Runs rich and high idle after restart

[siteunseen]

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

From the atlanticz tech tip link:

Trouble Shooting

If you suffer from a fast idle after the car is warmed up, simply use vise

grips to pinch off the hose between the throttle body and AAR. If the idle rpm

decreases then the AAR is not closing.

Also does your car have a BCDD? It might need an adjustment.

[FastWoman]

Other rich-running causes, besides the CTS and FPR:

Cold start valve. (Test by clamping or blocking the fuel line.) It might be stuck open, or the thermotime switch might be bad. Or perhaps something was miswired.

Bent AFM vane (from backfire). I had this issue in a '75 (which doesn't have the backfire valve). A backfire bent the vane, so that when it opened, it turned the potentiometer a bit further than it should have. I fixed the issue literally by tapping the vane out with a hammer.

AFM broken, misadjusted or out of specification.

As far as I'm aware, any other problem would cause the engine to run leaner, not richer.

[mjr45]

Siteunseen, the BCDD shouldn't have anything to do with a fast idle after a restart, just when slowing down, but it might be that it gets stuck after the car is driven, I'll check on it.

Zed, I'll post a pic of my intake later today, I tried to copy the pic from my FSM, but couldn't get a decent copy to post, I'll see what I can do later, because it is curious to have different diagrams from the same year FSM, curiouser and curiouser. I wonder of if a CA car has the heater and Fed models don't? I know the CA model had an EGR and the Fed model didn't.

[mjr45]

Zed, here are a couple of pics, one of the engine bay and one of the AAR, hope this helps with the quandary. No heater lines to the AAR. The engine bay pic is probably not real informative, sorry.

Mike

Edited January 26, 2014 by mjr45

[Zed Head]

I'm going to guess that somebody removed yours. The block would be mounted using those two bolt holes, but with longer bolts. A sandwich. To remove it you'd just use shorter bolts. The block is ugly and a real pain to get the coolant lines connected, and is a potential leak source. Not a big deal if the power to the internal heater still works. It does take about 40 seconds or more to fully close the valve using just electrical power though.

You can pinch either one of those hoses shut to see if it's the valve staying open that causes the high idle, as siteunseen suggested. If the hoses are old though, they might split. Then you'll get a really high idle that never drops.

On the BCDD - it lets air past the throttle blade like the AAR does. Whether it would cause a high idle at start would depend on if the passage is normally open (closed by engine vacuum or the solenoid) or normally closed (opened by the solenoid or vacuum). You'd have to study the Emissions chapter to know.

[mjr45]

Fastwoman, the FPR, CSV and Thermotine are all new <6 mos old. All the rubber lines in the engine bay are new. I have suspected for a while that the AFM is the culprit, when running the tests in the EFI Bible some of the specs were off not real off, but not close enough to call it good. I've looked at the AFM (out of the car) and couldn't figure out how to take it apart to see if the vane was bent, looking at it with a light it looks OK but who knows. The engine did have a couple of front fires in the past so maybe its bent.

Zed, I'll look at the BCDD section and see if maybe that's a culprit, it won't hurt to just disconnect the electrical line and see what happens. Also, Fig. EF 115 in my FSM shows the "fuel pipe removal." Go figure?

Is it possible the ECU could be at fault on the rich running? I have a spare and just might swap them out as a trial.

Thanks

Mike

Edited January 27, 2014 by mjr45

[FastWoman]

Just look at where the flap comes to rest. As I recall, the '75 AFM has no bumpers to stop the travel of the vane, but it's rather obvious looking at it where the vane is supposed to stop when fully closed. If it's somewhat curved and rests past that point (mine was bent maybe 1/4" past), then it's bent. As I recall, I cut a block of wood to stick up through the throat of the AFM as an anvil, and I tapped a block of wood on the other side to straighten the flap. All I did was to straighten the curve. My engine instantly ran better.

There's also the possibility that your AFM's clock spring has been adjusted by a well-meaning mechanic. Visit the Atlantic Z website for a re-calibration procedure. And it's also possible a well-meaning mechanic wrapped up a fixed resistor in your fuel injection harness. Such was the case with mine. I removed mine and ultimately inserted a variable resistor (potentiometer) to tune the mixture.

