Engine Backfiring

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Engine Backfiring

Postby Hockeylife on Sat Aug 22, 2009 5:50 am

Hey guys, I have a red 240sx SR20DET and it basically runs like a piece of crap right now. This car has been sitting for about two years and I am trying to bring it back to life. I got it running after changing the oil, new clutch slave cylinder and removing the clutch damper and got the car moving (and stopping) under its own power (it was also pissing oil from the lower oil pan but that has been fixed). I took it out for its first spin and it runs like a bag of crap. I am hearing some noise coming from maybe one of the pulleys. However, my main concern is when I drive it and get up to 3000 rpm it starts to backfire. It seems to be either a fuel, ignition, or swap issue (but I could and might be wrong :? ). I bought this car from a friend who had the swap done by one of his friends, so I am unsure as to how well and if the ECU was correctly installed. I was leaning towards it maybe being a wiring issue between the ECU and the engine or an injector problem. We tried to hook up the scanner to the car (which has the SR20DET ECU installed) and tried to communicate with the car using the 240 and the NX but nothing worked. So we can't take a look at the fuel trims or anything. Sorry about the lengthyness of this post. Also, I will post a few pictures and a couple videos of my car later on.

Thanks

~Kris
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Re: Engine Backfiring

Postby Nismo on Sat Aug 22, 2009 3:02 pm

A few easy things to check and scratch off the list.

1) Does it have the right ECU? Sometimes people get all hot and horny when they see that their engine came with a Mines ECU or JUN ECU. Sadly the Japanese are not very good tuners... and these aftermarket or modified ECU's tend to run like crap.

2) Make sure the ECU is properly plugged in. Its a bit of a pain... but here's how to do it right. Remove the big plug with the screw completely. Then wiggle the big plug in, tighten the screw, wiggle it some more, then tighten some more. Repeat this process a few times. You won't believe how deep that main connector goes into the ECU.

3) Crack the valve cover and check the timing. There are excellent tutorials on how to do this on http://www.freshalloy.com. Just run a search for "SR20DET Timing" and you will find it.

4) Make sure it has the right MAF.

The assumption here is that you've checked all the basic stuff. Good plugs, coil packs are in good shape and firing well, you've got good fuel pressure at the rail, etc.

Also... do you know if the swap has a full JDM harness? Or if the harness was a KA to SR splice job? The splices are getting more and more rare, but they still do exist out there. If it is... it might be done wrong.

I'm probably forgetting stuff but the lads will chime in.
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Re: Engine Backfiring

Postby Hockeylife on Mon Aug 24, 2009 2:32 am

Here are some pics of my car:

FRONT VIEW
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SIDE VIEW
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REAR VIEW
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FRONT OF ENGINE
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TOP VIEW OF ENGINE
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VIEW FROM RIGHT SIDE
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VIEW FROM LEFT SIDE
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PULLEYS
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UNDERNEATH CAR
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Also, I know these pictures are a bit small but when I clicked on them, it took me to where I uploaded them and they were full size. If this doesn't work for any of you, just let me know and I will re-post them in the sorrect size (I really don't feel like starting over).
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Re: Engine Backfiring

Postby Hockeylife on Sun Aug 30, 2009 1:41 am

I have checked a couple of things since I last posted. I looked at the MAF voltages and got a 1.7v at idle and the voltage increased as the rpm increased. I was also having a hard time getting a reading from my TPS but from what I've read on the internet, it should be between 0.45-0.55v at idle and around 4.5v at WOT. I have also ordered a JDM S13 SR20DET stock wiring harness so I won't have to worry about any splicing (which was done on my car). Apprently I only have to extend the O2 and MAF sensors b/c of the RHD to LHD conversion. As for my ECU, I have no idea what type of ECU I have, and I haven't gotten around to re-installing the harness as I am waiting for my new wiring to get here. I will take a look at my ECU and write down all the info and post later.

That is all I have done up until now and I am still having the same problem (obviously). Once I get a reading on the TPS and find out what ECU I have, I can strike those of my list. Also, I was talking to one of the techs I work with and he was wondering if I had the correct sized injectors. I was also talking to a person (really weird guy) from a JDM store about the injectors and he said that I need to use purple injectors and the ones I have now are grey. I would have to assume that the colour of the injectors referes to the CC's. Any insight you might have into this would be greatly appreciated and I will be most definitly be looking on the forum for topics on injectors. I just thought I would throw that out there in case it was a simple/straight forward answer.

