Miata running lean - fixes?

1994 1.8L (I had thought it was a 96)

Stock intake and exhaust

Stock computer

NKG wires and copper plugs done in October 2013

1999 injectors, cleaned and rebuilt June 2014

1999 fuel rail

Fuel pump replaced June 2014

Fuel filter replaced September 2014

I pulled the plugs yesterday to do a motor soak (car smokes a little on decel), and noticed that they were a bit white.

I have a new intake on the way (upgrading to a 3d printed intake), so if I was getting any leaks on the intake tract (didn't see any) that should be fixed. I will be replacing the plugs when I'm done with the soak. I will also clean the MAF.

Anything else you guys can think of that would cause this, or any other ways to fix? I've been running the car on 87 octane and never noticed any pinging.

1999 injectors are smaller than 1996 ones, so that's not helping.

What's your long term fuel trim look like? That'll help narrow down what's going on.

Keith Tanner wrote: 1999 injectors are smaller than 1996 ones, so that's not helping. What's your long term fuel trim look like? That'll help narrow down what's going on.

I have no idea what that means.

Crud on the plugs doesn't necessarily mean it's running lean. I've seen engines do that to the plugs (white-ish buildup) from burning oil (but not enough to actually foul the plugs). The black carbon on the outer metal bit of the plug supports this, IMO. Generally lean plugs won't have much carbon there, while rich plugs or an oil burner will.

You can access the fuel trims with an OBDII scanner. That might give some idea of whether it's actually running lean or not. Or better yet, get a wideband O2 sensor on it and find out for sure.

Are you running leaded gasoline ? all that fuzzy stuff looks odd. Lack of fuel/ too much air cause a lean condition. find the cause. Often a vacuum leak. Or false air.

Nope... regular unleaded.

I do have an OBD-II dongle. Anyone recommend software to use?

rslifkin wrote: Crud on the plugs doesn't necessarily mean it's running lean. I've seen engines do that to the plugs (white-ish buildup) from burning oil (but not enough to actually foul the plugs). The black carbon on the outer metal bit of the plug supports this, IMO. Generally lean plugs won't have much carbon there, while rich plugs or an oil burner will.

It's an oil burner for sure. I had no clue that the buildup could be a result.

Use whatever OBD-II software you want to use (Torque on Android, Dash Commander on iOS are two I know) and check the long term fuel trim (LTT) number. It'll be a plus/minus number that could be as high as 25.

If you have high LTT numbers, then the ECU knows things are running lean and is trying to do something about it. Then it's a mechanical problem and you start looking at things like low fuel pressure (I don't care what you've replaced, measure the actual real fuel pressure) or undersized injectors.

If your LTT numbers are close to 0, then the ECU doesn't think you're running lean. Ensure that you actually ARE before proceeding. If the ECU doesn't know, that means the sensors aren't telling it it's lean. Check your O2 numbers via the scanner as well.

Why are you running the small 1999 injectors?

Gimp wrote:

rslifkin wrote: Crud on the plugs doesn't necessarily mean it's running lean. I've seen engines do that to the plugs (white-ish buildup) from burning oil (but not enough to actually foul the plugs). The black carbon on the outer metal bit of the plug supports this, IMO. Generally lean plugs won't have much carbon there, while rich plugs or an oil burner will.

It's an oil burner for sure. I had no clue that the buildup could be a result.

When the oil isn't enough to foul the plugs and they burn hot enough to keep the tips clean (so no oil or dark carbon buildup on the tips), oil seems to lead to a bit of white ash ending up on the plugs. I've never noticed it hurting anything though, as I've seen engines with a good bit of buildup like that not run any differently when fresh plugs were put in.

Tell me more of this 3D printed intake. I was a part of a discussion on them in another forum and would like to know more about it. Your design or someone else's? Also is it straight abs or whatever it is it frp or something?

But about your plugs, are they all white like that or just a few? I've seen blown/leaky headgaskets make some similar deposits on plugs.

Edit: is that 3D printed intake or intake manifold? Sorry I thought it was an intake manifold. Anyways carry on.

Keith Tanner wrote: Use whatever OBD-II software you want to use (Torque on Android, Dash Commander on iOS are two I know) and check the long term fuel trim (LTT) number. It'll be a plus/minus number that could be as high as 25. If you have high LTT numbers, then the ECU knows things are running lean and is trying to do something about it. Then it's a mechanical problem and you start looking at things like low fuel pressure (I don't care what you've replaced, measure the actual real fuel pressure) or undersized injectors. If your LTT numbers are close to 0, then the ECU doesn't think you're running lean. Ensure that you actually ARE before proceeding. If the ECU doesn't know, that means the sensors aren't telling it it's lean. Check your O2 numbers via the scanner as well.

