Running like crap again

Well, my miata is running like crap again, exactly the same as before the motor swap (except with more compression now).

Symptoms:
EXTREMELY rich (to the point of fuel vapor out the exhaust when its wamed up)
fouling the #3 plug
bad idle and running on 3 cylinders all the time
problem seems to be confined to #3 (unplugging the #3 plugwire does not affect idle)(unplugging the #3 injector seems to make the car run better)

Knowns:
Injector harness is damaged on #3 from a botched alarm install (same harness as before the motor swap)
new plugs
new wires
tried two different sets of coils (old vs new motor)
good compression on the new motor (better than the last)
spark seems to be strong on all cylinders
new injectors (old vs new motor)
car will run ok for a few minutes after the plugs are cleaned then fouls out and runs like crap again

This all makes me believe that the harness is screwed up and the #3 injector is sticking open, but this is confusing for a number of reasons. First off, the damage seems to be limited to the insulation on the wires near the plug. I've taped them very carefully so there shouldn't be a problem there. Second, injectors are normally closed, open with a +12V signal and close with a spring. If there was any problem with the signal the injector would just not open, it wouldn't hang open like it seems to be doing. Even if there was a short I wouldn't think the injector would hang open.

Anybody have any ideas? I have a harness I can try, but I won't be able to get it for a few weeks. I really need to get this car fixed so I can get started on the celica.

Thanks guys.

Have you tried scoping the 12v line to the injector?

Or putting an analog meter on it? (digitals don't usually have fast enough response to show something happening... analog will show the meter jerking back & forth)

If it's sticking open due to a PCM (computer) issue... then there ya go.

They are probably driven by a mosfet or something similar in that "black box" ;)

Also check to make sure you have a good ground on the other wire.

RJ

Wait a sec...

What year do you have? In looking through the wiring diagrams I see a couple of different things depending on whether you have a 1.6 or a 1.8...

The 94-97's have 12v to one side of the injector constantly... and are switched to ground through the computer.

Turn the key on and see if you have 12v on one side & check the other side (with the key now off) for continuity to ground... If you have a 94-97 I bet you have a short to ground on the wire that goes from that injector back to the computer or you have a bad computer.

On the 90-93's you have #1 & 3 and #2 & 4 are connected together and controlled as a pair by the computer. One side is always hot when the car is turned on. So maybe you have a short between the connection from #1 to #3 on the common wire if you have a 90-93 model.

If you don't have the wiring diagrams I can email them to you.

RJ

Are you sure the Alarm isn't part of the problem?

try switching the #3 injector with a differnt one, say the #1 and see which cylinder it is doing it on, if it continues on #3 then it would most likely be the injector harness, and if it does it on the #1 then it would mean that the injector is in need of a rebuild. rc enginnering charges 109 plus shipping to rebuild and flow them all out.

just some ideas

Just so you know, I have a spare fuel rail, and injectors off of a 99. If they fit you are more than welcome to use them for your diagnostics

I have 4 (or was it 8?) spare 1.6 injectors, and I might have a spare injector harness laying around. I also have pretty much any other 1.6 fuel-related part that came off the engine. Let me know if you'd like to try any of the parts, they're just laying around taking up space in my car-parts shed at the moment.

he has a 1.8l, although they are smaller, they should work on the 1.8 for diagnosis.

I don't think it's the injectors as they were switched w/ the motors. I think channelmaniac might be on to something. I'll mess with it some on monday. Thanks for all the ideas, I'll keep you all updated.

If it's the computer, lemme know...

I'd love to get my hands on a broken one to tear into it & see what makes it tick :D

RJ

I also have a spare 1.8l injector harness (I have way too many spare parts laying around).

Update:

The #3 injector is firing, I can hear it (with a stick). All the injectors have +12V with the key on as they should. I don't have an analog meter to see if the ground is switching but I can hear them all firing. The cars runs ok (on 3 cyl) when the injector is unplugged, but starts running really rich and fouling the #3 plug when its plugged in. Now I'm thinking ignition but I've changed the plugs, wires, coils, etc. I suppose it would be possible that the one harness that we used from the old motor was damaged somewhere around the ignition stuff (that harness has both ignition and efi stuff on it). But what doesn't make sense is that plug has good spark when I ground it. I'm starting to get really stumped here. What am I missing???

thanks for all the replies so far.

I'd bet you did, but did you review all the basics?

http://www.miata.net/garage/ignition.html

Can you disconnect the alarm wire from the #3 injector? I know that alarm controlled the ignition, since when we pulled it in the garage for it motor swap you could pull the key and it would keep running. Wonder if it’s sending a ghost signal to the injector????

Is it kicking any codes???

I did disconnect the alarm wiring from the injector. I might try disabling the alarm totally soon. I really don't think thats it, but I'm seriously running out of ideas.

Didja figure out what was wrong?

Raymond

Negative ghostrider. I've been at laguna seca since wed; just got back. If I can find out spare harness, I'm going to switch that tonight. I'm just totally out of other ideas as to what it could be.

Hey Evil is it kicking any codes??

It's not triggering the CEL. Do miatas throw codes w/o the CEL? Hm....

Have you checked for a code? Maybe the bulb is burned out ;)

Haha, how would I check if the bulb was burned out? I just checked. It comes on with the key, so its good.

I don't want to speak too soon, but I think I fixed it. I swapped injector harnesses last night and it seems to be running fine. I spent 30 min or so with the old harness and a multimeter but i never really found anything. Does anybody have a spare they would sell me? I have to replace the one I used.

Thanks!

Bring it with you tomorrow night & I'll take a look at it over at Moe's.

I don't have a replacement one though.

Raymond

Sounds good. I got a replacement harness from a friend in houston so the racecar can be dynoed next wed. I would still like to fix this one tho. Just to have a spare.

What time does everyone arrive at Moe's?

between 8 and 10. I'm hoping to be there about 9 ish.