2.3L ('83-'97) 96 2.3L Hard Start & Thick Black Smoke

[gkoenig]

Hello, new to forum, been reading a lot, great resource.

I have a 96 with 180k miles, it sits a lot at our vacation home, it started billowing black smoke, rough start, and rough idle. I have a lot of fuel in the oil. It runs good when driving but still smokes. All 4 plugs were covered in black soot. I also replaced the fuel pressure regulator with no change, there was no fuel in vacuum line. I will check cylinder compression and fuel rail pressure and report back. I may pull the computer and look for failed capacitors. The instrument panel appears to have problems, no fuel level gauge, no engine temp gauge, no CEL light. I will also use Forscan to check for codes.

I am thinking old leaking injectors because the oil has a lot of fuel in it, or bad rings allowing fuel into the oil and oil into the combustion chambers.

I replaced the timing belt for good measure a while back and it ran better than ever, it didnt blow smoke afterwards.

Thanks in advance

 

[RonD]

Welcome to TRS

So its WAS blowing black smoke before you changed timing belt?
And got better
But went back to blowing black smoke?

1996 instrument cluster diagram below check those fuses

No capacitors to check on a 1995 and up computer, but you can have a look at the computers circuit board for signs of corrosion or burnt circuits

Upstream and downstream O2s are most likely bad if they are also soot covered, but wouldn't have been the cause of the problem, but may now add to the problem

ECT sensor, 5volt 2 wire sensor, is used by the computer for Choke Mode, i.e. rich running and high idle after cold start, its possible ECT sensor is telling computer is -20degF so you get rich running all the time but that should set a code if ECT is not warming up after 4 to 6 min of run time

Dash temp gauge uses a 12volt 1 wire sender, no connection to computer, just FYI

Ultimately, it could be a computer issue, there is no tests for that, you can only eliminate everything else and then bite the bullet and try a new computer

There is a Mode on all engine computers, called "Clear Flooded Engine" mode
Turn key on
Press gas pedal down to the floor and hold it down all the way
(at 0 RPMs and throttle at WIDE OPEN the computer will shut off fuel injectors pulses, but spark is still on)
Turn key to START, still holding down gas pedal
Engine should just crank and not start or even fire, because there is no fuel

If engine starts then you may indeed have leaking injectors, but could still be a computer issue
To have ALL 4 injectors leaking at the same time would be very very long odds
And all 4 would have to be leaking for all 4 spark plug tips to be black.....................one would be blacker than the others if one injector was leaking
1996 runs sequential fuel injection

So it has to be something common to all cylinders
Fuel pressure regulator was a good guess
Maybe ECT
And of course computer

 

[gkoenig]

Welcome to TRS

So its WAS blowing black smoke before you changed timing belt?
And got better
But went back to blowing black smoke?

1996 instrument cluster diagram below check those fuses

No capacitors to check on a 1995 and up computer, but you can have a look at the computers circuit board for signs of corrosion or burnt circuits

Upstream and downstream O2s are most likely bad if they are also soot covered, but wouldn't have been the cause of the problem, but may now add to the problem

ECT sensor, 5volt 2 wire sensor, is used by the computer for Choke Mode, i.e. rich running and high idle after cold start, its possible ECT sensor is telling computer is -20degF so you get rich running all the time but that should set a code if ECT is not warming up after 4 to 6 min of run time

Dash temp gauge uses a 12volt 1 wire sender, no connection to computer, just FYI

Ultimately, it could be a computer issue, there is no tests for that, you can only eliminate everything else and then bite the bullet and try a new computer

There is a Mode on all engine computers, called "Clear Flooded Engine" mode
Turn key on
Press gas pedal down to the floor and hold it down all the way
(at 0 RPMs and throttle at WIDE OPEN the computer will shut off fuel injectors pulses, but spark is still on)
Turn key to START, still holding down gas pedal
Engine should just crank and not start or even fire, because there is no fuel

If engine starts then you may indeed have leaking injectors, but could still be a computer issue
To have ALL 4 injectors leaking at the same time would be very very long odds
And all 4 would have to be leaking for all 4 spark plug tips to be black.....................one would be blacker than the others if one injector was leaking
1996 runs sequential fuel injection

So it has to be something common to all cylinders
Fuel pressure regulator was a good guess
Maybe ECT
And of course computer

Huge thanks Ron, good stuff

No, sorry, was running fine before and after timing belt change. the smoke came months later, but the truck only gets driven around the property or down the street. It sits a lot.

There is quite a bit of fuel in oil but I just discovered it, may have been this way for a while. Needs a compression test first.

I will test the fuel pressure and try your method for clearing fuel.

I will read up on ECT now, thanks again!

Also replaced PCV and 4 passenger side plugs, been running ethanol free fuel for couple years.

 

[gkoenig]

More info, truck has 283k miles, 175lbs compression on each cylinder, 35lbs fuel pressure while running, immediately drops to 25 when I kill it, then to 18 or so after 10 mins.
Replaced temp sensor, no luck, still smoking.
The clean out procedure, pedal floored, will not make it start, no signs of ignition.
I found that it will smoke until the engine reaches operating temp then after idling higher for a minute something with trigger, the idle will drop slightly and start rough idling and then start smoking heavily. I can then rev up the engine to presumably get it over a heat threshold and it will idle clean for a minute then soimething triggers again and starts blowing smoke. It runs well when driving, sluggish but well, no apparent smoke or missing or stumbling.
If I unplug the idle air controller it will not start.
I removed both O2 sensors and will try the upstream next.
The MAF seems clean to the naked eye.
I did not get a chance to pull codes, the light is burned out.
Replaced engine oil.

 

[gkoenig]

I replaced the IAC, no change. t
I started messing with the MAF sensor, if I unplug it while its running nothing will change, literally does not make even the slightest of difference on idle. I can also plug the intake hole with my finger and it changes nothing. the elements look fine, clean etc. soaked it with alcohol for a bit.
I need to pull codes for sure but thinking MAF next. EGR perhaps stuck open.

 

[RonD]

Good testing and info

Bluetooth OBD2 reader is under $15(ELM327)
Needs your smartphone as the display, APPs are free or $5
(works on any vehicle 1996 thru 2023 and on, OBD2 required by law)

If possible hook up OBD2 reader and watch LIVE DATA from the computer when engine is running cold and then after warm up
Pay attention to STFT(short term fuel trim) and LTFT(long term fuel trim)

STFT is what computer is using at that exact moment, it changes fast like O2 sensor
LTFT is what computer "remembers" from last few drive cycles, an average of STFT over time so computer doesn't have to re-learn the engine systems at each start up

Could be the computer has "lost its mind", lol
Computer runs air/fuel mix from pre-set tables stored in memory(factory tables)
Only after warm up does the computer calculate air/fuel mix "on the fly", and if this is when problem comes up.............

 

[gkoenig]

Good news, it was the MAF sensor, cleaned up immediately upon startup. Smooth idle and no smoke. Good for another 100k. It must have been the circuit board as the elements were intact and clean. Thanks for the help.
I did bring my laptop with FORSCAN and cable this time so will pull codes for fun.
$40 Amazon/Chinese MAF