Mrmerlin

its a good idea to clean the 2 grounds at the back of the V with running issues as this is the ground for the injection system

jeff spahn

Well it’s good issue to clean all the grounds every year and touch them up with Deoxit as well.

merchauser

does the Temp II switch have anything to do with the cooling fans running on (properly) after the car is shut down?

more often than not, after a long run, and the temp up a bit, the fans will run at idle just before shut down, but as soon as I turn the key off, the fans will shut off (this is of course with AC off)

at other times with the same temp reading, the fans will continue to run, (properly), after shut down.

any thing to do with Temp II?

voskian

The low speed fans will run after shut down if the intake temp switch (at the back of the intake with two wires coming off the top) senses the intake temp at 87degrees C. If you open the hood, the hood switch will stop the fans from operating to avoid potential finger in fan issues.

FredR

Temp 2 is not a switch but a temperature sender with an analogue output. The brains consider this output and decide what fan programme to run. If the a/c is running both fans run [not sure whether it is at full speed or not]. The sender has two outputs- not sure which one the brains refer for cooling but the outputs are the same as I understand.

When you shut down the brains consider temperature and if that temperature is above a certain point the fans run on until the engine has cooled to that point and then they shut down. Not sure what that temperature is but I have a feeling it is 80C, possibly hotter.

merchauser

OK, thanks

is there any correlation between the fans not properly running on after shut down and the stall at full temp with AC on???

FredR

If the fans are not running on after shutdown [however caused] does not mean there is a problem and most likely infers the conditions to cause the fans to keep running are not met.

There could also be other issues such as the bonnet safety switch not working correctly- the fans only run on if that contact is made and the other criteria are met.

merchauser

thank you Fred

I replaced the safety switch a few months back and it is working fine. my wonder, is that at a fixed point on the temp gauge, when I am ready to shut the car off, the fans will be running, suggesting to me that a sensor is communicating that the engine needs to cool off, but sometimes, at that same point on the gauge, with key off, the fans will continue to run and sometimes not.

perhaps I am splitting hairs here, but wondering if either the Temp II sender or the air sender a the rear of the manifold, could also be the culprit with my intermittent stalling?

FredR

I have always worked on the basis that fan run on after engine shutdown is controlled by the engine temperature but given the brain shuts down with the engine that logic may be flawed and maybe as Bob says it is controlled by the air intake switch but why is beyond me. If this function was to be controlled by a switch i might have expected it to be the temperature switch in the radiator but...?

Your original problem as you can see from the various inputs, could be caused by a number of things. About 16 years ago I had a similar problem and the min agents told me the ISV was shot and needed replacement. At that point I said "enough" and did my first inlet manifold job. This is quite easy and the only thing I found difficult was undoing the ISV control connector under the manifold. Nowadays I install it without the retaining clip so I can simply pull it off. When I had everything in pieces I inspected the ISV and found that the shuttle that moves to regulate idle air quantity entering the engine was sticking and seemed to be coated with a grey dry powder. Cleaned it all out, sprayed a bit of WD40 into the shuttle and put it back- same ISV still working today but I suspect it is now causing a little bit of a surge I have at idle.

worf928

There exists in the WSM a straightforward multimeter-based diagnostic procedure for the fans that includes all the inputs to the fan controller.

FredR

Indeed- forgot about that!

Seems the run on is controlled by two inputs, one from the inlet air switch that drops out at 82.5C and the cooling water sender that drops out at 83C.

Why it considers the inlet air temp no idea other than looking for heat soak possibly?

As I understand failure of the inlet air temperature switch has little consequence.

merchauser

all good info and very much appreciated!

I know I should being doing my investigation a bit more logically in testing circuits... just thinking that something may ring a bell with someone regarding a similar problem.

to the original problem:
just back from a very long hard drive with AC on trying to "force" the issue. I have eliminated the full on stall! a

driving at about 3-4000 rpm with AC on and fan on high, depress the clutch, the volt meter takes a dive, and then quickly recovers and all is fine. but I don't think it is suppose to take that dive and the (perhaps) one second to recover; pretty sure it should happen instantaneously. RPM's do not seem to suffer much, just the volts. with fan on anything below high, this does not happen.

I was able to eliminate the stall by just "waiting" for the system to recover. if I reacted too quickly with a shift, then the car would stall.

ALSO: after the run, sat in the driveway and put the fan on high, AC compressor on, headlights on with high beams, fog lights and radio as well and volts were reading at nearly 10. with each successive addition of a power drag, volts would decline, till I got to 10. as I shut down each accessory, the volt gauge would increase until it settled right between 12 and 14.

could I have an alternator problem???

FredR

The electrical system at best is known to be a bit marginal when everything is working. That the voltage drops at idle should be no surprise. Once the voltage is don to 12 volts you know the battery is making up the deficit. If the voltage is down to 10 volts indicated then that sounds a bit steep to me suggesting that something may be experiencing undue resistance loading.

Take a look at the earth strap [both ends] where the braid is soldered to the connector and see if ti showing signs of fretting or corrosion. Also take a look at the wiring at the hot post [passenger side inner wing in the engine compartment. Take a look at the condition of the 16mm2 red cable going into the post and see if the insulation is still in tact- it will probably look brown. Also take a look at the condition of the cables going into the adjacent 14 pin connector coming from the engine bay side and report back as to what you find.

As to why your voltage is taking a dive are you keeping the revs up when you pus in the clutch or just letting them drop?

The alternator needs a certain number of engine revs [2k rpm+] to produce any meaningful output and if you have everything maxxed out you probably need about 3k rpm on the engine to generate enough power to stop the battery drain all else being OK.

Do you have the rear a/c option just to add to the burden or any silly powerful ghetto blaster kit?

merchauser

hi Fred

I was not keeping the RPMs up, just depressing clutch and letting them drop, but per the tach, the RPMs were not taking a dive below say 750. its the volt meter that takes the dive

I do have the rear AC but never use it, and only a plain jane stock radio set up

all ground straps and wires and cables at front and rear look excellent.
measuring at front post with multi meter:
engine off 12.8
car running and no acc: 13.9
with AC and fan low 13.8
with everything on 11.5

dash gauge is clearly not calibrated and accurate, but these numbers don't seem right?

FredR

At 750 rpm with that lot on your voltmeter is going to take a dump.

Those numbers look quite normal to me. In the days when my daughters were young and being driven around in the back of the 928 at night time with my Hi Fi, fans blowing hard, rear A/C etc etc the voltage at idle was borderline unacceptable.

Nowadays the only time I use the rear a/c is to see if it still works.