**Is it possible the ECU could be at fault on the rich running?**

Yes and no. The ECU drift issue seems to plague the later models (77 and especially 78). I believe Datsun made a shift from Bosch (your year) to Hitachi (my year) somewhere along the line. The ECUs would have been functionally similar, but with somewhat different circuit designs. In the '77/78, there seems to be a pattern of drift towards the lean side. This would represent a common failure mode characteristic of the design. Could a '77/78 ECU drift the other way? Not likely. It would be more likely that the unit took some sort of damage to cause it to suddenly run rich.

None of this is to say how a '75 Bosch ECU might drift. Frankly I wouldn't have a clue. I've not heard of the '75 ECU drifting, but that doesn't mean it doesn't happen. It's possible. Time and heat are the enemies of electronic circuits, and 40 years (almost) is quite a long time for these circuits to keep running within spec. I would be astonished if the circuits in your ECU hadn't drifted. The trick is whether the designers were clever enough to design in compensations to keep the behavior of the ECU relatively stable, despite the drifting of individual components.

[mjr45]

OK toady I checked the coolant temp circuit and got NO continuity on the wire harness, good, read 4.5ohms when really cold (38 outside and coolant not much higher) and 0.4 ohm after getting to 145° which by the FSM shows the sensor to be good. I'm thinking the culprit is the AFM, I'll pull it later and see if the vane is maybe bent, as I stated, I've already adjusted the toothed spring gear 8 or 10 teeth clockwise which should have really leaned it out and I don't think I should go any further with that. I'll run the tests in FSM on the AFM and that might give me some more info. I hate the idea of spending $200 for a rebuilt unit, but oh well its gotta run right before I sell it.

The AAR is sticking which is causing the fast idle, so I'll clean it out some how, I checked today when it was "fast" idling after warmed up by clamping the hose on either side and it almost died out, so the AAR is not closing properly. I tapped on it with wrench and the idle dropped after each tap so its sticky.

Thanks for the help.

Mike

Edited January 27, 2014 by mjr45

[sscanf]

Have you performed the yogurt cup test?

I had some idle problems with my 76 and thought there was no chance of a vacuum leak but the yogurt cup test revealed that I had a torn diaphragm in by BCDD.

[siteunseen]

The AAR is sticking which is causing the fast idle, so I'll clean it out some how, I checked today when it was "fast" idling after warmed up by clamping the hose on either side and it almost died out, so the AAR is not closing properly. I tapped on it with wrench and the idle dropped after each tap so its sticky.

Thanks for the help.

Mike

You're welcome.

Please try this $5 fix 1st, http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

Edited January 30, 2014 by siteunseen

[mjr45]

If my AFM is out of spec, would using the 1K pot on the temp sensor make up for the out of spec AFM? Also, would turning the pot CCW decrease the amount of fuel the ECU signal would send, since the article seemed to want to add more fuel? I checked the resistance on my AFM according to the EFI Bible and got these Test #1 212 ohms, should be 180, test #2 112.4 ohms, should be "around 100", so I believe the potentiometer in the AFM is off. I'm not real sure how to "measure the injector duty cycle......and adjust the AFM spring so that the duty cycle matches the same as above." as stated in the Atlantic Z write up. Maybe ya'll can shed some light. Thanks.

Mike

Edited February 3, 2014 by mjr45

[FastWoman]

Maybe you can measure duty cycle with a dwell angle meter wired between +12 and the output of the ECU (note: not the contacts on the injector, which would have a lower voltage differential across them.

The answers to your other questions all "depend" on other things:

Would a pot on the CTS make up for an out-of-spec AFM? It depends on how it's out of spec and how the pot is wired. Not enough info here.

Would turning the pot CCW...? It depends on how the pot is wired. Adjusting it to a higher resistance gives you a richer mix. You can determine which direction raises resistance with your multimeter.

Your resistances aren't "awfully" out of spec. However, there's much more to a properly operating AFM than just those resistances. The ECU actually looks at the output voltage. The pot inside the AFM acts as a voltage divider. So if ALL your resistances were 10% high, it would make no difference at all.