Alright, so I've searched around on here and the other less important forums, but haven't found too much. So I'll start with what I have done to it. It's a 1990 still with the 1.6 in it. Engine is bored .020" over, with an older Begi kit bolted up to it with a brand new Garret GT2560R, all coming out to a 3" straight pipe from the downpipe back. Everything held together with some ARP studs. Only at 5 lbs of boost, stock ecu (I know, I know), rising rate fuel pressure regulator, Walbro 255 fuel pump. Exedy clutch, Fidanze flywheel, 1.8 driveshaft and axles, with a Torsen Type II 4.3 LSD.

I've had it on this set up for the last 5-6,000 miles. Now last week the engine just started cutting in and out under normal driving. When it first happened I thought it was just because I was a little low on fuel at the time, but even after I put gas in it it still does it, but it only does it when it is under half a tank of gas. Basically you feel the engine cut out, then it stays like that for however long it feels like it, normally between 5-20 seconds, and then it'll go back to normal.

First thought was it being a fuel issue. I bought the Walbro 255 fuel pump brand new when I did the build, so I turned my attention to the fuel filter, figuring I just picked up some garbage off the bottom of the tank when the gas was low. I replaced the fuel filter, which did turn out to be pretty filthy, but that didn't solve my issue. Any help here would be great!

 

What's your ignition setup?

Too bad about the ECU. Data logging really helps with issues like these.

 

The only thing I touched on the ignition setup is I swapped a ignition switch cause the one I had was going bad. Did that at the same time as the engine build though.

 

What's the wideband say?

 

Forgot to mention that part. I have a small boost leak and a pretty significant exhaust leak from my manifold gasket. That being said, my wideband has a mind of it own. Before that, my afr's were normal for idle, in boost, and cruising.

 

Anyone have any ideas?

 

The wideband should not have a "mind of its own" at the operating conditions where you are having issues. Even with an exhaust leak, you are simply pushing exhaust out of the leak, not drawing air in. Can you log the wideband readings? Keep in mind that once you start misfiring, the wideband will necessarilly read lean (O2 present) even if the cause of the misfire was not leaning out.

Are you able to monitor fuel pressure while running?

 

Correct me if I'm wrong, but the boost leak in the intercooler piping would throw off afr's. At cruising it stays between 13.5 and 15. Under load and in boost it shoots into the high 17s, which I know is off because its running fine as far as power goes. Not misfiring or anything. Right now i don't have a fuel pressure gauge on it. Someone told me that it's cutting in and out when it's under half a tank because the exhaust is heating up the gas tank and creating pressure, and that the answer is to put heat shielding in between the exhaust and gas tank. Not sure if that makes too much sense though.

 

Why don't you fix your obvious problems (boost leak and exhaust leak) before you worry about gas tank pressure.

 

I'm waiting for my Flyin Miata intercooler setup to come in cause this Begi one is terribly designed. Once that comes in I'm pulling the engine again and fixing all the little issues with it and cleaning up the engine bay. I'm just trying to figure this out in the meantime.

 

You are still using the AFM, so a boost leak means your engine is not getting the amount of air the ECU thinks, and the exhaust leak means your wideband readings are useless.

Fix your known issues, then worry about what else might be wrong.

 

GIGO.

What do you want from us? You know that several key things that could be culprits or present impediments to proper diagnosis exist and yet want us to guess the problem without you expending any effort to rectify them.

Have you even read the spark plugs?

 

jeez, i wonder what the problem is. hopefully mt.net can help you figure out what the issue is

 

I know I know. My reason for posting wasn't to hear you rant on how I should fix the obvious issues. Rather merely to see if anyone else had a similar issue that was possibly unrelated to my known issues. That way, if its something I can do in the meantime I can do that, or if its something easier to take care of while the engine is out I'll do that then.

 

We are not going to be able to help you until you clear up the obvious problems - it's simply not possible. You have too many variables for us to even come close to answering this.


Here's an algabraic rendering of what you're asking us to do.

Can someone help me solve for B given these 3 equations??

(A+35/.4C-2^Y)-6/B=X
A=14.3*-Z(Pi+G^2)
D=0

 

P.S. - If your AFR is reading 17 under load, and you do it more than once, you're a moron.