Engine rough running - at wits end

[siteunseen]

When I first bought my 280 I dropped the tank and coated it, waste of time as it wasn't rusty.  The fix was adding a potentiometer in the CTS wires to the ECU.  Mine would spit and sputter up to 2,500 RPMs then clear up and pull like it should.  The way I figured that out was pinching the return line to the tank to build up higher fuel pressure making it richer, negating the lean signal to the ECU.

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

Before you go through all the trouble put in a clear filter coming out of the tank before the the fuel pump, you can see rusty particles if they are in there.

EDIT: the pic below is my 240's filter.

http://atlanticz.ca/zclub/techtips/fuel/g3filter/index.htm

Edited March 13, 2017 by siteunseen

[the_tool_man]

47 minutes ago, siteunseen said:

The fix was adding a potentiometer in the CTS wires to the ECU.  Mine would spit and sputter up to 2,500 RPMs then clear up and pull like it should.  The way I figured that out was pinching the return line to the tank to build up higher fuel pressure making it richer, negating the lean signal to the ECU.

How does this compare to just installing an adjustable FPR?

[siteunseen]

13 minutes ago, the_tool_man said:

How does this compare to just installing an adjustable FPR?

There's not an adjustable FPR that works on our cars.  I've read hours on that and even bought one just to see if it helped and it did not.  They lose pressure.  Airtex is the only one I read about that worked okay and it was like $249.

 

[siteunseen]

You can buy the potentiometer at Radio Shack for $5, that was what fixed mine and many others on here.

I almost bought this Bosch but it doesn't have a vacuum port.

https://www.summitracing.com/ga/parts/bch-0280160001/overview/?cm_mmc=pla-google-_-shopping-_-srese1-_-bosch-automotive

Here's the one that I found that may work, $269

http://www.thezstore.com/page/TZS/PROD/classic17b06/11-3073

Edited March 13, 2017 by siteunseen

[siteunseen]

53 minutes ago, the_tool_man said:

How does this compare to just installing an adjustable FPR?

$$$$$ 

[the_tool_man]

On ‎3‎/‎13‎/‎2017 at 3:39 PM, siteunseen said:

Before you go through all the trouble put in a clear filter coming out of the tank before the the fuel pump, you can see rusty particles if they are in there.

EDIT: the pic below is my 240's filter.

http://atlanticz.ca/zclub/techtips/fuel/g3filter/index.htm

I picked up a G3 filter to install.  Quick question...the linked article refers to the fuel hoses being 3/8".  But all the ones in the engine room of my car are 5/16"  I got under my car last night and measured just over 5 feet of hose.  It measures the same OD as the 5/16" I've used elsewhere.  Which size is it?  At something like $7 per foot, I don't want to buy the wrong size.  Yes, I know I don't have to use the FI hose on the suction side of the pump, or the return line.  But my local supplier doesn't have low pressure hose rated for alcohol.  So I plan to use the good stuff everywhere.

Edited March 24, 2017 by the_tool_man

[Zed Head]

The big hose is for between the tank and the fuel pump.  There is none in the engine bay, for fuel flow.

"

One way to proactively prevent this problem is by placing a fuel filter between the fuel tank and fuel pump.

A Fram G3 disposable filter is the perfect choice:

• It has 3/8" fittings (the G3 is really G3/8"). This works well with the 10mm Nissan fuel hose. "

[siteunseen]

23 hours ago, the_tool_man said:

I picked up a G3 filter to install.  Quick question...the linked article refers to the fuel hoses being 3/8".  But all the ones in the engine room of my car are 5/16"  I got under my car last night and measured just over 5 feet of hose.  It measures the same OD as the 5/16" I've used elsewhere.  Which size is it?  At something like $7 per foot, I don't want to buy the wrong size.  Yes, I know I don't have to use the FI hose on the suction side of the pump, or the return line.  But my local supplier doesn't have low pressure hose rated for alcohol.  So I plan to use the good stuff everywhere.

I'm sorry to just be getting back with you, but like Zed Head says it's the only big hose that I know of on a 280.  The one coming out of the tank to the suction side of the pump.

On a 240, the Fram G2 works better for me, that hose is smaller.  

[Patcon]

Ok,here's where we're at. We have the car running again tonight and I have a fuel pressure gauge on it.

What is the factory pressure supposed to be? I don't know this 280z stuff off the top of my head but I know someone does. The pressure gauge is just after the fuel filter and before the fuel rail. We were seeing pressures of between 26 & 28#s. That seems low from my memory. Also the pressure bleeds off pretty fast one we kill the power

 

[Yarb]

Mine ran around 32 after the initial start. Mine bled off rather quickly meaning over but was never a problem on a cold start.

[Captain Obvious]

Fuel pressure should be 36 psi minus manifold vacuum (in psi).

So for example, if manifold vacuum is 16 inches of Hg, then the fuel pressure should be (36 - 7.8) or about 28 psi.

The conversion for inches of Hg to psi is about half. One inch of mercury is about a half psi.

[Patcon]

8 minutes ago, Captain Obvious said:

Fuel pressure should be 36 psi minus manifold vacuum (in psi).

So for example, if manifold vacuum is 16 inches of Hg, then the fuel pressure should be (36 - 7.8) or about 28 psi.

The conversion for inches of Hg to psi is about half. One inch of mercury is about a half psi.

Thanks for the quick feedback. I will put a vacuum gauge on it next time I have a chance. Should the fuel pressure gauge fluctuate when you rev the car or does it not respond that way or that fast?