four cylinders not firing, oil in each; stock 240z

[jwilliams905]

Check the screens in the banjo bolts, replace the fuel filter and do a flow test. The rear screen may be clogged and with the front line blanked off enough pressure can be built up to feed the rear carb. Cutting on a gas tank and welding for that matter is a very bad idea. The tank has to be absolutely clean and your welding has to be very good to not have pinhole leaks. I weld a lot for a hobbyist and I wouldn't try it. There are kits that can be used for cleaning the tank and resealing. Clean with acid, neutralize and coat with tank sealant. A much easier and safer idea...

Charles

Yeah, it didn't take long to give up on that idea. I'm assuming banjo bolts are the two nozzles on the sides of my fuel pump?

(circled here in faint red)

Edited September 2, 2013 by jwilliams905

[Captain Obvious]

I may be completely off base here, but I think you're off in the weeds...

I think what you're calling oil on the rear three plugs is actually gas and not oil, and I think that when you disconnected and plugged the fuel supply to the front carb you were still running off the front carb and were simply consuming the fuel that was in the front float bowl. (The engine will run for at least thirty seconds with the fuel line disconnected.)

So... When you disconnected the front carb supply and the engine started suddenly running on the rear three cylinders, how did you verify that it was the rear three? Did you suddenly discover that the rear three exhaust tubes were now hot and the front three were now cold? Or were you just assuming that since you had the fuel line to the front carb disconnected, the engine must be running on the rear carb?

If your rear three plugs are wet, I think your rear carb is running too rich. So rich, in fact, that those three cylinders won't fire and the plugs are drenched with unburned fuel, not oil.

I don't think you ruined your rings. I don't think you're having a problem with the restrictor orifice... I think you're dumping in too much fuel through your rear carb. I think you're overcomplicating this. Like I said, I may be off base, but that's my read.

[Stanley]

Might be time to give it a rest. I'd just sit back with a cold beer and some chips, and try again tomorrow.

[Patcon]

Captain Obvious may be right on this. He nailed an earlier diagnosis. Banjo bolts are at the intake to the SU float bowls. The intake tube has a bolt that goes thru it, fuel goes thru the intake port, then thru a small screen around the bolt, then thru the bolt and into the float bowls. Google "SU Banjo bolt"...

C

[jwilliams905]

I may be completely off base here, but I think you're off in the weeds...

I think what you're calling oil on the rear three plugs is actually gas and not oil, and I think that when you disconnected and plugged the fuel supply to the front carb you were still running off the front carb and were simply consuming the fuel that was in the front float bowl. (The engine will run for at least thirty seconds with the fuel line disconnected.)

So... When you disconnected the front carb supply and the engine started suddenly running on the rear three cylinders, how did you verify that it was the rear three? Did you suddenly discover that the rear three exhaust tubes were now hot and the front three were now cold? Or were you just assuming that since you had the fuel line to the front carb disconnected, the engine must be running on the rear carb?

If your rear three plugs are wet, I think your rear carb is running too rich. So rich, in fact, that those three cylinders won't fire and the plugs are drenched with unburned fuel, not oil.

I don't think you ruined your rings. I don't think you're having a problem with the restrictor orifice... I think you're dumping in too much fuel through your rear carb. I think you're overcomplicating this. Like I said, I may be off base, but that's my read.

I agree about the oil actually being fuel. I know the rear three were running at that point because I used a wet rag to compare the temperatures at the header, and I also pulled the 6 and 5 plug wires and it quit running. Before then, I had it running with all three of the rear plug wires unplugged. I haven't got the tools and means at the moment to run a fuel pressure test, so tomorrow, I'll get the proper equipment.

Is that fuel pump in the picture I posted the stock fuel pump? It looked that clean when I bought the car, so I don't know if the original owner put some crappy aftermarket pump in.

[Patcon]

That is a stock fuel pump, and if you buy one from a parts store it may not even look like that. Some of the newer cheaper pumps don't have that type cover. whether that is the original pump or not who knows, but I doubt it.

C

[Captain Obvious]

Well if you're convinced that it's a fuel delivery issue it should run on all six cylinders if both carbs are getting the right amount of fuel...

Pull and plug the fuel supply tubes off both carbs and fill the float bowls with a funnel and a short piece of tubing while checking the float bowl level with a clear piece of tubing on the outlet nipple on the bottom of the bowls. Once you're convinced that both carbs are filling to the correct level, then start the car.

If you're right, then it should run well on all six cylinders for at least thirty seconds until the float bowls are sucked dry. If not, then it will still run like crap.

[beermanpete]

Well if you're convinced that it's a fuel delivery issue it should run on all six cylinders if both carbs are getting the right amount of fuel...

Pull and plug the fuel supply tubes off both carbs and fill the float bowls with a funnel and a short piece of tubing while checking the float bowl level with a clear piece of tubing on the outlet nipple on the bottom of the bowls. Once you're convinced that both carbs are filling to the correct level, then start the car.

If you're right, then it should run well on all six cylinders for at least thirty seconds until the float bowls are sucked dry. If not, then it will still run like crap.

Good idea. Divide and conquer!

[jwilliams905]

Yeah man, that sounds like a plan. Sadly, it'll be friday before I can touch the car again, so I'll get a few parts ordered and perhaps an electric fuel pump just in case. Does anybody have a reccomendation for an electric fuel pump? There's a lot to choose from, but I wanna go ahead and get the best one I can get.

[madkaw]

RX-7 carbed pump

Check that fuel rail

[jwilliams905]

RX-7 carbed pump

Check that fuel rail

I have already blown the rail through from both the fuel line and the return line end and it blew through fine (according to my innexperienced perspective). Somebody mentioned that there could be a pin hole or something in the diaphragm of the fuel pump. Now that they mention it, I recall when I pulled it apart that there was fuel under the diaphragm. By my understanding, that should not be.