running rich, totally lost

[98s14se]

First off, I have read the fuel injection bible, and searched for about 2 weeks now with no solid answer as of yet...

Here is the issue...

The car runs rich at all times, warm, cold, you name it. Does not smoke black. Smokes a little grey at times. Idles lopey as though it has a cam (it may for all I know, engine came from a racing zcar that was wrecked I'm told). Will idle ok, and drive for about 20 miles with new plugs. It will then foul the plugs and die will not start again for a few hours. Upon starting, it will barely idle, and will not run well enough to move more than a few feet.

Replacing the plugs starts the cycle anew.

Inspection of the plugs reveals a heavy gas smell, and heavy black carbon deposits from even 20 miles of use.

I have done the following:

Replaced all vacuum hoses and fuel lines with new (vehicle run so poorly at idle that even unplugging a large line has little to no effect).

Replaced coolant temp sensor. Replaced wiring for coolant temp and coolant time sensors

Unplugged coolant time, and coolant temp sensors both shile starting, and while running, when both hot, and cold. Both are operating as intended.

Replaced coil and spark plug wires

pulled fuel pressure regulator, and checked for blockages. Seems to be operating fine

Replaced fuel filter

Checked AFM for proper operation. Flapper moves correctly.

Doubled checked routing of all vacuum lines. Lines are routed correctly.

Blocked flow of fuel to cold start valve. No effect while warm or cold.

Swapped ECU with another known good ECU. no effect.

Replaced cap and rotor. No effect. Noted that distributor is loose. Moved distributor both counter and clockwise, and while some effect was felt as expected, nothing was corrected.

Banged my head against the wall repeatedly, still with no effect :-P

Here are a few things I was thinking:

Cleaning the injectors or swapping them out with new. I'm thinking maybe poor atomization is causing the poor running condition and making it seem as though it is running rich. (the lack of black smoke makes me think this)

Replace the AFM

Aaaaannnnddd then I'm at a loss.

Any ideas anyone?

[FastWoman]

WOW! You've about covered it all.

OK, did you check your throttle position switch? You might be getting full throttle enrichment all the time.

How's your fuel pressure? (Yes, I know you checked your FPR for blockages, but did you measure pressure?) If it's too high, you'll be injecting too much fuel.

Another potential problem would be that your AFM's main spring is too loose, perhaps because someone tampered with it. Atlantic Z has an article about adjusting the spring to alter the fuel/air mix.

I doubt poor atomization by your injectors would be to blame, but it probably couldn't hurt to change them. Do you think they might be sticking open from varnish? (Do any of the plugs foul more than any others?) You might run some Chemtool B12 in your gas to dissolve any deposits.

If all else fails, you might try tricking your ECU into cutting your fuel back a bit. Just like some of us run a resistor in series with the coolant temp sensor to enrichen the mix, you might try running some resistance in parallel with it to lean the mix. I wouldn't do this until you've ruled out the above, though.

Good luck! And welcome!

[conedodger]

After all these years, I think our harnesses are finally giving up the ghost. If someone has a 280Z harness that they can send me, I will give it to my electrical engineer friend who builds Porsche harnesses and have him make new Z car harnesses. If they are anything like 914 harnesses they would be about $350 + core and shipping. But here is the big upside, When we plug his 914 harnesses in, we almost always have instant happiness.

As for the OP, all it would take is a broken wire in your CHT or WTS harness and resistance would go to infinity telling the ECU that you're running really hot. The ECU would 'protect' the engine by increasing injection time and making the engine full rich.

Edited April 15, 2011 by conedodger

[FastWoman]

Rob, that instant happiness thing might well be worth $350! There's someone else on this forum who is suffering with a wiring mess that used to be a working harness before some kid got hold of it.