this is a question on 5g civic, but should be the same no matter what year...


my friend and i installed a vtec head on his turbo 5g civic dx. car ran fine before the new head. it was a pretty straight forward install. the BIG problem is that when he starts it up, the idle will bounce. then, if he hits the gas, it will actually rev down, and just about die...and start to backfire really bad. what could be the problem?

we checked and replaced a few things:

new timing belt/checked timing 3 times
replaced headgasket
replaced intake manifold gasket 2x's
changed injectors
changed fuel filter
changed distributor 2x

we changed NO WIRING.

 

umm, isn't the dx dpfi and the vtec head mpfi, so you would need to do the dpfi to mpfi wiring changes

 

4g are DPFI, 5g's are MPFI.

Check things like IACV and fast Idle solenoid. I have had problems like these and it simply was the idle screw needed to be backed out a bit.

Also Ensure that all the timing is correct. I don't know what all has to change with the head you used, but It's also been a timing problem before for me.

BTW: What head? Assuming it's SOHC is a y8 or z6?

 

its a d16z6 vtec head on a d15b7 block. checked the timing 3 times just to be sure, changed the pcv out. we used the d16z6 intake manifold/throttlebody combo which worked perfectly fine before the swap.

 

Are all of the wiring connections solid?

 

yea, its a stock wiring harness. all grounds are on, no open wires..etc

 

so you jumped the green plug and checked the ecu for codes too right?

it may sound stupid, but you didn't say you did so....

 

yea, jumped the plug...and nothing!

 

What ECU is he running? Also doulbe check all your work, it could be right under your nose, happens to everybody Did you leave any sensors unplugged?

 

hes running the stock ecu. hes not going to hook vtec up until he gets the car running right. everything worked properly until the head install. we went over the wiring harness a few times to check if anything was unplugged, but it can't hurt to check again...