guys am runnin out on ideas.....ive a d16z6 (p28- ECU) totally stock and the idle is as if the motors got a veryyyy wild cam. its something like a built v8.. somethin like misfiring.. the vaccum when da idle was fine used to be around 23-24 in.Hg and now it has dropped down to 15-16 in.Hg. . The RPM stays at 750 but the motor shakes like crazy as if its misfiring but its actually NOT. Sometimes it dies at traffic lights. things already checked are:

Distributor - Fine
Fuel Supply - Fine
Injectors - Fine
Spark Plugs - Fine
Checked all the sensors (TPS - ECT - O2 - MAP - IACV) - perfect - No CEL as well
Spark Plug wires - Fine
PCV - Fine
Valve Lash intake = 0.20mm and exhaust = 0.25mm
NO Head Gasket Leak
NO VACCUM LEAKS
Did a compression test and it comes to 175 Psi EXACT in all four cylinders.

Could it be bad valve seats thats causing the cranking compression to be low @ 175 Psi.. i believe it should be 200 Psi.. ?? and the bad valve seats are cauing the idle problem as well. any way to check for that???

The car revs great all the way to redline.. no sputters or anything...

Thanks in advance

 

I thought valve lash was like 1.0 - 1.1 mm or .039 - .043"??

If your valves are too tight, that will cause a drop in vacuum.

A plugged catalytic converter will also cause this problem (or a restricted intake). If you have a vacuum/pressure gauge, you can remove the O2 and measure the amount of backpressure present. Do this at idle and at like 2-3k.

EDIT - missed the part about it revving freely to redline. Your cat is probably fine - tight valves would be my guess then.

 

thanks for ure prompt reply.. ive the honda workshop manual and according to that the valve lash shud be set @ 0.18 to 0.22 mm for intake and 0.23 to 0.27 for exhaust.. and ive always had the valve lash within these specs and never had a problem.. have three other hondas in the garage and they're all fine with these specs.

for the restricted intake am running an aftermarket air intake and i just got a new filter..... and also a straight through free flow down pipe without the cat..

 

When did the problem start? Out of the blue or after you did some recent maintenance?

When you did the compression check, was the motor warmed up and were you holding the throttle plate wide open?

 

i recently changed the piston rings... got new valve guides and new valve seats grinded.. thats it...after that this thing started..

for the compression test...the motor was warmed up and the gas pedal was fully pressed.




Modified by acidz_z6 at 8:53 AM 3/2/2005

 

http://www.centuryperformance.com/vacuum.asp this should have all the info you need

 

hey thanks for the link... k i cant relate my problem to any of the needle readings there.

wat actually happens is
1- when i start the car cold the vaccum guage shows steady 18 in.Hg
2- when it gets warm it fluctuates between 15 and 16 in.Hg
3- while driving and doing engine braking like u let go of the gas in third gear the vaccum guage shows 24 in.Hg .. this is the value which the guage used to show when the idle was perfect.

what basically is happening is that when the car is at idle the vaccum guage shows a different reading than the one when ure decelerating in gear.

how would u relate these symptoms to the descriptions in the link?

 

Does that motor have an egr valve? I had a motor one time the egr valve was hung open and it idle like it had a big camshaft. Replaced the egr valve it fixed my problem.

 

well yehh. am using the y8 style intake manifold from the d15B (three stage vtec)

that manifold has got an EGR valve but its all good. its perfect but is obviosuly disconnected cuz the p28 doesnt support EGR. already checked that

btw when the EGR is stuck open wudnt it sound like a muscle car all the way upto redline?

 

No when the valve is stuck open it only affects idle vacuum because technically it is a vacuum leak. I would take the egr valve off and build a blockoff plate for the manifold just to make sure.

