Backfiring issue (ECU? TPS?)

Andjeti · Post by **Andjeti** » Wed Jun 29, 2011 11:23 am

As topic says my car is backfiring.

Firstly, some background info. I have two ET's. The first (Red/"The Whore"), 1984 (leaded), it has T25G, 3" turbo-to-canon straight through exhaust, Log removal (MAF meter relocated to Filter-MAF-Turbo), 530x230 FMIC, Atmo BOV, VL Throttle Body, CA injectors, Adjusted MAF meter spring, etc (None of these was my doing, all done by previous owner). The second (Blue/"Mitch - My Bitch"), 1985 (leaded), it has no mods apart from a 2.5" Straight through turbo-to-canon exhaust with cat (hollowed out due to leaded car, and me thinking it may have been clogged at one point), adjusted MAF meter (previous owner), and the air-box was missing so I replaced with a pod style filter (still where the air-box should be), it still has the log and over-boost valve (thank goodness as I just found out the waste-gate is seized shut, will be fixing that this week some time). Neither car has air-conditioning.

Red was my daily driver until about 6 months ago when the head gasket was damaged. Now it is my "project". Red always used to have the ECU drama's, to the point I actually pulled the plugs apart and cleaned/re-tightened the terminals, with no effect, I was going to pull ECU apart and check for semi-dry joints, but then the gasket went. When it had the issues it felt like, under acceleration, you would get to approx 2250-2750 RPM and then it would feel like something, a "blockage", had been shoved into the throttle body, choking the hell out of the engine and making it feel like it was going to stall. Same thing when cruising, if in between above rev range, felt like someone blocked the throttle body, and it was going to stall. Give the ECU plugs a little wiggle, and it would come good, the "blockage" was gone, and it revved fine, and drove well. Red also had that unmistakable exhaust "burble" on deceleration, which I found too loud for my liking. When the head gasket went, I got Blue at a really good price and it is now my daily driver. It goes OK, however I've noticed when I am cruising on the highway, or slowing down for corners/lights (going back through the gears), under deceleration (foot totally off throttle), at approx 2500RPM, sometimes I get a rather large backfire through the exhaust. It is definitely not a "burble", it's a medium to large "BANG!" (the volume varies). This doesn't happen every time I take my foot off the throttle, maybe 6 out of 10 times, enough to annoy the hell out of me. I've noticed if I let the throttle off until my foot is only just depressing it, there is no backfire at all, however deceleration isn't as good, and if I am going back through gears and braking, I don't have a spare foot to keep on throttle, and heel-toeing get's tiring after a while.

At first I thought this may have been a TPS issue because the ECU was showing the TPS code, however if I depress the throttle before start-up (as per manual), the code goes away, and I am left with just AC code. So not too sure now if it is TPS. Could the ECU plugs cause just a "little issue" like this one, rather than the standard issue most of us have felt at some time? I'm assuming Blue has had ECU issues in the past, unless the previous owner zip-tied the plugs for preventative reasons. I've pretty much come to the conclusion it is one of three things, TPS, ECU, or some weird by-product of the waste-gate seizure.

Any other thoughts/opinions/remedies are appreciated guys, it's rather embarrassing and legally sketchy (excessive noise), when I'm just cruising down the highway and I let my foot off the throttle cause the wanker in front has slowed down, then suddenly "BANG!".

Cheers
Jay

PAC_ET · Post by **PAC_ET** » Wed Jun 29, 2011 1:29 pm

exhaust leak check dumpipe, turbo, exhaust manifold. Theres always fuel in ur exhaust fumes let a bit of air in and if the ratio is right bang,

Post by **tassuperkart** » Fri Jul 01, 2011 8:34 pm

Richen idle mixture slightly, mebbe 1/2 a turn and look for exhaust leaks close to the engine as Andrew mentioned.
L8r
E

Kimmo · Post by **Kimmo** » Sat Jul 02, 2011 5:44 pm

Your terminology is wrong; unless you have an aftermarket CPU, you have an idle switch instead of a TPS, and same goes for the MAF.

A mass air flow sensor looks likes this:

We have air flow meters (AFM):

Andjeti · Post by **Andjeti** » Sun Jul 03, 2011 10:50 am

Thanks Kimmo, my misconception.

