The Wierdest Thing!!! HCPA Coolant Temp Sensor

[StephenA]

Since it's been too cold and snowy to work on extracting my ^*(&^(@@ frozen turbo crossover bolts, I picked up a new HPCA coolant sensor - the one that goes in the coolant crossover and turns on the cold advance and fast idle solenoids on my DB2-4911 mechnical IP in cold weather-

and I've run into the WIERDEST THING!!:

1. I have 12v going into the sensor connector, which, when the two terminals are shorted to each other, delivers enough current to easily power both the cold advance and the fast idle solenoids. Engine advances properly and speed up from 700 to 800 RPM, per specs on manifold lable.

2. Old "inoperable" sensor switch shows proper resistances from 0 F to 220 F and correctly passes 12v current when below 95 F which is spec listed in GM 6.5 Factory Training Manual. In other words, it's working properly when removed and powered with separate battery.

3. Neither the old or new sensors pass any current to either solenoid when connected and installed in coolant crossover, engine temp is cold -about 30 F,- both batteries at 12v & brand new!!!!! Truck starts easily, despite lack of solenoids.

4. I replaced the old connector with a new one, and can still power both solenoids by crossing the terminals... - but not with either the old or new sensor!!!!

5. Per my GM 6.5 Factory Training Manual, there are no other sensors in this circuit, just the gage fuse, which is obviously working, or I wouldn't get power at the solenoids by simply jumping the connector terminals...

6. Terminals on switch and connector are brand new and clean - I even bent them over a bit to insure good contact. Connectors and spades on both solenoids are clean and pass plenty of current when sender connector is jumpered.

7. I've checked with 4 dealers and I have the right part number (15326386) and each dealer confirmed the crossover location of this part.

8. I think I hear someone/thing giggle everythime I scratch my head... (just kidding).


WHAT IN THE SAM HILL CAN IT BE!!!!!!!!????

[gmctd]

Shouldn't show any resistance, Stephen - HPCA Temp Sw is a temp controlled switch, open at warm or closed at cold - no in-between.

If you're measuring varying resistance based on temp, that is a gage sender you're troubleshooting.

The two solenoids draw ~2-5amps, collectively, iirc.

'91 HPCA Temp Sw was in right head, rear - the resistive sender in the t-stat\crossover was for the 4L80E TCM, also iirc.

Either case, the HPCA sender is a switch, not a resistive element.

[StephenA]

Hey jd! Great to hear from you!! I was hoping you'd make a posting -you're knowledge and application is always so vast. I also suspected that my switch should be a simple temperature controlled reed switch or whatever with simple open or closed terminals, but according to the following posting (as well as my tests on the original stock temp sensor), it appears to be a resistance switch where by a voltage or current differential is used to close a transistorized switch which passes a full 12v current or not according to a set threshold. Same result- i,e, full 12v is delivered only when temps are below 95 F:

This is topic- How do I test the Coolant Temp Sensor? in forum 6.5L Turbo Diesel at TheDieselPage.com Forums.


To visit this topic, use this URL:
http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=009979

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Posted by Dennis Galligani (Member # 10379) on 01-30-2006 06:15 AM :

Concerning the Coolant Temp Sensor in the T-stat housing - can it be Ohm tested? What would the appropriate reading be? Will the reading vary depending on temperature?

I recently replaced one and immediately got better fuel mileage, but I was just wondering how to actually test the sensor.

[ 01-30-2006, 07:18 AM: Message edited by: Dennis Galligani ]

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Posted by JohnC (Member # 2493) on 01-30-2006 11:55 AM :

T(F) resistance
210.....177
194.....241
176.....332
158.....467
140.....667
122.....973
104...1,459
86....2,238
68....3,520
50....5,670
32....9,420
14...16,180
-4...28,680
-22..52,700
-40.100,700

[ 01-30-2006, 10:25 AM: Message edited by: JohnC ]


This threw me for a loop at first, because as you can see, the resistance rises as temp drops, which would pass less voltage/current if not for the fact that it actually acts as a transitorized switch, when hooked up to a 12v battery. By actual tests, both my new and old sensors return about the same resistance curve when measured at cold & hot temps. And when hooked up to 12v, they both allow no current at temps above 95 F and full 12v at 5 amps at any temp below 95. My surmize is that an IC oriented switch was engineered because of the mean time to failure ordinarily encountered with mechanical switches.

I also read that the coolant temp sensor was moved from the 1985 block, cyl 8 position to the coolant x-over/T-stat housing in the 92-93 version, which was a blessing, since reaching the other was a real PITA. In any case, it's definitely on the x-over on my truck, and the gage sensor is on the head under the cyl 1 glow plug.

Before kickoff today, I intend to take out the new sensor and it's accompanying harnness/pigtail and bench test the whole rig, Gremlins tend to resent this sort of an approach... Could be the new connector, but this doesn't explain why the old switch was inoperable, unless the old contacts were too oil & debri soaked to pass the current. Will report after game...

If I actually have the right part, and it performs correctly on the bench, then perhaps I have an actual gremlin, which if bottled, could be patented and sold to Iran for use in their atomic program...
Steve

[BobND]

As the other poster said, your '92 with mech IP will use a simple "on or off" temperature switch for the HPCA and fast idle control.

It MAY use a thermistor sensor for the emissions computer, as it does for the heat gauge.

If I recall correctly from your first post of this thread, when you jumper the wires at the sensor, the solenoids activate.

If this is true, you are at the correct sensor location, but have the wrong part # sensor installed.

Simple on or off. NO thermistor with varying resistance.

[gmctd]

Right - that post is correct for a '98 OBD-II PCM EFI system, where the crossover sender is PCM temperature ref for FI control.

Also same sender for OBD-I system, replacing that one could alter fuel mileage in cases where resistance did not reflect actual coolant temps.

And it is a negative temp coefficient probe - resistance is hi at low temp, low at hi temp.

If yours matches that post, then it is for the 4L80E temperature input for emissions-control - different shift-points and pressure when cold.

Can also be as you state - resistive sender for an electronic switch module - but you'll need to pull-trace the green HPCA Sol\Fast Idle Sol wire back to it's source in the wire loom, where you'll likely find a rectangular relay-looking module.

The resistive temp sender wire colors are yellow\black, iirc

[ 02-05-2006, 12:34 PM: Message edited by: gmctd ]

[More Power]

Stephen, We see this sort of behavior occasionally with the Oil Pressure Switch. The switch will read battery voltage correctly at the lift pump connector when unplugged, but not when it see the load of the electric lift pump. Bad/burned contacts typically cause this.

In your case, since you're using a new HPCA thermal switch, you may need to go further back in the circuit - like the ignition switch or fuse panel, to find the source of the problem.

If you can power one side of the thermal switch with a direct connection to a battery, and the HPCA operates the way you expect, then you've more or less discovered the cause of your problem as being a bad ignition switch or bad fuse, etc.

Jim

[StephenA]

Thanks Jim. The dealer ended up sending me a replacement for the GM PART # 15326386 he sent me originally... Same problem as before. I'm wondering if it really could be the circuitry from the ignition switch as you mentioned. Except, it seems to me that if this were the case, it wouldn't have enough power to work when I jumper the two terminals on the connector-which, as I explained in my earlier post, works just fine.
Also, when I power the HPCA thermal switch with a jumper directly from the positive terminal on my two new batteries. I still get no results - this sort of rules out she bad ignition/ circuitry idea, right?
Do you think that despite all the dealers swearing I have the only part made for my 92 application, that I'm using the wrong part after all? Does anyone have a different part number I can try? Thanks, Steve

[ 02-21-2006, 11:31 AM: Message edited by: StephenA ]

[More Power]

Use a multimeter to measure the resistance of the "switch" terminals. If it's a simple thermal switch it should read near zero ohms. If, on the other hand, you're actually dealing with an engine temperature sensor... it'll read some resistance that'll change with temperature. I've got the chart somewhere.... but just knowing whether you have a thermal switch or a thermistor will help solve the problem.

