I have built a turbo Locost with a 1990 1.6 Miata motor with a custom turbo setup.
The setup is a DSM T25 turbo running 8-10 psi tan top 1.8L injectors and a Walbro 190 external pump. I am also running MSD timing control unit and Flying Miata O2 modifier. The car is running the following FMU that I think mighth have failed.




The car runs great and pulls hard until you let off the gas to go around a corner in an autocross and then it bogs down big time. No matter what adjustments I do to the FMU nothing seems to change. Before you ask no I do not have a wideband I was planning on borrowing my buddies this weekend but he has misplaced the sensor.

How can I test the FMU?
Anyone know what brand the FMU is?
If I was going to replace the FMU with a vortec band what ratio would I want?
12:1? 10:1?

Thanks Mike

 

What fuel tank are you using? Cutting while cornering sounds suspiciously like fuel starvation at the tank, the FMU shouldn't be affected by cornering forces.

 

I am running a foam filled fuel cell. The corner force is not the problem as much as I think it's the lifting off the gas quickly after being at WOT to take the corner.

 

I don't see a control line to the FMU and suspect it is a constant pressure unit. What happens if you go WOT around the same speed in a straight line and lift then accelerate?

If one of the O2 clamp lines breaks contact on a corner and you try to accelerate under 4000 rpm you can also bog rich.

 

Your right hte lines are not hooked up in that picture. The vaccume line is coming from the manifold and there is a 4" line with a check valve on the needle valve.

 

T'eed off the stock FPR vacuum line, correct?

 

No it from one on after the throttle body.

I just read this.....

Ideally you want to be able to run larger injectors at a lower fuel pressure, however, without additional fuel management this is not possible. The stock ECU has some wiggle room to run a larger injector, it usually requires tuning with the AFM to idle. The 1.6 ECU should be able to idle up to 330cc injectors. However it will require tweaking the AFM idle-mixture settings and spring tension.



Anyone know how to do this AFM tweak? I have an extra AFM

 

You don't need to tweak it for tan tops, but if the brushes are not making good contact, the AFM can put out no signal and cause rich bogging also.

If you want to go with larger injectors, you can open the black plastic top and tighten the spring slightly. On a 20 year old AFM it would be a good idea to tighten the brush against the contact also.

 

This may help a little.

http://www.miata.net/solo/airflowmtr.html

Here's a bit of discussion on it also.

https://www.miataturbo.net/general-miata-chat-9/afm-adjustments-spring-vs-screw-13182/

 

Do you think with running 9psi that is intercooled and has the timing retarded by the MSD system I can get away with running the stock injectors?

 

I would stay with the tan tops and make sure that the FMU can get you to 90psi on the fuel at 9psi

 

Guess I will need to adjust the AFm then because the tan tops are flooding the car at idel. I pulled the spark plugs last night after the car was just ideling and the plugs were wet with fuel.

 

First make sure that your fuel pressure is not being raised at idle and then adjust the contact of the brushes in the AFM. There should not be a problem with 1.8 injectors running rich at idle unless your O2 sensor feed is low or interrupted or the AFM is sending no voltage to the ECU

 

So I popped open my extra AFM to see inside. What do I do to lean it out a bit?

 

It's more of when the flapper opens. You can see the clock spring. Tighten it, and it'll open a little later/harder. Loosen it, and it'll open sooner/easier. The spring tightness also determines how much it's open at idle, so the tighter it is the more closed it is, and I think the leaner it is. Fiddle with it while watch your wideband, you'll see. Feel free to pop the lid on your "good" AFM. I ran mine with hardly any of the glue left on the cover for years. Cover never popped off, and it was spotless in there every time.

 

what screw is it that I tighten?? the allen key one?

 

need more this: