After head gasket change, no start. C1500

[Skylar M]

Failed starter drive?

But the truck was cranking yesterday before this ground wire fix and wasn’t popping a starter code yesterday when the code reader was connecting again.

 

[Skylar M]

Here is what I found.
More than likely this is the result of a weak battery. The starter doesn't have enough power to fully engage, so instead it's making this noise. It's possible the starter is the issue, but most often when this happens, it's the result of a battery that doesn't have enough power to fully turn the starter.

 

[Road Trip]

For what it's worth, here's the Fuel Pump Relay circuit that we're currently troubleshooting as seen on p.1693 in Vol. 3 of the '98 FSM .pdf file:

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When I get back I'll add some real-world voltage measurements to this schematic.

OK, finally got a clear, cold, and dry stretch of weather, and came up with the following photos
and voltage measurement on my known-good '99 C2500.

Big Picture - Driver's side of engine bay

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Bird's Eye View of Underhood Fuse Block with cover removed:

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Troubleshooter's note: All (4) large Relays are *identical*. Allows easy relay substitution in order to verify individual relay health. (!)


Underneath of Fuse Block Cover provides legend identifying which components are responsible for what electrical loads:

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Fuel Pump Relay is located in the socket closest to the engine fan.


Fuel Pump Relay socket marked up w/schematic numbers. (Virtual > Physical translation)

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(Reference the wiring diagram in reply #53 above)

Actual measurements on Known-Good '99 C2500:

Pin 86 - Ground: 0.1 Ohms

Pin 85 - Relay Control Voltage from VCM: +12V

NOTE: With relay installed, 454 fires in <1 second in 20° weather.
With relay removed, engine cranked for ~3 seconds w/no fire before I stopped. This means
that I need to revisit this down the road when we're not in the middle of a cold snap. (ie: Verify
that the 4 psi backup switch in the oil pressure sending unit is working on this truck.)

****

As for your current status, we need to get your VCM to reliably respond to your code reader.
Also, I'm with Schurkey, it sounds like your starter motor drive is inop?

The biggest takeaway from the above? That +5V reading was bad - the control (enable) voltage
from the VCM is the full +12v battery voltage. See if you can get the starter working and
the VCM responding & we'll return to getting this Fuel Pump Relay working on your truck.

Best of luck --

 

[Road Trip]

Pin 87. If I use a jumper wire to pin 30 from 87, it does turn on and run. But now after that, I checked again and it is reading 12v at pin 87.
Now the code reader does connect. It pops 2 codes that I had before this as well.
P0453
P1351
Also the fuel pump does not turn on and run with the relay installed still.

OK, just to make sure that we're both on the same page.

Pin 87 = +12v power (From 20A ECM-B Fuse) that will be switched to the fuel pump
when the Relay is turned on by the VCM. You have verified that it
works by jumpering it directly to Pin 30 and the fuel pump comes on.

Pin 85 = Control (Enable) Voltage from the VCM. This should read
battery power when:

* For 2 seconds after Key is turned to the Run position. (And if the
engine isn't turning over the control voltage disappears.)

* Whenever the engine is cranking/running. (VCM is getting
pulses from the CKP indicating engine rotation.)

* For 2 additional seconds after the key is turned to the OFF position.

****

Given the above, the fact that you had voltage on Pin 87 but at the
same time the fuel pump didn't turn on via the relay is both possible
and makes sense.

We need to see the VCM send +12V to Pin 85 per the rules above.
Assuming a good fuel pump relay, this should in turn connect Pin 87 to Pin 30,
giving you a running fuel pump.

Let us know what you discover.

 

[Skylar M]

It was the battery not having the juice to kick the starter. That’s why the loud whine when trying to start. Charged up and all good. Cranking again. - good

Fuel pump relay test is - good

Ecm fuse - good

oil pressure switch power wire (orange) has 12v - good

85 with key on - has battery voltage 12v - good
(Multimeter grounded off battery)

86 - has battery voltage 12v - good
(Multimeter charged from battery)
Which means ground is good.

87 - has battery voltage 12 volts
(Multimeter grounded off battery)

pin 87, it is charged at 12v even with the key off?

