Hello All!

I currently own a 94' buick century, 3.1 V6 with 104,000 miles. It'* white and it has been absolutely lovely to me... until recently.

A few problems to list:


Upon a cold start (overnight or a few hours) hard starting, once started idles extremely low and can stall
Pushing on the accelerator too far will result in bogging down and possibly stalling, have to "ease" throttle to gain RPM and keep running. Once warmed up for 5-10 minutes, will run OKAY until vehicle is placed under load.
Placing a load on the vehicle (In Drive or Reverse), immediately runs rough, bucks, hesitates, and then gets up to momentum. It slowly works itself to normal the longer it'* running.
Sounds like a possible misfire when running
Fuel pump is NOT making any noticeable sound near rear tire when key is "ON".


Parts replaced (related and non-related):


IAC Sensor
PCV Valve
Coolant Temperature Sensor
Cleaned Throttle Body (TB Cleaner) and MAF Sensor (MAF Cleaner)
New Throttle Body Gasket
Cleaned EGR Passage Way and EGR Valve
Completely new Emissions / Vacuum Harness (All Intake Manifold & Emissions Vacuum Lines)
Fuel Filter
Fuel Pressure Regulator
Oil Change + Filter
Spark Plugs
Alternator and Battery
Sea Foamed Gas Tank


Things I haven't done:


Compression Test (I have the compression tester, might do it soon)
Fuel Pressure Test (Need fuel pressure tester)
MAF Sensor Test (Need multimeter that can test Hz, mine doesn't)
TPS Sensor?
Intake Manifold Gasket Leak Test?


My patience is running low; I am a very patient guy.

Please if any one has experienced this issue before or has any guidance on what to next that doesn't involve a lot of money, I highly appreciate it!

Thanks,
Dan

Welcome to the forum Dan!
Wow you sure have replaced a lot of parts!
Did you ever get the car scanned for stored codes?
Did any MiL (service soon or engine light) come on?
Did you replace the spark plug wires?

I'm not sure what'* wrong. You have done a lot to it. The only thing I can think of is maybe the cat or exhaust restriction. But I am not sure.

First things first Which style 3.1L do you have the Early 94 Gen II or the late 94 Gen III. Your car 94 is a mid year change.

I am going to tell you what I would test:
I would pull the upper intake off (gaskets are cheep) and OHM test my fuel Injectors. I would also make a noid light out of a 194 bulb and make sure I have signal to each injector.

194 blub with wire added to each leg, jam wires in injector power plug. if pluse light will flash. no lightm no power or ground. Light with no flash, no ecm spray signal.

I would also go threw the TPS Test and the EGR valve test. If the EGR pintle is hung in the 'Open' position your engine will not run rightm and codes may not set.

Thanks! Yes I have, a little too many lol.

I can't get it scanned, no shops around have obd1 scanners :(

No CEL

Did not replace spark plug wires.

Thanks

Yes I've thought heavily on cat but I don't want to spend $100 to figure that out.

How can I tell which generation? I know I've looked at obd port and from what most diagrams say to jump a and b pins to enter diagnostic mode. Well, those pins are not next to each other and completely different.

TPS sensor = 5 volts?

EGR test? The car has a non vacuum powered EGR it'* electronic.

Ehh, not looking forward to taking intake manifold off lol.
Testing with light seems good but doesn't measure if injector is clogged only dead? Does light dim if clogged?

Thanks
Dan

i would test the fuel pressure, a failing pump can cause all these issues, and they rent them free with deposit.

tps test;
https://www.gmforum.com/trouble-shoo...sensor-279319/

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

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,.