Hi guys,

a friend of mine has an 1992 civic SI and blew his engine so we replaced it with an 1994 civic SI engine ( D16Z6 )
now we got like a misfire at about 6K rpm.
i taught it was the head so i had took it out and brought it to the machine shop to get it milled.
put the head back on and still misfire in the top rpm.
i have changed the dizzy, cap and rotor with one that has no prob and worked fine but still has the same prob.

when standing still and you rev it slowely the wideband give when missfire an 12.8 AFR if i'm not mistaken.

What could be the problem cause we are trying to sort it out so we can race this sunday.

please let me know guysss

Thanks

 

Any CELs when this happens? Don't know why you thought milling a head would cure a misfire you didn't even identify properly.

 

Nopes not any cell.
i did because the engine came with an broken Timingbelt and an broken waterpump, so he said he better do that because with his first car he had an waterpump failure and needed to miledown the head, tha's why he let them did it.
could it be an mapsensor maybe ??

 

learned this one last week...

If your thermostat is stuck open and the motor never reaches temp it will throw it in limp mode and cause this...

worth a look

 

but when in limpmode it should throw a cell and rev til 4K, this wil pas the 4K rpm and do this thing on about 6K.
Temp when i datalog i get 200 F.

 

Datalog? What are you running? Hondata?

 

nopes, Neptune

 

he will be back on friday with the car so i wil be loging what hapens on the rpm rage to try to see, but any help would be apreciated.
btw it is an turbo D16Z6 engine stock internal

 

Sounds like your tune is crap.

 

The car ran with that tune on the old engine a same D16Z6 also turbo an performed VERRY VERRY well, but i will be tuning the car again Friday to check.

 

Well check the plugs and wires just to be on the safe side. Other than that my initial bet is on the tune. No 2 engines are alike.

 

i fully agree on you on the 2 engine not the same part.
new plugs and new wires, but i will be tuning the car again so i will check.

thnx for the info

 

tps sensor? exhaust valve lashes?

 

OK so far i chaged : Mapsensor, TPS sensor, Dizzy, Cap, Rotor, Wires, Plugs ( 3 sets ), Vtec selenoid, Fuel pressure regulator, Fuel pump and still it does the same, i also tried with tuning but still nothing.
opend the wastegate to check and everything is ok in there.
what i will do is change the head.

when standing still it does it above 6300 RPM, below that it's fine, but when driving it does it at about 5K rpm.

what else could be the problem ??

 

What octane gas are you using? How many pounds are you running on?

 

What happened to the tune?

 

octaan is 95 boost is lowerd to 7 psi was 11.6 psi first.

i checked the tune and can't find anything wrong.
i'm gonne check from the weekend to change the head and see.

 

How about the ignition timing, or considering a ignition upgrade

 

Did you replace the fuel filter? Have you measured the fuel pressure? If you unplug the O2 sensor, is the problem eliminated?

 

Timing is OK set at 16 deg, i locked it into Neptune to set it down.
fuel filter i did not replace, that's a good one, and he does not have an fuel pressure gauge.
O2 is disabled in the system, he use an AEM wideband only

 

This is in essence an upscale O2 sensor, so the same point applies here.

 

Is the wideband tied into the ECU or is it just feeding signal to the gauge?

 

Both, but what i find so weird is why is he doing that now and with the old engine the wideband was the same.
could it be like a bended valve ??
compressuin is 200 to 210 PSI on each cylinder

 

If it was a bent valve it would only affect that one cylinder im pretty sure. I dont know much about turbo applications and how much compression you're going to have but that seems like a lot to me. If you have that compression i'm pretty sure you need a higher octane gas.

 

interested in your issue, if the machine shop checked out then its not your head! something though!!