Hey all, finally got the car running and it's been great over the past week, yay!

Today, something new. I drive to work, and I as soon as I get off the highway, the car is running a bit leaner than usual. As in, at idle it will be about 18AFR

Also just low speed cruising around the base, I get inconsistent drivability and jerking, all the while the AFR is hovering (as though offset) by 3-4 points higher than normal.

Since I haven't touched the tune in months and months and it was driving perfectly fine over the past week, is there anything I should be on the lookout for? I haven't noticed any cracked hoses or leaks, but I literally just observed this this morning. I don't know if I should just baby the **** out of it on the commute home or just tow it. I don't have my laptop so sorry I cannot be much help.

Just probing your collective minds for troubleshooting this evening.

Things I know I need to do:
Tighten up the alternator belt, it squeals on startup
Replace Idle Control Valve (could this be the culprit?)


Maybe bad fuel pump?

 

do you have baro correction working right? is ts afr lining up with gauge?

 

Unfortunately laptop is at home. I'll check this for sure when I get home.
This is on the MTX-L

Barometric pressure history shows fluctuations of less than an inch over the past 3 days. But no change from yesterday when the car was working fine.

 

Do you have a fuel pressure gauge on the car? Not Miata or megasquirt specific but I've had fuel delivery issues before. I've had an in-tank filter sock pick up rust/junk and clog. It would be fine for 15 minutes or so, then start leaning out after driving a while. I've also blown a o-ring on the fpr on a returnless fuel system that did the same thing you describe. Fuel pressure would show if something like that could be the issue.

The only other thing I've seen randomly affect afr like that is a cracked/pinched/disconnected MAP sensor, but that will typically make you rich at cruise not lean.

 

Thanks for the insight. I don't have a fuel pressure gauge until I swap in my fuel bits. I did note that a couple days ago the fuel pump (which is usually loud on startup, kept wining even after warming up). But I didn't want to jump to conclusions and it hadn't happened since. I'll check around but aside from starting my fuel system project sooner than desired, I don't know what else to do if in case this thing is clogged.

There's also plenty of gas in the tank.

I hope to god it's not the injector(s).

 

Is it only lean after getting off the highway and immediately after?

I'll idle lean at highway off ramps, haven't been able to figure out why. After idling for a while it will fix itself.

It almost acts like a lean hot restart, I notice it more lately since I've switched back to 91 from e85. I'm wondering if it's not because my cruse PW is so low, maybe the injectors cook a bit while rolling down the highway for 30 miles?

I'd try and limp it home, if it were me. You'll have warmup fueling helping for a while, and hopefully ego to pull back some. Stay under 75 kpa or so and you can get away with a lot on the fueling, just doesn't always drive so smooth, melts sparkplugs...

 

It's actually everywhere now. Idle, cruise, slow, Swift but not loaded. Egt's are higher than normal

 

Might try replacing fuel filter just for ***** and giggles

 

log first.

 

I hope I can make it back, it doesn't want to stay running at idle.

 

So i dropped into Rosenthal and bought a fuel filter anyway and changed it out. Topped off the tank too.

This log is after the 6th attempt to get it to start without stalling out. The log starts of just idling in the driveway then took it out around the block. I didn't want to drive too much on it.

I haven't plugged my computer up to the car for a long time so I don't know what would change between yesterday and today.

 

What fuel pump you running, and how old is it?

Fuel pump is my guess based on your comments and the log you posted.

 

Did you check fuel pressure yet?

Do you have a vac leak?

 

are you in Arlington during the day?

 

Unfortunately no, I'm in Bethesda. Though if you're willing to take a peak, I can leave a key somewhere among your favorite beer and a bunny. We have lots of rabbits in the area.

Just replaced the idle control valve as well. I want to say it's the fuel pump, only because I don't know any better.

Why can't I use an NA8 fuel pump in my NA6? Can I harvest the wiring from the Walbro? Is this real life?

 

your MAT is showing 180°F and your MAT corrections are pulling 20% fuel.

you need to make your MAT corrections flat at 100% across the table and replace your AIT sensor.




I may have a spare GM open element if I didn't give it to Lars, otherwise disconnect yours to drop the temp down to 70° which is the failsafe.

Try to recalibrate it first, seems really odd it's pegged like that.

 

probably shorted

 

Holy crap. I'll take a look tonight. I hope it's not shorted, but if it where, perhaps unplugging wouldn't help and we'd know for sure.

I can pick this sensor up locally from parts stores I imagine?

 

If you unplug it and it still says 180 then it's shorted in the wiring.

 

My favorite demons. Thanks guys, I'll try this tonight. In the rain. Outside. On my muddy dirt way. Hopefully I can hobble this thing together again.