Bump-Starts and runs great, won't start with key - P0335 - ECU replacement fixed

I'd like to see them as well.
I'm sitting back observing this one.

Nice job to both of you on the diag process here.

 

I haven't looked.
And it may not even be plausible.
But it there any ECM power feeds that only have power when cranking?

Just brain storming here......

I haven't looked into anything yet.

It's odd this only happens when cranking.
Almost as if an ignition (Ignition Key) signal (signal while cranking) is being lost when cranking?

 

Thanks that was helpful, got continuity and realized my back-probing wasn't deep enough, man I should do better:

So STA signal is fine...

 

The STA terminal but that only tells it to turn the fuel pump on which it's should automatically do once it sees a signal from the crank sensor. Besides we aren't doing anything with that terminal when push starting it so if it needed a signal there it shouldn't start.

I was thinking that as well but the only ignition feed to the ECM is from the IGN fuse which is fed off the same leg of the ignition switch as the GAUGE fuse and the gauges are staying on while cranking.

 

No worries, I know it's not the easiest thing to get backprobes in there. Trust me I've done alot of poking around on mine to get known goods, I can have that glovebox out in 5 seconds lol.

 

I've been looking closely at these diagrams (if you haven't been already), maybe something there will come up more clearly...

 

Just for grins have you tried starting it via the Clutch Start Cancel switch? I don't think it would change anything since all it does is bypass the clutch switch but hey at this point...

 

I have access to all the OE diagrams and service info, thanks though.

I'm just at a loss as to why it can "see" the crank signal when push starting it but it can't "see" it when cranking from the key even though the signal looks fine.

Does your scan tool do live data so you can see what the RPM shows while cranking?

 

Yup, been trying with and without constantly...

Scan tool seems to work LIVE (MAF reading goes up when cranking) but won't budge from 0 RPM, as is the instrument dial.

 

That just blows my mind, see if you can get me those scope captures. I wana see what's different with the signal between cranking and push starting.

 

This sounds like a case study we'd see in one of Ivan's videos.

We'll figure it out.

I'm just sat down and have some time to look at things.
We're missing something. Or we haven't "seen" what we're missing yet.

Those scope captures when cranking and push starting would be nice.

What are we missing........?

 

BTW, @hyharari

You are awesome for doing this.
You aren't the only one learning from this.
And most guys don't have the means, or the want to, to do it themselves.
Let alone post the data and process online.

Good job man.

 

In the title is says we are dealing with a p.340.
Is this still the case?


Case 1

1. No Camshaft Position (CMP) sensor signal to ECM while cranking ( 2 trip detection logic) - Scope shows a signal. _is the ECM just not "seeing it"? Even though it is there?

Case 2

1. No CMP sensor signal to ECM at engine speed of 600 rpm or more (1 trip detection logic)

Hmm.....600 rpm or more?

RPM? They are lower when push starting........

But yet, we have a cam signal.

What is going on here......LOL

 

My bad I believe it's mostly a P0335, then sometimes P0340 joins along, will correct the title.
I think it shows up once bump starting, will confirm tomorrow and try to get those scope readings too.

Funny enough I got a brand new P2102 today but I think that's from probing and jumping the wrong wires...

 

I think I may have found the root of the problem.
Looking at the diagram below I figured let's test the "stop light system"



So I hooked the scope to ST- and here's the reading:


Here's the scope reading:

*Blue line like before fore reference...

Also I notice my headlights don't turn themselves off while cranking (not sure they ever did actually, but never paid attention).
So if I understand correctly that "stop light system" isn't working and maybe that's what's making the ECU "blind" or confused?


*edit: I just realized that's for the break lights, not cutting the power to the lights while cranking I guess I should let go and pick up tomorrow...

 

Looks fine to me, the brake switch has 2 inputs to the ECM for redundancy. ST1- which is normally closed (12v) with the brake released (opens when the brake is depressed) and STP which is normally open (0v) when the brake is released (closes when the brake is depressed). Their main purpose is to cancel the cruise control and also to activate Brake Override (reduces engine power if the ECM detects the brake and accelerator are depressed at the same time).

Also normal, they don't turn off during cranking.

 

No man.
You can't find a problem if you never look.
It's good you are looking.

Let just say, If there isn't a rabbit hole to go down.
I'll dig one......

 

The only ECM connection I see while cranking is the STA input?

See....I'll dig a hole. LOL

Do we have a STA signal at the ECM?
What happens if we don't?
What exactly doe the STA signal do in the ECM? (Other that tell the truck it's cranking)

 

Yup, that was the screenshot giving 12V only while cranking:

Could the 4WD ECU have anything to do with this?
It seem to also be wired to a cranking signal for some reason.
That's the only thing I feel we haven't explored yet.

 

I either missed that one. Or forgot about it.

The mystery continues.......


Let me hunt a bigger shovel.......