350 TBI Boggs and surges under load

[Schurkey]

Kinda guessing that .zip files will not be well-received, as they're associated with viruses.

If you could post your data in some other format, it would be better.

 

[Madcrafter52]

Kinda guessing that .zip files will not be well-received, as they're associated with viruses.

If you could post your data in some other format, it would be better.

Anything you recommend?

 

[PlayingWithTBI]

Kinda guessing that .zip files will not be well-received, as they're associated with viruses.

They're accepted on this and other forums I subscribe to. I downloaded and played it with no issues.

Anything you recommend?

TL;DR

What is your issue?

Did this log contain your issue?

 

[Madcrafter52]

TL;DR

What is your issue?

Did this log contain your issue?

The issue is that the RPM's surge when I hold the throttle as I posted a video of a couple posts ago. Also the truck has no power and struggles to get up to normal driving speed.

Yes the Log contains the issue
The log is just of me sitting in park holding the throttle and then letting off a couple times. The surging of the RPM's should be pretty obvious.

 

[Madcrafter52]

I'm at my wits end with this truck. I've looked over and over the sensor data and everything seems fine. I rechecked all the stuff that I've checked already and again it all looks fine. I have no idea where to go anymore.

Is it possible that this is an ECM issue? Somebody had hacked the wiring pretty bad to install an aftermarket anti theft system which I removed when I got the truck. Is it possible that system fried the ECM?

I'm honestly thinking of selling the truck because this is taking way more time and money than I wanted to put into it.

 

[Road Trip]

I'm at my wits end with this truck. I've looked over and over the sensor data and everything seems fine. I rechecked all the stuff that I've checked already and again it all looks fine. I have no idea where to go anymore.

Is it possible that this is an ECM issue? Somebody had hacked the wiring pretty bad to install an aftermarket anti theft system which I removed when I got the truck. Is it possible that system fried the ECM?

Anything is possible, especially if the PO had a Humpty Dumpty moment, and you are now trying to
put it all back together again. If I'm reading the intent of your question correctly, IF you were to replace
the ECM, would it straighten up and fly right?

Before I would replace the ECM, I would have to answer the following questions and have them indicate a replacement is the fix:

* With a bad ECM, how is it that all the sensor data is fine? (If blown, I would expect one of more sensor subsystems to be out of whack.)
* Does the SES light come on with Key ON, then go OUT once the engine is started? (Showing me that both the light can be lit by the ECM, -and- can also be turned off?
(NOTE: Constant SES light ON from Key on with no stored codes is an illegal condition.)
* Are the following DTC codes kicked: 51, 52, or 55? If so, then the hardware self-testing is indeed failing, requiring replacement if the normal seating/reseating
checks don't clear the failure. Conversely, no 51,52,or 55 means that at a *hardware* level the ECM passes whatever selftest the designers could figure out/implement.
* Advanced ECM confidence check: Can it correctly run Field Service mode and translate O2 sensor activity into SES light activity. (Yes it did per your videos and what I
was able to decode in reply #17.)

****

So, to sort this out we need to figure out which of the 3 layers we need to focus on in a GMT400 engine bay:
From most abstract to most concrete, the layers are:

* 1) Software running on ECM. (Variously described as: code, firmware, operating system, calibration, image, etc)
* 2) ECM hardware. The computer itself, whether loaded with correct, incorrect or no code.
* 3) Engine and associated sensors. This is where the majority of us have the most hands-on experience.

If you come back and tell me that the SES light is working correctly on normal startup, and then only gives
you a repeating 12, 12, 12, when you jumper the ALDL pins during KOEO -- then for now I'm going to look elsewhere for the fix.

And if you come back and report good compression in all 8 cylinders on top of all the sensor data looking good,
then for now I'm going to have to look elsewhere for the fix.

This only leaves the top layer. And when troubleshooting, you always go back to the last time something ran right,
and what has changed since then. Since the PO took it upon himself to change out the original TBI motor for a TPI
short block, and then installed the TBI setup on top of it, we have to keep this in the back of our mind. (ie: How does
the TPI cam play with the TBI system, especially when it goes closed-loop? (Engine Bay Context)

OK, so when I reframed the problem description to the above, I wanted to find out if anyone else has slid a TPI short
block under TBI engine management, and what did they run into?

Well, thanks to @N9nefingers, I found exactly what I was looking for:

I did exactly what you are talking about in my truck...89 RCSB K1500. I rebuilt a 350 TPI with iron heads from a 89 Camaro. I also did the ultimate tbi mods, turned up the fuel pressure to 15 psi and used a tbi intake without all the smog stuff. My truck runs great but it didn't right after the swap. It fired up no problem but ran terribly on the stock chip. I'm tuning it now with the ebl flash. I'm happy with it.

(Here's the LINK to that thread.)

I won't regurgitate what was written there, but from over here it looks like
both the ECM hardware is passing self-test, the sensors are giving you
rational data that stays within parameters, then 2 of the 3 layers are accounted
for, and you need to try to tune the TBI software to be more compatible with
what the TPI engine (camshaft) needs in order to get the most you can out of
the unique combo under your hood.

