1993 buick century 3.3. BOOK WARNING

[Will L.]

1993 buick century with 3.3 v6 gas with 166,000 miles.

Currently runs HORRIBLE cold. 5 minutes idle and rough high idle- runs great. No codes.
Ideas?

Now the book of details and parts:
Bil car. He bought it year ago or so and put on probably 12,000 miles no problems. He never did anything other than oil change and quicky lube. (If that)

Couple weeks ago on freeway going up a descent hill- runs out of gas. My wife went rescue him and i sent her with 3-4 gallons of either heavy mixed 2 stroke or gas/diesel mix. (Loaned that can to my nephew who owns 6.2 and a street bike). It smelled like gas but when my bil poured it in he saw it was a little dark he tells me later.

Car never started- tow truck to my house.
Thinking maybe fuel was a little old- I go get 5 gallons of premium grade chevron.

I checked fuel pressure just by hitting schrader vale- low pressure. I swapped fuel filter which is next to tank- very plugged up. Still no start. Disconnect filter and use intank pump to get sample before filter. Dark fuel, tiny amount of water in fuel, rust in fuel. Call bil, this is when he tells me he thinks it was diesel fuel. Only I smelled it and so did a friend of mine that was over who is top notch mechanic- he confirmed not old gas, should be good. So maybe some junk in bottom of plastic can?

With new fuel added and we run till clean fuel comes out, car starts but runs rough. No time to keep messing with it, my big fuel pressure test kit is gone- so just pressing the schrader Valve on engine fuel line we think pressure is low & low volume. Car can drive barely. next day Bil drives car to trust d mechanic in town but doesn’t tell the mechanic what I said about fuel pump.
Mechanic after week of back and forth because bil did not share what i said to tell him...
Replaces all fuel.
New fuel pump (was at minimum spec pressure and volume first time)
Another fuel filter
plugs & plug wires (looked original before going there) check timing
new air filter
new MAF
new temp sensor (known issue for this engine and with cold running problem seems likely guess)

When you first start it cold- 40° or 55° - just engine not ran recently- idle is real rough. After few seconds you can rev up rpm but missing bad. If at idle you put it in gear, engine dies. But after idling for 4-5 minutes or high rpm in park for 2-3 minutes- engine clears up a bit. Put it in gear and drive away. By time you are at 5 mph- runs great. Feels like a car ok to take across country.


All below I did, mechanic did at his shop also.
Checked all the vacuum lines, sprayed starter fluid hunting for vacuum leaks on them, intake, brake booster- no vacuum leaks anywhere we can tell.
Injectors signal the flashing light style tester shows all injectors firing ok.
Removed vacuum line from fuel pressure regulator- no leaking fuel.
New fuel pump 1 psi below top spec, improved flow volume according to mechanic (i haven’t rechecked)
Mechanic added a fuel injector cleaner to fuel hoping some debris may get cleaned up.
But i need my lil pickup back from bil so he has to deal with 1930’s style warm the engine before driving for now.

I read clean electrical ground connections on engine near oil filter so will do that in morning.
The mechanic that did the work is late 50’s pro that I have seen work on things for 20 years- he is top notch usually and amazing on older gas rigs, and new electronic cars as well. Total trust in this guy. He just feels horrible to not have solved this one, but has only few minutes to test with it running before problem disappears, so he gets 2 tries for 3 minutes a day then it has to all cool down.

I am stuck on what else at this point. Still getting over covid and have “covid brain fog” bad right now still. Had to ask for directions to take my son to his dr he has been going to once a month for 6 months today- been eating a restaurant newr that corner for 25 years with my wife- couldn’t envision the intersection. Covid fog SUXXXX!

Ok boys and girls, ideas please?

 

[WarWagon]

What do the fuel trims look like?

Please tell me it's been over 45 MPH long enough for the idle air pintle position to set?

Fuel pump low pressure = going lean. Melted cat? Other damage from being lean under power for hill climbing?

I recall the fuel rails would get crystalized krap in them esp if it doesn't have a fuel return off a rail regulator aka the dead space in a rail. Your engine parts cleaner or WTH-ever was in the can may have broken this stuff loose and clogged an injector screen, jamming one open, or wonked out a 29 year old injector.

