Still runs rich!!

[mjr45]

75 280Z with 79 block and dizzy. After replacing the temp sensor and adjusting the AFM 4 teeth CW, it still runs very rich, plugs are covered in black soot, black soot and condensation blowing out the exhaust pipe when first started. The idle will not remain steady and requires adjustment almost every day, I've already replaced AAM which helped. I also know there is a vacuum leak, but can't find it anywhere, vacuum is about 12 psi with all new lines, AFM boots, etc. Timing is about 8 degrees and I know the oil pump is off about 1 tooth, which prevents advancing the timing any further. Could the timing being off cause it to run this rich? I really hate to try and tweak the AFM any more. the engine runs well with no missing, surges or hesitation and I see no smoke after initial start. Any suggestions will be greatly appreciated. I'm still chasing down multiple electrical gremlins, i.e. no oil pressure gauge, no back up lights, no defroster, what a mess this "refresh" turned out, but I'm seeing the light at the end of the tunnel, just hope its not the on-coming train! Thanks

[240260280z]

Readjust the timing:

1. JAck up front or drive up on car ramps

2. Pull plugs

3. Put in neutral

4. With 27mm socket, turn crank nose bolt so that engine is at TDC

5. Loosen sway bar end links

6. Disconnect 4 bolts holding swaybar to engine frame rails

7. remove bolt holding distributor (10mm wrench) and lift distributor

8. Note position of spindle tang in distributor mounting hole.

9. remove 4 bolts to oilpump and pull out (watch the gasket!)

10. re-align the dot (hole) in the spindle rod just above the gear with the oiling "wedge-shaped-hole" in the neck of the oil pump.

11.insert the pump a and bolt up

12. check the "11:30" alignment of the tang in the hole.

~ 30min max job.

[darom]

Did you download and read the "280-Z ELECTRONIC FUEL INJECTION • THEORY • TROUBLESHOOTING", aka the Fuel Injection Bible? I think pages 14, 15, 52 and 54 might help.

I realize that you said that you had replaced the water temp sensor with a new one. Have you checked its resistance cold and hot?

Have you tested the air temp sensor in the AFM? What are its resistance parameters?

Have you tried testing the operation of the Cold Start Valve (CSV) while it is out? Does it continuously spray fuel? Have you tried unplugging it and see if the car runs leaner?

What is your fuel pressure? Excessive fuel pressure with a malfunctioning fuel pressure regulator will cause the car to run rich.

What happens if you unplug your AAR? Does the idle stabilize?

Here is a good thread:

http://www.classiczcars.com/forums/thread41966.html

where FastWoman mentions the "yogurt cup test" to find the vacuum leaks.

GL!

[Wade Nelson]

Take your car to a mechanic with a smoke machine and smoke the manifold to find your leaks. (They only apply 1-2psi) Alternately, find a heavy smoker to exhale large amounts of tobacco smoke into the brake booster line. Then check the brake booster itself. You may need to do both engine cold ' engine warm to detect a manifold gasket leak that seals up when the engine iscold.

A vacuum leak should be causing your vehicle to run LEAN, not rich. the 280 doesn't have an 02 sensor, right?

So the things telling the ECM how much fuel to inject include:

Air flow meter

Coolant temp sensor

Throttle position sensor

Signal from distributor telling ECM rpms

Could you have been dialing the AFM the wrong direction?

No, I don't think advanced or retarded timing would cause your engine to run rich.

Since the 280 does NOT have a catalytic converter, I would EXPECT it to blow a certain amount of soot on startup when the Cold Start Valve is practically flooding the engine with fuel. But your plugs should clean up within 3 minutes of hitting the highway. What happens when you try and start it with the CSV disconnected?

Are you positive you replaced the CTS and not the GAUGE sender? Unplug the other one and see what the gauge does. Aren't the Aux Air Valve and CTS connectors the same? Do you have them swapped?

Pull the hose off the fuel pressure regulator and plug it witha golf tee. Now put on a fresh piece of vacuum hose, longer, and try sucking on it with the engine running, see if you get any rpm change. Or "Tee" a fuel pressure gauge in and watch that while you suck on it. If you get a mouthful of gas, well, spit it out, and then go buy a new FPR.

If your idle won't remain steady, I would STRONGLY suspect your throttle position sensor is either failed or out of adjustment. The ECM isn't getting the signal TELLING it your foot is completely off the pedal. A failed TPS can definitely cause rich running, because the ECM is being told it's under load when in fact it's actually loafing.

So there, I've talked myself into throwing a new TPS on it, or at least testing the old one throroughly with a DVOM, per the Fuel Injection Bible. (you've already downloaded and begun memorizing that, right?)

That should keep you busy for 3-4 hours. Get back to us with what you find.

