Hi guys,

I am looking for your advice before I open my AFM unit and start messing with it.

Symptoms: when the car is cold, it runs very lean, bogs down, popping noises, lack of power. When it warms up, more manageable to drive, although it occasionally makes the same popping noises. it also smells lean from the exhaust.

What has been done:

1. Remanufactured AFM, sealed up. Adjustments to the air bypass screw don't help richen up the mixture.

2. I went through all the FI Book tests, the air temp sensor in the AFM/water temp sensor in the t-housing, all pass. Cold and warmed up.

3. Throttle positive switch - adjusted, at idle, middle position and at wide open per FSM.

4. The fuel pressure gauge shows 30 psi and idle, 36 psi at acceleration. New fuel MSD-2225 fuel pump with a pre-filter, clear gas, no rust in the tank.

5. Vacuum gauge shows 14-15. I am guessing this is a low reading.

6. Idle - 850/900 rpm, 11 BDTC

7. Some time ago I installed an inline pod resistor for the t-stat water temp sensor. If it is at 0 Ohm, the car runs lean, revving up from idle produces lean popping. If I set it at 1000-1200 Ohm, the car can be revved up.

8. This is a CA car, came with a functioning EGR valve, while testing I disconnected it.

9. New intake/exhaust gasket, valve cover gasket, no air leaks around the oil pickup/oil filler. Removing the oil filler cap, reduces the RPMs, engine wants to stall.

10. Air regulator was tested, it closes up after 10 minutes. Pinching the hose produces engine stumbling.

11. The injectors were replaced with brand new units a while back.

12. The timing chain was replaced a while back. I haven't done any valve adjustments.

 

I am wondering if there is anything else I missed before I open up the remanufactured sealed AFM and start messing with its CCW movement to richen up my mixture. I also have another used ECU unit I can swap. What bothers me is why the AFM's bypass screw doesn't make any changes?

The car spent all its life in CA and was a joy to drive. Once we moved to WI with colder climate and mornings, I found myself adjusting the in-line pod resistor to add 1000-1200 Ohm. This week-end we had temps in the 40s, I went to fill it up and noticed this leaning mess.

Thanks!

Den

Edited November 5, 20231 yr by darom

Thanks for the resource! Found the part number, 14035-N3500, gasket manifold, looks like it is available. Will order/replace it once I confirm the leaks in that area.

no double stack they are pretty thick, if it takes more then there is something wrong. I dont know if there is any real preference, the one I used was a felpro, seemed kind of wimpy to me, more like thick cardboard, so you may want to try a different brand than that. IF nissan has them I would go OE.

 I did a quick check here in the US. No availability but 3 Canadian dealerships did not say unavailable . You might get lucky or check Amayama in Japan.

Thanks Yarb, for looking it up.

Just in case I ordered a gasket, Mahle MS16717 (composite) from rockauto. I found a forum chat in the Help Me section where a 280z owner compared it to the OEM from Nissan, they looked identical (with the exception of the price). The plan is to do a valve adjustment as well.

Hi guys,

I ran the smoke tests, found a few areas:

1. valve cover gasket, firewall side - big leak.

2. electric EGR solenoid (leaks inside, not vacuum hose), EGR valve (inside again, not the vacuum line). little leak.

3. oil pan gasket - medium leak here.

4. oil dipstick - little leak.

I replaced the valve cover gasket with a cork one, it still leaked. The valve cover/cylinder head appear to be flat. I ordered a silicone one from Milkfab Engineering ($28), the new gasket sealed all the leaks. I made a delete metal plate for the EGR. Replaced all the old spark plugs with new NGKs, replaced the fuel filter. The aux air regulator was replaced with a 300zx unit, which was adjusted to shut. It takes about 6 minutes.

The valves were adjusted. The car's ignition timing is set at 15 bdtc, idles at about 900 rpm. The vacuum is at 17. The car has a strong pull, no hesitation while accelerating.

 

Observations:

1. I think once I replace the oil pan gasket, I might get another 1-2 of vacuum. This is a spring project (it is too cold in the garage).

