Author Topic: 87 V10 TBI - No check engine light & inconsistent idle  (Read 3802 times)

Offline buzzman351

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #30 on: October 27, 2022, 03:04:19 PM »
Nah it’s fresh. I filled up with 93. Idk. All those codes just give me a feeling the computer is faulty but it does run and drive but it’s just not right


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Offline bd

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #31 on: October 27, 2022, 04:43:55 PM »
More considerations...

Keep in mind that every ground wire has at least two ends.  Poor electrical connections can occur in the wiring harness attachments to the ECM as well as the engine and/or chassis attachments. 

Before condemning the ECM, unplug and thoroughly wash the PC board (PCB) edge connector terminals with some CRC or DeoxIT D aerosol electrical contact cleaner to remove any accumulated dust and oxidation. 

In addition, the harness connector terminals can actually deform or even break and lose contact tension against the PCB.  Although tedious to perform, tension can be restored by gently reforming each terminal with a very fine point pick tool.  But the learning curve is steep and calls for terminal-specific release tools, requiring excruciating care so as not to damage the small terminals and make circumstances worse.  If necessary, many of the ECM-purposed terminals can be procured brand new from Mouser, Waytek, Digi-Key, et al and replaced if broken or damaged beyond use.

Lastly, the fine 22-gauge wires used to manufacture the ECM harnesses can break at or near their terminal attachments due to flexing or rough handling.  At the very least, ground wire continuity should be verified using voltage drop tests and/or resistance measurements.

« Last Edit: October 27, 2022, 05:02:33 PM by bd »
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline buzzman351

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #32 on: October 27, 2022, 05:45:17 PM »
So how hard would it be to replace the harness? I imagine pretty tough but I’m at a standstill. Also I can check continuity but I do that from the ecm connections to under the hood?


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Offline VileZambonie

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Offline bd

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #34 on: October 27, 2022, 07:06:44 PM »
So how hard would it be to replace the harness? I imagine pretty tough but I’m at a standstill. Also I can check continuity but I do that from the ecm connections to under the hood?

I think that replacing the ECM harness this early in the game is a panicked overreaction with no valid cause.  Don't let the circumstances overwhelm you.  Really, it's all just nuts and bolts.  Perform some tests.  Use the resources and guidance provided by VZ.  He has astonishing experience and skill.  And, yes, wire continuity is validated end-to-end; grounds are validated appliance-to-battery negative.

Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline JohnnyPopper

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #35 on: October 27, 2022, 07:32:10 PM »
You can also do a amp draw test from Battery + to the negative pins on your connectors.

JUST MAKE SURE THEY GO TO GROUND FIRST!! ;)
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline buzzman351

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #36 on: October 27, 2022, 07:41:21 PM »
But when i remove the ecm b fuse the truck will not start so that tells me something in the ecm is working. Maybe I’m getting a bs set of codes from a faulty aldl connection. I’m using a innova 3120 scanner


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Offline bd

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #37 on: October 27, 2022, 08:17:53 PM »
ECM B also powers the fuel pump.  Have you perused the library posted in our Technical Forum?  Study the 1987 Light Duty Truck Fuel, Drivability and Emissions Manual.

Trouble codes are generated by the ECM for whatever their cause.  I think faulty ALDL connections would more likely result in no scanner reading than false trouble code reporting.


You can also do a amp draw test from Battery + to the negative pins on your connectors.

JUST MAKE SURE THEY GO TO GROUND FIRST!! ;)


 :o

Okay.  The way that's been worded, "You can also do a amp draw test from Battery + to the negative pins on your connectors.  JUST MAKE SURE THEY GO TO GROUND FIRST!!" will make the ammeter the circuit load, momentarily producing 4TH of July fireworks just before blowing the meter's internal fuse.  I know that you know what you mean, so what am I missing?   ???

Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline buzzman351

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #38 on: October 28, 2022, 05:21:53 AM »
using my innova 3120 code reader on this truck. do you think maybe its showing me false codes bc its not reading correctly? also i cant do the check engine light code read out. there isnt a check engine light. im pretty sure there wasnt one from factory. there isnt a wire for CEL at the ALDL or on the harness

Offline JohnnyPopper

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #39 on: October 28, 2022, 12:18:03 PM »
B+

Load (light bulb)

Ammeter (digital)

Ground pin

Any significant variance would indicate a poor ground wire/pin/grounding point.
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline bd

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #40 on: October 28, 2022, 01:36:02 PM »
Thanks for clarifying!   ;)

That makes perfect sense, now.    ;D    8)


Time for a nap...

Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline buzzman351

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #41 on: October 28, 2022, 03:27:59 PM »
well if the ALDL is in fact giving me correct codes the 55 code says to replace ECM. that would probably explain the rest of the codes.

Offline buzzman351

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #42 on: October 28, 2022, 03:35:47 PM »
but i was just reading on the link you posted BD and while running i was unplugging and wiggling a few things and i did uplug the electronic spark control module and nothing changed with the truck performance. my guess is that its bad

Offline buzzman351

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #43 on: October 29, 2022, 05:41:45 PM »
The two ecm grounds from the ecm connector to the negative battery terminal have continuity a little over 5 ohms

Offline bd

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Re: 87 V10 TBI - No check engine light & inconsistent idle
« Reply #44 on: October 29, 2022, 09:33:15 PM »
The ECM grounds for a SBC TBI engine are pins A12 and D1 (image).

Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)