Hey Guys,

I have replaced my engine with a reman unit from ATK. I have replaced all sensors that I know of on this engine as well. I have also replaced the fuel pump. When the engine is cold (after sitting all night), it will never crank up on the first attempt. It sputters then dies. You can then re-crank it, and it will start every time, most of the time running pretty smoothly. If you attempt to apply throttle, it will mildly backfire through the intake and you can hear it in the air filter canister. But, if you let it run for about 3-4 minutes, it seems to run fine. It also acts this way when it has sit for a few hours (like when I go to lunch during the work week) but it is not as pronounced..

Do you guys have any suggestions to where I should look next to try to remedy this problem?

Thanks in advance...

 

This could have been continued on your old thread about the same thing: https://www.zdriver.com/forums/280zx-s130-forums-77/cold-natured-engine-16123/ Sorry... I'm **** about making new threads on the same topic / problem.

Anyway, it sounds like it's a fuel pressure problem, or AFM problem. Have you ever adjusted your AFM?

Also... have you checked to see if the Cold Start Injector is working?

 

I have a new cold start injector. Is the AFM you are referring to mean air-fuel mixture? If so, then no I have not adjusted it. I don't really know how other than to turn the dime sized flat head air adjustment screw beside the throttle body.. All I could ever get out of that thing was to adjust the idle speed.

My car runs good once it is warm, but it seems down on power and kind of sputters when it is cold. Give it 5 minutes and everything is fine... So frustrating...

 

AFM = Air Flow Meter.

There is also an Air Regulator on the intake manifold that opens & closes to control cold idle.

Do you have a Hanyes manual?

 

I have a new air flow meter, it is a reman from Advance Auto.. I dont remember seeing any way to adjust it. Is there a way to adjust it?? I also have a new air regulator, (I just put it on and it did make a difference, but still did not fully remedy the problem) I got it from Courtesy Nissan in TX. I do have a Haynes Manual, I have read parts of it several times..

When I say I have replaced every sensor, I have.. From the three way thermal vacuum valve to the head temp sensor to thermotime switch, distributor - cap - rotor - wires - NGK plugs, Throttle position sensor, cold start valve, and the list seems to go on... I am hoping I missed something quite actually..

 

You can adjust the AFM. But you have to open the plastic cover. J has a whole write up STICKY on it: https://www.zdriver.com/forums/240z-280zxt-s30-s130-tech-tips-275/js-how-rebuild-your-afm-15277/

Have you checked your fuel pressure? Maybe your FPR isn't holding the pressure in the lines & so when it sits for a while, you lose the fuel pressure.

 

Thanks for the advice and the link. I have also replaced the Fuel Pressure Regulator when I replaced the Fuel Pump.. That helped a great deal as well. It seems like every sensor or fuel injection system item I replaced has had a positive effect, but it still runs rough when it is cold. I don't see how the reman AFM could stand adjusting, but I will give it a try. Maybe that lean/rich screw will help matters. I will have to look and see if it has one. If not, I may just send it back and buy an original Nissan AFM..

Thanks again..

 

What about the wiring? Have you checked all the wiring to the sensors and components? The Air Regulator may be good but if the connector or wiring to it is bad then it's not going to work. Your problem really sounds like an air regulator/cold start valve problem. The only reason I dont think it's the AFM is because you say you have no problems once the engine has warmed a little bit. Check to make sure the Air Regulator and Cold Start Valve are both getting voltage and that their connectors aren't all corroded. And don't just stick the meter in the connector to test it. Jiggle it around a bit and see if you get a break or anything like that.

 

check the ignition timing, that has a big effect on the system when you go to start it, if its a little too far one way or the other and the a/f ratio is out a bit, it will cause problems. just cause the afm is new or rebuilt, doesnt mean its right, each one must be properly tuned to each individual car.

 

Thanks Guys,

If I can find an air/fuel ratio meter... What should be the correct ratio for this engine? Is it in the Haynes manual? I don't recall seeing it..

I will check these things you have suggested (timing, wiring etc.) I know that when I replaced the cold start valve, it did run quite a bit better when cold, but I will put an ohm meter on it.

Thanks again for your input..

 

SLOW DOWN EVERYONE! Before screwing with the very tempermental AFM check your thermotime switch. This switch is what activates the cold start valve. It's located in the themostat housing and has two wires coming off of it. The following link will help everyone here out a lot. For you though check the EFI section and at the bottom of the page is the EFI Bible. It will help you find your problem easily.
Blue's Tech Tips

 

I have a new thermotime switch. That and the cold start valve were the first two things I replaced to try and remedy this issue. I will check the connections for corrosion though. I don't recall seeing any, but obviously that is good advice and I will do so.. Thanks for the advice..

 

the air regulator connector is in a pretty bad location and the wires there can see a lot of wear over 20+ years.

 

Well Guys, I believe that I have found the solution to my problem. After reading the link about modifying the AFM, I thought I had found my solution. I had hoped to adjust the air bypass screw in the AFM but the reman unit I bought from Advance Auto Parts did not have that screw. It had the bypass chamber, but the hole where the screw should have been was sealed. In hindsight, it appears as if my engine was running extremely lean. I took the AFM off this afternoon, removed the cover, and decreased the spring tension by 4 teeth. This made the air/fuel ratio richer. After re-installation, I had no more rough idle. No more front fire through the intake. I then proceeded to adjust my TPS to specs outlined in the manual. I did not have time to re-seal the AFM, but I did put a big rubbber band around it temporarily to road test it. It runs like a different car. Much smoother and more power. Now, I want to play with it to see how much richer I can get it before the power goes the other way..

Thanks again for your input.. It helped me a great deal.. Hopefully in the future I can help out one of you...

 

Yippie! Well done!