Sparkplug reading
 

I know this is the shadetree mechaninc way of telling an engines running condition, but what do these plugs look like? The ceramic is tan, the ring around the thread base is black, and the electrode is white? Rich on bottom lean on top?

My setup is a 91 with afpr, jrsc, header, no cat, bipes.

Looks okayish? Needs more or

I wil be getting a wideband in the near future. I took it to a dyno today and it was running a bit lean. I maxed out the afpr and got it almost to the safe zone. Attached is my grapg from the dyno the lower line on the afr readings is the last run with the afpr turned all the way in. Would 1.8 injectors be the ticket or should I look for some rx7 ones? I was thinkig itd be nice to have the headroom of an rx7 injector so everything wouldnt be working so hard.

Your stock ECU is going to limit you on the injectors you can run with the afpr and bipes. Read up on options changing injectors here: Fuel Injectors - Miata Turbo FAQ

I'm far from being an expert, but your 15:1 AFRs in the "upper" line are super scary. The lower line looks likes its running 14.5~14.25 from like 2750 to 4800 RPM? Am I reading that correctly? What did the dyno guy say about those AFRs, because while its better, it still looks way lean. Again, I am no expert.

Also, do you have a cat and where was the dyno's wideband tapped into your exhaust system?

You are reading that pretty correctly. I don't have a cat, and the wideband was just resting inside the tailpipe. Yeah it's definitley something I want to get fixed. The dyno guy said it was still lean, but didnt have much advice on how to rectify it. If I backed my timing down would that help? I am currently running 12 degrees static, and pulling 6 beginning at 1500rpm

You're gonna blow your shit up, buddy. Stop driving it until you figure out a way to get more fuel in it.

Concealer beat me to it, you need moar fuel. Like 2 points worth. 14.5:1@5psi and 3,500 RPM is no esta buen. I have no idea how this thing is still holding together at this point unless your bipes is pulling ALLOFIT from the timing.

If the dyno guy wasn't scared or "worried about it" I would question his judgement. By that I mean "Fuck dude! 14.5 is bad news!" vs "Eh, its a little on the lean side. You might want to look into bigger injectors or something."

Well shoot, I am glad I posted here. So then do you think that 1.8 injectors would be sufficient Given the amount I need to richen? Would turning the timing back down yield an equivalent result?

I don't think pulling more timing is going to help you at this point.

You are hamstrung by your stock ECU. Read the link I posted earlier about fuel injectors, then read it again. Then read the part about fuel pumps.

Any injector on that list that is bigger than your current injectors and will give you more fuel. How much more? No clue. No one can tell you that except a wideband. You should be able to adjust your AFR in boost by turning down your AFPR if you find you are stupid rich. Are you on a stock fuel pump? This may also be part of the issue. Like I said before, read up.

You are several years behind the curve on this type of data. It's been a long time since anyone around here recommended a AFPR and BIPES to keep things under control. You are going to have to do a lot of searching and digging for that data.

Without a wideband you are literally shooting in the dark. Make decisions based on data. You did good by getting it to a dyno and posting up on here to get a second opinion. You learned some stuff from us but don't stop now, keep reading and keep learning.

BTW: The answer is always Megasquirt. ;)

You can pick up a wideband, a set of modern injectors and a used MSPNP/MS1 or MS2 for very reasonable money these days. You will be lightyears ahead of the BIPES and AFPR and you will have some real data to work from. It's definitely worth considering.

Sweet! I got my innovate lc-1 today, going to wire that in here this weekend.

Another question...

Last night I was bored and decided to check my radiator fluid. I found some bad news, there are some oily looking blobs floating near the fill cap, and in the reservoir. I did a compression test today with a harbor freight gauge, and my readings were;
Cylinder #1 108
Cylinder #2 108
Cylinder #3 106
Cylinder #4 113

After seeing these readings, I wonder if there might have just been some gunk built up in this engine I installed, after all it had been sitting for at least 2 or 3 years. I did notice a bit of coolant splashing out when I loaded it into my truck upon buying it, but it still looked bright green. Given these compression readings, would you think the head gasket is possibly blown? Does a compression test rule out a blown head gasket? I am worried that they dyno session with the guy who wasn't concerned with my afr might have done it...

With the HF gauge, the main concern is that he cylinders are even across the board. I also ASSume that this was a cold test?

The car was warmed up by idling for a few minutes before doing the test. I know the #'s seem low, I more or less attribute that to the HF gauge though. The car certainly feels like its got plenty of punch. I drained the oil last night as well and saw no signs of water in the oil.

When you were turning it over was the throttle wide open? It should be. It also helps to have the other three plugs out so that it spins more quickly.

Well I wanted to do a follow up / resolution post.

I installed a wideband and was able to tune my afrs down to the 11 / 12 range in boost and 14.7 in cruise. The afpr is pretty sensitive to small adjustments.

My head gasket blew (probably from running lean on the dyno) and my head was warped. The oil was making its way into the coolant on cylinder # 4. The machine shop took .004 off to make it true again. The car now runs smoother and better than before. My plugs are now a nice tan / brown color FWIW.


I will do another compression test some day and see if the #s came up with a true head / sealed head gasket.

Those AFRs are much better. It looks like you are only running about 4psi according to the dyno, so those AFRs are plenty safe.

Keep in mind compression test numbers will be lower at higher elevations.

It's always number 4. Look into a coolant reroute (roll your own to keep costs reasonable).

Thanks for the replies. The info about compression #s being lower at higher elevations eases my mind a bit.

FWIW:

If anybody is looking for a mls head gasket, I found one on ebay through a seller named eportuning. The kit was 50 dollars and it was a fel-pro gasket kit. The brand was not listed on his ebay listing. I only used the head gasket from the kit since I wound up doing the timing belt and w/p while I was in there. (had a different t-belt / wp gasket kit I used for the others)

I also had read some debating on wether or not to use a head gasket copper spray. The machine shop that resurfaced my head highly reccomended it. I used it. All seems to be well. I sprayed the gasket, let it dry for a few minutes, and put it together. Buy the time I got the car all put back together again was about 18 hours later so everything was surely dry by then. I have about 500 miles on the completed job. I will post information if I have anymore failures or failure related to the copper spray. For prep work on the block, I used an 80 grit sand paper, followed by 120, then 320, then scotchbrite pad. The head just needed a good cleaning.

I reccomend using an engine hoist or shop crane to remove / replace the head if you ever have to. It made it a 1 person job.

That's how I do it too. Great tip.

I've used copper spray on the head gaskets for the '68 Pontiac with success, but never on the Miata yet. My MLS gasket already had something on it.

This MLS felpro gasket was somewhat tacky out of the package as well. It has a grey surface to it. I figured the copper spray on the HG and head bolts would be cheap insurance. The copper spray's instructions reccomended using a coat on the head bolts to help with heat transfer / expansion of metals happening at different rates.