30 - has battery 12v - which means the ground at fuel pump is good
(Multimeter charged off battery)

Fuel pump runs if jumped at relay location between 87 & 30 - good

Try to start while jumping and just cranks and no start. - bad

No 2 sec (prime) control power to pin 85 - bad

Nothing with relay installed - I don’t hear the switch or fuel pump at all when I turn key on. - bad

I don’t have a pressure gauge, so I can’t see if the fuel pressure is shooting up while I jump it though. So there is no telling if the pump itself is actually working correctly. But I know it was before this head gasket job.

Code reader - no connection

 

[Road Trip]

It was the battery not having the juice to kick the starter. That’s why the loud whine when trying to start. Charged up and all good. Cranking again. - good

Fuel pump relay test is - good

Ecm fuse - good

oil pressure switch power wire (orange) has 12v - good

85 with key on - checking ground - has battery voltage 12v - good

86 - checking ground - has battery voltage 12v - good

87 - has 12 volts - good

30 - connected to battery and checking ground - has battery 12v - ground at fuel pump is good

Fuel pump runs if jumped at relay location between 87 & 30 - good

Try to start while jumping and just cranks and no start. - bad

No 2 sec (prime) control power to pin 85 - bad

Nothing with relay installed - I don’t hear the switch or fuel pump at all when I turn key on. - bad

I don’t have a pressure gauge, so I can’t see if the fuel pressure is shooting up while I jump it though. So there is no telling if the pump itself is actually working correctly. But I know it was before this head gasket job.

Alright,

The results I've marked in green look good from here. However, I've marked
in red your results for Pin 86. On my truck that is a 0.1 ohm resistance to
ground. Pin 86 should NOT have "battery voltage 12v" on it?

If it is sitting as 12v, then you would end up with 12v on both sides of the
control coil, (Pin 85 to 86) no current would flow, no electromagnetic field would be created,
so the switch contact would never swing, hit the Pin 87 contact, and deliver the 12v power
to Pin 30. (!)

If you look at the schematic below, Pin 86 must be a solid ground to G103 & G104 via splice
103. (S103)

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Please reverify your results at Pin 86 of the relay. (Actually Pin A1 of the Underhood Fuse Block)

1) You should measure a near-zero (0.1-0.3) ohm resistance between Pin A1 and ground. If it is
anything other than this, then you have a bad ground, not allowing current flow *through* the
coil in the relay when 12V is applied through Pin 85, and giving you the no-function results you are
experiencing.

Please note: No 'tone' here, I am just being extremely careful with my communication to ensure we
stay on the same page.

2) If you want to cross-check the functionality of your fuel pump relay, you can temporarily swap it
into the Starter Relay position and verify that your starter still operates. (They are all the same
part number.) This cross-check would confirm that there's a problem with the wiring feeding the
Fuel Pump Relay socket position.

Feels like we're closing in. Fingers crossed!

 

[Skylar M]

I went out to double check just in case. Pin 86 is (no tone) and 0 resistance.
What i meant is that with the multimeter charged off positive and connecting to pin 86, reads 12v meaning that the ground from 86 is good.

I did switch the relays not knowing I can because of the 5 pin for the fuel relay. But that makes sense because pin 87a is nothing. Anyway, all is good with the relays.
Still no fuel pump kick on.

 

[Road Trip]

I went out to double check just in case. Pin 86 is (no tone) and 0 resistance.
What i meant is that with the multimeter charged off positive and connecting to pin 86, reads 12v meaning that the ground from 86 is good.

I did switch the relays not knowing I can because of the 5 pin for the fuel relay. But that makes sense because pin 87a is nothing. Anyway, all is good with the relays.
Still no fuel pump kick on.

Copy that. The relays are cross-checked, ready, and waiting for the Enable signal from the VCM.

Code reader - no connection

Whenever we are dealing with more than 1 thing inoperative at the same time, it's
always good to look for a shared single point of failure. (Of course it's quite possible
to have 2 or more issues at the same time, but unrelated to each other.)

Anyway, since the relays have been cross-checked and the ground has been verified,
but we still can't get the Fuel Pump Relay to operate, we need to go upstream,
back to the VCM, and figure out why there's nothing on pin 85?

Actually, that's being too specific, for if the VCM isn't responding to the code reader
we need to figure that out first! IF the VCM isn't responding to the code reader, then
I'm assuming that it isn't doing anything, including sending the enable power down to
the Fuel Pump relay?