Jim

[StephenA]

Jim, all of my sensors, old and new, correspond more or less with the following chart:

Posted by JohnC (Member # 2493) on 01-30-2006 11:55 AM :

T(F) resistance
210.....177
194.....241
176.....332
158.....467
140.....667
122.....973
104...1,459
86....2,238
68....3,520
50....5,670
32....9,420
14...16,180
-4...28,680
-22..52,700
-40.100,700

[ 01-30-2006, 10:25 AM: Message edited by: JohnC ]

[gmctd]

On my mech inj engine, that resistive sender in the crossover was used to set glow duration.

The one-amp minimum Fast Idle and HPCA solenoids were powered up thru a two terminal single contact thermo-switch, via a large dark-green wire.

Pull-trace that green wire to its source.

That resistive sensor is hi-res at low temps, when FA\HPCA needs to be on, and lo-res at hi temp, when FA\HPCA needs to be off - diametrically opposite to solenoid voltage\current requirements.

Find the source of the green wire, you'll find the driving element.

[StephenA]

GMCTD
Can you give me a part # for your switch?
Jim
Given that my switches don't work when powered directly from the batteries-do you think I can rule out ignition switch/fuse panel circuitry?

[More Power]

gmctd, I'm looking at GM's 1993 model year wiring diagrams book (#ST 375-93 EDD pages 126-127) as I type this. There is no external resistive element/sensor used in the glow system to determine glow time. It's all done internal to the glow controller.

I suspect Stephen is looking at the engine temperature sensor..... smile.gif

Jim

[More Power]

Stephen, If you apply a jumper wire directly from a positive battery terminal to the HPCA electrical terminal on the injection pump and/or the fast-idle solenoid, and they do nothing..... Either both solenoids are defective (not likely) or you're not jumping power where you think you are....

Jim

[JohnC]

IIRC my '93 had 3 temperature sensors. One was resistive and drove the temp gauge on the dash. One was an on/off switch that disabled the glow plugs when the engine was warm. That one has been superceded by an always-on jumper. The last one was another on/off switch that controlled the HPCA and fast idle solenoids. These last 2 are not "active" devices, just simple on/off switches. They should read near 0 ohms (like 0.03) when cold and infinity when hot. Nothing in between.

[Inspector]

The cross over unit (switch) is nothing but a switch that when cold supplies a ground for the HPCA curcuit when the water temp is below 95 degrees. Get it out of your head a correlation of resistance to temp in this instance. Cold continuity, hot open. If you have power at the two solinoids when you ground the the connectors but don't when they are hooked up with a cold engine then the switch is bad. Determine the voltage with a multi-meter with the key on. As I said that particular switch is just that, a switch that completes a curcuit. I suspect that the dealer still hasn't given you the correct part.
Denny

[gmctd]

GMCTD
Contributor
Member # 1505
Glow duration is determined based on engine coolant temp - longer duration if cold, shorter duration if at operating temps.

Was that scheme altered for the '93 year?

The PCMs still use ECT to determine glow duration.

Unplug the ECT connector, get much longer glow duration.

IIRC - that thermo-switch p\n is in Member's Area archives.

On re-reading this, it appears rather blunt, maybe confrontational - it is not intended to be that, rather information exchange.

[ 02-22-2006, 03:17 PM: Message edited by: gmctd ]

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jd
'96 Dodge 3500HD cc 2wd drw
5-sp 5.9 12v 330hp TST
DODGE makes it CUMMINS shakes it
6 in a row makes it go
******************************************
GMCTD
Contributor
Member # 1505

Usually, the service manuals address one concept at a time - the Glow Controller will be on one set of pages, the Engine Coolant Sensor on another set, somewhere else in the manual.

The Glow Controller set will not, however, mention the Engine Coolant Sensor - where the Engine Coolant Sensor set will show routing directly to the Glow Control module, on it's respective pin, with no reference to associated circuitry.

As an example, for instance.

