Rebuilt Motor Backfiring No Start

[Road Trip]

Okay so I went through hell since Wednesday I worked on the truck day and night. The truck WOULD not fully start for the life of me no matter how many times I put the engine at TDC. Everyone kept saying timing, timing, timing.

heyitzjoel,

Believe it or not your problem really was timing, timing, timing.

Absolutely everything having to do with triggering the fuel injectors
to firing the spark plugs are 100% dependent upon the master signal,
which we refer to as the CKP signal.

From a safety standpoint, if the ECU can't 'see' that the engine is spinning,
it will absolutely not fire the fuel injectors. There's a lot of sensors that, if
they drift out of calibration, the ECU will substitute a 'nominal' value and keep
the engine running, albeit with a lesser efficiency and power delivery.

But without the all-critical CKP signal, there's no life in the engine bay.

And there's the 4 levels of troubleshooting based on increasing test equipment capability/resolution.

* Old school voltage measurements using a multimeter & following fault trees. (No ECU codes, you are on your own.)

* Code reader. OK if a code is stored and the fault trees are extensive enough.

* Scan tool with live data display capability. A large step up, for now we get to
know exactly what the computer is made aware of, is it being lied to, and how it has
decided to respond.

* And then there's the scope dudes who look at the raw analog signals in order to
fix beyond what the computer was programmed to anticipate understand. This proves helpful
when a signal or sensor has failed in a way in 2024 that wasn't anticipated by the
designers back in the '88-'98 timeframe.

It goes without saying that the higher you go with test equipment resolution the
easier/faster it is to locate a tough no-start like this.

To do this with just a multimeter is no mean feat.

Well played.

 

[heyitzjoel]

So I had a handful of problems after getting my engine started and I scoured the internet to find abandoned threads with no resolutions. The first problem was engine stalling upon sudden throttle application, despite numerous adjustments to the idle position and cleaning of the AIC. It turned out that the MAP sensor was loose, with its grommet sucked into the upper intake. Replacing it with a snug-fitting new one resolved the issue, restoring the engine's throttle response.

Then came the persistent misfire on cylinder 7, prompting multiple valve adjustments to no avail. Eventually, misfires spread to cylinders 1, 3, 5, and 7, leaving me stumped. Observing closely with my scanner, I noticed that misfires happened only when the engine warmed up, implicating the O2 sensor's role in controlling the AFM. Through extensive research and analysis of O2 sensor readings, I identified abnormal behavior in Bank 1, where fuel trim soared to 50%, triggering rough idling and misfires. Despite ruling out vacuum leaks, and the fact this only happened on the drivers side, the faulty O2 sensor persisted, necessitating its replacement.

Removing the stubborn old O2 sensor became a daunting task, requiring hours of heat application with an oxygen torch and eventually resorting to using a pipe wrench due to the crumbling nut. Even fitting the new sensor posed challenges, the threads were ruined so I needed to purchase a thread chaser. However, with perseverance, I succeeded, and now my engine runs flawlessly, enriched by the newfound knowledge of sensor diagnostics and troubleshooting techniques.

 

[Schurkey]

We love success stories.