3tgte idle poor with electrical load

[pauljones1976]

I'm running a 3tgte with RX7 injectors, a high flow CT26, custom plenum, rb20 throttle body. It's running an MTX8 Microtech. It has surge tank & upgraded lines. It has also had the battery relocated to the boot. All this work was done prior to me buying the car, and the electrical problem has existed since day dot. I suspect it is even down on spark.

I've just done the conversion to the EA 85A alternator on my 3tgte, hoping to solve my erratic idle when I turn on my lights, or the thermo-fan kicks in.

While it has improved things significantly once there are a few revs up, at idle it hunts terribly, and of a night time with lights on and the thermo-fan kicking in it often stalls.

I have checked and re-earthed both at the engine, and the rear of the car (where the battery is located). I have also added a large 12mm lead from the alt to the distribution point at the front of the car.

I have suspected this is an electrical issue based on the fact that it happens only when the load is increased. Obviously it's worse if the stereo is running & up loud.

Has anyone got any ideas of where to look? I'm at the point where I'm seriously considering taking it to an auto-electrician to have a look at it but I really don't like other people prodding around in it to be honest.

Any ideas would be great!

[TA22 GT]

Have you checked the voltage from the alternator when under load? Eg Get someone to help you and check the voltage with a multimeter while your driving. Check it by contecting to any power supply wire inside your car....

Should be around 14 volts. If its low then at least you know if its related to the alternator..

Cheers,
Simon

[Duk]

Highest current draw should be when the engine is cranking over. What is it like when trying to start?
What are Microguess like for idle speed control and voltage compensation?

[pauljones1976]

Simon, it's not really giving any problems once it has a little throttle and the revs go up. There seems to be plenty of current, more now that I've changed to the 85A. It's really only at idle under high electrical load (ie: all lights + brake lights + thermo fan at idle = idle hunt)

There's plenty of charge in the battery for cranking. At idle with no load it's reading 14-14.1V. I haven't read it with the lights on and thermo running yet but I will do that this coming weekend.

I've been wondering if it's to do with the microtech so I'm considering chasing the wiring on the ecu to check poor earth or +12v connections. Does anyone know if a Microtech will start getting cranky if it's short on power?

I've noticed also, at times, that the stereo volume decreases under braking. I've since changed the head unit with the same result, which is really really weird. I suspected maybe a speaker wire shorting but i've since changed all the leads and still have the same problem. I guess the next step is to actually try simon's idea of running a multimeter off the ACC 12v while driving to see what it's doing. Maybe that might shed some light on the whole deal.

I'm suss on the distribution point at the front of the car also, as there are two relays mounted in a dual plastic socket attached to the firewall. I'm going to have to have a good look at that soon if I can't find a solution. Maybe the relays are shorting once latched on and that's causing an extreme load? Strange that it happens with the thermo too though... Very much a mystery this wiring!

I guess I'm hoping someone has had a similar problem before so that I don't have to rule out everything as I may as well just rewire the whole thing if I can't find some relevant experience! It could be a very expensive trip to an auto electrician if it comes to that...

[frag_dog]

Do you have an Idle Air Control Valve fitted? It might be an issue with the load of the alternator, and the engine then not getting enough air.

If it were me I would add a 'T' piece to one of the vac lines off your intake and have it ideling with it plugged, then try allowing a small amout of air in, if that fixes it your IACV might be shot, or you might need one.

My $0.02

[TA22 GT]

I'm running a Mircotech LTX8 on my 3T GTE and yes it gets cranky when the voltage drops too far below 12V.

I have the same problem but only if I run all lights plus high beam too at idle. My high beam lights are upgraded to 100 watt spot lights so that wouldn't help. There is no need to high beam at idle, so I have no issues and my alternator is the stock 3T GTE unit.

My guess is simply that the current draw from all your electrics is above what the alternator delivers at idle....

Maybe increase idle speed a little or just reduce electrical load..