 

I also have a d16z6 I was recent ly scratching my head with it did the exact same thing. I found I had the IACV connector switched w/ the intake air temp sender(so it pretty much wasn't plugged in). You are definitely having either IACV issues or bad ECM signals to the ecm or a vaccuum leak. It also may be a leak in the vaccuum line. Take some carb cleaner and spray a mist around the vaccuum hoses with the engine running, and if you hear the engine increase in idle, you have a vaccuum leak and need to replace all your IACV vaccuum hoses.

 

alrite.. took the EGR off and got a plate made from a local machine shop.. about 0.5 inch in thickness. STILL THE SAME THING

as far as the IACV and the IAT being switched... ive checkd the wiring a couple of times with the multimeter and its good.
the iacv is also good .. ve chekd .. it makes that click sound and the idle is high when the car is cold and drops gradually as it warms up.. that means it working.. i dont ve the fast idle valve so that means the IACV is working.

 

How many miles are on the motor now?

Maybe the combo of fresh rings and a valve job are the 'problem' here.

 

about 300 miles after the new rings and the valve job.

 

k if someone can host a short video clip i can email the video clip so u all can better see how it sounds

 

Get a leakdown test done and post back some results.

 

but if the valve guides were bad wudnt that cause oil to leak to the spark plugs.. plugs are normal.

second for the valve seats i poured like 250 ml of motor oil in the intake and it didnt help too. also the compression test was 175 psi in all four cylinders exact..

juz cuz of the fact that we dont ve a leak down test facility over here.

 

Leakdown test facility....its a gauge just like the compression tester only you plug your air compressor into one side of it and plug the other side into the spark plug hole.

Leakdown test has nothing to do with valve guides...its got everything to do with ring seal and valve-to-seat seal.

 

my bad.. i know its a guage.. but its not available here.. a local mechanic suggested to put some oil in the intake and if valve to seat seal is bad the oil shud fix that for a while and the car should smooth out for a while.. i tried that out and it doesnt help .

second if the valve to seat seal was bad wudnt the compression figures vary from cylinder to cylinder.. am getting 175 in all four.????

for the ring seal the car doesnt smoke AT ALLLLL.. ve got new rings in dere

PM ure email ill send a video of how it behaves..

nyway its nite time here.. ill try to do the leakdown with an aircompressor tomorrow..n post some results..

 

k i did the leakdown.. used an air compressor and the numbers came out to be really good

1st cylinder @ 100 psi.. after 15 mins - 99.62 psi
2nd cylinder @ 100 psi.. after 15 mins - 99.47 psi
3rd cylinder @100 psi.. after 15 mins - 99.70
4th cylinder @100 psi.. after 15 mins - 99.54

the air compressor guage was digital..

NOW WHAT

 

NYONEEEEEEEEEEEE

 

Pumping 100psi straight into the cylinder with an air compressor isn't the same thing as a straight leakdown test. The leakdown gauge consists of two gauges - one to show input pressure and the other shows pressure lost.

So your results for the test may not be valid.

For the hell of it, have you tried disconnecting the exhaust right after the header/manifold - just something to try cuz' I'm running out of ideas.

 

ive got a 2.5 inch straight down pipe with no cat.. and yes ive run the car with open headers as well.

wat about sticking valves.. cuz in cold its good (not perfect). when da thing starts to warm up maybe the guides expand and cause stickiness. thats the recent most thing ive done - new valve guides and valve to seat seal grinding with new rings

is dere any damage that can occur from sticking valves if i keep it driving?
wat is it that can happen?

 

Well, if the valve(s) stick in the guide(s) and hang open....there would be piston to valve contact and it would be disastrous.

I had a similiar problem with my engine.....turned out to be a vacuum leak at the brake booster port.

Also, get a proper leakdown test.....no facilities in AL?!

 

actually am on vacations till summers back home... i just checkd the brake booster. disconnected the big fat vaccum hose from the back of the manifold and had my thumb on the port. NO HELP..

i highly doubt if the valves wud hit the piston even if they stay open. its a d16z6 @ 9.1 compression. the reliefs are pretty deep on the p28s.

anyway ill take the head off tomorrow morning n ill let u guys know.. hope its worth it .