Runs rich and high idle after restart

[mjr45]

Been gone for awhile and took the Z out the other day just for grins in the balmy 45° weather. Couple of issues, 1. it still runs very rich, lots of black soot from the exhaust and on the plugs. 2. after driving for awhile 10-20 minutes, shut her down and went to the store, came back out and started her up and the idle went to 1800 and very slowly dropped back down to normal. Things I've done in the past 6 months; adjusted the AFM to the lean side(ccw) 8 notches, new AAM, Cold start injector, injectors replaced about 500 miles ago, new FPR, new fuel lines, new filter. Probably some other stuff that I can't remember. Fuel pressure is right on. The rich running has been an ongoing problem but the high idle is new and doesn't seem to matter what outside temp is, did the same thing last fall when it was 70°. I need to fix this stuff since I will be selling her off in the Spring, don't want to, but need some $. Thanks.

[Zed Head]

The high idle sounds like your AAR is not getting hot and staying hot. Do you still have the coolant line running to the mounting block for the AAR? That's what keeps it warm. And the power line to the AAR warms it up when the coolant is cold.

On the rich running - have you confirmed that the fuel pressure drops with intake vacuum? You can have spot-on pressure, not running, but be rich running if the FRP is not adjusting pressure.

[mjr45]

Zed, there are no coolant lines running to the AAR. The new FPR should be adjusting the pressure, there is no fuel leaking from it when disconnected from the vacuum and a definite drop in RPM when disconnected. I'm not real sure how to check a drop in pressure from the FPR, I thought it was there to maintain a constant pressure in the rail. I've only checked fuel pressure with the engine running. Thanks.

[Zed Head]

If the idle speed changes when you remove the hose odds are it's working right. If you measure pressure with the hose on and off it will tell you a lot. Numbers are always good, "right on" just means that you feel good about it (no offense).

The AAR came from the factory with a heating block under it, with coolant lines attached. If yours is gone, the AAR will not get as warm as designed and stay open. Could be part of your problem. You didn't mention the power line to the AAR. You can check power with a voltmeter, it should have power when the engine is running. It's on the fuel pump circuit.

[mjr45]

Zed, I'll check the power line to the AAR, but there is no coolant line or a connection for one on the AAR which is the correct one for the year, no offense, the old had no coolant line either. As for fuel pressure numbers, I got 36.5 to 37 at idle. Just for reference, on a completely cold start(in the AM), the idle goes up to about 1300 then comes down after only a couple of minutes of driving, its only after driving for 15 minutes or so and then a restart after 10-15 minutes that the idle goes up and takes 1-2 minutes to come down to normal. Thanks.

[siteunseen]

If it just started the high idle, I'd take the AAR off and clean it. Your '75 has the older routing of the hoses and gets cruddy.

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

Forgot to say you'll not be able to take it apart like in the tech tip, I used spray brake cleaner. Cleaned it right up.

Edited January 25, 2014 by siteunseen

[mjr45]

siteunseen, the AAR is less than 6 months old but I suppose it could be crudded up, I'll check, thanks.

[Zed Head]

siteunseen makes a good point. The AAR's tend to get gummed up.

I can't find a specific reference to the heating block but I did find a picture. I added red lines to indicate the inlet and outlet coolant lines.

Check your coolant temperature sensor resistance at the ECU connector and compare it to the chart in the FSM. You might have dirty connections somewhere, raising resistance.

[FastWoman]

I'd bet good money that the rich running problem is the coolant temp circuit -- a bad connection or too high a resistance. Mine had a resistor wrapped up inside the fuel injection harness by some prior mechanic. Anyway, if you have a bad connection (infinite resistance), you'll definitely get black smoke!

[siteunseen]

Oh ok that's pretty new, you can clamp that hose to see pretty quick though. Hopefully it's a bad plug, dirty or loose?

[mjr45]

Zed. mine doesn't look like that all, the lines in your diagram don't show in my FSM at all.

Fast Woman, I'll check the coolant temp circuit tomorrow, the connectors are all new, but I don't remember if I changed the coolant temp sensor, I know I changed the thermotine sensor. The rich running has been a persistent issue, but the car runs great so I haven't been real concerned.

Siteunseen, not real sure what your last post is about?

Thanks for all the help.

Mike

[Zed Head]

The drawing is from the 1975 FSM. Odd. A picture of the top of your manifold would be illuminating.