Misfires, fuel/air issues. Where to start?

[Zimmerly]

Hey there,
Just an update- I've been really busy lately with projects at work, and with general life as a new dad/new homeowner.
So... with the little time I've had to give this truck attention lately, I took some time on my lunch break to start tracing the orange 12v wire from the fuel pump relay. Just as you said, Road Trip, about 12cm down from the fuse box, the orange wire branched off from the ECM wire. The junction is just barely inside the large loom, and is a little tricky to seperate from the rest... BUT- I can clearly see it is shoddily wraped in electrical tape, with some hanging off, which tells me the condition of this connection is par for the course when dealing with this truck. I got a photo of the wire. I'm going to rewire the connection this weekend.

You must be registered for see images attach

Also, I bought a Denso downstream sensor for my B2-S2 issue. I know I should've gotten all 4 sensors, but I'm running on a low budget and had some other things I needed to buy (rear u-joint, new diff cover, fuel line to fix my vent-to-evap line, misc other things).
I'm hoping this one sensor will get things back in order. If not, I'll buy the other 3.
Hope all is well!

-Jacob

 

[L31MaxExpress]

Hey there,
Just an update- I've been really busy lately with projects at work, and with general life as a new dad/new homeowner.
So... with the little time I've had to give this truck attention lately, I took some time on my lunch break to start tracing the orange 12v wire from the fuel pump relay. Just as you said, Road Trip, about 12cm down from the fuse box, the orange wire branched off from the ECM wire. The junction is just barely inside the large loom, and is a little tricky to seperate from the rest... BUT- I can clearly see it is shoddily wraped in electrical tape, with some hanging off, which tells me the condition of this connection is par for the course when dealing with this truck. I got a photo of the wire. I'm going to rewire the connection this weekend.

You must be registered for see images attach

Also, I bought a Denso downstream sensor for my B2-S2 issue. I know I should've gotten all 4 sensors, but I'm running on a low budget and had some other things I needed to buy (rear u-joint, new diff cover, fuel line to fix my vent-to-evap line, misc other things).
I'm hoping this one sensor will get things back in order. If not, I'll buy the other 3.
Hope all is well!

-Jacob

I see a factory heatshrink with adhesive inside covered splice.

 

[Zimmerly]

I see a factory heatshrink with adhesive inside covered splice.

Wrapped with tape, it does look like factory heat shrink. It's the large amount of unraveled electrical tape below, leading up to it that concerns me. Going to look into it more after work.
Since I'm pretty confident that's where the issue lies, and I have the pump working otherwise, I'm glad this is only a small issue compared to the others I've got.

 

[Road Trip]

Wrapped with tape, it does look like factory heat shrink. It's the large amount of unraveled electrical tape below, leading up to it that concerns me. Going to look into it more after work.
Since I'm pretty confident that's where the issue lies, and I have the pump working otherwise, I'm glad this is only a small issue compared to the others I've got.

I went back through this thread, and the evidence of the PO's hackery that you showed us in reply #24 could have
been initially motivated by a bad connection originating in S101.

So if the current problem description remains a loss of 12v power between the ECM B fuse output (pin G12) and
the fuel pump relay input #87, (pin B1) ...then I think that an eventual inch-by-inch inspection of this power
path will unearth the root cause. (Reply #38) Since the splice in the photo above tells me that you are getting
closer to the actual bad spot. And the good news is that this path is both short and *not* under the
dash. :0)

Just the fact that you have figured out how to jumper power in such a way as to get the fuel pump relay to start
working again tells me that you have a firm grasp of the situation. (!)

Finally, it's good to see that the FSM didn't lie to us about where you would find the factory splice -- it's always good
to verify another data point in the FSM library for future use. Looking forward to the photo of exactly where you track
the power loss down to, followed by a report that fuel pump relay is once again working with the permanently repaired
harness.

Keep up the good work. This GMT400 is going to be better for you having adopted it.

Cheers --

 

[Zimmerly]

Alright, back again, and guess what- new problem!
Due to a lot of personal issues in life right now, I haven't made any progress on the truck.
I do have a new issue that kicked my butt tonight. If you haven't read-up on these posts, please refer to post #33 on this thread... (Fuel pump relay's constant 12v hot feed was dead. Instead of jumping from my heated seat fuse as I originally planned, I jumped power to the relay's [dead] 12v constant hot wire directly FROM my AUX B post at the fuse box, with an in-line fuse put in place on the jumper.)
I've been driving the truck daily, without fuel issues except the usual misfire and rough idle (Most likely B2S2 O2 issue).

