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Old 01-12-2013, 05:09 PM   #1
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Default 1990 Turbo 1.6 running rough at high rpm, cuts boost

So I seem to have a never-ending supply of problems with this car.
Background: I swapped a used 1990 motor into my car with all of my turbo parts that I had previously been using, except with a new much smaller turbo. I've been driving for at least a few hundred miles with no problems, save for an oil leak at my turbo feed line.

Problem: When I push it above even 4k or so, seemingly regardless of the gear, the exhaust changes tones, and the motor seems to struggle to accelerate. Usually when this happens, I get a nice pop out of the exhaust on shifts. It may be boost-dependent, and if it is, it looks to be around 6psi, at which point I no longer build boost. Or at least not at any acceptable rate. Injector duty cycles are around 30-40% at most. The turbo is a .42A/R compressor with a .48 or so turbine I believe. Well matched to this motor. I'm running MiataLink by Link Engine Management, with a built in MAP sensor. Needless to say, there is no POS MAF sensor. My wastegate operates properly as far as I can tell, and it's set at about 8-10 psi.

The problem happened immediately after at some point on a cold start I decided to push it near my rev limiter. Which is low, 6200 or so. But it was right after I started it up, and I wasn't really thinking. I still get strong pulls on low end, until that particular point when it just changes. Kind of like a reverse VTEC. Up until then, great turbo spool, great power, then nothing.

I have tried to watch my AFRs on my wideband, but I get nervous pushing it into that section, and haven't really gotten any definitive results there. I am running slightly rich on idle and cruise, as well as in acceleration from slight vacuum through low boost ranges.
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Old 01-12-2013, 06:02 PM   #2
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Sounds like spark blow out, get new plugs, gap them down to .032. Then report back!
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Old 01-12-2013, 07:43 PM   #3
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Sounds like spark blow out, get new plugs, gap them down to .032. Then report back!
Gonna love you if that works, I bought a new set earlier today and they're gapped at .035 right now. Should I really take the time to knock them down that much more? I'll throw em in tonight and see what happens.

Not sure if it matters, but I have really nice throttle response and lots of low-end torque right now, it's just high rpms that bog.
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Old 01-12-2013, 07:46 PM   #4
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In my personal experience every thousandth has counted. .032 is my cars happy place
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Old 01-14-2013, 12:52 AM   #5
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So did you get a chance to swap plug?
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Old 01-14-2013, 10:27 AM   #6
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So did you get a chance to swap plug?
Yeah I did. It's much better, but still likes to cut out around 5500. I also fixed an exhaust leak before the turbo as well, and its quicker but still not right. I put in stock heat range coppers because that's all that was available to me. I'm ordering some 1-2 step colder iridiums soon.
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Old 01-14-2013, 11:18 AM   #7
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still with the stock heat range copper... why waste $40?


have you tried logging the issue, reviewing it in DataLog Lab, and tuning out the issue?
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Old 01-15-2013, 02:51 PM   #8
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Originally Posted by SprungMS View Post
Yeah I did. It's much better, but still likes to cut out around 5500. I also fixed an exhaust leak before the turbo as well, and its quicker but still not right. I put in stock heat range coppers because that's all that was available to me. I'm ordering some 1-2 step colder iridiums soon.
Definitely recommend colder plugs. NGK BKR7E's are very inexpensive and easy to find.

Colder plugs, and a smaller gap. Hmmm, I *think* I am at 0.030 with BKR7E's, or possibly 0.033. I will have to check my notes. Running 6psi with JRSC. No misfires.
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Old 01-15-2013, 02:54 PM   #9
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factory 9093 plugs are already 1-step colder than 94-05 plugs, which all have a bit more HP and weigh to them.

STOP DOUBTING THE ADMIN.
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Old 01-15-2013, 03:02 PM   #10
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OP needs COPS.
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Old 01-15-2013, 03:10 PM   #11
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Didn't mean to doubt you, Brain. I misread you.

Perhaps you meant "stick" instead of "still"?

Otherwise I wouldn't have brought up the colder plugs. I didn't know the 90-93 plugs were already colder. Perhaps it is on 'other' forums that the BRR7E's were recommended for FI setup's.

The consensus would be that stock heat range for 90-93 (6) should be good, and that a misfire sounds like tuning, gap, or needing COP's?
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Old 01-15-2013, 03:56 PM   #12
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Originally Posted by mc85 View Post
The consensus would be that stock heat range for 90-93 (6) should be good, and that a misfire sounds like tuning, gap, or needing COP's?
Steps I would take.

1) new plugs, .30 gap.

2) check your tuning, make some logs, make sure you aren't hitting boost cut or something stupid, make sure the AFR's are good and timing is safe and it's not detonating.

3) if its still doing this, fix your ignition system. you could waste money on new plug wires and a coil, or you could be a man and read the COP thread and do it on the cheap. It cost me about 150 bucks, and I bought brand new coils, brand new pigtails, etc. You could certainly do the COP mod for about 75 bucks if you go for used cops w/ pigtails.
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Old 01-17-2013, 06:38 PM   #13
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Steps I would take.

1) new plugs, .30 gap.

2) check your tuning, make some logs, make sure you aren't hitting boost cut or something stupid, make sure the AFR's are good and timing is safe and it's not detonating.

3) if its still doing this, fix your ignition system. you could waste money on new plug wires and a coil, or you could be a man and read the COP thread and do it on the cheap. It cost me about 150 bucks, and I bought brand new coils, brand new pigtails, etc. You could certainly do the COP mod for about 75 bucks if you go for used cops w/ pigtails.
Wow, you managed to magically quote what the people above you previously said, impressive!
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Old 01-17-2013, 07:06 PM   #14
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Wow, you managed to magically quote what the people above you previously said, impressive!
The point was that I put them in order of my personal recommendation, not that I came up with something new and revolutionary. I mentioned cops above, but gave the OP a checklist of things I would do before going to said cops.

That said, stfu
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Old 01-17-2013, 08:03 PM   #15
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The point was that I put them in order of my personal recommendation, not that I came up with something new and revolutionary. I mentioned cops above, but gave the OP a checklist of things I would do before going to said cops.

That said, stfu
Sorry, huge props to you for putting them in order, must have been a complicated task
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Old 01-17-2013, 09:49 PM   #16
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Sorry, huge props to you for putting them in order, must have been a complicated task
As someone who has troubleshot the EXACT issue OP has, I'm contributing to the forum and giving my $.02. Unlike your posts in this thread.
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Old 01-18-2013, 01:34 PM   #17
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As someone who has troubleshot the EXACT issue OP has, I'm contributing to the forum and giving my $.02. Unlike your posts in this thread.
Lol
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