That scenario has been my experience with all the later Helm\GM Service Manuals.

I'm having some difficulty imagining how the GC would know to extend glow for a cold engine, with multiple reglow, while reducing glow time and reglow for a warm engine.

--------------------
jd
'96 Dodge 3500HD cc 2wd drw
5-sp 5.9 12v 330hp TST
DODGE makes it CUMMINS shakes it
6 in a row makes it go
************************************************
BOBND
Contributor
Member # 14993

posted 02-22-2006 20:08
The 1992's and 1993's, at least the Federal emissions units I am familiar with, have the glow duration controlled by a thermistor built into the glow plug controller at the back of the engine.

For 1994, and altered controller was used, with the electronics "gutted out", and only the relay remaining, which was then controlled by the PCM.

I have a 1992, and a 1994, and a friend had a 1993, and I have worked on all three, and they are set up as I described above.

On all the 1992, and the 1993, the fast idle and the HPCA are controlled by the simple temperature switch, and, of course the 1994 has the DS-4 pump, with the HPCA solenoid eliminated, and the PCM also controlling the glow plugs.

Am I missing something here???
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GMCTD
Contributor
Member # 1505

posted 02-22-2006 21:09
No - you are both correct - the voltage sense line fed the thermistor, and the sensor in the crossover was a light-duty thermal switch, similar in appearance to the resistive ECT sensor.

That switch in the crossover is in series in the voltage sense line.

If disconnected, longer glow is the result

Hadda go back and check my build notes, don't you know.

So - Stephen should be looking for the FA\HPCA thermal switch, usually in the rear of the passenger-side head.

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jd
'96 Dodge 3500HD cc 2wd drw
5-sp 5.9 12v 330hp TST
DODGE makes it CUMMINS shakes it
6 in a row makes it go
************************************************
BOBND
Contributor
Member # 14993

posted 02-22-2006 21:43
Now THAT'S a good one! One can never assume they know these sytems inside and out! I am going to look tomorrow to see if any of my schematics show this!

Any idea of the resistance of the resistor that is bypassed by the switch, when warm?

That sounds a lot like the "glowplug circuit mod" resistor some have been using to extend glow time!

Thanks for clearing that up.
********************************************
GMCTD
Contributor
Member # 1505
posted 02-22-2006 22:24
Well - don't forget wysiwyg - I've not worked on any 'fresh' truck, as shipped oem, and do not have the '92-'93 manual to cross-ref my notes.

Not even second-owner.

Jim did an article or two on modifying the module for variable glow event - should be around here, somewhere.

And, re-reading Stephen's post, seems to indicate the crossover probe is a switch, as it passes voltage when cold, and no voltage when hot - just doesn't pass current required to energize solenoids.

--------------------
jd
'96 Dodge 3500HD cc 2wd drw
5-sp 5.9 12v 330hp TST
DODGE makes it CUMMINS shakes it
6 in a row makes it go
************************************************** **
STEVENA
Contributor
Member # 10550
posted 02-23-2006 10:11
Hello Everyone!
All you're input is very much appreciated!

That said, let me attempt to clarify what is "known" about my specific situation thus far:

1. The Helms factory manual, GM Training manuals, and dealer computer parts figures all verify that the HCPA water temperature sensor, sender or switch, as it may be referred to, is located on the water crossover on my 92 and not in the block # 8 cylinder position as in earlier models. The gage temp sensor is located below the #1 cylinder glow plug, and operates fine.

2. There is a wiring harness and pigtail which supplies 12 volts to the Fuel Shut off Solenoid via a red wire, and to the HCPA solenoid and Fast idle solenoid via green wires which are both connected via a connector to one of the 2 terminals on the HCPA temp sensor/switch. The other side of the sensor/switch attaches to 12 volts from said harness via a green wire. This wiring is exactly per the diagram in my Gm Training manual and is independent from all other circuitry or sensors, including any or all Glow Plug controller circuitry. I will gladly scan and post this GM wiring diagram (which checks out exactly with the existing wiring on my truck), should anyone be interested.


