4AGE Ignition advance woes - Fixed!

[Wiggles]

Hi all,

I've got a problem with the 4AGE in my AE86. It's a 7 rib bigport from an MR2 - the AFM version.
I bought it from a bloke who had it rebuilt and couldn't pay the mechanic, so got a cheap rebuilt longblock (still wrapped in plastic!) with a big box of all the ancillaries, injectors loom etc and put it all back together and into the Sprinter.
It's all stock (except for the cold start injector which was removed), i just lengthened the factory MR2 loom in the appropriate places and spliced in power, ignition switch and ground and away i went.

Car setup:
Ebay special extractors
Fujitsubo (spelling?) 2.25" exhaust, new hi-flow sport cat
Pod filter (did have a celica airbox, put the pod on temporarily to eliminate that restriction)
EGR valve is installed, but i made a blocking plate that stops the exhaust gas from entering the plenum.
In-tank ae92 SX pump w/modified bracket to suit sprinter tank, full tank of fuel.
VL fuel filter.
New spark plugs, leads, rotor and dizzy.
Rebuilt and flow tested injectors. 3 are within a few % of each other, one was cactus and was replaced with a new one.
Quadruple checked cam timing.
Double checked Zero reading on the crank (rod down No.1 spark plug hole w/ a dial indicator on top) all good.

The symptoms are: It starts and runs ok, drives well enough to get around but it gets seriously asthmatic above 4.5-5K and runs out of puff. At this point i'm flat to the boards and being passed by old ladies in Geminis and small children on scooters.

My first thought was TVIS operation - but it switches on/off at the correct point, and it makes no difference to performance if i physically wedge it open or closed.

Ran through FSM tests for TPS, AFM, dizzy etc, no problems found

Upon investigating, it seems that i'm not getting spark advance. At all.
I've set the initial timing as per the FSM (up to temp, bridge T and E1 terminals, start, set to 10 deg BTDC, stop engine, remove jumper, start engine) but the timing does not advance to 16 degrees.
Revving the engine with the timing light on it shows a slight retard in the timing as she revs up.

I hooked up an LED to the check engine light and got a code for G signal, i traced this to stuffed wires coming off the dizzy.
I repaired that and got the all clear signal from the ECU.

Checking voltages on the ECU against the manual, everything looks good except i had no 'IGT' signal coming from the ECU.

Followed troubleshooting advice in the manual

Resistance on dizzy pickups ok,
coil resistance was ok,
Replaced the dizzy with a re-manufactured unit,
replaced ignitor with a 2nd hand unit
wiring between ecu and dizzy ok
wiring between ecu to ignitor ok.
Swapped ECU, still no joy.

After all of that, the problem still exists. I have the Check engine light hooked up and it is on all the time. When i check the codes, i get the 'everything's ok' series of rapid flashes.

Sorry for the long read but i've been banging my head against the wall on this one for a while now and i'm out of ideas. Well, i ran out of ideas a while ago and started throwing parts at it as you can see

Anyone know what it might be?

[knightrous]

edit: mis read

[Harreh]

Hows the knock sensor? Mine was doing very similar things when the knock was unplugged

[Wiggles]

I didn't think there was a knock sensor on the big port?
It's just a GE, not GZE.

[wiso]

this is possibly a really stupid suggestion, you say the check engine light is on all the time. is it on from the second you start it, or is it a few seconds after starting?

could your T1 wire be grounding out somewhere so it always thinks it in diagnosis mode? would explain the 0 change on the timing when the connector is removed. but would not explain the light being on constant solid. so I don't know

Mine was similar when I had the bad pickups int he dizzy, but you have already eliminated that.

yes 4age bigport does not have knock sensor

[Wiggles]

this is possibly a really stupid suggestion, you say the check engine light is on all the time. is it on from the second you start it, or is it a few seconds after starting?

There are no stupid questions at this point in the troubleshooting process

It's on whenever the key is in the start or run position, even before it's started.
I expected that it should illuminate briefly and then turn off after 5 seconds or so like in other cars (is that right?) If i turn the key to run but don't actually start it, the check light stays on for however long you sit there.

Anyway, i'll check for a short. Although, yeah, it wouldn't explain the light being on solid rather than giving me the no-code code.

[Wiggles]

Tested the T1 wire and it has no continuity to ground, so it's ok.

Reading the manual, it looks like the Check engine light should illuminate when in the start position and turn off once the engine is running. But obviously this isn't happening.

Does this mean that the ECU hasn't figured out the engine is running?

I'm getting 13v to the STA pin on the ECU while cranking (as per the manual) but it looks like i've still got the same voltage while it's running as well.
Is that what i should be seeing?

[Wiggles]

I'm getting 13v to the STA pin on the ECU while cranking (as per the manual) but it looks like i've still got the same voltage while it's running as well.
Is that what i should be seeing?

To answer my own question: No, that isn't what you should be seeing.
STA should have 12v While cranking and zero when in run.

I pulled the STA pin out of the plug and it's running properly. Hooray!

I believe that when the ECU gets the start signal, it pulls all timing advance to aid starting, then goes to normal advance mode once the key is in the run position.
Looks like the ham fisted idiot that did the wiring (me) tapped the wrong power feed from the ignition switch and the ECU was seeing a Start signal the whole time it was running, so never added advance.

Gah! So simple!

Thanks to Wiso and Harreh for your suggestions. Sorry for wasting your time!

Next question, who wants to buy a perfectly good ECU, Ignitor or distributor?