I picked up my second Miata yesterday. A 93 in primer (formerly white) that is running bad.
Tonight I ran through the diagnostic spectrum:
First I ran it to warm it up some. no smoke for that minute of running.. I was hopefully (foolishly?) optimistic.
Vacuum test showed normal expected vacuum, until it started to sputter and load up, and then vacuum dropped as it almost died. However a throttle blip cleared it up and vacuum resumed normal status. I never got the creeping down vacuum reading that would indicate clogged exhaust.
Plugs came out. They were hard to read having been in there for some time. But at least they were not oily.
Compression test was fine at:
175 psi
175psi
160psi
155psi
Famous ground strap corrosion on rear of the head fell apart in my hand. I rigged up a different ground strap until I can buy the right one.
Brand new plugs I had lying around for my 95 Miata went in, and we went on a blast up and down the street.
At WOT it ran pretty good. It hesitates and stutters when you tip in on the throttle some attempting a smooth low rev corner.
More WOT and it runs pretty good. Idle and pause for 5 seconds to do a u turn and it loads up and nearly dies. I clear it out with some revs, belching smoke of unknown color (it was dark outside and I couldn't see) and quickly return home. Oil pressure was good. I LOVE the real oil pressure gauge in the 93 and older Miatas. Oil is clean and full.
Car had 160K miles, but looks well maintained under the hood.
Total distance on new plugs 1/2 mile, maybe 2 min of running.
New plugs came out to get a quot;readquot; Me thinks I need injectors. Opinions?
Plus there is a significant oil leak from what I think is the front crank seal, behind the timing belt. And a definite donut gasket exhaust leak at the manifold to pipe, which is where the smoke started coming from again. Damnit I don't WANT to do another timing belt / Water pump / Radiator hoses / seals Miata job..
I'll start with injectors. If she runs right then off to fix the exhaust and oil leaks, and do a timing belt when I can't stand the marking of territory oil leak.
Richard
Check O2 sensor operation Its the only sensor I can think of that's out of the loop during warm-up and WOT operation, which is where you say it runs fine. If you are really adventurous, you could swap injectors around and see if it changes the results on the plugs since one looks new, two look dark, and the last looks white. take 1 and 4, and put them in 2 and 3's spot. If the plug color follows it, you have a winner. Some brake clean and a rag will make those plugs as good as new for quot;round 2quot;
+1 on the O2 sensor.Depending on how bad and the location of the exhaust leak,the leak may have something to do with a bad O2 sensor reading.
Just me,but I'd start by correcting the obvious problems first.
A plug wire or connection could be bad, even a weak coil, the 2 and 3 plugs share a coil and any problem in the circuit affects both plugs usually.
A bag or diaper in the right place under the oil drip keeps your parking place from being so obvious.
+1 for the injector swap, looks like some rich conditions, or bad swap..try to find a known working coil, or looking in Haynes check the ohms to test the coil. Check injector funtion, check spark....and also +1 for checking the O2 sensor.....hmmm dunno 2 and 3 are dark, 1-4 look good...i almost wanna say coil now...with out a doubt, test first, then replace.
Excellent thoughts. Which is why I love this forum.
I'll check out the coil tonight. I'm at 50:50 blaming the coil or the injectors.
If the coil checks out via static ohms (and I think it might because I seem to run fine until the plugs start fouling) Then I'm going to swap the injectors around and see if the problem follows the injectors.
The O2 sensor will be done at the time I correct the exhaust leak. I'm omitting it from the immediate problem list, as the O2 sensor would effect all four cylinders identically, and I have definite 2/3 rich problems. or so it would seem...
I'll repeat the test with no changes first just to see if the problem stays a 2/3 problem. It just quot;feelsquot; like a over rich fuel problem. I know that's hard to explain, but spark just doesn't feel like the problem.
Richard
Originally Posted by sydwayz
Check injector function,
Do you have a good method of checking spay pattern and injector operation?
I'm thinking:
*very important* doing this outside while well ventilated
a bright light behind me
injectors out of the head, but still in the fuel rail
a black trash bag flat covering the engine as a dark backdrop
one by one electrically connect the injectors
then crank and look for a good atomization of fuel pattern
Will i have to wire tie the injectors into the fuel rail to keep them from popping out?
Is there an easier way?
Richard
I am going to be eating crow here I'm betting....
I am hesitant to break out the Avian cutlery just yet, as I have only 5 miles and 20 minutes of running to judge on, and we'll see if the fix holds..
Remember I thought it was a fuel issue? But the astute observations of the forum noticed 2 and 3 were the pair of cylinders that were fouling out. Well I swapped the injectors around 1 for 2 and 3 for 4, and measured the coil resistance to find the coils perfectly in spec.
But when putting the craptastic new plug wires back on the 2/3 coil they didn't feel right. So I pulled more wire through the boot to make sure the metal end of the wire was well seated into the coil, and that the dust cover boot was not pulling the wire up out of the coil body. (these aftermarket boots just don't fit right!)
I did this as a quot;just because it feels rightquot;. I wasn't even thinking that loose wires at the coil could possibly be my issue. I was pretty damn sure it was injectors.
However when I fired it up, I waited, and it didn't load up, and it didn't bog out. It did drop the idle too low for a second, but that didn't repeat.
Then I blasted around in it for 20 minutes, and it never missed a beat; idles fine, smooth acceleration quick to rev up.
If the injectors were bad, I would have started missing on 1/4 now. but I'm not.
So here's a +1 more for NGK blue wires being the ONLY set of wires for Miata. I'm likely going to put new ones in when I tear into the timing belt to fix the oil leak.
Richard blackbird muncher
I've posted on the problem getting a good seating of the plug wires at the coil myself. I pull the covers, use both eyes and fingers as best I can to be sure the wires seat well, then slide the covers in place. One poster, at least, commented that his covers were cemented in place. NGK Blues, in both our cases, IIRC. Seems production varies. I'd remove the cement or get new wires. |
Post at 2-7 04:36 AM
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