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Old 08-17-2010, 09:22 PM   #1
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Default New Build Missfire under vacuum and low boost

"Finished" my build about a month ago. I've got a missfire that I'm trying to figure out.

Symptom: Engine makes a sound like pup..pup....pup..pup.,pup... which to me sounds like a missfire. It does this from idle to about 3,500 rpm @ no load: 20 to 10 vacuum and it will miss about 5 psi boost.

Older FMII with some upgrades. FMLink engine management from 2003, 1.6L, Garret 2560 bb, FM intercooler, GFB BOV, stainless braid oil and coolant lines. Innovate LC-1 (but I'm not convinced it reads right...it does read 14.7 under vacuum but only goes down to 13.6 under 10 psi boost even though I'm running the default "Turbo 1" setting)

Things I've done/checked:
Compression: 179 - 185 psi on an automatic engine with manual intake valve
Plugs: gapped down to .024 with Flyin'Miata plugs (NGK Extended Reach)
Coils: New Goodwin 45kV performance coils
Wires: New Magnacore 8.5 Competition
Injectors: New RC550
Intake: New gasket when built, studs & bolts still tight
Sprayed carb cleaner around intake for leaks
tiewrapped all vacuum connections
Disconnected PCV, plugged hose and does not change the pup..pup.pup...
I can't detect any exhaust leaks

It seems to be getting worse so maybe something will fail totally ..but that could be expensive.

Appreciate any ideas. I'm definately a noob to turbo

Thanks in advance,
Rob.
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Old 08-17-2010, 10:04 PM   #2
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What are you running for engine management?

EDIT:

Just saw the link, but could be in your tune?
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Old 08-17-2010, 10:20 PM   #3
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Could your cylinder head be warped by chance? Did it overheat on your car, or did you buy it from a seller in a condition unknown to you? Did you send it to someone to rebuild the head, and perhaps they substituted a "known good" head for your core? Remove the spark plugs and inspect the cylinders for water. With the spark plugs out, crank the engine a few times and see if it spits anything back at you. Post results.

My car ran like **** after I did the original turbo install/head swap (at the same time)...turned out the head came off of a car that overheated, and it was warped. At idle/cruise, it was running on 3 cylinders. For some reason, under boost, it felt like it was running on all 4. After I discovered the problem, I had the head planed, and the issue cleared up immediately. I never noticed gasket 'blow-by' from combustion leaking into the cooling system. Seems the gap sealed up under heat or something, and opened up to let coolant into the cylinder once everything cooled down.

How much vacuum are you seeing at idle?
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Old 08-18-2010, 12:20 AM   #4
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It might be my tune. I added some fuel in the vacuum and low boost maps and it seems to make it about 80% better. I'll tweak it a bit more.

The engine came from a Miata I ran as an automatic until I did a 1.8 swap. 143 hp was not enough so I sold the 92 with the 1.8 and decided to tubo my 93.

I'm seeing 20 in-hg vacuum at idle.

Thanks for the suggestions. I'm going to figure out the LC-1 issues and work on my tuning. I might also change to sequential firing on the injectors and see if that helps.
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Old 08-18-2010, 11:25 PM   #5
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Investigating the sequential firing I found my injector wires were mixed 1&3 and 2&4 instead of 1&4 and 2&3. Still some tuning to go, but I think this might have been a big part of the "missfire" issue.
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Old 08-19-2010, 05:43 AM   #6
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sounds like lean tip in to me
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Old 08-22-2010, 11:24 PM   #7
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Quote:
Originally Posted by huntleyrob View Post
Investigating the sequential firing I found my injector wires were mixed 1&3 and 2&4 instead of 1&4 and 2&3. Still some tuning to go, but I think this might have been a big part of the "missfire" issue.
Ya think?
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Old 08-23-2010, 10:08 PM   #8
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Thanks for the support.
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