Btw, I am tring to find wiring diagrams and any manuals for the SR20 and I was wondering if the NX2000 had the same engine. If you know of any U.S. cars that had this engine (preferably the turbo model), that would help because I have access to ShopKey. Maybe I might be able to find a Silvia in the list (this just occured to me :slap: ).

Thanks once again,

~Kris
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Re: Engine Backfiring

Postby Nismo on Sun Aug 30, 2009 1:45 pm

Purple injectors = 370cc. Although they do tend to gray with age. Especially if the motor was left out in the sun for a while.
Yellow = 550cc, 555cc, or 815cc.
Red = 740cc, 850cc.

Silvia and NX2000 did not share the same motor.
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Re: Engine Backfiring

Postby bartyb on Mon Aug 31, 2009 4:10 pm

This might sound like a stupid question, but did you change the fuel? You said it was sitting for a few years, so I had to ask, I've seen it happen. :mrgreen: Did you change the fuel filter?

Your car looks solid, you gotta watch for the rust under the rear spoiler though, it will only get worse.

Assuming you checked for spark, fuel pressure, and all vacuum lines specially to the fpr,
Did you check for leaks in the IC system?

A leak in the intake piping will most likely cause engine backfiring. Check your A/F ratio which is the main cause of misfiring, an incorrect ratio will cause this, which can be caused by a leak, a leaky injector, bad fpr, electrical (maf, o2 sensor, etc)

Things to check as well: ignition timing, cam timing, although you don't have a distributor so..

But once you'll get it running right, you will be rewarded, those are very reliable engines, and they go like hell, just make sure they get what they need, enough fuel and good oil. I drove mine for the past 3-4 years all year long without any problems other then wheel traction.
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Re: Engine Backfiring

Postby Hockeylife on Tue Sep 01, 2009 4:30 am

As for changing the fuel, I did not take it out but I did add 10 litres of 94 octane before I started it. I did not replace the fuel filter and I probably will now that you mentioned it (even if it isn't the source of the problem).

The rust under the spoiler (which is made out of foam :ugh: ) I am planning to get a completely new carbon fiber hatch and hood, but that is a bit further down the line (I want to get engine running properly first).

I have also checked all of the coil packs and did end up replacing one of them but the rest were fine. I haven't hooked up a fuel pressure gauge to my car but I will add it to my list of things to check (which is getting longer and longer). I didn't see anything too obvious with any of the vaccum lines (leaking) but I will take a closer look at them just to make sure. I also didn't see any leaks in my intake system, but again, I will take a closer look just to make sure.

As for the injectors, the car was in the sun for 2 years so I guess that might have to changed the colour of the injectors (but just to be honest, I have no idea why or how that would happen). I am thinking of just replacing the injectors regardless of whether it is causing my problem or not cause I want to up the CC because a larger fuel pump was installed.

Lastly, when it comes to checking ignition and cam timing, I am sort of unsure as to how to properly do that without a scanner ( and the scan tools won't communicate with my ECU :wtf: ). I will look on the forum and other places for this information but I am hoping to get my ECU communication working by ordering a completely new (uncut) SR20DET wiring harness direct from JDM (all I have to do is extend the O2 and MAF sensors) and hopefully I will get communication from my ECU. If not, I might end up trying to get my hands on another ECU to see if that might be the problem. I don't really want to buy another ECU (unless I win the lottery or something).

Thanks again for all your help.
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Re: Engine Backfiring

Postby Nave on Wed Sep 09, 2009 4:17 am

Coles notes:

1) Drain tank, put in fresh gas

2) New fuel filter

3) Check for any piping leaks

4) Change plugs

5) Check cam timing. You can use a timing light to do this but I have found the best way is the mechanical way. When don't properly you will KNOW it is right or at least within a degree. Timing lights can be a bitch to get to work and if you aren't close to beging with can have you chasing your tail. Follow the procedure for "SR cam alignment" mid way down the page: http://rs-enthalpy.com/info.html

6) Larger fuel pump does NOT mean larger injectors. I would ensure you have a good set of stock ones running properly before upgrading. Bigger injectors means you HAVE to re-flash the ECU (assuming it has been converted to begin with) or use some sort of piggyback/standalone system to offset for the bigger injectors. Piggy back systems, IMO, are old and a waste of time... either go with a programable ECU or a standalone sytem that plugs into the stock harness (Apex'i Power FC or AEM EMS).

