VP Commodore / No Thermo without aircon - ECU Reading temp fine...

[camstatic]

Hey guys I've been searching around for a couple of days now but I can't find any info on what I'm experiencing here... Any help would be hugely appreciated!

Ok we have a 92 VP Commodore, Automatic V6 Executive (with factory cruise control for what it's worth).

The other night I noticed my car idling up and down quite erratically, 800-1500/2000rpm pulses in neutral, a lot more calm when I had it in a gear.
I've also noticed that now my thermo fan doesn't engage when it warms up either, I have to either drive or switch the a/c on to get it to cool back down.

My first thought was to check the coolant temp sensor, so I plugged in a borrowed scantech diagnostic computer and brang up the vitals... Coolant temp would rise to over 94c (apparently where the thermo should cut in), and still no sign of the fan spinning.

At this point I noticed something funny, as temps climbed over 96c, every few updates it'd read out something like '36...96...38...97...' I'm assuming this could be the scan tool fudging up the readings, so moving on...

Anyway, today just as I got ahold of the scan tool the thing decided to idle perfectly again (this car always makes a liar out of me), so with that out of the way, I only have the fan to worry about.

Where do I go from here? I'm assuming if the fan circuit was faulty, then the a/c override wouldn't be able to engage it either... all the sensors have been replaced under the bonnet of this thing by the way(I'm kinda obsessive about this stuff)... The only original engine-related electrical component left is the ecu.

Thanks in advance to anyone who can help me out here.

 

[delcowizzid]

i fixed a vn a while ago with the same sort of thing would run rough cutting in and out had the same issue with the coolant temp would jump down to 30 ish degrees then back to normal over and over on my laptop if it stayed low to long it would die with no throttle changed sensor still there put new plug onto wires still there replaced ecu all good still going strong

 

[camstatic]

Thanks delcowizzid, I'm hopefully getting hold of an ecu to try tomorrow, fingers crossed! Keep the words of wisdom coming people.

 

[delcowizzid]

could be the same reason for no fan as well all linked to the coolant sensor circuits in the ecu

 

[camstatic]

Yeah I was aware that was the case, hopefully I'll kill two birds with one stone. Found recon Delcos mega cheap today too so if the loaner ecu fixes it I'll be set.

-semi related-

My car has always hunted to some degree though, not sure how common it is but for example, idling into a carpark it would hunt a little as I lost speed, sometimes causing a little "clunka clunka" on my driveline as the revs rose and dropped. Hmmm...

 

[delcowizzid]

can be the swing of the o2 sensor my vp did it to and it matched up too the swing of the o2 sensor volts when in closed loop only did it when nearly stopped rolling up too the lights and stuff

 

[camstatic]

gotcha, does it help that my erratic idle problem is non-existant just after start-up in open loop mode? It only starts to hunt when it goes to closed loop.

 

[delcowizzid]

how old is the o2 sensor.mine was more tune oreintated as i fixed it with a few changes to the ve table in the tune .

 

[camstatic]

It's a 1.5yr/25000km ish old sensor, bosch from memory...

 

[delcowizzid]

it could also be due to the same coolant issue jumping below the closed loop temp enable threshold and cold engine fuel and stuff the vn i fixed with this issue would drown in fuel when the temp dropped from going to cold start mixtures