3. The green wire from the harness goes directly to a two terminal connector on the HCPA sensor/switch on my crossover and then Y's off from the connector to the HCPA and Fast Idle solenoids, respectively.

4. Bypassing the HCPA sensor/switch and jumpering the two terminals in the connector powers both solenoids up and the engine advances properly and RPMs increase by 100 as per specs on the valve cover.

5, This confirms that there is enough current coming from the harness to power both solenoids WITHOUT the sensor/switch in line and that both solenoids are operable.

6. When the sensor/switch is connected in line, it passes 12 volts at temperatures below 95 F but not with enough amperage to drive the solenoids and does not advance or speed up the engine at all.

7. The original OEM sensor/switch as well as the two new switches from the dealer -GM PART # 15326386- all return approximately the same resistances as given in the above chart.

8. Reversing the polarity on the sensor/switch has no effect on powering up the solenoids properly.

9. Powering either side of the sensor/switch with 12 guage wire directly from new batteries at 12.3 volts makes no difference- the solenoids will only power up when the sensor/switch is by passed. (When testing, the test wire is bolted to the battery and firmly held on the sensor/switch terminal). This would appear to effectively rule out inadequate amperage from the harness as a potential cause.

10. No less than 6 different dealers as well as GM Parts Direct all swear that GM PART # 15326386 is the correct and only part available for the HCPA sensor/switch on all 92 6.5s and that it is located on the han water crossover and nowhere else.

11. I have verified that the connector is contacting both switch terminals properly and reads the same resistances listed above when in line.

12. I am not on any drugs or medication whatsoever and neither is my truck...

I hope this clarifies things a bit!

Thanks, Steve

[ 02-23-2006, 07:30 AM: Message edited by: StephenA ]

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92 K2500 4X4 6.5LTD Std Cab, 5spd, Airbox Mods-K&N, 195 rbrtshaw T-stat, ATS DnPipe 3" Exhst & mflr, ATS Wastegate mod, Dmax 21" fan, 97 fn clch, Mobil 1 & Amsoil Frt-Rr,225k-Still runs great on original IP & nozzles :-)

[gmctd]

GMCTD
Contributor
Member # 1505
posted 02-23-2006 11:04
I don't think you're on drugs - or your truck - but I wouldn't vouch for those parts guys.

It would appear they're giving you the Engine Coolant Temperature sensor for the PCM, which is negative temperature coefficient resistive.

The temp switch contacts will go resistive from arcing caused by reverse emf when the solenoid fields collapse - this prevents sufficient current flow required to energize the solenoids, but will still indicate full voltage, without the solenoid inductor loads.

Jim indicated this in an earlier post, and your eyewitness report tends to confirm it.

Usually those sensors have the part number imprinted on the brass body, may be only the last four digits.

The thermo-switch usually has the temperature trip point stamped into the brass body, as in 125*F.

I seem to recall someone posted the correct thermo-switch part number in a parts listing in the Member's Area, but I've forgotten my password again, and cannot access that.

May also be in Jim's article on the DP Project Truck, where the DS4 to DB2 Inj Pump conversion was done

[ 02-23-2006, 08:17 AM: Message edited by: gmctd ]

--------------------
jd
'96 Dodge 3500HD cc 2wd drw
5-sp 5.9 12v 330hp TST
DODGE makes it CUMMINS shakes it
6 in a row makes it go
************************************************** *****
STEVENA
Contributor
Member # 10550
posted 02-23-2006 14:14
Thanks gmctd -Here's the data according to

The Diesel Page
GM Part Numbers
Updated December 11, 2003

listed under
GM Part Numbers, diesel related & misc:
in the members forum,
Coolant temperature sensor - 1995 Chevy 2500, P/U, 6.5TD. GM pn#15326386. Group.3.682. $16.99

All my dealers -8 now- tell me this is the part number for the 92 year as well. I'm with you. -I say it can't be so, but they just stare at me blankly. I searched the forum for the DP Project truck which I must have seen 100 times - but can't locate it... Directions or Hints?

