blacktop 20v no high rpm power

[kyle20v]

Hello everyone thank you for taking the time to read this.
this will be kind of a long post but i want to go over everything to make it easier to understand. So, I just bought an ae86 with a blacktop swap 2 weeks ago. When i bought it the car ran perfectly and pulled very hard just like it should. Then at some point around the second or third day having it i started to notice it seemed sluggish in high rpms (around 5500 onward.) I read about the hydraulic tensioner going bad on these cars and thought i would check it out in case I had skipped a tooth on the timing belt. sure enough the timing belt was very loose and the tensioner had failed but everything was lined up fine. regardless however i converted the tensioner to manual and double checked the crank and both cams marks lined up perfectly. afterward still same issue. over the past few days it has been seeming to get worse. it almost sounds like it is pinging after 6k but its hard to say. it could just be misfiring and the itbs make it seem louder.
to go into detail the car idles a bit high but pulls fantastic in vvt in the midrange. feels healthy with no hesitation. then at about 5500-6000rpm it starts to fall on its face and sounds very sick. Here is what i have checked.

*fuel pressure/fuel filter
*tested vvt (both by jumping the plug and the idle dropping and by leaving it unplugged for a drive.) and found no faults
*vacuum lines for leaks
*ignition timing (might not be perfect because the diagnostic port is nowhere to be found on this swapped car... regardless the issue appeared without a change to the ignition timing in the beginning)
*spark plugs.
*compression tested and got 182-185psi on all cylinders
*filled up with fresh US 93 octane just in case it was bad gas

Here's the real kicker and what is making my life 100% harder. the check engine light does not appear to be hooked up to the dash (light comes on with ignition on but I unplugging the tps sensor with the car running and it did not light up) and the diagnostic port is nowhere to be found. so im sorry guys but i cant read the cel code if there is one...

Any ideas? I am getting desperate and frustrated, especially only getting to enjoy the car for two days before it started having this issue. anyone ever have an issue with 20v running fine until high rpm?

EDIT: Also of note is the car is a coil on plug conversion with 1zz coilpacks. I assume they are still fairly new because the swap was done only about a year ago.

[yoshimitsuspeed]

First thing you need to do is resolve your CEL issue. Find out if someone ghetto rigged the light to something or if it's hooked up properly.
If it is hooked up properly then start looking at the ECU. Strange CEL behavior is a pretty common sign of ECU issues.

Next I would start looking at the COPs.
On the stock ECU they need to be batch fired which can cause all kinds of problems including overheating and cooking the coils.
We are currently working on a module that would trigger the COPs sequentially. If you want to stay with the stock ECU and COP it would be a good option.

[kyle20v]

Thanks, definitely agree on figuring out whats up with the cel and diag port. I didn't know that the COPs were batch-fired. bad COP's would definitely explain my issues, and i had dismissed them since they are only a year old... but being batch-fired I could definitely see them being bad that quick. good call on that and i'll be on the look out for that module, especially if new COPs fixes my issue. Thanks again for the help and taking the time to read my long ass post.

[kyle20v]

well i replaced my coils with known good ones and that unfortunately was not the issue. Still reluctant to rev past 6 and possibly pinging. I set up a gopro watching a fuel pressure gauge and it definitely stays pegged under full throttle, no pressure loss at all so i'm pretty confident that leaning out is not the issue, especially since it was fine before. listening to it again it kind of sounds like a pinging... im going to try messing with the ignition timing again, but i feel that isnt the issue since i would imagine it would continue pulling strong before it pinged if the timing was too advanced. any other ideas?

