One solution for Blacktop 20v 7000 rpm limit

ns270r
Club4AG Regular
Posts: 20
Joined: Mon Nov 11, 2013 6:06 am

One solution for Blacktop 20v 7000 rpm limit

Postby ns270r » Sun Jun 01, 2014 12:12 am

Setup: stock BT20v, 1zz COPs, stock bt20v harness and ecu. swapped into ae86.

Problem: My blacktop 20v started to limit the revs at 7000 rpm randomly. Previously, 8200 rpm.

Bottom Line: ECU threw code 12 after a double fault and lowered the limiter. Solution is to clear the code, turn key to IGN ON for 5 seconds before STA. This seems to keep my ecu from faulting code 12.

How Code 12 works: When Code 12 is tripped, due to no G or NE signal, it only remains on for the duration of the fault. The code is not stored after the first fault. The code is stored after the second fault, but the CEL will not stay on. The CEL will only be on for the duration of the fault.

When this first happened, I did not have a working MIL, CEL. So I tried all these things with no success:
--I assumed it was ignition break up from the coil-on-plug setup, and replaced the 1zz coils.
--I reset base timing, which is a PITA with COPs. Used a 16v coil wire from the 1zz COP to the spark plug in order to use an inductive timing light.
--I tested the sensors. all of them.
--I cleaned the throttles, IACV, and replaced the vvti solenoid.
--complete teardown and reseal/regasket the engine.
o-rewired the harness. (added the MIL/CEL wire)

after adding the check engine light wire, i immediately ran a te2-->e1 test.
--I noticed that the CEL stays on for about 5 seconds after the engine is running. This turned out to be the Code 12.
--no other codes were tripped. confirming that the SPD and STA wires are properly connected and functional.
--the car ran all the way to 8200 rpm during this test.
--i cleared the codes and drove on.

After the second time driving the car (after double faulting code 12), the ecu lowered the limiter to 7000 rpm. I cleared the code and it revved to 8200 again.

Solution: I turn the key to ON position and wait 5 seconds. Then I crank and the CEL goes out immediately after the engine fires up.
--If i get impatient and crank right away, the CEL stays on after the engine is running and I know to reset the ecu.


There may be an underlying wiring issue with the Distributor/CAS, the Ignitor, COPs, or even the ecu, but the 5 second rule works for me.

I wrote somethings oddly to help with searching, since I searched a lot for this problem and only found one solution, that didnt work for my situation.

ns270r
Club4AG Regular
Posts: 20
Joined: Mon Nov 11, 2013 6:06 am

Re: One solution for Blacktop 20v 7000 rpm limit

Postby ns270r » Fri Oct 31, 2014 8:57 pm

After some time, the 5 second Key-ON solution stopped working, and the car wouldn't start at all.

NEW SOLUTION:
- Relocate stock coil and coil-to-ground wire away from Distributor wiring.

^^^This got the Code 12 to go away, but it still didn't get started. Just cranking away.
The solution to this problem was a failure in the second IACV. Since the factory IACV didn't work well, there was a 16V idle-up valve placed in series. This idle-up valve failed in the closed position and after removal the car started fine.

Now the car started fine and revs to 8200 without issues. No CELs.