Hpca

[tRustyK5]

I have two 6.2's, one in my DD 1983 pick-em-up and one collecting dust in my garage that used to live in my old '81 Jimmy.

In colder temperatures the 6.2 from my Jimmy would fire up noticeably louder (clackier) and have a noticably higher idle speed for the first 5 minutes of running. Very obvious operation of the HPCA.

My '83...not so much. In fact I can't recall ever noticing an idle speed change or 'noise' change with the '83.

So, how exactly does the HPCA work, and is there anything I can check? Is the HPCA affected by where the pump timing is set?

Rene

 

[kennyw]

There is a sensor mounted to the back of the passenger side head. That is what triggers the system on/off.

 

[MaxPF]

What Kenny said. There is a coolant temp switch that opens when the engine is somewhat warm. When cold, it is closed and energizes both the HPCA solenoid and the fast idle solenoid. Just follow the wires on the IP and you should find the temp switch in the cylinder head. You can try putting 12V to the wire when the engine is running - the change should be obvious.

 

[6.2Blazer]

On my '90, it's very obvious when it's working. However there have been times when I fired it up without pushing on the accelerator and the high idle wasn't working (obvious the idle was not higher, not sure about the timing), if I just barely tapped the pedal then the high idle would kick in. Presuming it was just slightly stuck or something.

 

[tRustyK5]

Well, I just went and put the multimeter to it. Turned the key to run and back probed the connectors at the IP. Pink obviously shows batt voltage, but I got nothing at either the fast idle solenoid or the cold advance dealy.

Passenger rear head has a black off port, drivers side has the glow plug controller (it's an 83). How is it the glow plug controller knows when it's warm enough to stop cycling the GP's, but not know it's cold enough for fast idle and cold advance?

Rene

 

[tRustyK5]

OK, just compared it to my other 6.2 which is sitting in my garage with the complete wiring harness. My other 6.2 has a sensor on the passenger side rear head. Two blade, one of which is the green wire that goes to the HPCA and the fast idle solenoid.

Back to the '83 for an more in depth look...not even a plug or anything. I can't easily de-loom the wiring because it's trapped up behind the injector line brackets. At every junction I see no green wire...but they must go somewhere.

My other 6.2 and the wiring for my other 6.2 is from an '83 C30 pick-up. The 83 1/2 ton is all stock, harness never molested...

Any other location for a temp switch that might be possible?

Rene

 

[kennyw]

Is there a pipe plug in the head port where you found the switch on your spare motor?

 

[MaxPF]

OK, just compared it to my other 6.2 which is sitting in my garage with the complete wiring harness. My other 6.2 has a sensor on the passenger side rear head. Two blade, one of which is the green wire that goes to the HPCA and the fast idle solenoid.

Back to the '83 for an more in depth look...not even a plug or anything. I can't easily de-loom the wiring because it's trapped up behind the injector line brackets. At every junction I see no green wire...but they must go somewhere.

My other 6.2 and the wiring for my other 6.2 is from an '83 C30 pick-up. The 83 1/2 ton is all stock, harness never molested...

Any other location for a temp switch that might be possible?

Rene

Not unless they put it in the water crossover in those years. There's just not too many locations for a temp sender/switch to go. There's a pipe fitting on the outside front of the driver's head, a matching one on the opposite corner of the passenger head, and one or two in the water crossover...

 

[tRustyK5]

Well, had a chance to scour the engine compartment looking for two things. The temp switch, and the plug for the temp switch coming out of the harness somewhere.

I found the plug which I thought would help me find the temp switch. The plug wasn't plugged into anything, and could only feasibly go to one location which is the rear of the passenger head.

There is no temp switch, I can only surmise some shop removed it for whatever reason. I know Paul did maintenance only, the bigger stuff it got taken to a shop for. That shop did do some weird stuff when they replaced the IP ('J' code intake gaskets, EGR disabled and blocked from the underside, pump turned up) all without Paul's knowledge or consent.

Anyways, for the meantime I wired it up with a toggle switch. The fast idle and HPCA work, and cold starting is noticably eaiser and smoother.
I'll have to source another coolant block plate with the temp switch provision sometime...but at least for now it works.

Rene