In another thread I posted my fuel trims asking questions about them. Long term fuel trims are between -10% and -15%, so someone told me that's likely a fuel injector stuck open.
This is the other thread https://blazerforum.com/forum/engine...m-leak-103649/
My downstream O2 sensor also doesn't look good, so I don't know if the sensor is bad, or if the rich fuel concentration damaged the cat. Can't say how long it's been like this. I'm noticing decreased fuel economy and power/acceleration.

So what's the best way to test these injectors to know if they need to be replaced? Or should I just replace the spider-thingy anyway?

 

Put a fuel pressure gauge on it. Does it maintain fuel pressure after you shut off the ignition? If it does, your injectors aren't stuck open. Maybe the MAP sensor or coolant temp sensor are not reading accurately and causing it to run rich?

 

I answered your questions in the original thread.


George

 

It does maintain pressure. At least last time I looked at it. I'll have to confirm it again.
MAP sensor has been replaced recently, but I bought a cheap one. https://www.rockauto.com/en/moreinfo...pt=11207&jsn=8
I hear a small vacuum leak around the manifold that I haven't been able to locate yet.
I guess I could take a look at the temp sensor, but I haven't seen the gauge act weird.

 

Spray water around the suspected leak area a listen for Rpm change.

George

 

Rather than replacing parts, you should hook up a scanner to it and check the values that those sensors are reporting. As an example, if the engine is fully warmed up and the temp sensor is reporting 30 degrees, it's going to run rich. Same thing if the MAP sensor sees low vacuum and interprets it as high engine load.

 

@Tom A

I pulled some data and shared it in a different thread.
https://blazerforum.com/forum/engine...m-leak-103649/

The challenge for me is understanding what the data means. I know what "correct" should look like. My dumb way of trial and error is to install a new part or swap and look for changes to find improvement.

 

One thing to keep in mind , building on Toms point is that swapping out a perfectly good AC Delco part with an inferior after market part can cause even more problems. Swapping with a known good part has its place but not if proper testing is possible. Example: a crappy after market cat can fail in a few months but a proper factory cat is very expensive and then there is the welding and labor. Why would you do that when it can be tested and its function verified?

Cold engine, off:

ECT is ambient
IAT is ambient
MAP is ambient
TPS is smooth with proper endpoints through the pedal travel

Warm engine:

ECT is operating temp
O2 sensors are switching correctly and respond properly to forced lean and rich
Fuel trims are less than 10 (ST+LT, each bank)
MAF is in the ballpark at idle and proper at full load shift using a VE calculator

If problems:

Check 5v hi & lo ref if used
Check wiring and connector
Test sensor out of the truck if possible such as an ECT in boiling water


George