coils for hair line cracks

AFM for correct output voltage

Look for any form of vacuum leaks. You can use aero start to identify if and where the leak is by spraying it around the hoses. The revs will change if there is a leak

Perhaps check the TPS also for correct output voltage. Should be 0.5 at closed throttle and 4.5-5v at full throttle.

In checking the TPS also make sure the Idle switch that is built into it is reading closed when its closed and vice versa.

Check for correctly adjusted ignition timing.

But honestly my guess will be a miss fire caused by either plugs or coil packs.

The list goes on, EFI diagnosis is no easy task.

Good luck

[jutstar]

Might be the flux capacitor getting old, might need replacing ?

[chrissyo]

thanks for the feedback guys

ive got a new o2 sensor just need to find the tool to remove the old one grrr

[siddr20]

Deff change 02 sensor, and change your spark plugs.

If you only running under 1 bar boost, then use heat range 6 plugs.

This will deff make a difference to your milage.

Coz it did to mine

[chrissyo]

thanks guys ill let you know how i go if i ever get the o2 sensor in! having trouble getting the old one out as i cant find the tool

Cheers

[Dose Pipe Sutututu]

That Jaycar Boost controller is far from dodgey...

A dodgey O2 sensor will not cause backfiring, sounds like a fcked up timing as other have pointed out

Coil packs, will cause the car to mis fire & splutter, and perhaps backfiring

ECU, I doubt it would be the stock ECU

[Finny]

Backfiring is usually from restarted timing. loosen the screws on your crank angle sensor and turn it full clock wise if it pings wind it back a tad.

Also check that your igniter is earthing properly, my car was running retarded timing even with CAS turned fully clock wise until I ran a separate earth wire too my igniter.

[DECIM8]

Dont touch the timing mate, your a newbie by the sounds of it and dont have to much idea what your diving into. Leaning out your engine could make it ping and eventually blow it..

Please take it to your mechanic, and if it has a ECU upgrade which I assume it does please skip the mechanic and to a tuner and ask them to squeeze some more kms out of it.

Please keep in mind that a new engine requires to run somewhat rich to run it in to prevent any mishaps, such as pinging. How long ago was it rebuilt?

Edited April 3, 2008 by DECIM8

[Finny]

Backfiring is usually from restarted timing. loosen the screws on your crank angle sensor and turn it full clock wise if it pings wind it back a tad.

Also check that your igniter is earthing properly, my car was running retarded timing even with CAS turned fully clock wise until I ran a separate earth wire too my igniter.

[chrissyo]

The engine was redone around 1000km ago now. I dont want to touch the CAS as i know nothing about it. im not sure if its stock ecu or not either...yep im a newbie

[chrissyo]

My car is now having problems idoling i wonder if its related? when i start the car in the morning i have to give the accelerator a bit of a press as the revs start to drop thats never been a problem before. Also the revs have started going up and down...like on a few occasions when the turbo timer is on. It goes from arount 750-1200 up and down, sounds like someones just tapping the pedal like this /\/\/\/\/\/\/\ Is this at all related?

[R338OY]

Dont touch the timing mate, your a newbie by the sounds of it and dont have to much idea what your diving into. Leaning out your engine could make it ping and eventually blow it..

Please take it to your mechanic, and if it has a ECU upgrade which I assume it does please skip the mechanic and to a tuner and ask them to squeeze some more kms out of it.

Please keep in mind that a new engine requires to run somewhat rich to run it in to prevent any mishaps, such as pinging. How long ago was it rebuilt?

+1

The engine was redone around 1000km ago now. I dont want to touch the CAS as i know nothing about it. im not sure if its stock ecu or not either...yep im a newbie

Yes, stuffing around with the CAS isn't worth it. A tuner can fiddle with it in 5 mins and costs you very little.

My car is now having problems idoling i wonder if its related? when i start the car in the morning i have to give the accelerator a bit of a press as the revs start to drop thats never been a problem before. Also the revs have started going up and down...like on a few occasions when the turbo timer is on. It goes from arount 750-1200 up and down, sounds like someones just tapping the pedal like this /\/\/\/\/\/\/\ Is this at all related?

Could be many a thing. A stuffed sensor (i.e. O2), bad plugs, a leaking injector, BOV problem, idle control issue. If you're not prepared to go through every single thing then give a measly $100 to a mechanic and they'll tell you in 30mins exacly what's wrong.

Then pay him another $1000 to fix it hahaha

jk, jk.

[chrissyo]

thanks for your reply. Maybe the idol prob is the o2 sensor...i did replace it last week! cant think if the problem started just before or after it though

[4drftn]

My car is now having problems idoling i wonder if its related? when i start the car in the morning i have to give the accelerator a bit of a press as the revs start to drop thats never been a problem before. Also the revs have started going up and down...like on a few occasions when the turbo timer is on. It goes from arount 750-1200 up and down, sounds like someones just tapping the pedal like this /\/\/\/\/\/\/\ Is this at all related?

mine had idle problem very similar, i changed the plugs and got rid of the miss, but i still had it idling up and down.

so i cleaned my throttle body. stopped it from fluctuating. but be careful when cleaning throttle body, apparently there is a seal around the butterfly, dont rub it of as i did. it will cause your car to idle at 1500 and while driving at 2500!. but i have adjusted my tps to drop the idle until i build a new seal around the butterfly.