Pro60modman

Have a 98 Civic Turbo Hatchback I'm diagnosing for a buddy. Misfires badly under load. Pretty much anything past cruising load it will start to get a single cylinder misfire and backfire out of the exhaust. Started doing it midway through a tuning session. Originally it didn't run at all and that was traced to bad coil fuse. Then it idled like crap and that was due to the fast idle valve so we stuck a OBD2 throttle body on it. Now it idles and drives fine, but misfires when trying to accelerate.

Specs:
98 Hatch
OBDII harness with jumper to Hondata S300 V3
Dual Treadstone 340lph fuel pumps w/10AN feed 6AN return
ID2000 Injectors
Full Blown Fuel rail
Can't remember fuel regulator brand
Victor X Intake
Ferrea SS Valves and Springs
CTR cams
GE Cam Gears
ERL GSR Block w/GSR crank
B16 Head
Dual 44mm WG T4 manifold
BW S366
3" Hood Exit
AEM 30-4100 Wideband
AEM MAC Solenoid for Boost control

Problems:
Car idles irractically - Identified and fixed, bad fast idle valve.
Hard to start - Indentified and fixed, coil fuse
Misfires under medium to high load. Gradually started happening when owner was tuning to the point of happening all the time.

Visual:
Interior driver side fuse box burnt near coil fuse
Coil Fuse Blown - Replaced, has not blown again since
Two bolts holding dizzy cap on - Doesn't seem to be source of the issue in lieu of other distributors yeilding same misfire issues
Loose Vacuum connections - Tightened
AFR doesn't seem to go extreme rich or lean when misfire occurs but hovers around 12.4-13:1, possible fueling issue.


Tests Performed:

Injector resistance - 12 ohm
Injector continuity - PASS
Compression Test - 197-192-200-200
Leak Down Test - 7-10% on all cylinders
Distributor - Tests good, tried three others from good running cars - no change
Throttle Body inspection - FITV Bad, TB w/TPS replaced. Car runs and drives at low load well now
Datalog - All sensors datalog within expected ranges including TPS, MAP and Ignition tracing
Ignition Check - Set at 16 BTDC
TPS - .48v Idle - 4.58v WOT Acceptable spec
MAP - Tested with 3 others from stock to 4BAR, no change.
Hondata S300 ECU - Used another V3 from a perfectly working car, no change.
Direct power to fuel pumps - no change
Fuel Pressure Check - 50psi at idle
Direct power to ignition coil - no change
New NGK BKR7E Spark Plugs - gapped .030" no change, gapped .020" no change
New spark plug wires - no change
Timing Belt Check - in time
Smoke Test - Minor leaks, fixed
Valve Adjustment - no change

fcm

What is fuel pressure under "medium to high" load?

Are the injectors all pulsing at "medium to high" load?

It does sound like a fuel issue. 94

Pro60modman

Fuel pressure goes up 1psi per pound of boost, 53psi at 0psi manifold pressure. I can't confirm the injectors are all pulsing but the misfire doesn't feel like a completely dead cylinder so I'd think they are. Unfortunately I can't read individual pulse on Hondata.

JRCivic1

What type of distributor are you using and where was it purchased from ???

fcm

Ditto the above,^^^ it could be electrical, [poor spark] .

Try a few "pulls" then immediately pull the spark plug and see what they look like, color of spark plugs can tell you a lot at the very least point you in the right direction, easy to do and costs nothing but a little time.

I had those symptoms once when I was auto crossing, turned out to be moisture in the spark plug wells, [and moisture on the leads in the well] and only under heavy load. 94