7) I can rent any parts you think you might need. :grin:
- 90 Coupe a la SR
- 90 Coupe a la KA
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Re: Engine Backfiring

Postby Hockeylife on Mon Oct 05, 2009 5:24 pm

1) I will remove the gas and put new 94 octane in it. The only thing I need to figure out is how to siphon the gas from the tank. Maybe I will get one of the Canadian tire hand pumps used for Jerry cans. I have to get at the fuel pump anyways because I am not getting any fuel to my injectors. I had my mother turn the car over and see if there was any pressure in the lines (manufacturer procedure says to pinch the fuel line when cranking). I can't hear the pump turn on either so I am going to see if it is getting power.

2) I am going to buy a new filter today.

3) No leaks, all though I did find a coolant hose going to my heater box that is 3/4 on :P and leaking slightly (but that is a quick fix).

4) All of the plugs are good so I think I am going to hold off on buying a new set until I get some more dough $$.

5) I have been reviewing your documents along with the manual and I think I will tackle the cam timing soon.

6) I would like to avoid the hassle of re-flashing my ECU (all though I don't know how to do that) so putting in stock injectors would be the best bet. I have heard that stock injectors are 450 C.C. and the lowest C.C. I can find (at least on FRsports.com) is 550 C.C.

7) Thanks for the offer bud.
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Re: Engine Backfiring

Postby Frankyy on Wed Oct 07, 2009 11:26 pm

Hockeylife wrote:1) I will remove the gas and put new 94 octane in it. The only thing I need to figure out is how to siphon the gas from the tank. Maybe I will get one of the Canadian tire hand pumps used for Jerry cans. I have to get at the fuel pump anyways because I am not getting any fuel to my injectors. I had my mother turn the car over and see if there was any pressure in the lines (manufacturer procedure says to pinch the fuel line when cranking). I can't hear the pump turn on either so I am going to see if it is getting power.

2) I am going to buy a new filter today.

3) No leaks, all though I did find a coolant hose going to my heater box that is 3/4 on :P and leaking slightly (but that is a quick fix).

4) All of the plugs are good so I think I am going to hold off on buying a new set until I get some more dough $$.

5) I have been reviewing your documents along with the manual and I think I will tackle the cam timing soon.

6) I would like to avoid the hassle of re-flashing my ECU (all though I don't know how to do that) so putting in stock injectors would be the best bet. I have heard that stock injectors are 450 C.C. and the lowest C.C. I can find (at least on FRsports.com) is 550 C.C.

7) Thanks for the offer bud.


removing old gaz is not necessary just fill up with some 94 and if u have alot of old gaz left maybey consider octane booster, and i dunno where u found that 450cc are stock injectors but i heard that stock are 370cc...
300zx TT gaz filter is a bit better but thats not the major problem of ur back fire.
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Re: Engine Backfiring

Postby Nave on Fri Oct 30, 2009 12:13 am

Frankyy wrote:
Hockeylife wrote:1) I will remove the gas and put new 94 octane in it. The only thing I need to figure out is how to siphon the gas from the tank. Maybe I will get one of the Canadian tire hand pumps used for Jerry cans. I have to get at the fuel pump anyways because I am not getting any fuel to my injectors. I had my mother turn the car over and see if there was any pressure in the lines (manufacturer procedure says to pinch the fuel line when cranking). I can't hear the pump turn on either so I am going to see if it is getting power.

2) I am going to buy a new filter today.

3) No leaks, all though I did find a coolant hose going to my heater box that is 3/4 on :P and leaking slightly (but that is a quick fix).

4) All of the plugs are good so I think I am going to hold off on buying a new set until I get some more dough $$.

5) I have been reviewing your documents along with the manual and I think I will tackle the cam timing soon.

6) I would like to avoid the hassle of re-flashing my ECU (all though I don't know how to do that) so putting in stock injectors would be the best bet. I have heard that stock injectors are 450 C.C. and the lowest C.C. I can find (at least on FRsports.com) is 550 C.C.

7) Thanks for the offer bud.


removing old gaz is not necessary just fill up with some 94 and if u have alot of old gaz left maybey consider octane booster, and i dunno where u found that 450cc are stock injectors but i heard that stock are 370cc...
300zx TT gaz filter is a bit better but thats not the major problem of ur back fire.


Putting higher octance fuel or an octane booster will do absolutely NOTHING for you if there is old bad gas in the tank. You NEED to drain it. That said, it takes a lot longer to go so bad that diluting it with fresh fuel won't be enough but once again once it is bad it is bad.
- 90 Coupe a la SR
- 90 Coupe a la KA
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