[mjr45]

Yes I have the EFI Bible, fuel pressure is 34-36psi at idle, haven't yet checked the TPS, but have opened it and adjusted it to the correct positioning at idle and WOT. Positive on the CTS, not the temp gauge, I'll check the TPS again and also the FPR. I've tried the CSV disconnected and it makes no difference. I used Fastwoman's yogurt cup test and couldn't maintain a vacuum, the engine has new gaskets all around and new vacuum lines, I tried the blowing smoke test and got leakage around the TB butterfly no where else that I could see. Today, I took her out and any revs above 3K caused it ti miss and the tach bounced all over the place above 3500, would go from 3200 to 5K and drop back then bounce some more, below 3K no misses and steady tach, it amazes me because I haven't touched anything in days and it ran fine until today. I'll also check the air temp sensor, haven't done that yet, and I'll try unpluging the AAR to see what happens. Thanks for all the answers.

Edited September 18, 2012 by mjr45

[Wade Nelson]

Couple of things 12" (not psi) of vacuum at idle isn't NEARLY enough. That's an indication of a REAL problem, like a broken valve spring, MAJOR vacuum leak, COMPLETELY clogged exhaust system, timing chain off a link, SOMETHING major. Vaccuum that low tends to indicate major mechanical problems with the head.

Your "Tachs gone wild" above 3000 rpm sounds more ignition related to me, like your distributor pickup is failed or the toothed reluctor has a crack in it so at higher rpm's the ECM is seeing a very invalid signal. A crack in the reluctor can be damn near impossible to see without bright lights, etc. Your best shot is to put an oscilloscope on it and WATCH the signal above 3000 rpm and see if it goes to hell.

Did you test the FPR as I suggested? If the diaphram is "holy" then raw fuel is pouring into the intake manifold directly from the FPR. That could easily explain the rich condition, although it should favor the two closest cylinders.

I'm still leaning towards a failed TPS, connector, or wiring because its failure modes explain SEVERAL of the symptoms you describe. Very similar to a 4-Runner I owned with a failed TPS, erratic idle, lack of power under load, hesitation /stumble, misc.

[darom]

With such a low vacuum, you are getting 34-36 psi fuel pressure? IMHO, this is too much. You should be getting this pressure when the engine is under load. At idle, the numbers will be in mid/high-20s. I don't think your fuel pressure regulator is doing its job.

Here is another good thread to consider (the guy is running aftermarket cam with 5 in of vacuum):

http://www.classiczcars.com/forums/thread40602.html

[Wade Nelson]

Here is another good thread to consider (the guy is running aftermarket cam with 5 in of vacuum):

http://www.classiczcars.com/forums/thread40602.html

I'm gonna put that one in the "Nightmares I hope I never buy into" category. 300cc injectors? .

[mjr45]

Will be spending today going over all the things suggested to check as well as rechecking the electrical connections and let you all know what I come up with. The head was recently redone with couple of new valves, springs and guides all checked out OK, so just basic 3 angle grind and leveling of the head top and bottom took off 0.008 on the bottom and 0.002 off the top. Has new chain and guides and I'm sure I lined the chain up properly, so I am at a loss as to where the vacuum leak is. Just as an FYI, the injectors are new (stock) as are all the EFI connectors, the fuel rail and FPR are from a 79ZX. Thanks again.

Edited September 19, 2012 by mjr45

[240260280z]

WRT leak: PCV and hose installed under the manifold?

[mjr45]

Blue, yes new PCV but old hose, I think I'll change that out. Just finished doing some of the checks mentioned, the TPS may have been slightly off towards the idle position, so I changed that a bit, also, the Air Temp sensor in the AFM maybe off, outside temp was 74 and the Ohm reading was 1421 and should be at 2250 or better @ 68 degrees so I'm not sure if it is really off, also the dizzy vacuum diaphragm moved the reluctor slightly, but doesn't hold any vacuum, taking off the vacuum on the FPR and applying suction with a small hand pump made no change in RPM, RPM increased when line was off and not plugged. Vacuum is still at 12" drops to 0 when revved and then jumps to about 16 when throttle is let off and then back to 12.

Edited September 19, 2012 by mjr45

[Zed Head]

Looking through this thread a couple of things stand out - "it ran fine until today" and "the tach needle jumps around".

If it ran fine, then you can be reasonably sure that the mechanical stuff was all correct.

If the tach needle is jumping around, you either have an ignition problem, as Wade suggested, or the tach died all of a sudden. So looking at the FPR and the TPS and the vacuum advance is probably a waste of time. None of those will cause the tach needle to jump around or be affected by the ignition system.

Fix the known problems first, that would be my approach. You know that something is wrong with your ignition system, or your tachometer.