Awesome. This is super helpful. I'll get those numbers in a bit.

Keith Tanner wrote: Why are you running the small 1999 injectors?

Because the guy I bought the car from did all of this before I got it. Would I be able to install the correct injectors on the 99 rail, or do I need to find a 96 rail as well?

The 1999 rail is weird, I don't know why you'd do that either. But yes, you could put 1996 injectors on a 1999 rail. If you want the newer design injectors, the purple 2001-05 units are closer in size to the original 1996 units.

Are there any significant benefits to the 2001-05 units?

IIRC they have better fuel atomization than the NA units. Plus they're smaller and weight less, so you go faster .

Keith Tanner wrote: The 1999 rail is weird, I don't know why you'd do that either. But yes, you could put 1996 injectors on a 1999 rail.

From the seller's notes (he's a friend of mine, so I could always ask a follow up) - "Used injectors out of 99 miata from Jared. Used rail, FPR, fuel pump assembly from parts place to try to fix not starting in morning"

I would check the actual fuel pressure just on general principles. I'd love to know more about where all the FRP parts came from and how they're plumbed, as there's quite a difference between the NA and NB in this regard.

Keith Tanner wrote: I would check the actual fuel pressure just in case.

Also a good idea. I'll get the LTFT first and go from there.

I haven't been able to look at the LTFT yet, as I can't find my dongle (personal problems, I know). I did go ahead and pick up some stuff from the autoparts store, including a new PCV valve. Old one wasn't fully stuck, but didn't rattle - rather just a slow thunk back and forth. I know that likely isn't the issue, but it's nice to find little things to fix up while I'm in there.

I'm still soaking the pistons in MMO to see if I can help the unrelated smoke on decel issue.

Gimp wrote: I'm still soaking the pistons in MMO to see if I can help the unrelated smoke on decel issue.

Might not be so un-related. Smoke on decel is likely oil being pulled past the valve stem seals, which could easily crud up the plugs (being that the most oil is being pulled in when it'll be burned off the least effectively).

rslifkin wrote:

Gimp wrote: I'm still soaking the pistons in MMO to see if I can help the unrelated smoke on decel issue.

Might not be so un-related. Smoke on decel is likely oil being pulled past the valve stem seals, which could easily crud up the plugs (being that the most oil is being pulled in when it'll be burned off the least effectively).

I hope it's not the valve stem seals. According to the service records, those were replaced in November 2013.

We have found a significant quality difference between OE and non-OE valve stem seals, BTW. But smoke on decel and idle does point in that direction.

I'm in the boat that believes the previous owned kludged it up with 99 parts (are the returnless? I can't remember) and using inferior valve stem seals because as everyone has politely nodded to, smoking on decel and after idling points to valve stem seals.

chiodos wrote: I'm in the boat that believes the previous owned kludged it up with 99 parts (are the returnless? I can't remember) and using inferior valve stem seals because as everyone has politely nodded to, smoking on decel and after idling points to valve stem seals.

Unless I shoot him an email, I won't know why he used the 99 parts.

As to the valve seals, the records say "Viton exhaust and regular intake valve seals to replace current leaking ones causing smoke on start-up." He got them from 949 Racing, so he didn't cheap out (at least on the exhaust side). Is there any easy way to inspect these?

I don't have any noticeable smoke at idle. I see it when the car is being autocrossed and you let off after being hard on the gas.

I don't know why he wouldn't put the better Viton seals on the intake side too (and that's the side likely to cause decel smoke). If you let it idle for a while and then give it a rev or get on it, does it smoke a little at first? If it does, that further points to valve stem seal leakage. Especially if there's no smoke under steady load (which is when bad rings would smoke the most).

Gimp wrote:

rslifkin wrote:

Gimp wrote: I'm still soaking the pistons in MMO to see if I can help the unrelated smoke on decel issue.

Might not be so un-related. Smoke on decel is likely oil being pulled past the valve stem seals, which could easily crud up the plugs (being that the most oil is being pulled in when it'll be burned off the least effectively).

I hope it's not the valve stem seals. According to the service records, those were replaced in November 2013.

Also, if the guides are worn, new seals won't help for very long.