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Discussion Starter #1
I've got a stockblock y8 on about 7psi. Had it tuned on stock injectors and ran great for a while. One day I was driving and idle/part throttle pegged rich, like 10:1. Fried the wideband it was so rich.

With a new wideband I decided to tune out the low load richness and got it ballparked, and wide open AFRs never really changed. What did change is it backfires and jerks in boost, even though AFRs stay in 12s. It scares me so I let off too early to really get a feel for it. Put new plugs in, gapped to .030" (.035" worked great before) and I even swapped over my spare dizzy with no difference.

Since it was abnormally rich on stock base maps as well I know it's not the tune. Fuel pressure is around 42psi. Seems something mechanical happened. Maybe my stock rebuilt ebay injectors broke and started flowing unevenly? Other ideas are bad plug wires, crank position sensor, main relay. I'll try to get some logs.

Any ideas?
 

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93 Civic HB SI
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523 Posts
Its possible the injectors are uneven. Does it run generally rough, or does it only show signs of this roughness/jerking when under boost and idle/cruise fine?

No CEL? It sounds like you have the ability to street tune, what tuning setup do you run? You should be able to check for faults though the software, although if you key cycle, faults are cleared from memory on OBD1 hondas. You will need to induce the problem and the recheck in the current ignition key cycle for any sign of a fault code.

The way you describe the jerking in boost to the point of it scaring you, are you sure you aren't hitting a boost cut, or running out of fuel/ignition table provisions? Depending on how boost cut is setup, it could cause backfiring and jerking. I know my boost cut, sometimes I accidentally hit cold cut from being in the throttle too hard during warm up conditions, I swear when the cut happens I about slam my face into the steering wheel lol, its a violent decel event haha. Maybe something has changed and your boost is higher now? What kind of boost controller do you run, a manual turn knob or electronic with a MAC solenoid? If electronic, maybe the solenoid is plumbed in where wastegate pressure is not the normal fail safe and there is something wrong with boost control?

MAP sensor going bad? Is it stock or do you have an aftermarket version with a larger pressure operation range?

For a boosted application, I typically gap my plugs between .017 to .020, not saying there is anything wrong with 30thou, I just like em tight because I've had secondary ignition related misfires under boost because of wide gaps before. Typically on 7 pounds it's not really an issue, but troubleshooting is troubleshooting, you can try tightening the gap if you are at wits end.

What do the plugs look like? Could they be fouled out from the previous rich operating conditions?

Chassis/engine grounds come loose? The one on the thermostat housing still in tact?

Do some datalogging of key parameters, then go for a drive and duplicate the issue, then come back and review the log playbacks looking for any sign of something cutting out?
 

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Discussion Starter #4
It's always hard to tell how the idle feels with these Yonaka mounts, engine is always shaking the car. But it drives fantastic out of boost, smooth and not down on power.

I was not aware of fault codes clearing that way and will check again. I'm using an s300 p28 and I'm no tuner but I can make adjustments.

I thought my boost cut worked like my lean protection, which feels like hitting a brick wall but never back fired or kept fueling. I'll take a closer look. I'll also double check fuel pressure as I don't trust the built in gauge on my china FPR.
Shortly after getting the car tuned it ran a little rough in VTEC so I gapped the plugs down to .035" and it ran beautifully so .030" should be good. Old plugs looked fouled but also kind of ashy which is odd but they weren't the worst plugs I've had and they were all even. A set of gently used, caramel brown plugs off my shelf have the car running exactly the same.

To keep the car from running stupid rich when cold I have to pull back so much ECT compensation.

Also it's on gate, no controller. I'll take a deeper look at boost cut... I just now realize this is the turbos first cold weather.
 

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Sloppy Jalopy
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make sure sensor outputs look realistic in datalogs..

maybe iat enrichments need some work?
 

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Discussion Starter #6 (Edited)
Alright I'm back with results. OMW home at the on-ramp I hit it in third, reached full boost everything looks good then it lean cut. But I only know this from the log because my eyes were locked to the AFR gauge and it was reading well. I guess it cut too fast for the buffer so I couldn't see it. Log shows steady duty cycle when it jumps to 18:1, what the heck? Boost never comes close to cut.

Before that I got it to cut in 4th but the weird thing is my tach dropped all the way when it happened, and I did not push the clutch. How is that even possible? Is the crank position sensor unable to read under heavy load or something? Also log shows 4mph the entire time, idk what's up with that.

I attached the log, just change the extension to .s3d, I swear I was wide open yet it reads 79% tps even though it tracks fine when I test it. Also, grounds look okay but I'll double check.
 

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Discussion Starter #7
make sure sensor outputs look realistic in datalogs..

maybe iat enrichments need some work?
Well when it lean cut the gauge read 12.4 ish yet the datalog shows MAX lean just before it cut, and even a bit after. That cannot be right, I'm suspect of my wiring work. Spad connectors might be shorting on frame or something...
 

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1993 Del Sol
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Distributor. A friend of mine had a similar problem in NA form on his y8 for ever. Turned out to be a bad dizzy. Try swapping in another.
 
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