What could cause this on a Z32 TT? The car runs, but it is so fat that it blows black soot out the tail pipe and loads up under hard acceleration around 2500-3000 RPM's. I believe this is the root of the rest of the problems I've been having. Z1 advised O2 sensors, dirty air filter or boost leak. I'm not buying any of these. The O2 sensors are new. The air filter is not dirty and all of the vaccum hoses are brand new.

I plugged in the conzult program and everything appears to be reading within specs.

For those who dont know...these are the mods I have.
ASH ecu
555 injectors
DOOLZ intake
Z1 525 turbos
Stillen SMIC's
split downpipes
midpipes w/hi-flow cats
Stillen catbacks
Hones upper and lower plenums

I'm just thinking about taking it in to have someone else diagnose it, but I don't know a reputable shop up here. There are two Nissan dealerships up here, but I've never been comfortable with dealerships.

 

OK, well... O2s are a possibility, and they're easy to test, so let's start with that. Connect conzult and go to the O2 sensors. They should cycle between rich and lean 10 times in 10 seconds. If they do that, they're fine. (And for anyone else reading this, you now know why narrowband O2 gauges are useless... these sensors are made to cycle like that, and they give no meaningful reading whatsoever.) Speaking of which, you don't have a narrowband O2 gauge, do you? Scavenging this signal could cause a rich condition too... which would go away above 3000 rpms, when the O2s are ignored by the ECU. (The fact that it goes away above 3k rpms suggests an O2 problem.)

Test your injectors next. If you have one that has really low resistance, it's going to dump excess fuel. At higher RPMs, this problem would go away as the cylinder needs the more fuel. I'm sure you already know, but for reference for anyone searching this site in the future, they should be 10-14 ohms.

If you're air filter is clean, I'll trust you on that.

How does your vacuum read at idle? You don't list a boost controller, but I'm hoping you have an electronic boost controller or an aftermarket boost gauge, because the stock gauge is horrible for precision vacuum readings. You should be below -400 mmHg at idle (my car sits normally around -470 or so). If it's more than that (-400<) you have vacuum leaks, which would cause a rich condition.

If you come back after looking at all those and it's still inconclusive, I'll advise further, but start there. Personally, I don't like the DOOLZ kit and am wondering if that is a contributing factor (you did get the ECU rechipped for DOOLZ, right?), but we'll have to cross that bridge when we get to it.

 

Any chance of pinched o-ring(s) on the newly installed injectors? Have you vacuum checked the fpr & dampener to make sure they're o.k.?

Be careful with engine oil dilution from the excess fuel too.

 

Good points on the fuel system.

A next step in the diagnosis would be to get an in-line fuel pressure gauge and start testing fuel system components.

If the fuel pressure fluxuates rapidly, your dampener may be bad.

if the fuel pressure is high or low, doesn't vary with engine vacuum, or if the fuel pressure isn't maintained when the car is turned off, the fuel pressure regulator may be bad.

A bad FPR could result in high fuel pressures which could result in running rich.

 

Vacuum reads at -20 psi. O2 sensors are fine. My fuel pressure guage has never worked right, so I guess it's time to get it to work. Thanks for the ideas.

 

don't forget to test your injectors... you didn't address that after I suggested it.

 

Will do...I tested them all before I installed them and have had the problem since I turned the key; which is why I don't think it's the injectors, but it's still something I will be testing.

Hopefully this weekend...

 

black smoke is usually a running rich prob--perhaps something went wak during installation?

 

I'm thinking Pinched O-rings.

 

I think I've got it figured out, but won't know for sure until I can drive it tomorrow....I replaced the dampener and the FPR....no more black soot out the tail pipes. Revs smooth all the way to 6k at full throttle. Idles more smoothly than before also.

 

That will be cool. I added a fuel pressure gage to my car so that I can monitor my fuel system. Hopefully you'll be back on the road.

 

It's better, but still not right.....

I think I've got it now though....I think Zlover was right about the O2 sensors. At idle, they don't alternate between rich and lean. They will at higher RPM's, but not at idle.

Can O2 sensors get so sooted up that they don't work properly? The O2 sensors have been in the car for less than 2000 miles. I installed Bosch sensors, so I'm having a hard time believing they're bad.

The plug on the left came out of the driver side. The plug on the right came from the passenger side. The passenger side plug looks good...driver's side...not so good. I might just spin all the plugs out to see what the rest look like.

All injectors check out good.

 

well clean the plugs and drive it around, I think u just got to clan up the system from the extra fuel it was getting. I blew my injector o rings a few times, my plugs went bad and so on. I cleaned the plugs and turned on the car let it idle for a while and went on a drive to let it burn al the unburnt fuel acumulated ont he system, (exhaust pipes exhaust manifold turbo and so on.) definetly get a fuel pressure gauge so u can monitor the fuel system. I think your 02 sensorts should be good. Ive personally never heard of an 02 sensor going bad from running rich. good luck and let us know how swhe runs

 

My o2's will stabilize at idle. Give it a little gas and they start bouncing from .1v to .9v . Let it idle and they stabilize again. If anything, the plug on the right looks like it's running lean. It shouldn't be white like that. But if you've only idled the motor, or drove around slowly, it's hard to determine. A true plug check is done after runing the motor hard for a bit and then not run long at idle or low speeds after the hard run.

You're sure all of the plugs are firing?

 

Yes, all plugs are firing. I'm going to pull out all the plugs and make sure it's not just one cylinder acting weird. What was wierd is that I did a power balance test with Conzult. The 1st time, #1 and #6 failed. The 2nd time, all holes passes. The third time, #2 - #5 failed. These 3 tests were done within 5 minutes of each other. I could feel the program alternating from one hole to the next, but I guess that the RPM difference is what the program goes off of.


I found another symptom; which leads me away from thinking it's an excess fuel problem. It happened before, but I didn't think much of it. The tach bounces....I don't mean like 100-200 rpm dips due to the bucking that it's doing, but more like dipping from 4500 to 1000 RPMs instantaneously. It goes right along with when the bucking happens. It doesn't do it all the time. That's sounds more like an ignition problem to me. All in all, I think the plugs look fine. Yes, CC is right about when to check the plugs. That test could still reveal something down the road. I'll take it for another ride and check again. I think that something is going on with the CAS or the PTU. Doesn't the CAS send the signal for the tach (among many other things)?, and doesn't the PTU control the spark. I think there isn't enough spark to burn all of the fuel. Anyone agree with this idea?

 

Yes. That is where diagnosing problems is tricky. The white sparkplug suggests ignition problem as opposed to fuel. Can you get another PTU to try? Are you sure the ECU harness connector is straight and tight?

 

sounds like maybe a HKS twin power ignition is in your future.

 

yeah well the symptom of the bouncing RPM gauge points it more towards the CAS, simply because even if the PTU (ignitor chip) was bad you would get an acurate RPM signal. and not only would All the cylinders be affected by it it would not switch arround. or from personal experience aztleast. I woudl try a cam angle sensor first my friend does have one laying arround so let me know if u wanna try it. the CAS is from a 95 n/A motor (the one I did a tt conversion for) we also have the ignitor chip if u wanna try that too.

 

Yes, ecu is straight and tight. The CAS makes more sense to me, but I'll test them both.

I'm not sold on that HKS ignition system...I've been told that it helps, but only in high boost applications. I haven't even pushed past 15 psi yet. I've also been told that at high boost, the spark can get blown out. How? All the valves are closed when the spark plug ignites. I can understand wanting a more intense spark to completely burn the extra fuel that is present during high boost, but I'm not going for the spark getting blown out.