[ta22 3tgte]

Hi,

I think the distribution block would be worth looking at, how is it set up? Does the battery positive go straight to the block and then send power elsewhere? If this is the case then at low rpm, ie: idle, you could be getting just enough voltage drop through these relays to be causing the Microtech to have trouble.

Just for interests sake, I have the battery in the boot, positive cable running straight to the starter, and basically use the starter pole as the main connection, it runs a Haltech, and I have upgraded the alternator to a 90amp Landcruiser item. I have never had this trouble, even with the old standard 3TGTE alternator, but I haven't driven the car all that much.

Cheers Brendan

[oldcorollas]

have you got the right size pulley on the alternator?
usually they do not charge much at idle anyway, and if it is runnign slow, it is probably not doing anything.
if you have a smaller pulley available (pinch off other car?) it is worth a shot.. but only after using multimeter to check voltage. if you are not running to high rpm, a smaller pulley can help. if you are, then you will need to work out pulley ratios to not overspeed the alt.

if you have gone from an old style alt to a new comact style alt, be aware the new ones may need higher rpm..

is the new alt internally regulated? is it connecting to an external reg as well?

[pandaah]

check all the earth straps of the vehicle.. seeing as youve done all this work have you still got the earth straps that usually go from the chassy to the engine block?... or something similair?

[oldcorollas]

or are their mounting surfaces painted??
same for alternator.. it need to earth through the block (unless you have a seperate lead)

[thechuckster]

stereo volume decreases under braking

are you using the chassis to carry the earth up to the engine bay? the above suggests the earth return is fairly woeful and relying on random chassis spot welds to carry sizable current loads is questionable.

I'd suggest you measure resistance across the (-) on the battery and various spots in the electrical system.

And then consider running a large cable from battery (-) up to the engine block with a sizable sub cable from it to the chassis-electrical main earth point in the cabin.


edit: are you running a separate 12V sense wire from battery to the alternator? if not, then it's probably not charging correctly either. Using the 12V line at the starter or charging outlet on the Alt is not ideal. A separate wire to the battery doesn't have substantial - just continuous.

[oldcorollas]

oh.. does the microtech have an adjustment for injector pulsewidth vs voltage? if it doesn't compensate with longer pulsewidth when voltage drops, car can stall..

[oldcorollas]

are you using the chassis to carry the earth up to the engine bay? the above suggests the earth return is fairly woeful and relying on random chassis post welds to carry sizable current loads is questionable.

good call..
if the current from the brake lights (say 4-6amps) is enough to decrease the voltage, then there are serious earth issues...

second the -ve cable from batt to engine idea....

[pauljones1976]

Thanks for all the ideas guys, I'm definitely going to re-earth as I've wondered about this for a good while now. I have run a second earth strap from the engine to the chassis at the front, but I have been relying on the chassis to earth from the rear of the car to the front.

I'm not too sure about the way the new alternator is regulated as compared to the old one. The original alt that was on my 3tgte had three connections on the regulator - L, IG, and S. There were two 'extended' wires running to the L & S and it looked like the IG was connected to the B+ connection. I can't remember exactly, but I did mark the connections/wires so that I would know once I removed the Alt, although I marked them location-wise and they didn't match up correctly once I'd removed the Alt. So basically, I'm not entirely sure where each of the wires went now.

The new Alt had only two connections on the regulator - S & L. The guy I bought it off was running it on his 18R and it was supplied without a pulley (I used my original 3tgte one). I've connected it up to what I thought were the right wires but I don't get a charge light come on while ignition is on but the engine not running.

How do I check if the Alt is charging? Can I just run a multimeter off the B+ and ground?

[pauljones1976]

Ok, I've sorted out my L & S connections now and I get a charge light at the right times so I'm pretty happy about that... (it means the battery voltage sensing wire is in the right socket now which is the critical part)

So my next trick will be to figure out what the problem is (is it too little charge at idle, or is it a bad earth?)

I'm going to see if I can find some jumper leads and run one from the battery negative terminal to the engine... Dodgy, but should provide an answer!