4AGZE ECU issues but no fault codes.

[worldwalker]

Hi guys,

I'm trying to suss out an idle and hesitation/load issue with my 4AGZE. I figured I'd start with a search and have looked at all the obvious.

The idle problem is the "common" issue: Ticks over fine (first time every time), revs up to about 1800 then settles at about 14-1500.

If its warmed and left parked eventually idle comes down and settles about 900RPM, revs fine, runs fine, timing is good, the only problem is as its warming up the idle is up and down +-100rpm every couple of seconds until it finally settles.

If its driven, whether its allowed to warm up completely first or before its completely warm, the idle issues begin. The idle can be anywhere from 1400-2000rpm. Sometimes it looks like it's starting to drop then it surges back up. When its at this point, unplugging the TPS and ISC can bring the revs back to about 1000-1100 but thats it and once they're back on the RPM is back up. The only thing that drops the RPM back to the set idle is unplugging the coolant sensor but that throws a code.

The hesitation/low power is only below 2,500-3000rpm and it feels as if the engine is labouring with no load (whole car shudders), as the revs creep theres a hesitation then it surges and away she revs (feels like really bad turbo lag). Cruising anywhere around 2000-2500 and the whole car shudders at the sight of an incline and the exhaust sounds like a trombone. It also bucks a little cruising at this rpm too, nothing drastic but the worse the idle the worse the bucking. Finally, its impossible to take off from the line without massive clutch slip. If its idling at 2000rpm it does not want to drop below this, again the whole car starts shuddering and kicking like its on the verge of stalling.

The cars an AW11 4AGZE Manual running Auto ECU, with the neutral start bridged (possibly should be disconnected after start?) and the Auto computer disconnected; though, I've just found that while this doesn't throw codes it alters the throttle voltage and possibly others?

I've checked the coolant temp sensor and compared it with another.
Checked the AFM
checked the vac lines
bled the coolant
checked the ISC
timing is set to 8DTOD.
earths are good and ran extra to try to alleviate the issue.
New plugs
new diz
leads are ok
and spent hours getting the TPS perfectly within tolerance (surprisingly hard to get 0.8Ko at closed and infinite at .65mm).
All ok.

Finally I've checked the ECU and not so good.

TPS-ECU ohms VTA-E2 0.77 closed (0.2-0.8 tolerance) Open 1.77 (3.3-10 tolerance) Where did the rest of the 3.5ko I measured at the TPS get lost?
(IDLE/THA/THW-E2 all ok)

TPS-ECU Volts IDL-E2(open only) (auto comp off) 4.55V, (auto comp on) 11.55V. AT tol 10-14V MT tol 4-5V
VTA-E2 (trottle closed) 0.51V tol 0.1-1V, Open 3.05V tol 4-5V

W-E1 1.57V tol 0.5V or less.

Everything else was ok...

Another issue I've noticed is my temp gauge never stays still! I've checked the sensor and compared with another and its fine; but its bouncing around like a yo-yo (not physically bouncing, just never stays at one temp). Again if the car is left parked it climbs fans come on and everything is stable. If I drive it, the temp drops back to cold within a few mins at 40-50km/h regardless of how I drive.

I've done all the suggested quick fixes but can't seem to trouble shoot a solution. My best guess is the ECU is confused by sensors but is happy to accept the signal and just adjusts as it sees fit.

Any other ideas from the guru's?

Nick

[worldwalker]

I've had a bit more of a play around and not much luck, tried it with the auto comp on and same deal.

The leads are all about 8Ko.

It now sounds like its pinging while free revving but the timing is staying advanced.

It really seems like its something to do with the cooling sensing side but everything there is working fine, the only thing the computer is getting wrong is the VTA-E2 and I have no idea where the resistance drop could be coming from (or how its even possible).

This is the most confusing part! How is it possible for resistance to drop between the sensor and the computer but if the sensor is unplugged increases to infinity? I'd have thought it was a leak but jumping to open when its unplugged indicates to me thats not the case.

I've attached a photo of the plugs for no reason at all.



Nick

[worldwalker]

Ok, I've isolated the leak to the E2 wire link in the AFM. Its meant to be there. I've checked it against a second loom, second AFM and second TPS and its designed that way. The back up set does exactly the same, with the AFM plugged in, TPS output reaches 2ko (under tolerance) with the AFM unplugged TPS output reaches 6.5Ko (right in the middle of tolerance). I've double check timing again and its still fine. I've triple checked the temp sensing and its all exactly within spec, yet it runs perfect when its disconnected. What am I missing?

