Why is my car missing?
 

Sorry for the long post, but I want to get as much info out there as I can. This thing is making me nuts and I want it to run right once and for all.

Info on the car is that it is an intercooled Greddy kit, running on 460cc RX-7 injectors, Emanage Ultimate, Automatic TB, and has 227K miles on it. I have an Innovate LC-1 WB to monitor A/F ratios.

The car has had a miss at idle and also with no load on the engine (cruising) for some time now. It is quite intermittent and I have tried to see if there is a pattern with data logging and I am at a loss. It seems to miss less when the A/F ratio is really rich (12:1), but the only problem with that is it has no power and then throws a check engine light. Here are the steps I have taken to cure the problem. Replaced plugs, wires, and coil, but no help. Played with lag times on injectors through the EMU, but no help. Sent the injectors off to have serviced, no help. The funny thing about that is that I put my stock injectors and the Vortech back in and it ran quite a bit better, but still had a very occasional miss while cruising and still missed at idle. By occasional, I mean like once every 10-15 minutes instead of several times a minute with the 460's. When a miss occurs, the A/F ratio jumps to about 15.5:1 right after the misfire, but is always 14.6:1 right up to that point.

I have done a leak down and compression check and the numbers are:
#1 - Compression: 170 Leak down: 1%
#2 - Compression: 165 Leak down: 6%
#3 - Compression: 165 Leak down: 4%
#4 - Compression: 175 Leak down: 3%

When the car is idling, I can hear a slight hissing like I have a vacuum leak, but all the vacuum lines are new and I have tried to find it with carb cleaner and can not detect one and the vacuum numbers are right at 20 in/hg at idle.

A few last ideas I have to possibly try are: fuel filter and igniter module? vacuum leak where the intake meets the head? All the obvious leak points appear sealed.

I am at the end of my rope and considering a newer, lower mileage engine at this point just to be dome with it, but the fact that it ran pretty well with the stock injectors has me baffled and afraid to spend the money on a new engine only to have it do the same thing.

Any ideas? Thanks.

Brian

I am assuming this is on your '90. Have you replaced the AFM with the MAP sensor using the ultimate?

What are your spark plugs gapped at?

Yes to the '90, No on the AFM removal.

.038"

https://www.miataturbo.net/forums/sh...ighlight=alive

I'm on a crusade. The thread may apply to your problem.

Interesting. How is the best way to do what you described to someone who has never opened up the AFM? That thing scares me. :ugh:

You can do it in the car, but I found the kitchen table to be better. You need to carve what looks like rubber cement or silicone from around the black pad and pry it out.

If that fails I'd get your injectors tested. A friend of mine has the same issue with a miss at idle and while cruising not under load. Turned out 1 of the four RC injectors he had was way out of spec and he was running lean on on cylinder. The miss sounded almost like morse code.

Been there, done that.

Maybe a leaky injector o-ring? I know that you said you checked the vac lines, but any fuel smell? Maybe check the injectors for any leaks?

All new o-rings. I just got them back from service. No gas smells either.

Put in a new fuel filter today. I also did what olderguy said and everything seemed to check out. I then built an airflow output map so the ECU would not be getting its signal from the afm, but a map instead, and the miss was still present!

At this point I think it may just be a burnt exhaust valve as I had suspected earlier? I really don't know and I am so frustrated I really don't even feel like working on it anymore.

I put the stock injectors back in again last night and the miss is gone again. Either I have a bad injector that tested good or there is another problem that is being masked possibly when running the stock injectors. I am just going to drive the ever loving piss out of this thing like it is for the time being. I am sick of messing with it.

Well the cheapest way would be to find a single RX-7 injector and run down the line replacing each injector and testing to see if it goes away.

Frank