Is It Possible For A Fuel Injector To Work Fine When Cold But Malfunction At Operating Temperature?

Dont fret. I took my car in for a diagnosis today. You are helping me solve a mystery.

Can a fuel injector work fine when the motor is cold but malfuction once the the motor reaches operating temperature?

Just trying to narrow the possibilities. I have a no codes shudder during acceleration at operating temperature.

Thank you so much for your input and patience.

How about telling what the diagnosis was ? That will help people give you better replies.

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Forgive me! Diagnosis was a “pending code” something about running “lean”

This is a common mode of failure in many types of electrical and electronic devices: thermal induced failure.
One case occurs because most materials expand with rising temperature, causing strain and breakage at a weak point.
When it cools the bits come back together.

Back in the '70s (in high school) I worked in a TV repair shop
One handy tool on the workbench was a can of “freeze spray” with a narrow nozzle.
It could spray (ozone depleting) freon on individual components to identify thermal failures.
A hot soldering iron could do the same in the opposite way.

Sounds like you are getting the pending code P0171. This is a two trip DTC (diagnostic trouble code). That means that the condition must be detected on two sequential trips. The basic trip is cold start, warm to operating temp and shut down and cool back down to ambient temperature.

The first time the code is detected, it is stored as a pending code. If it isn’t detected during the next trip, it is deleted. If it is detected on the next trip, it is saved as a DTC and the check engine light is turned on.

The code does not mean that the engine is running lean. The O2 sensor is controlling the A/F ratio and keeps it in the correct zone. But, in the computer (PCM or ECM), there is a table of expected fuel needed based on temperature, coolant temp, mass air flow and manifold vacuum and maybe some other parameters. The fuel injection is having to inject more fuel than the table expects. This is your LTFT (long term fuel trim). When the amount of fuel needed is 20% greater than expected, a code is set.

Now the PMC is not actually seeing the amount of fuel being injected. It is calculating the fuel used based on the fuel pressure in the fuel rail (at least what it is supposed to be) and the pulse duration (PD) that the fuel injector is turned on. It can’t change the pressure but it does adjust the PD to compensate. When the PD is 20% or more longer, the code is detected.

The mechanic should have looked at the misfire register to see if one cylinder is affected. That would identify if there is a bad fuel injector that needs cleaning/replacing. You could run a couple cans of Seafood or Techron through your fuel system and maybe that would work.

But the problem could be something else. A leaking intake manifold gasket could do it. A worn engine could simply be the reason. You mechanic probably should have done a compression check as well.

One very common reason for this is a dirty mass airflow sensor (MAF). They are easy to clean. Also a manifold air pressure sensor (MAP) could also be the cause.

Right now, the first thing I would do is clean the MAF. Also look for any possible air leaks in the intake duct between the air filter and the throttle body as well as a dry cracked PCV hose or PVC makeup air hose.

@ArgosNoble I hadn’t seen your other thread when I made my earlier post, so my answer was generic. This is why it’s not a good idea to start two threads for one problem.

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Argos , maybe you should just start all over again . Make one thread , put the vehicle info and what you have done with the symptoms you have and close the other ones .

There just has to be a shop that can solve this .