My AE86 Issues/History

1984 Toyota Corolla Sport SR5 (RWD), partially converted to Corolla Sport GTS spec. Engine is out of a 1987 or 1988 Corolla FX16 GTS (FWD), a slightly different variant of the engine that came with the GTS spec. Wiring harnesses aren't entirely correct to spec, the engine main harness is correct to 1986/7 GTS wiring, with some modifications to interface with the 1984 SR5 body harnesses. In addition, part of the original engine harness for the previous engine is still inside the engine bay, as that portion is also responsible for the headlights and other electronics, this is of little consequence except that it can be confusing when trying to diagnosis any potential electrical issue.

The car's motor is a 4AGECL, the California emissions compliment, originally transverse mounted, variant of the 4AGE, the same engine that was in the first generation Toyota MR2, due to this, and the cars own previous popularity in drifting motorsports, a lot of aftermarket parts are still made for it.

This engine is nearly identical to the 4AGEC found in the 1985-1987 GTS models. However as this is the only Front Engine, RWD version of the motor, there are a few differences, most of which are found on parts that have already been replaced with their RWD counterpart, such as the intake and exhaust manifolds. The only differences I'm aware of are that my engine has the reinforced block introduced in the 1987 FX16 and 1988 Corolla GTS, as well as a different power steering pump bracket and belt tensioner that was modified to fit in a transverse layout, but functions fine in a RWD layout.

I own the 1984,1985,1987,and 1988 official toyota repair manuals, and can loan or photocopy them if necessary.

 The car does not have the EGR system installed, the ports for it are currently plugged, and I have all of the parts minus the piping. This shouldn't cause any problems other than fuel economy and NOx emissions. The car is also missing a charcoal canister, I'm still attempting to source a mounting bracket so that it can be reinstalled. the vacuum line to control it is capped off, so this should pose no issue to the vehicle running. Neither is required to pass Oregon emissions.

I still plan on reinstalling these, as the computer expects EGR, and the ignition timing tables reflect this, increasing the chance of engine knock at cruising speed/loads, however this should be mitigated by higher octane fuel until I can get it reinstalled.

The O2 sensor is disconnected, as the wiring harness for it is damaged and has no connector, however this was the case when the vehicle was purchased, and should not inhibit the vehicle from running & driving. The sensor itself is brand new, just needs to be rewired into the harness. This should only pose an issue for passing emissions, and with my limited time, getting the car running was/is my priority.

Lots of information is available online, the car is commonly referred to by its chassis code "AE86." It's worth noting however, the USDM model has a number of differences, as at the time we imposed the tightest emissions standards of the market countries. These primarily take the form of the use of an AFM/Air Flow Meter rather than the MAP/Manifold Absolute Pressure sensor, which decreased emissions at the cost of ~15hp. The other major difference being the presence of a catalytic converter and the EGR system.

As for work done to the car:

Purchased car, didn't pass oregon emissions, and as it's my daily driver, would not qualify for any exemption from testing.

Lots of time was spent chasing the cause of the emissions. The distributor was rebuilt due to a failing oil seal, the cap, plugs, wires & rotor were all replaced. Engine passed compression test. The Airflow Meter was disassembled and showed no signs of wear, and all of the measurements were within spec.

Ultimately discovered via a leak down test that the car had 2 leaky exhaust valves.

Car still ran at this point, completely reliable, but still not passing emissions.

Took cylinder head off, had it rebuilt by machine shop.

Reinstalled head, replaced the head bolts and all the gaskets that were removed.

When reinstalling head, 2 of the original intake manifold bolts snapped before reaching specified torque, potentially causing a vacuum leak due to an inadequate seal between the manifold and head.

I discovered that the engine did not have the intake manifold brace, which means the intake manifolds entire weight was supported by the bolts, likely the culprit behind the snapping bolts. This shouldn't pose much of a problem other than making the bolts non reusable.

Blew fuel pump relay when reinstalling head due to a wiring mistake, fuel pump is currently wired to a breaker in the engine bay that was originally setup to provide power to a high power subwoofer amp, currently I manually switch the breaker off when the car is not in use.

Currently, the car will start, but will stall within 2-3 seconds, unless the throttle position sensor is disconnected. My suspected reasoning for this is that the EFI computer enters an open loop at idle and WOT (ignores sensor data in favor of pre-programed fuel/timing tables). With the throttle position sensor disconnected, the ECU will not idle the engine, and remains in closed loop, allowing it to adjust the fuel injection and timing based on sensor data.

When the car is running at idle it seems to run fine, if the throttle is depressed very slowly it will rev up, but the engine has very little power and struggles to climb a minor incline in first gear. If the throttle is depressed quickly the engine drops to extremely low RPM and struggles to run, a couple times I heard it backfire out of the intake.

My thoughts for the cause of this were either vacuum leak, fuel pressure, or fuel injection system. Fuel pressure tested okay at the fuel filter.

The likely culprit is the broken intake manifold bolts, the intake manifold and fuel rail is currently disconnected so the snapped bolts can be removed.

However I'm hesitant to believe that's the sole cause, as the gasket it designed to compress a bit, and as there's no visible gap, I would expect very little air to get through.

The engine block is close to needing a rebuild, as the honing on the cylinder walls is almost entirely worn away, and the oil pressures drops a bit more than it should at idle, which I've been told is indicative of a failing oil pump.