I was under the impression that both the ones you pictured were MAF sensors/meters (Mass Air Flow sensors/meters), the difference being the top one is a "hot/cold wire" style, and the lower is a "vane" style. But I am always willing to be corrected, and learn something new. As for the TPS vs Idle Switch, yeah that is my mistake, I am too used to thinking about the setup on Red (VL Throttle body), which has a TPS even though only the idle switch is connected.

Thanks Andrew and Evan, when I pull the Turbo off to fix the waste-gate issue through the week (gotta love being on 4 weeks holidays from uni), I'll rip the exhaust out at the same time and double/triple check the flanges for sealing, might even replace the studs/washers/nuts. Won't be too hard there are only 2 flanges on this exhaust (Turbo-Dump and Dump-Exhaust). Finding time between other tasks I've been putting off has been an issue, but hopefully all my other jobs will be complete this week, I got to learn to say "No" when people ask me to do stuff for them.

sashN12 · Post by **sashN12** » Sun Jul 03, 2011 7:20 pm

if its backfiring it could be getting a little too much fuel, check the diagnostic lights on the ecu just to make sure

et_rider · Post by **et_rider** » Mon Jul 04, 2011 10:49 pm

correct me if im wrong but inst back firing due to timeing being to advanced where as if its to retarded that it will pop out the pod

Just an idea its what i do if i start cracling and poping out the back end lol

Post by **tassuperkart** » Tue Jul 05, 2011 8:30 pm

Nope nope and nope.
Backfiring and popping on overrun is from leanness and made worse by retarding the ignition.
Id say the TPS is not adjusted correctly as ET should have overrun cut.

l8r
E

Callumgw · Post by **Callumgw** » Wed Jul 06, 2011 7:03 am

tassuperkart wrote:Nope nope and nope.
Backfiring and popping on overrun is from leanness and made worse by retarding the ignition.
Id say the TPS is not adjusted correctly as ET should have overrun cut.

l8r
E

Surely backfiring can't result from leanness? there must be fuel to burn otherwise no backfire/pop. That is, an incomplete burn leave fuel in the exhaust gas that later burns when it gets the oxygen needed, with a high enough residual heat....

not sure how a lean burn (all fuel gone, but oxygen left) could cause a backfire or pop.

C

Post by **tassuperkart** » Wed Jul 06, 2011 7:58 pm

Oh not THAT lean C, usually in the vicinity of 15:1 and up to 18:1 will result in plenty of popping and farting in the pipe.

L8r
E

Andjeti · Post by **Andjeti** » Wed Jul 13, 2011 8:25 pm

Well so far no exhaust holes/leaks. (except Manifold-Turbo nuts, and several others not being tight enough). Went out and spent the whole $10 on a new multimeter today, I'll check the Throttle Switch when I get it all back together. I think I'll the manifold off as well, just to be certain that it is tight as well. Then I'll richen the idle (Are you just talking the air bypass on the AFM Tass?). Hopefully it was just a combination of undertight nuts'n'bolts, the Thottle Switch and Idle mixture doing it.

Post by **tassuperkart** » Wed Jul 13, 2011 8:39 pm

Andjeti wrote:Then I'll richen the idle (Are you just talking the air bypass on the AFM Tass?).

Set your idle mixture for fastest and smoothest idle when hot.
Also, check your idle ignition timing as retarded timing will also make popping worse.

L8r
Oracle

Andjeti · Post by **Andjeti** » Wed Jul 13, 2011 8:47 pm

tassuperkart wrote: Set your idle mixture for fastest and smoothest idle when hot.
Also, check your idle ignition timing as retarded timing will also make popping worse.

L8r
Oracle

The AFM Air Bypass Screw, or the top screw on the Idle Control Valve? Sorry man, I'm just not following things tonight. I think my brain has shut down while I am on uni holidays. Hopefully it turns back on before classes resume.

Post by **tassuperkart** » Wed Jul 13, 2011 9:42 pm

AFM bypass screw m8. other screws are just idle speed adjusters.
Turn the AFM screw INWARDS for richer and OUTWARDS for leaner.
L8r
Oracle