My 99 was acting crazy again last night. The instrument panel lights were going dim and bright every few minutes, the engine was idling high (1500 rpm after I was cruising at 75 for 40 minutes), and the coolant temp gauge was going up and down; almost with the same frequency as the gauge lights. It had the same symptoms of when my tensioner fell off before the coolant temps started climbing past the midpoint.

The cooling system is fine, I've replaced literally every part (including the water temp sensor) within the last year/6k miles except for the heater core. The alternator is a refurbed bosch unit that's about just as old as the cooling system parts. The battery is a 1 year old staab battery (http://www.staabbattery.com/product/...U1-Auto-Y.html) which has always been a bit weak in the winter, even when brand new. The alt/wp belt is brand new, about a week old. I've re-tensioned the belt with no success.

I'm currently running a cali ecu, I cracked it open a few months ago to check if any of the capacitors were leaking and it seemed fine with a brief visual inspection. Is there any sure-fire way to eliminate that as a possibility without swapping ecus? If not, what else should I be looking at besides the alternator, battery, and electrical shorts?

 

You could put a meter on the battery during one of the brown outs and confirm the whole system is dropping and not just a connection to the engine harness. Have you checked simple things like the ground straps on he engine? If it is the ECU, you could swap in an NA8 alternator if the rest of the ECU is working properly.

 

What is voltage at your battery while idling?

 

Should be battery voltage on 2O when the system voltage (injectors) is below ~14v, it should be at 0v when the system voltage is above that.

 

Thanks I'll try that. How many ground straps are on the motor? I only checked the one on the top. Is the NA alternator plug and play? I try not to do wiring on cars. Every time I do, I'm a nervous wreck for weeks. Then I forget about it. Then it fails.

Thanks. I bought an AIT sensor (I remember reading a while ago that it has an effect on the alternator, but now that I think about it, that might have been for NA's), I'm going to grab another ecu just in case, check the battery, and check 2O. If nothing else comes up, any other ideas?