Originally Posted by tsaw5500

tps sensor will show a 5 volt reference. you are wanting to check output voltage.

Originally Posted by RPH

How do you tell a Gen II 3.1 for a Gen III? Look at the upper intake manifold. If it looks like a 1988-1994 style, it;* a Gen II, if it looks like a 1995 to 2002 style it'* a Gen III.

Gen 2 engines are more prone to injector fails.

Either style removing the upper intake is required to access the fuel injectors.

The Test light is connected to the wiring harness on the engine, to check for signal from the ECM to the fuel injectors. Rare on those cars yet 1 out of 1000 might have that issue.

The Injector is checked with a Muilti-Meter on the OHMs Setting. Injectors have to fall between two spec to be acceptable. Injectors not in spec will NEVER fire. GEN II 2.8L & 3.1L engines will often not run at all if one is bad. They will not run at all if two go bad. It'* been a good 8 years since the last one of these I did.

There is a test procedure for Electronic EGR valve. I did it once 10 years ago and don't recall it. Common problem much like 4.3 V6 astro van: carbon chunks hold the pintle open when it should be closed. Others fail in the open position. This allows exhaust gas in to the intake stream at times it should not be entering. This effects the mixture and the ECM freaks out trying to compensate for an issue it can not,.

Originally Posted by Soft Ride

EGR test : https://www.gmforum.com/trouble-shoo...d-test-296250/
Hope that Helps.

Originally Posted by danjamesjr

Thanks! It'* Gen II.

I would love to know the test procedure for EGR valve. I took it off and cleaned passage way.

A mechanic also mentioned it could be the ECM? I guess it'* common for the computers to malfunction in Century'* (Gen II)?

Dan

Originally Posted by RPH

OBD-I ECM'* do tend to fail more then most OBD-II ECM'*.

Gen II vs Gen III in a 1994 Century the ECM'* have about the same fail rate. Both are OBD-I ECM'* with e proms.

Older OBD-i ECM'* some have a single Prom, some have 2 smaller proms. One of those is called a Calibrator.

When you buy a "New" or likely "Re-Manufatored" ECM even from a GM Dealership it will not come with the E-Prom. Often the prom fails with the Computer. Just replacing the computer often does NOT fix the issue.

Either find a good used ECM or buy a nbew one, and find a new E-prom. That is if your going to replace the ECM. Don't replace the ECM for no reason. Narrow down via diagnosis if your ECM is the likely cause.

As for the EGR valve you posted: 1993-1997 3 solenoid style. the test someone posted is a single solenoid style.

Originally Posted by jwfirebird

that seems more like a regulator issue. shouldnt go down that far, what do you have engine on vacuum line disconnected? try smelling the vacuum port on the regulator, if you can smell gas its bad and leaking past the seals