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Boosted d16z6 Running Rough, sounds like misfire

844 Views 12 Replies 3 Participants Last post by  mattliston
My semi-built, dseries sounds like its misfiring. I have to stay on gas for it to keep running. Before I pulled out the swap to clean/dress up the motor and bay, it ran great and strong. I didnt take the motor apart while it was out. The only thing that came off was the timing belt(for cleaning purposes and the timing is spot on) and the pcv system(installed a catch can, vented from the valve cover. Black box was removed in hopes of performing a "pcv delete"). Diagnosed MAP, TPS, firing order is straight. Cylinder #3 is reading 90lbs cold when i performed compression test(the other 3 read at just shy of 118lbs. Using Vitara psitons. It was that low when car was running strong, before it was pulled). Thought maybe a bent valve, but timing belt never broke. I did notice that when I installed the catch can and the hoses, I tried to eliminate the PCV Black Box and later on noticed that the hose coming from the catch can was loose at the port on the block. Was thinking maybe it was causing a huge vacuum leak(which could have been my problem the whole time). I also installed a complete harness from WireWorx. I thought it could have been that, but i realized it wasnt when I installed my old stock hatness and it ran the same way.. Below is my build sheet of the motor.
Someone please help me. I am quite knowledgeable, but I know I'm missing something. Never had any experience with catch cans. Thanks in advance.

D16Z6
Stock built head(New Valve Stem Seals. Shaved Head. Stock Cam.)
Fully Built Bottom End(Vitara Pistons, Manley H-Beam Rods, ACL Race Bearings, Block was Decked and Honed at Machine Shop, along with head.)
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can you do a datalog koeo to check the reading of the sensors?
Yeah. All sensors checked out fine. Meaning all readings were within limits.
so to make it short, you removed the powertrain, and only touched wiring and the timing belt?

If you do not have an adjustable cam gear, seems like you are simply off a tooth possibly.

Or a ground wire is unhappy somewhere. Make sure ONLY the harness ground is on the thermostat housing. ANy other extra grounds, be sure to keep them OFF that area.

Make sure the big battery ground is nice and tight.
so to make it short, you removed the powertrain, and only touched wiring and the timing belt?

If you do not have an adjustable cam gear, seems like you are simply off a tooth possibly.

Or a ground wire is unhappy somewhere. Make sure ONLY the harness ground is on the thermostat housing. ANy other extra grounds, be sure to keep them OFF that area.

Make sure the big battery ground is nice and tight.
I do have an adjustable Skunk2 cam gear and its at 0°, timing was off by 1 tooth, but I set it at factory spec and its still running the same. The grounds are exactly the way you stated, with brand new steel braided ground straps.
Does it idle at all by itself? or is it very sensitive, and easy to stall out?

See about getting a cross reading of RPM, TPS, MAP, IAT, and ECT.

With motor off, but ignition on, do a few full slow swings of the throttle and watch the data.

Check temperature sensors to approx ambient when the engine is cold.


Something is odd.


Hell, could simply be a spark plug or plug wire got upset. Or ignition control module is being finicky, and producing a weak ass spark
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Does it idle at all by itself? or is it very sensitive, and easy to stall out?

See about getting a cross reading of RPM, TPS, MAP, IAT, and ECT.

With motor off, but ignition on, do a few full slow swings of the throttle and watch the data.

Check temperature sensors to approx ambient when the engine is cold.


Something is odd.


Hell, could simply be a spark plug or plug wire got upset. Or ignition control module is being finicky, and producing a weak ass spark
I have done all of that. But I'm not opposed to re-do all of it again. Was wondering if the loose hose where the black box used to be was killing most of the vacuum.
I have done all of that. But I'm not opposed to re-do all of it again. Was wondering if the loose hose where the black box used to be was killing most of the vacuum.
And no, it dosent idle by itself at all.
very strange.

Does it start up fast, and die out? does it take quite a bit of cranking?

If it starts fast, you can rule out being pig rich, like a stuck injector or something.

If it cranks forever, then still dies, then maybe there is a crack somewhere on the intake manifold or throttlebody.

You could try spreading some wheel bearing grease around all intake seems to temporarily block leaks.


I dont think the block's black baffle box would matter, as I think if it were leaking bad enough, it would hiss like crazy
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very strange.

Does it start up fast, and die out? does it take quite a bit of cranking?

If it starts fast, you can rule out being pig rich, like a stuck injector or something.

If it cranks forever, then still dies, then maybe there is a crack somewhere on the intake manifold or throttlebody.

You could try spreading some wheel bearing grease around all intake seems to temporarily block leaks.


I dont think the block's black baffle box would matter, as I think if it were leaking bad enough, it would hiss like crazy
The port was definitely leaking, but heard no hiss. I will check the entire intake manifold and throttlebody. It takes 2-3 seconds of cranking before it turns over. Maybe re-install the pcv system, being that's the only major item that has been changed.
give it a try, but unless there is an obvious connection missing, I doubt it would be enough to cause your issues.

Cant hurt to go back to what was good before, and piece it together from there.

Engines are finicky at times.
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Aint that the truth. Either way I'm basically gonna do a mental tear down and rebuild. And maybe start from scratch. Thanks for your help brother. I'll keep you posted...
find a piece of paper, and write down everything you can think of that was touched. Then go through the lsit after a couple hours. IE, give yourself a break from the car for awhile.
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