 

[Will L.]

@WarWagon
Couldn’t get any numbers from the komputer.

Clue me in about the pintle please. Once the engine runs good enough to drive it at all, it runs perfect. I know the other guy drove it at 55-60 mph for 15 miles.

Cat seems ok- usually when they plug and the car does worse on the hiway and good idle this is opposite and whatever the problem is goes away as soon as the car warms up a couple minutes. Not even full operating temperature- just getting warm does it.

Goofy injector or two might be an issue. Not sure how being old makes it stick then warm is better maybe? But using the old school waekon tester they are all firing like they should the entire time.

I was wondering about pulling a couple injectors just to see if there is any debris in the line somewhere.

I did notice today a couple of wires to 2 injectors had the insulation nicked. No copper damage or corrosion. Nothing shorting. Those injectors firing same as the other 4.

 

[MrMarty51]

I dont se anything in tje lists about O2 sensors being changed for new units.

 

[Will L.]

O2 sensors working proper.
No exhaust leaks

 

[Will L.]

I am thinking it is something in the “cold idle” circuit.
Like- whatever the komputer is doing to take the place of a choke on a carburetor.

I mean, that is exactly like what is happening. Ever have carburetor car/truck and the electronic choke didn’t work- or cable choke but the cable came loose?
That is exactly what is happening here. I feel like if I could “choke” the intake to hetvit more rich fueling- it would be perfect.

So I am thinking the computer reads temperature and should command more fuel for first couple minutes. But somehow it isn’t.
Thats why I agree with him changing the temp sensor.

OH WAIT!!! 6.5 has 2 temperature sensors- one for dash one for cold circuit.
I wonder if there is 2 sensors for this thing?

 

[Will L.]

Does anyone have all data and could look up for me if there is multiple temp sensors?

 

[WarWagon]

Computer steps the idle air motor pintle closed over 45 MPH to "learn" it's position. It can have dirt build up on it that gets wiped off only the touch 'line' but the build up makes the valve 100 engine RPM lower. Even to the point of stalling out after startup. Common dirt buildup problem with using K&N krap.

High mile engines also have the PCV system clog up that can affect airflow the ECM tables say it "should" have.

The second "Closed Loop" happens it can correct for things that are outside the EPA lean table values. So an injector that is leaking gets corrected. This is why we need to ask the ECM what it's fuel trims are: is it correcting a lean or rich condition? Lean goes to vacuum leaks or debris clogging an injector screen aka from years of buildup in the fuel rails.

GM dealers were being taught or just seeing about this dead space crystal looking build up "problem" in the fuel rails in ~1998-1999.

You recall the TBI 350 that idled rich with good visible spray patterns? I snapped the throttle WOT and one injector suddenly was pissing fuel under a timing light...

I would static vibration test the MAF cold and see if it puffs black out the exhaust. (If equipped.) Oh wait they already hit the MAF with a parts cannon.

The hot summer murdered lots of my batteries this year - load tested the battery?

I would go back and re-think this.
Ran out of fuel: or did the fuel pump finally just die? Yeah: What damage happens when run LEAN from a bad fuel pump...

Cats melt. Spark plug damage. Valves burn. Knock damage maybe. If you cant get power enrich rich enough to "put the fire out" under specific loads the cats melt down.

I will give the pressure and volume weak from the test a pass as "true". How is the new pump? Borrow the tools to check it. A thought is GM pumps are known to fry/melt things on their way out during their short natural lives. Is the fuel pump connector bad or relay/OPS burnt up? Maybe check voltage to the fuel pump.

Is this a "two speed" fuel pump by voltage? IDK what years GM used them and if they were just for the supercharged engines of that era.

It's old enough to suffer from kinked or hose flappers. Especially if you handed em BioDiesel...

Why do you not have numbers from the ECM? If it's not going into diagnostic mode you have a grounding problem or bad ECM.

Last is the chemical O2 added to modern fuels that 1993 didn't have as much of. The 1993 was "leaned out" to the edge of just running in open loop for the EPA anyway.