2. The resistance pod is at 2k Ohms. I still can't kill the engine maxing it out at 5k.

3. The 'new' AAR is unpredictable. If I leave it alone, it will close (not completely) after 6 minutes. Two different days while testing - one day the idle is at 900-950 rpms, today it was at 800 rpms after warm-up. I feel the AAR shutter 'curtain' doesn't guarantee the same closure.

I would like to replace it with a similar mechanical device (like the 240z choke inside). Does anyone know of a part that might work? This way I will open it up when the engine is cold, and close it when it warms up. Once closed, I can set the ideal 850 rpm at idle.

4. When the engine is cold, within those 5-6 minutes of warm-up period, if at idle once rev'ed up, the engine will pop through intake.

5. I still can't kill the engine with the idle adjustment screw. Hopefully, it is the oil pan gasket leak that causes it.

 

Edited November 20, 20231 yr by darom

Some ideas for an AAR 🙂 Manually operating heater valve: https://www.amazon.com/Universal-Conditioner-HV-2211C-Control/dp/B003R31YVQ/ref=m_crc_dp_lf_d_t1_sccl_3_3/138-5872620-2836123?pd_rd_w=UzJvp&content-id=amzn1.sym.76a0b561-a7b4-41dc-9467-a85a2fa27c1c&pf_rd_p=76a0b561-a7b4-41dc-9467-a85a2fa27c1c&pf_rd_r=34220AX20P78YFH9FKCE&pd_rd_wg=aMQD8&pd_rd_r=2ead7de1-3b51-42e0-b3bf-74fcaef91ae1&pd_rd_i=B003R31YVQ&psc=1

or this with the timer relay (I use a cheap timer relay for my injector rail blower/fan from a later model): https://www.amazon.com/4inch-Normally-Closed-Electric-Solenoid/dp/B074Z5SDG3/ref=sr_1_31?crid=3G17GRQMH50IC&keywords=solenoid+valve+1%2F2in+12V&qid=1700513498&sprefix=solenoid+valve+1%2F2in+12v%2Caps%2C84&sr=8-31

Edited November 20, 20231 yr by darom

IMO no. Ned to find an AAR that works correctly.

A ball valve with a cable would work.  It would be, in essence, an idle speed control.  

https://www.homedepot.com/p/Apollo-3-4-in-Brass-Insert-Poly-Ball-Valve-POLYV34/300850934

Or go all the way with a Vintage Air servo controlled heater control valve and adjust idle with a dial on the dash!

https://www.vintageair.com/custom/product-pop.php?pn=50507-VUA

Thanks for the ideas!

I might be building a simple on/off solenoid with a cheap time relay board set for 2-3 minutes: https://www.amazon.com/Position-Normally-Pneumatic-U-S-Solid/dp/B06WGRLX58/ref=sr_1_13?crid=5V29CNB41DD4&keywords=12v+solenoid+1%2F4+in&qid=1700523538&sprefix=12v+solenoid+1%2F4+in%2Caps%2C86&sr=8-13

 

6 hours ago, darom said:

3. The 'new' AAR is unpredictable. If I leave it alone, it will close (not completely) after 6 minutes. Two different days while testing - one day the idle is at 900-950 rpms, today it was at 800 rpms after warm-up. I feel the AAR shutter 'curtain' doesn't guarantee the same closure.

An AAR that works correctly is pretty satisfying.  It just works.  Your varying idle speed might be due to one of your other problems, not the AAR.  If you apply 12 volts to the AAR pins and it doesn't close completely, it's broke.

Zed, I removed and inspected the inside of the AAR after a few test runs. Before the installation, I did the bench testing of it with a 12V and adjusted the curtain to be closed when the coil warms up.  Since it can't block air 100 percent, there is still some residual air flow which contributes to 900-950 rpm idle. If I pinch the rubber hose for the AAR, the idle immediately drops to 800 rpm, and it remains steady. In both of my tests so far the idle RPM was the same.