I've pulled the Ground Distribution wiring diagram for all items supported by G103 & G104.
Check out the fact that both the VCM and the Fuel Pump Relay share these grounds:

'98 Factory Service Manual, Vol 1, p. 8A-14-8

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The fact that the ability for you to successfully connect your code reader intermittently to the VCM
is not a good thing. Using the building block approach, we need the following, in the following order:

1) Engine not seized -- can be turned over by hand via front crank snout bolt. (Accomplished)

2) Ability to crank the engine over at will with the starter. (Accomplished.)

3) Ability to connect your scan tool to the VCM at all times reliably. (Not yet.)

4) Jumper 12v to pin 30 and hear the fuel pump run. (Accomplished.)

5) Verify known-good Fuel Pump Relay by testing for proper operation in known-good Starter Relay socket. (Accomplished.)

6) Using verified good Relay, observe 2 second fuel pump operation after key is turned to RUN position. (Not yet.)

7) Observe proper fuel pressure via free rental tool from local parts store. (Not yet.)

...And so on, building block style, until we hear your truck fire up!

****

Note: Steps #3 & #6 require an operational VCM. The 3 main possible troubleshooting scenarios are:

* Good VCM victim of bad power or ground.

* Bad VCM being fed good power.

* Outside chance: Double whammy. Bad VCM fed with bad power. (ex: any welding done on the truck elsewhere while the head gaskets were in work?)

Last Wednesday (reply #44) your reader wasn't connecting. But then on Friday (reply #54) you did
establish contact and got a couple of old Codes retrieved.

To recap, at this point we have steps #1, #2, #4, & #5 working. We need to focus on getting step #3 to work
100%, and my hope is that once this happens step #6 will also start working. Don't know if you have a good VCM
and you don't have the full 12v across it (both + and - good) or if you have a bad VCM. The probability is
that you have a good VCM with an intermittent power feed issue...but if you exhaust that avenue then the VCM
is the next step. (But I don't think so at this time.)

Once you get reliable communications re-established with the VCM, let's continue down the building block list above.

That's all I've got for now. Good luck, sir.

 

[Road Trip]

The weird thing is that on pin 87, it is charged at 12v even with the key off?!

Skylar M,

I noticed that you added this comment to reply #65.

Good news, this is expected behavior, for we are actually working upstream of the ignition switch!
Better yet, that power sitting on pin 87 isn't a parasitic draw, because until the fuel pump relay is
activated, there's nowhere for the current to flow. Pin 87 is hot the entire time that a charged 12v
battery is in the truck, and that's OK. :0)

Going back to the wiring diagram in reply #66, notice that pin 87 is wired directly to 20A fuse 'ECM-B',
and directly above that there is a sign stating "Hot At All Times". Also note that there's a feed arrow
pointing to "Power Distribution Cell 10". And here's that Cell 10, showing the direct wiring of ECM-B
(located in the Underhood Fuse Block) to the battery positive terminal:

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So, it may seem weird to observe 12v power with the key off, but the reality is that we're working
on the circuits upstream of the Ignition Switch. You are in deep, my friend. (As a matter of fact I wouldn't
be half surprised to unearth the fuse for the Dilithium crystals in here somewhere. :0)

**** (Optional Reading) ****

Seriously, since we're here, I happen to find the 'when to expect to see power on this circuit'
hints in the General's prints to be very helpful during a troubleshooting session. For example,
when working on circuits that are controlled by the Ignition Switch, look for the various power
hints at the top of the various circuits:

* Hot in Start
* Hot in Run
* Hot in Run and Start
* Hot in Run and ACC (ACCessory)
* Hot in OFF, Run, and Start

For what it's worth, I've attached a couple of diagrams showing how the Ignition
Switch 'power timing' is documented. This is good to know when you are
trying to figure out why multiple things are intermittently not working, but instead
of firing the parts cannon indiscriminately, you instead dig around a bit and discover
that all the symptoms can be explained by a shared reliance on a particular flaky/janky section
of the Ignition Switch.

The punchline? One does not have to be fearful of old vehicle wiring harnesses. At least
when they are documented to the level that the General has done on our behalf. Wiring
diagrams are your friend.

Good stuff!