[kyle20v]

ok well to anyone else that might have this problem i got it working normally finally. unfortunately i am not 100% positive as to what it was exactly but I know it either had to do with vvt cam gear or the timing. Im leaning towards vvt cam gear. Basically I decided to set ignition timing again and rather than listen to the light i would just do it by feel (wrong i know but i was desperate) i set it what i thought was overly retarded (lowered idle, turning the dizy clockwise if facinging the back of the dizzy/front of motor) just to see how it would act. before i test drove it though i messed with the bolt holding down the vvt cam. i loosened it and re tightened it less tight. well when i went on my test drive it all of a sudden pulled like it should up to 7 and then sounded like it detonated or pinged much louder than before. i drove it back and then moved the distributor counter-clockwise up past where it was originally and now the car runs 100%. feels like i have less mid rang power but still pulls so much harder after 5k so i dont mind. this is at least how it was when i got it. i think messing with the vvt cam was what fixed it. I think the timing was a coincidence but im honestly not 100% sure. My theory is i had the vvt cam bolt too tight and maybe it wasnt able to switch back at high rpm?

[jondee86]

If the engine is pinging, the knock sensor will pick it up and the ECU
will pull timing. Just in case you don't have it, here is the page from
the BT FSM covering checking the timing. Engine warmed up, all
accessories off, and TE1 and E1 jumped to put the ECU in diagnostic
mode.

Of course, you would have to have a diagnostic plug, or at least a
couple of wires hooked up to the approriate pins on the ECU, before
you could get into diagnostic mode. If you were going to do that, you
could probably hook up a CEL at the same time.



Since you have COP's you will need to make up a short high tension
lead from an old spark plug wire... one end with a cap to sit on the
plug, and the other end whittled down so that when you poke it into
the COP it will catch the spark. Put your timing light on the lead you
just made to check the timing.

Keep this test in mind if you have the same problem again. Sounds
like you did have a timing problem for some reason. But setting the
timing by ear and a bit of road testing will get you close enough.

Cheers... jondee86

[kyle20v]

thank you so much for the FSM pages. I'm working on getting one but since I just got the car I havent gotten around to it yet. I had set timing with the timing light before by connecting an old spark plug wire between the coil and the spark plug (worked great!) but like i said before i have no diagnostic plug so it was pretty pointless. either way thanks again and it currently runs very good so even if Its not as perfect as it could be, im just happy i can enjoy it again.

[jondee86]

I'd guess that just checking the timing with a light and not being in
diagnostic mode, you should see a warm idle (850+/- rpm) timing of
around 16 deg BTDC. That seems about right for most 4AGE engines.

Cheers... jondee86

[yoshimitsuspeed]

Definitely get it timed properly. I would not drive it till you do. You will be punching yourself in the face if you destroy the motor because the timing was off.

If detonation is audible you are damaging your motor.
Even if it's not audible to the naked ear you could still be doing damage.

[jondee86]

I'd guess that just checking the timing with a light and not being in
diagnostic mode, you should see a warm idle (850+/- rpm) timing of
around 16 deg BTDC. That seems about right for most 4AGE engines.

Ha !!! I just discovered tonight that there is another page to that
section on setting the BT timing. Basically it says that if the timing
is set correctly, without jumping the diagnostic box, you should see
10 deg or more BTDC @ idle.

This is a bit less than I guessed, so it seems the BT timing setup is
a bit different from the 16V engines. Therefore, I stand corrected,
and suggest that if you see 10-12 deg with the light, you are good

Cheers... jondee86

[kyle20v]

Well i just wanted to update this thread since i 100% discovered my issue and it wasn't what i thought it was. Turns out it was my itb trumpets being misaligned. Not by a lot, but i guess when i was putting on my uni filters better and loosened the bolts holding them on i didnt line them up perfectly and most of them were off by about 1/16 of an inch or less. Evidently that was enough to totally disrupt airflow at high rpms. I aligned them properly and now the car pulls better than ever. Thanks again to everyone who helped and cant believe such a slight misalignment completely destroyed the top end. Lesson learned.

[jondee86]

Interesting result !!! And just while I am thinking about it... you can have a sudden
change in the way the engine runs if you have to disconnect the battery for any reason.
The BT ECU has some learning ability, and will alter some fueling parameters to bring
sensor readings within the factory specified range. These are memorised, but the
memory is lost if the battery is disconnected. It can then take a few days of driving
for the ECU to relearn the changes.

Cheers... jondee86