2.3L ('83-'97) ‘94 2.3L starts and then stalls.

[ororion]

Truck will stall immediately after starting. Unless I unplug MAF. Then it will run solid for a minute or two…until idle goes rough and then stalls out. Looking for advice.
—
Current Knowns:

*KOEO Code Pass from Ford OBD1 scanner.
*Engine smells like burnt rubber when trying to start, not like gas.

FUEL:
*KOEO fuel pressure is 35psi
*KOER (MAF unplugged) is 29psi
*No leaks visible
-New Fuel Filter
-New Fuel Pressure Regulator
-Fuel Injectors clicking when running (MAF UNPLUGGED)
-Fuel injectors each getting 12v KOEO
>WHAT CONTROLS INJECTOR TIMING?
>BAD INJECTORS?
>BAD PCM?
>BAD FUEL PUMP? - pressure seems like it's in spec...
>BAD GAS OR WATER IN TANK?

AIR:
*System is air-tight. all vacuum tubes are good. no change in idle when spraying starter fluid around manifold seals...
-New Air Filter.
-MAF replaced. Wiring to PCM has continuity.
-IAC replaced.
-TPS voltage readings meet spec
-PCV is good

SPARK:
*has spark (test with jumper ground to battery, crank engine)
-new Wires
-new Spark Plugs
-new Crankshaft Position Sensor
-new CKP tone-ring
>IGNITION COILS?
>IGNITION CONTROL MODULE?

EXHAUST:
-no difference when disconnected pre-cat or 02 unplugged
-no difference with EGR disconnected

Electrical:
-PCM - No damage or corrosion to box. No signs of damage internally.
-All Fuses good
-EEC and Fuel Pump relays work great
-New ground wires - 1) from battery neg to frame 2) from battery neg to engine
>IGNITION SWITCH SOMEHOW RESPONSIBLE?

ENGINE:
*compression is a pass according to Haynes manual
1) 171 psi
2) 185 psi
3) 155 psi
4) 165 psi
-no leaks
-timing belt on time.
>CAN KNOCK SENSOR CAUSE STALL?
>COULD THIS BE VALVE RELATED?

Other:
-clutch good
-clutch Master Cylinder replaced

--
What could it be?

 

[franklin2]

The computer doesn't even look at the O2 sensor when the engine is cold.

The knock sensor just trims the timing a little bit

The ECM grounds the injectors to fire them

The bad gas/water in gas is a interesting and plausible theory.

Once you unplug the MAF and get it running, can you keep it running by spraying starting fluid or brake cleaner in the engine?

 

[ororion]

Yeah, I don’t think it’s O2. Just trying to think of everything, and keeping notes as I go

Wasn’t sure to what extent a Knock Sensor could adjust. if it could cause a stall even.

Yes, PCM grounds injectors to fire, but based off of what timing? Exact match as spark from ICM?

The problem with the water in gas theory is… idk why it would suddenly fire with MAF unplugged. I’ve added injector cleaner and noticed no difference. Got me to work and almost back a few weeks ago. Then it stalled out on the highway.

I haven’t tried keeping it alive with starter fluid, that is something I will definitely test.

-

at this point I’m leaning heaviest towards bad injectors or ICM.

 

[RonD]

Also watch the CEL(check engine light)

CEL comes on when key is turned on to tell you the Computer has booted up OK
When you crank the engine CEL will go OFF which tells you computer is getting a valid timing pulse from crank sensor, in 1994 via the ICM(ignition control module)
If CEL comes on just BEFORE engine stalls that could mean loss of timing signal

In a 1994 2.3l the ICM runs the spark system independent of the computer
Although once engine has started computer does change spark advance, similar to vacuum advance on older systems, so base spark timing is 10deg BTDC after start up it will go to 20deg BTDC which is normal

Crank sensor failure should set a code and usually they fail outright, stop working at all, so no restarts
ICM failure is known issue and has several modes which do not set codes
You could put a timing light on spark plug wire and see if spark stops first, which causes the stall, use passenger side spark plug wire only for that


Unplugging the MAF sensor puts computer into permanent Open Loop, so it only uses tables in memory for air/fuel mix, no calculations
Might also change spark advance to ICM, don't know

You can disable spark, unplug coil packs
Crank engine over a few times and pull out any easy to get at spark plug
Tip should be WET with fuel if timing pulse is seen at computer
Light it with a match/lighter, should burn fast and bright, if so fuel is OK, if not "it ain't fuel", lol

 

[ororion]

RonD replied to my post!!!


CEL turns on with Key On
CEL turns off during Crank
CEL turns on 1-2 seconds after stall


Disabled spark like you described, plugs 2/3 (the easy ones to pull) seem wet, smell fuel-ish, don’t appear to ignite from lighter. Seem fishy?


Let it run at open loop.
New symptom, there is a loud clicking coming from somewhere… high frequency. Moves with idle.
It wanted to die before I got out of car, so I played with throttle for a minute and then it stabilized again. A minute later it starts wanting to die again, I do the same thing and it stabilizes again.

Also starts with MAF and Intake coil unplugged. Idle slightly increases when I plugged the intake side coil back in, not a lot of change outside of that.

 

[RonD]

Well gasoline is very flammable above 50degF, lots of vapor to burn, so yes seems fishy

Not the computer if CEL didn't come back on until after the engine stalled

The 2.3l SOHC Lima engine ran just fine from 1974 to 1988 on 4 spark plugs, so no surprise on its running OK with intake side coil pack unplugged
The Dual spark plugs adds more power, but 4 valves per cylinder adds even more power so better use of head space in the next generation 4cylinders

But it does mean the 4 spark plugs on exhaust side and their coil pack are working OK

Just a heads up
The 1994 PCM has 3 capacitors that will fail and leak after 20+ years, and they effect Fuel pump and fuel system in general, causes odd issues

The blue capacitors in this picture: http://www.auto-diagnostics.info/ford_eec_iv

If you can pull out the PCM and have a look, its free, it would eliminate one possibility before looking at the ICM
Under $5 to replace those 3 caps, if you or a friend can solder

Had to do this in my 1994 4.0l PCM 2+ years ago

 

[ororion]

Well gasoline is very flammable above 50degF, lots of vapor to burn, so yes seems fishy

Not the computer if CEL didn't come back on until after the engine stalled

The 2.3l SOHC Lima engine ran just fine from 1974 to 1988 on 4 spark plugs, so no surprise on its running OK with intake side coil pack unplugged
The Dual spark plugs adds more power, but 4 valves per cylinder adds even more power so better use of head space in the next generation 4cylinders

But it does mean the 4 spark plugs on exhaust side and their coil pack are working OK

Just a heads up
The 1994 PCM has 3 capacitors that will fail and leak after 20+ years, and they effect Fuel pump and fuel system in general, causes odd issues

The blue capacitors in this picture: http://www.auto-diagnostics.info/ford_eec_iv

If you can pull out the PCM and have a look, its free, it would eliminate one possibility before looking at the ICM
Under $5 to replace those 3 caps, if you or a friend can solder

Had to do this in my 1994 4.0l PCM 2+ years ago

It was a high of 47degrees today, so maybe that’s out. I’ll try again when warmer out.

Thank you for the advice on PCM! I will put that on the list! That wiring info is exactly something I’ve been looking for!

 

[ororion]

My apologies for the wait! I ended up buying a new car because I had 3 break down in the same week! Crazy!!

-

Once I was ready to work on my truck again, I decided I wasn't getting anywhere playing with my old PCM.
So I bought a rebuilt part from Rockauto ($180).

Now it runs solid!

Thank you for the help everybody!

Will update if it dies again...