I noticed cylinder 2 spark plug was a bit different than the others when pulling plugs prior to dyno tuning. Didn't think much about it at first and though of it as an anomoly.

On the dyno, I pulled the plugs and cylinder number 2 was again different. On the electrode, it showed signs of heat warping as the tuner explained. Likely due to running lean, but my entire map is relatively rich.

I recently did the ls2 sequential coil setup on my DIYPNP. I also put a new set of wires on just before to rule out most other potential hardware issues. Pulled the plugs again about a week ago and Cylinder 2 was definitely much worse than the others and showing serious signs of high heat.

So, while I was rebuilding my motor late last year with the engine out, I plugged the fuel lines up with rubber caps. When I went to take them off, the fuel had affected the rubber a bit and I noticed some rubber bits falling out into one of the lines. I was hoping for the return line. I never get lucky when its a 50/50 chance.

So, now my thinking is that it was the supply line and some of the rubber made its way to the injector for cylinder 2. So, the injector is likely partially plugged.

My reasons for writing this is to see if this could potentially be a hardware issue, or software though less likely. It is sequential injection so, the hardware or software signal to injector for cylinder 2 could be off potentially. Thinking a blockage is more likely. Any thoughts? Does the blockage sound plausible?

Thanks.

Setup is 96 miata with fully rebuilt 99 motor. FM 2 turbo kit. 550cc RC injectors. Sequential fuel. LS2 sequential spark.

 

Send the injectors to RC for flowtesting and see. I bet #2 is plugged up.

 

Swap the injector with another and see if the problem moves with it.

 

Motors are expensive. I'd just get the injectors flow tested.

 

I will test your flow.

 

I don't like to burn people, but seriously: "Swap the injectors and" see if the detonation inducing issue tries to blow another cylinder through the cylinder wall? My goal is to fix the problem before it costs me another motor. Lost my first motor last year and I was out all AutoX season. Not doing that 2X around for a $25 clean-flow-balance charge. I'll send just this one to RC. No use on the others that aren't showing any issues.

 

Clean all four, like a man.

 

In fact, I would suggest ditching the POS RC injectors for EV14s.

 

Injector dynamics all the way. You might think the price is a bit steep and question yourself about spending that much on injectors, but once you start tuning with these suckers, all doubt disappears

 

What is heat warping? Pix?

 

I'm not suggesting that you swap them and go WOT across town. Swapping it with another, installing new plugs, and driving around relatively sedately would probably show you a difference in color. I would not have even suggested it if you had not already seen evidence of the problem on 3 successive sets of plugs...this suggests you are willing to take a risk.

But for sure, sending them out is the safest thing to do.

 

Clean them all. If the rubber got into one, they were all put at risk.

 

I think you've all made good points to send all 4 back. Wifey's not going to be happy though... If 1 shows really low flow, I think I'll have my answer and have to spend $80-100 to replace.

 

So, I talked to RC about my injectors after cleaning and flowing. They are nominally 550cc RC injectors. Prior to cleaning, they flowed at 537cc worst and 545cc best. Not too bad and not very dirty at all.

So, my thought now is that the plug for cylinder 2 was already fouled when I placed the new LS spark system into commission. The plug ended up worse only after more use and already having been fouled.

If that's the case, my current set of plugs, which have only been running on the new spark setup, should show no signs of fouling like the other set of plugs. Otherwise, any ideas for the witch hunt?

 

I checked my plugs again yesterday and even the new set is showing heat warping on the base of the electrode on the plug for cylinder 2. So, it's fuel but its not the injector. Not a software issue because settings are identical for all injectors by default. So, it's hardware somewhere on the board or wiring between the board and injectors. Could be my injector adapters. Don't remember exactly where I got them. Maybe ebay special. I'll check for continuity while wiggling them and get back.

Any other suggestions for the witch hunt? Not getting much out of the group here.

 

How about a picture of the heat warping?

 

The one on the bottom is what all three sets have shown for cylinder 2. The top is exactly what all 3 other plugs look like for all three sets of plugs. It is very definitive.

You can see the white ring at the base of the electrode and you'll also notice that there's less black on the whole plug than the others. Indicative of running leaner than the others.

 

Looks like you got it right. #2 does run hotter.

Seems that cylinder is either getting less fuel or more air than the others. Since you seem to have eliminated injectors, there may to be something funky with your air supply. Could this be a valve problem? Cam is looking good- no noise? Maybe do a leak-down?

When you put the engine back together, you did take the oily rags out of the intake runners of #1,3 and 4 right?

 

There was that one rag that spanned the manifold with a hole right over the runner for #2. I thought that didn't look OE, but who am I? (Poor sarcasm.)

More air, I didn't think about it that way. Actually, #2 had a little less compression than the others if I remember correctly, which could mean an intake valve open a bit more than it should be? I've got a compression checker so I can do the test again. Might be time for a leak-down test... I know a guy.

BTW, is there a way to give a little more fuel just to cylinder 2 with a sequential DIYPNP?

 

yeah if you are running seq you can do cylinder fuel trims, best though to have either wideband or egt a cylinder to be for sure. but you could do it with plugs as well.