I'm honestly thinking of selling the truck because this is taking way more time and money than I wanted to put into it.

FWIW, if you are willing to follow the lead of n9nefingers I think you can finish
the repair of this truck that was started by the PO. And as you know, a good
running truck will sell for more money than one that doesn't run right.

So the decision becomes do you want to learn/add the necessary skills to your
repertoire, fix it, then decide to keep it/sell it? Or is that a non-goal of yours,
and just want to cut your losses? I can completely understand either choice,
so I'm not trying to steer you in any one direction. I'm just trying to suss the
puzzle in your engine bay, and try to come up with a permanent fix using the
least number of parts/repair attempts.

FWIW --

 

[Madcrafter52]

Did a compression test today (Injectors unplugged, coil unplugged, battery charged with the charger still on, all plugs out, 5 cranks per cylinder)
here are the results:
Cylinder- PSI
1- 165
2- 170
3- 175
4- 160
5- 170
6- 165
7- 170
8- 175

While had the plugs out I scanned my peepers on them. I think a couple of the spark plug boots got loose with all my monkeying and was causing a intermittent miss, at least thats my best guess as to why the couple lean plugs.

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I pulled off the valve covers and everything seems fine in that department.
The ECM also checks out

Since the PO took it upon himself to change out the original TBI motor for a TPI
short block, and then installed the TBI setup on top of it, we have to keep this in the back of our mind. (ie: How does
the TPI cam play with the TBI system, especially when it goes closed-loop? (Engine Bay Context)

You need to try to tune the TBI software to be more compatible with
what the TPI engine (camshaft) needs in order to get the most you can out of
the unique combo under your hood.

Yeah that makes sense. I had no idea that the TPI cam was more aggressive and that the TBI wouldn't be able to compensate for it. That explains the low vacuum.

FWIW, if you are willing to follow the lead of n9nefingers I think you can finish
the repair of this truck that was started by the PO. And as you know, a good
running truck will sell for more money than one that doesn't run right.

So the decision becomes do you want to learn/add the necessary skills to your
repertoire, fix it, then decide to keep it/sell it? Or is that a non-goal of yours,
and just want to cut your losses? I can completely understand either choice,
so I'm not trying to steer you in any one direction. I'm just trying to suss the
puzzle in your engine bay, and try to come up with a permanent fix using the
least number of parts/repair attempts.

One of the main reasons I got this truck was to learn how to work on TBI and OBD1 but I definitely didn't think I was jumping this far into the deep end. So its not that I don't want to see this truck through its just that I was hoping to be able to drive it sooner. I have 0 experience doing any tuning on fuel injected stuff so I have no idea where to start on this. However I'm totally willing to give it a shot. Any suggestions?

 

[Schurkey]

Did a compression test today

Compression is fine.

thats my best guess as to why the couple lean plugs.

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The problem is not the "lean" plugs, the problem is the black (oil-fouled?) plugs.

 

[1990Z71Swede]

Tested the fuel pressure, 12 PSI solid no matter what (as it should be with a brand new pump)

Checked the distributor and the magnet does look a little worse for wear. However the ohms on the pickup coil are okay ~1300

I double checked a few other sensors and everything seems fine.

I also took some videos of my truck running so maybe that will give you guys a better understanding of what's going on
Engine Bay and Interior (Yes the oil and temp gauges aren't working. got bigger fish to fry)

Darn electronics, Any input on a carb swap? lol

Thats an aftermarket distributor. Which does not have to be a bad thing, considering you replaced all the problematic parts... All but one...
When I bought mine I did some digging in the Amazon Reviews and the ICM and Pickup coil seem to be failiing/faulty at somewhat high rates.

Theese threads might be usefull:

Longevity of OEM distributor?

Went to grab my shiny shaft today.:cool: Super simple to take apart. No visible issues so far. There are quite a few differences though. Firstly the machined diameter at the bottom of the chinese one, where the oil passage is, measure 31,6mm. The GM one measure 31.65mm. Not sure if that is...

www.gmt400.com

Which Ignition Control Module do I need....ACDelco D1943A or D1984A ?

The two different modules in question regarding performance differences were referred to "in the old days" as # 369 and # 048, with the 369 being "better" ... how those #'s cross to modern day part #'s I have no idea. I used to keep a few known-good OEM modules in my toolbox and had several...

www.gmt400.com

 

[Madcrafter52]

The problem is not the "lean" plugs, the problem is the black (oil-fouled?) plugs.

Definitely not oil, just fouled from a rich mixture. Could that be because of the misfiring cylinder causing the computer to add more fuel? Or would that be the opposite?

When I bought mine I did some digging in the Amazon Reviews and the ICM and Pickup coil seem to be failiing/faulty at somewhat high rates.

I replaced the ICM. I don't think it's the distributor because when I unplugged the electronic timing advance and set base timing at around 15⁰ the truck ran much better, and vacuum was much higher. To me this really feels like a camshaft issue. Seems like the computer is feeding both the ignition system and fuel system bad information.