TBI 454 Misfire

[Minn95Dually]

Thank you for mentioning that! I totally forgot, the original battery froze solid shortly after buying the truck, so I got a new deep cycle AGM battery and new alternator. The voltage has never been great, 14 volts cold with no load then drops to about 12-13 after warm, and less when the lights are on. You can even see the voltage drop when the turn signal goes on and off.

*Edit* there was a weird one-time electrical issue shortly after replacing the battery and alternator. The truck lost all charge from the battery overnight like the lights were on (they werent). This only happened once.

Deep cycle batt? You need a starting battery. The batteries are different.

 

[Rock Hard Concrete]

Deep cycle batt? You need a starting battery. The batteries are different.

Interesting, I never knew that there was a difference. I thought deep cycle just meant it had more cca. That being said, it was a stock replacement and definitely not causing my issue.

 

[Road Trip]

Are there grounds in the cab that are serviceable without destroying the dashboard?

Greetings RHC,

The short answer to your question is yes: G202.

Physically located under the dash, on one side of the DLC. (Assembly line Data Link Connector,
where you connect your OBD1 scan tool.)

Here's a picture of G202 as implemented:

You must be registered for see images attach

And as you can see from the G202 Ground Distribution schematic, there are a lot of circuits
that both rely upon it *and* share it. In other words, lot's of counterintuitive weirdness can happen
IF this ground isn't in tip top condition:

You must be registered for see images attach

NOTE: Not only should G202 be tight, but splice S207 should also be verified good. (File under looking for trouble and not finding any is OK!)

That's the short answer, courtesy of the Factory Service Manual, available for free download over HERE.
Highly recommended.

****

For a much longer discussion of the GMT400 ground distribution and how to interpret the
the FSM documentation, here's the jumping off point. (Ground Distribution rabbit hole)

Hope you find this helpful. Best of luck getting this all sorted out...

 

[Schurkey]

Deep cycle batt? You need a starting battery. The batteries are different.

Thanks for that.

I thought deep cycle just meant it had more cca.

Generally, deep-cycle batteries have fewer CCA than an equivalent-size starting battery.

That being said, it was a stock replacement and definitely not causing my issue.

It cannot be a deep-cycle battery and be a "stock replacement". It might be the same case-size as the "stock replacement" but the construction is different.

 

[Minn95Dually]

Interesting, I never knew that there was a difference. I thought deep cycle just meant it had more cca. That being said, it was a stock replacement and definitely not causing my issue.

Plates are different. Deep cycles are designed to provide a continuous draw of power. Starting batts are designed for that burst of cranking amps needed for starts. Deep cycles aren't designed for that kind of duty.

 

[Road Trip]

Plates are different. Deep cycles are designed to provide a continuous draw of power. Starting batts are designed for that burst of cranking amps needed for starts. Deep cycles aren't designed for that kind of duty.

RockHardConcrete,

My understanding of the deep cycle vs 'starting' (conventional automotive) batts is the same as
Minn95Dually's & Schurkey's above. There is a physical difference in the design of the thickness of the individual
plates -- essentially for a given size battery, fitting more (but thinner) plates = more surface area
for the chemical process to occur, which in turn provides a greater peak amp delivery to support the
starter demand on the coldest mornings.

Conversely, the deep cycle battery has thicker plates, providing a better DoD (Depth of Discharge), but
at the same time since there's less surface area, a lower peak amp delivery capability.

Here's a good write up comparing the two, in simple English, from Continental Battery:

https://www.continentalbattery.com/...en-a-deep-cycle-battery-and-a-regular-battery

****

I know that we aren't currently troubleshooting a slow cranking issue. And if your setup is starting
reliably on a deep cycle battery, then that reflects positively on the fact that your engine is willing &
able to start on that style battery.

 

[Road Trip]

My headlights do take a couple of seconds to come on after pressing the switch and the dash lights take a few more seconds to come on after the headlights do.

That's an interesting observation. In electronics, in order to set up timing
circuits we will on purpose vary the relationship between the Resistance and
Capacitance so that we can achieve whatever frequency is needed. In these
conversations the phrase 'RC Time Constant' is overheard.
(RC Time Constant)

...but I digress. The point is that the lighting circuits you are powering
have a certain amount of natural stray capacitance from Day 1, which is normally
a don't care bit of trivia. But if there's increasing Resistance to current flow
feeding this circuit, then it seems that between Mother Nature and Father Time
we now have a homegrown 'RC Network' that is causing the power applied to
ramp up slowly (instead of immediately) ...giving you the symptoms that
you are observing?

Hang in there, I'm going somewhere with all this. Earlier you mentioned
that you have already cleaned up all the 'engine grounds'. That's good news.

But the exterior lighting circuit does *not* rely upon the engine grounds.
(Or the G202 described in my earlier reply.) Instead, on the GMT400s there
are not 1 but 2 "sheet metal grounds" on the radiator support. 1 on each side,
close to each headlight, and they support the current flow for the headlights,
turn signals, horn, etc.

Here's the ground distribution circuit for the exterior lighting:

You must be registered for see images attach

Although the fuel pump is your primary focus right now, as soon as you get that issue
sorted out, I'd like you to find G104 & G105 and make them as good as new again.

And in order to provide a solid current return path for G104 & G105 on the radiator support,
you should also perfect the condition of G101 near the battery. IF you do all this and it still takes
noticeable time for the voltage to rise high enough to make your headlights come on normally,
then we need to take a look at the power side of things. (In my following reply.)

****

Why the flood of info on your truck's electrical system? Well, in reply #14 above you
described how much money you've paid others to do their job & they came up short,
and that sux. So if we can pool all our knowledge & experience in order to get all the
electrical gremlins tracked down & eliminated, then all this can be charged to the
School of Hard Knocks tuition column instead of just writing off the whole shebang as
a lost cause. (And also help others reading along researching similar issues can follow
your lead towards a successful resolution.)

Keep fighting the good fight. Looking forward to your status updates.

Cheers --

 

[Rock Hard Concrete]

I was mistaken about the battery. It is a agm starting battery.

New Developments:

The issue is NOT caused by the:

ICM
TPS
EGR

The timing, at least at idle is stable. All the plugs are getting power when they need to. Unfortunately I cannot put the truck under load and check, it idles okay especially when warm.

The problem used to really only happen at partial throttle but it happens at any throttle position now even WOT, which is the only way the truck was happy running before.

Ginna start the really not fun **** tomorrow if I have time.

 

[Spareparts]

Off the wall suggestion but could the cam be going flat?

 

[Rock Hard Concrete]

Off the wall suggestion but could the cam be going flat?

The problem wouldnt be intermittent.

It feels like timg being pulled, almost.

The problem is also NOT:

The MAP sensor

Knock sensor