---------- THE PROBLEM:
Today, I drove the truck across town, and on the way back home I got some major hesitation accellerating from a red light. Engine died, I was able to safely pull over and troubleshoot.
Cranks and cranks, no start. Not even a sputter.
Looking at fuses, I jumped straight to the ECM-B fuse...
[Now some background on my ECM-B, in case you haven't followed along:
The fuel pump relay's constant 12v hot is originally fed from the ECM-B fuse via an orange wire. Having prior issues with the FPR's 12v hot on this wire (dead wire), this is the wire I jumped 12v into, with a 20a fuse added for safety.
In hindsight, I should have ran a seperate 12v hot to the FPR, and terminated the original shared orange 12v hot to avoid a possible double positive situation (ECM-B positive running with AUX-B positive), in case that ECM-B+ wire decided to carry volts again... Well, I didn't do that... And here we are.]
---------- Back to the scenerio:
Checking the small 20a ECM-B fuse, sure enough, it's blown, and I would assume the reason is because that orange wire finally decided to carry volts, for whatever reason (loose connection I'm sure).
Easy enough! I'm thinking I'm prepared for this.
I replaced the fuse with the 20a from my horn. I unplugged the 12v jumper from AUX-B, assuming ECM-B's 12v+ was working again...
Crank, crank, crank... nothing.
Decided to test the original FPR's constant hot wire by jumping it directly to the FPR's feed wire terminal. I got spark, and the wire is hot. Crawled under the fuel tank, and I can hear the pump running.
Tried starting again. Crank, crank, crank. Nothing.
All other fuses are VISUALLY good, including the fuse I put into my jumper wire (No test light to verify, but visually good).
I had to leave the truck on the side of the road. I didn't have any tools or my scanner with me.
So, I won't be able to troubleshoot anything until tomorrow after work.
Until then, I'm clueless. Any ideas?
Thanks again.
-Jacob

 

[HotWheelsBurban]

Alright, back again, and guess what- new problem!
Due to a lot of personal issues in life right now, I haven't made any progress on the truck.
I do have a new issue that kicked my butt tonight. If you haven't read-up on these posts, please refer to post #33 on this thread... (Fuel pump relay's constant 12v hot feed was dead. Instead of jumping from my heated seat fuse as I originally planned, I jumped power to the relay's [dead] 12v constant hot wire directly FROM my AUX B post at the fuse box, with an in-line fuse put in place on the jumper.)
I've been driving the truck daily, without fuel issues except the usual misfire and rough idle (Most likely B2S2 O2 issue).

---------- THE PROBLEM:
Today, I drove the truck across town, and on the way back home I got some major hesitation accellerating from a red light. Engine died, I was able to safely pull over and troubleshoot.
Cranks and cranks, no start. Not even a sputter.
Looking at fuses, I jumped straight to the ECM-B fuse...
[Now some background on my ECM-B, in case you haven't followed along:
The fuel pump relay's constant 12v hot is originally fed from the ECM-B fuse via an orange wire. Having prior issues with the FPR's 12v hot on this wire (dead wire), this is the wire I jumped 12v into, with a 20a fuse added for safety.
In hindsight, I should have ran a seperate 12v hot to the FPR, and terminated the original shared orange 12v hot to avoid a possible double positive situation (ECM-B positive running with AUX-B positive), in case that ECM-B+ wire decided to carry volts again... Well, I didn't do that... And here we are.]
---------- Back to the scenerio:
Checking the small 20a ECM-B fuse, sure enough, it's blown, and I would assume the reason is because that orange wire finally decided to carry volts, for whatever reason (loose connection I'm sure).
Easy enough! I'm thinking I'm prepared for this.
I replaced the fuse with the 20a from my horn. I unplugged the 12v jumper from AUX-B, assuming ECM-B's 12v+ was working again...
Crank, crank, crank... nothing.
Decided to test the original FPR's constant hot wire by jumping it directly to the FPR's feed wire terminal. I got spark, and the wire is hot. Crawled under the fuel tank, and I can hear the pump running.
Tried starting again. Crank, crank, crank. Nothing.
All other fuses are VISUALLY good, including the fuse I put into my jumper wire (No test light to verify, but visually good).
I had to leave the truck on the side of the road. I didn't have any tools or my scanner with me.
So, I won't be able to troubleshoot anything until tomorrow after work.
Until then, I'm clueless. Any ideas?
Thanks again.
-Jacob

I've had several fuses on both my 400s that looked perfectly fine, no broken loop, but replacing those fuses made the problem go away.