[jondee86]

I'd chuck a new thermostat in it for a start. And then I'd check the ignition timing procedure. A lot of 4AGE's need the diagnostic box shorted when setting the base timing. If you set yours to 8 deg BTDC without putting the ECU into diagnostic mode, the timing will be retarded.

Cheers... jondee86

[worldwalker]

Thanks, yeah I probably should have mentioned that too, the timing is set as per the workshop manual, and now back to 10BTDC. The thermostat was tested before going in and working well.

Also visually checked the ECU and its ok. I don't have a spare to test though.

It has to be something else simple like this I've missed?

[jondee86]

Another issue I've noticed is my temp gauge never stays still! I've checked the sensor and compared with another and its fine; but its bouncing around like a yo-yo (not physically bouncing, just never stays at one temp). Again if the car is left parked it climbs fans come on and everything is stable. If I drive it, the temp drops back to cold within a few mins at 40-50km/h regardless of how I drive.Nick

This sounds like air in the cooling system. I'm not familiar with the AW11 cooling system, but if the temp sensor is located in a position where air could collect, you can get these symptoms. Likewise, if the ECU water temp sensor is gets airlocked, it can cause fluctuating idle. And, once the system is warmed up, you should not get the water temp dropping back to cold if the thermostat is working properly.

Cheers... jondee86

[worldwalker]

Might be a combination. I decided to recheck the thermostat again and it was opening way to early and the rubber has deteriorate jamming it open. I rebled the system again and it seems ok but I think it might still have a bit of air in there again.

The idle is now pretty much sorted and it warms up quick and idles pretty well, but still has hesitation issues, I can now confirm that its between 2,000-3,000 with a miss at 2,700RPM and now a hunting issue on overrun. The shudder is still there when you try to slip the clutch at idle and obviously the voltage problems are still there.

At least the idle is sorted and slowly knocking down the list.

[jondee86]

There are a couple of things that come to mind...
1. Lean miss due to air leak after the AFM.
A split in the air intake ducting can let in enough unmetered air to mess pretty good with the mixture and idle at low rpms. Once the engine gets a few thousand revs on, the leakage becomes a much smaller percentage of the total airflow, and the engine will run good enough.
2. Cam timing out.
Ignition timing can be spot on according to your light, but if the cam belt has jumped a few teeth on the crankshaft sprocket, the spark will be happening at the wrong time (retarded I think). If so, this will give you a loud exhaust and a possibly a glowing manifold

Cheers... jondee86

[worldwalker]

Thanks for the persistence! I'm thinking I might need to go through my vac system and intake piping to check for leaks. I know some people have played with the adjustment screw (bypass) on the AFM with mixed results perhaps this could be part of it? Is there a guide to correct adjustment or is it all by feel?

I've checked the cam timing a few times now (never sure of myself) and its all aligned correctly, including the diz gear.

Thanks.

[jondee86]

There is no valid reason for fiddling with the AFM bypass screw. Providing the flap opens far enough to close the FP switch, and the FP stays on at your lowest rpm your engine sees, it is good. Some people fiddle with ("click") the clockspring to fool the ECU into thinking there is more air going into the engine than is actually passing the flap. This gets a richer mixture at all times, and wastes fuel with little (if any) performance gain. You can usually tell if the "lid" if the AFM has been prised off. Difficult to calibrate back to factory, so easier to get another AFM that hasn't been messed with.

Cheers... jondee86

[worldwalker]

Checked my AFM and it was clanging a bit on closing so I replaced it and also replaced all the vac hoses while I was at it. All was running great for about the first 10-15mins, cold and full temp no problems, no major surging, hesitations or other problems. Switched it off to fiddle with something then ran it again and it started surging and hesitating below 3000RPM, like before. It seems that once it hits 3000 its at about 8-9psi and is happy, but anything before that and it feels really underpowered and jerky. Under light throttle without the SCer on, it feels smooth all the way.

Hopefully this is all coming to an end now. I've got a manual ECU coming soon so I'll be able to test the ECU shortly too.

Thanks, nick