Tbi 350 has no power on the road

L31MaxExpress · Feb 13, 2024

I have seen a lot of people set the base timing without disconnecting the EST connector as well. That will make the Initial advance setting 15-20* off, timing retarded by whatever advance the ECM is commanding for idle and the engine will run like garbage. Higher mileage engine I would question the accuracy of the balancers timing mark all together as well. I use the balancer as an initial starting reference point, then feed it more timing 2* at a time until it runs best. I have seen balancer timing marks and timing pointers 30* or more off. Could also grab a TDC stop, install it in #1, roll the engine lightly against it forward with a socket and ratchet on the crank bolt, then roll it backwards, marking each point on the balancer where it lines up with the TDC mark on the pointer. If the mark is accurate, should be halfway between each mark you made if you measure it.

L31MaxExpress · Feb 13, 2024

I have also seen more than one fuel pressure regulator spring break into multiple pieces, resulting in very low fuel pressure. To the point it is like 6 psi. Somehow a TBI will start and idle with 6 psi of fuel pressure.

Mitchell93 · Feb 13, 2024

I unplugged that one wire pigtail, ik what base timming it, also can not say for sure if the balancer is accurate, another thing I can check...

JDGMC · Feb 16, 2024

Mitchell93 said:
Thank you all for your quick response, I'll go down the list...
So both of the injectors are differently working, I can see a clean healthy looking cone shaped spray from both, I have not held it wot wile watching it, it does Rev up great in park, I'd have no way to watch it wile I drive it...
I did forget to include that it has a shiny new muffler with the catalytic converter cut out, and replaced with a chunk of pipe, no tail pipe, has a turn down right off the muffler...
Also has a new o2 sensor, sorry I completely forgot to mention exhaust, the air cleaner is new as well...
I have not been able to check fuel pressure because I did not have the correct adapter, I have it ordered and will definitely be checking that, but the pump and filter are both new, and I know new parts can be bad... previous owner put all these parts in it, so who knows how cheep the parts are..
I have not checked vaccum, I will though, and the new spark plugs look kinda black, I can get a picture of them. I work 3 hours from home so I'm only home on the weekends so I can check fuel pressure and vacuum, I'll have my wife snap a picture of the plugs. Atf looks and smalls clean, nice bright red. I do not know how to know if the pcm or prom is correct, how would I verify this?

The spark plugs appear to indicate there may be issues related to your compression, spark/timing, or fuel delivery (timing). Your 4L80-E transmission has a Powertrain Control Module (PCM) or GMP6 which uses a Memory and Calibration unit (MEM-CAL). I should mention that the 4L80E W/8600 GVW does contain a backup-fuel circuit (sort of like limp mode) in case the system becomes faulty and may not throw a code. It also has a learning period. Keep that in mind when clearing codes. One other thought is regarding the 30 mph max. This is when the TCC engages. Any signs of valve body mods? Harness?

Your ECM (square metal box) should be # 16147060 or 16127470 .

The Prom/Memcal located in the ECM will vary depending on your RPO codes. It will be a 4-letter code ( AWBK, BAAY, AWBK, BDPK, etc.) on a small sticker fixed to the memcal. Post what you find and the RPOs for your truck and I can let you know if it’s the correct one.

Open the glove box and remove the black plastic insert. The ECM will be to the lower right. Good luck.

Mitchell93 · Feb 16, 2024

I got a piston stop, checked the balancer and it is perfect, checked compression, getting 140 to 150psi for all of them, steady 13 to 14 psi for fuel pressure. my pcm is the 16147060, the memcal says AWBK. The tcc won't be my issue because i can feel there's something off just leaving my uphill driveway, it's doggy right off the bat, just real noticeable when it's in 2nt gear... it kinda seems to me now maybe the pcm isn't advancing the spark under load like it should be. This is a dually truck too btw

JDGMC · Feb 17, 2024

Mechanically the vehicle appears to be sound. It's possible you indeed have a computer command control issue. The PCM and Broadcast Number for the memcal are correct. There have been issues with that particular memcal where GM went through three revisions up to 1993. You can try testing the PCM QDR.

Attached Files:
Your K3500 specific RPO and VCVS info
Mem-Cal revisions
QDR Test procedure

Mitchell93 · Feb 17, 2024

Got a different pcm from a salvage yard today, matching everything, and runs the exact same...

Oddballcreations · Feb 17, 2024

If there was a long-standing issue with running, which sounds like it might’ve been by the previous owner dumping so many parts into it. I would definitely check to see if the cats are plugged.

JDGMC · Feb 17, 2024

Unfortunately, the only way to understand what's happening is to monitor the PCM inputs (information sensors) and PCM outputs (controlled components). Do you have access to ofb1 data monitoring software? Replacing components is sometimes only part of the troubleshooting process. The physical connections are are just as important. Testing this network is difficult in real-time - ie you could have a new temp sensor, but the PCM is getting fluctuating data due to bad/intermittent ground. If you haven’t already done so, check all your wiring and connectors to the components below.

PCM Information Sensors

Manifold Absolute Pressure (MAP), Exhaust Oxygen (02), Throttle Position Sensor (TPS), Coolant Temperature Sensor (CTS),Vehicle Speed Sensor (VSS), Electronic Spark Control (ESC) Knock).

Computer Controlled

Fuel injector, Idle Air Control (IAC)
Fuel pump relay, Transmission Converter Clutch Connector, Electronic Spark Timing Distributor (EST), Remote ignition, Electronic Spark Control module (ESC), Oil pressure switch, Exhaust Gas Recirculation (EGR) Vacuum Solenoid

H2814D · Feb 18, 2024

All good advice so far. I know you said they were new, but I would closely examine every one of your spark plug wires. I had a similar problem a long time ago. I actually thought I was having a transmission issue, since it didn't seem to do it when in overdrive. Was a weird thing to diagnose. I replaced the wires and the problem went away. I think one or more of them were sending the spark to ground, instead of the plug.

Tbi 350 has no power on the road

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