7mgte idles great but has a rich issue/stalls

[IndigoMKII]

Okay so here it is, my recently dropped new long block 7mgte idles great but sometimes if you rev it up and hold the throttle at around 2500rpm it sounds as if the cylinders are loaded up. The car occasionally puffs a nice big cloud of black smoke during a rev, not after. I've looked around on the car for any vacuum leaks but vacuum leaks would cause a lean condition. I've also noticed that the blue wire on my 3 wire o2 sensor is broken, thanks to the previous owner.:3d_frown:

So here's my questions, could the o2 sensor cause a rich enough condition to make it puff black smoke? I know the o2 sensor has no effect on idle. Also could the o2 sensor make the car stall when you push the clutch in? I do have a vented hks ssq bov and I know that causes the maf to get upset. The dashpot is also properly adjusted to make sure the throttle doesn't 'snap' shut because I had to adjust it so the bolt head would actually hit the dashpot push rod.:3d_frown:

Mods on the car are ct2657 on wg pressure, apexi intake and borla catback.

 

[topekamk3]

The o2 sensor could cause it, however 1st thing I would check is that the bov isn't sticking open or fluttering. If either of those is happening to the bov you are letting out air that the maf already added fuel for which would then cause a rich condition.

 

[jetjock]

No. An open O2 input alone can't cause that. It's the law in fact. You have other problems. Course, that doesn't mean known broken stuff shouldn't be fixed.

 

[IndigoMKII]

An o2 sensor is on order, I was wondering if just the o2 would be causing that. Could poor vacuum to the stock fpr cause rich conditions like that? I can't tell how it acts under boost as it's a new engine and I'm not wanting to run it hard with these problems.

 

[IndigoMKII]

Okay so following the tsrm, I have no codes. The ignition timing is dead on, double checked it with my timing light. Mechanical timing is good. Doesn't the cold start injector only work during cranking? Is there a way to test the injectors without removing them? I've used the solid bar test to make sure they are all firing. Spark plugs are brand new NGK's gapped to .029. I recently bought a new tps so that is set per the tsrm. Only things left to test would be the injection circuit, which is probably good, and the oxygen sensor, which I have one on order.

 

[D.J.T.]

No. An open O2 input alone can't cause that. It's the law in fact. You have other problems. Course, that doesn't mean known broken stuff shouldn't be fixed.

Enlighten me with your knowledge please.. When i had the old O2 sensor (broken blue wire) i was getting 8MPG (driving like a grandma...) & when i replaced it i started getting around 19 MPG (driving like a grandma) i get 15-16 MPG if i drive regularly.. Why did the O2 sensor make any difference? The only way i can come up is that it was running rich but you say that the O2 sensor input failure ALONE can't cause that.. what other factors play part? Thanks for any useful input in advance.

 

[jetjock]

I said it wouldn't cause his symptoms. A 60% fuel economy reduction? I dunno what your issue was but it couldn't have been O2 alone. Not on a stock engine.

Have a wideband? If so run the engine at 2500 rpm and disconnect the sensor. Then short the input to ground. Follow that by applying 1 volt dc to it. Note the mixture in each case. Although I've done it many times using an emissions analyzer I'd still like to know what happens on your car.

Remember, the ECU does things when it detects bad sensors. It has to because of emissions law and O2 sensors are all about emissions. For the car to do as you claim it could not have been certified by the EPA for sale in the US. Not to mention O2 sensors have the least authority of any sensor in an engine for reasons that, if you think about it, should become clear. This is all EFI 101.

 

[IndigoMKII]

Could you help point me in the right direction to fix this problem? I'm not one to want to be handed things because you learn nothing that way but a sense of direction is always welcome.

 

[jetjock]

Fix the O2 sensor and then verify the engine is in fuel control. See the TRSM for details. If it isn't fix it so it is. Then report back with a better description of the symptoms. "Loaded up" isn't that helpful.

 

[IndigoMKII]

I mean loaded up like when you hear a cylinder stumbling from being flooded.

 

[IndigoMKII]

Okay so I found a broken wires to the front VSV connector. I'll report back if anything changes when I get the O2 sensor installed and these broken wires fixed. Does anyone know the PN for the VSV connector? Does it come with a pigtail on it like the knock sensors?

 

[jetjock]

Front VSV is for the FPU system. No harm in fixing it but not the cause of your problem.

I mean loaded up like when you hear a cylinder stumbling from being flooded.

You mean rich misfire. The O2 sensor doesn't have enough authority by itself to cause that. In fact with it disconnected and everything else working right the engine will run smoother and cooler but burn more fuel. It's because the default mixture condition with a bum sensor is close to best power which is slightly richer than stoichiometric. It's why your engine idles so well.

 

[IndigoMKII]

Okay so with a rich misfire, it could be many things. I guess I have to start knocking them off one at a time. I'm not sure what the previous owner has done to the car, it did have a ghetto setup afpr on it, so it could have a different fuel pump in it. Could the walbro 255(If it has one) without the j tube drilled cause a constant rich condition? Is there a way to check for a leaking injector without pulling the manifold down? The idle doesn't change much with the stock fpr vacuum line plugged in or not plugged in, is this operation normal?

Also would there be a way to check if it's a walbro 255 or stock fuel pump without dropping the tank?

 

[topekamk3]

A walbro 255 without a drilled jtube could cause it. To look for a leaking injector you could try to shine a light in the intake manifold area and look for traces of fuel as the car is running.

 

[IndigoMKII]

A walbro 255 without a drilled jtube could cause it. To look for a leaking injector you could try to shine a light in the intake manifold area and look for traces of fuel as the car is running.

I meant leaking injector such as clogged or a bad spray but wouldn't a leaking injector cause a bad idle as well? Or only when the injector cycle duty has to go up?

 

[topekamk3]

I meant leaking injector such as clogged or a bad spray but wouldn't a leaking injector cause a bad idle as well? Or only when the injector cycle duty has to go up?

Yes usually a injector that has problems would cause problems at idle and more often than not it would case a lean condition. Did you check your bov yet? If its fluttering at anything over idle it could cause a rich condition since it would let out some of the air the computer already calcuated for.

 

[IndigoMKII]

It's an HKS ssq vented to atmosphere, I'll be making a recirculation tip for it on the lathe. It doesn't seem to be leaking air in above idle by covering it with my hand.

 

[topekamk3]

Easy way to look for a boost leak is build a tester and then use a bicycle pump that has a psi gauge on it.
http://www.dsmtuners.com/forums/art...209898-build-boost-leak-tester-your-to4e.html

 

[IndigoMKII]

You're referring to a vacuum leak/boost leak. A vacuum leak at idle would cause a lean condition, not a rich condition. I haven't driven the car hard enough to get in positive manifold pressure. The car will rich backfire when revving at a stand still.

 

[topekamk3]

You're referring to a vacuum leak/boost leak. A vacuum leak at idle would cause a lean condition, not a rich condition. I haven't driven the car hard enough to get in positive manifold pressure. The car will rich backfire when revving at a stand still.

Sorry about that...Posted that from my phone and was suppose to go to a different thread on a totally different site(hints the dsmtuners link lol). Have you checked your spark plugs lately?