My kingdom for a part #...


Steve

--------------------
92 K2500 4X4 6.5LTD Std Cab, 5spd, Airbox Mods-K&N, 195 rbrtshaw T-stat, ATS DnPipe 3" Exhst & mflr, ATS Wastegate mod, Dmax 21" fan, 97 fn clch, Mobil 1 & Amsoil Frt-Rr,225k-Still runs great on original IP & nozzles :-)
************************************************** ********************
GMCTD
Contributor
Member # 1505
posted 02-23-2006 19:10
Try part no. 23504005, or maybe 25504005......

--------------------
jd
'96 Dodge 3500HD cc 2wd drw
5-sp 5.9 12v 330hp TST
DODGE makes it CUMMINS shakes it
6 in a row makes it go
************************************************** *********************
BOBBIEMARTIN
Contributor
Member # 1404
posted 02-23-2006 19:31
HPCA sender (cold start switch) 10154649 This one has 2 spade connectors.

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1995 Suburban 1500 6.5TD 2WD - DB2 Mechanical Fuel Injection
2005 VW Jetta TDI
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[StephenA]

-Wow -Love the new BB! Hope it has more email notification features for additions to selective threads... In any case, it represents a lot of work and looks great -thanks Jim!!!

The following posts were left off when transferring over to the new BB:

Thanks loads to Bobbie Martin for the new part number, which I am ordering today!! -Steve

posted 02-23-2006 06:10 PM
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Try part no. 23504005, or maybe 25504005......

--------------------
jd
'96 Dodge 3500HD cc 2wd drw
5-sp 5.9 12v 330hp TST
DODGE makes it CUMMINS shakes it
6 in a row makes it go
Grandpa's Big Truck

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Posts: 1686 | From: usa | Registered: Sep 2000 | IP: Logged |

Bobbie Martin

Contributor
Member # 1404

posted 02-23-2006 06:31 PM
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HPCA sender (cold start switch) 10154649 This one has 2 spade connectors.

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1995 Suburban 1500 6.5TD 2WD - DB2 Mechanical Fuel Injection
2005 VW Jetta TDI
mini1275@bellsouth.net
DB2 CONVERSION GUIDE INFO

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Posts: 409 | From: Jacksonville, FL USA | Registered: Aug 2000 | IP: Logged |

More Power

Administrator
Member # 1

posted 02-23-2006 07:24 PM
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Please post all new topics threads or replies on the New Bulletin Board. All new posts will be lost once this one is shut down.

Thanks,

Jim

[gmctd]

I was thinking the same thing, John.

The thermo-switch in the crossover looks similar to the ECT sensor.

The thermo-switch in the right rear head is short and squat, with two large spade terminals on it, as Bobbie posted, with the part number.

[StephenA]

-that's consistent with my new vs. old part structure -same thread size, though.

[gmctd]

That's the p\n from the Member's Area - the p\n I posted is for the crossover switch.

[StephenA]

Hi gmctd-what part # are you referring to- the one Bobbie Martin posted? All my dealers indicate this part to be the Injection Pump HCPA water temperature switch, though it hasn't arrived get for me to try. Seems like the the right part to me, finally! If it is, I'll ask Jim to update the members area.

[gmctd]

The p\n Bobbie posted is in the MA parts list, down towards the bottom.

Also check the p\n I posted - it is the crossover-installed thermal switch for the Glow Plug module

[StephenA]

Thanks jd -I found the part number Bobbie listed on the parts page in the member's area just as you said. I also searched GM parts Direct online and couldn't find a match for the one you listed for the controller. Supposedly, my 92 doesn't have a temp switch for the glow plug controller, which makes no sense... do you know where it would be located on my '92? I'd like to swap it out also before it fails.
Steve

[gmctd]

I meant that the switch would more closley resemble the one you have - you probably do not have the GP switch.

This switch uses a mini-connector, the other uses the standard connector, with large female spade-connections

[StephenA]

Understood-thanks! Can't wait for the new switch to arrive!