3.0 cold run issues.

[98ranger2023]

I have a 1998 ranger 4x4 3.0. Runs fine with warm weather. Once its cold sometimes it will start and idle rough. The rpms will bounce. If you put it in gear it will die or not move. Try to press the accelerator and rpms really bounce. Once the vehicle warms up it stops. Sometimes if you shut it off and restart it problem goes away. It does have new iacv, pcv valve and 02 sensors since i bought it. Only code it has shown was 02 sensor when i bought it a few months ago. No issues until it got cold. Any help on where to look at possible causes are greatly appreciated. Thanks i also have cleaned the MAF and throttle body. Egr valve also looked good.

 

[RonD]

Welcome to TRS

Gasoline engines need to be Choked when cold, colder it is the more "choke" is needed, fuel injection doesn't change that

Gasoline can not be ignited with a spark, yes the movie guys take liberties with that FACT, lol
Only gasoline VAPOR can be ignited by a spark
You know how gasoline really stinks in the summer, but you can barely smell it in winter, that's the VAPOR

Choke in this application means Richer fuel mix and higher idle
With a Carb you just needed a Choke Plate to restrict air flow into the top of the carb so more fuel was sucked out of the Jets, richer mix and a cam for idle screw, higher idle
Gasoline engine cylinders need 30% VAPOR to start
The colder the engine and gasoline, the more gas you need to add, if cold gasoline is 15% vapor then you need at least twice as much for start up

Fuel injection systems all have an ECT(engine coolant temp) sensor, added just for this purpose, 2 wire 5volt sensor, not to be confused with 12volt Temp sender used for dash board temp gauge, which has been around since the 1930's, lol
ECT sensor's temp reading tells the computer how much Choke is needed

So what you describe is possibly a failing ECT sensor, if it was bad(or unplugged) it would set a code, just failing it may show 60degF on cold start when its actually 40degF, so not enough choke, stumbling start and idle, but OK after warm up

The temp SENDER will have a red/white wire, and maybe a black/white wire
ECT sender a grey/red wire and a green/red wire
Both may have 2 wires in 1998, senders just had 1 wire until mid-1990s and the start of plastic engine parts, no grounds
Both are located at top front of 3.0l engine, usually near thermostat housing

 

[rusty ol ranger]

@RonD

The ECT should toss a code though right?

 

[98ranger2023]

Ill buy both. There $70 together. My innova 5610 shows no codes. Ill check the ect temp once i get home. If that dont fix it i guess i can have it diagnosed and fix whatever the issue is.

 

[Uncle Gump]

98 is OBDII.

You should be able to see ECT values in a data list with your scanner.

 

[RonD]

+1 on OBD2 reader, you can see what computer sees from any sensor, would be good to have a look at ECT, and IAT sensor temps before cold start

And ECT issue is just a guess from description of the symptoms

ECT sensor will set a code if its not passing the 5volts thru it, broken sensor or unplugged
And it will set a code if voltage is not changing after engine is started, not showing warmer temp
And it will set a code if its not getting above 150degF

But if its showing the wrong cold temp at startup, but shows good warm up, no code

IAT(intake air temp) sensor uses the same scale, but doesn't have as much "weight" in fuel calculations as the ECT

All the sensors share a 5volt power supply in the computer
Each sensor has a wire back to computer with return voltage

ECT(and IAT) get 5volts, and if its 30degF out they send back 4volts
As the ECT warms up the voltage starts to go down, at 150degF its about 1volt, 0.75-0.50volt from ECT is operating temp, 185-195degF

 

[98ranger2023]

Once up to temp when i got home it was 199 degrees. I did get a ccodejust now for B1352 ignition key circuit fault. Have never had this code.

 

[RonD]

B codes are Body codes
Generated by GEM module in 1995-2003 Rangers
In a Ranger it can mean the "Key in Ignition" circuit is no longer showing a ground at GEM when key is in ignition
This system activates the Chime if you open drivers door with "Key in Ignition", to prevent people locking their key in the vehicle
Do you still get that Chime?
B codes can't effect engine operation

199degF reads high, expected is 180-185degF, they tend to read low
Need to check it when stone cold, if its scale has shifted 10deg up then wrong choke setting when cold

 

[98ranger2023]

Yes, i do still have the chime. Nothing noticeably different. Ill iinvestigatethat too this weekend.

 

[98ranger2023]

Well the sensor/ sender are both replaced. Temp when warm up was 185-190. Idle was 1200 now is 850-900. Stft and ltft are slightly closser together than before. If this dont fix it. Could the egr pressure feedback sensor cause this issue? Egr valve itself works fine. Not cold enough right now to see if it happens. Supposed to be warm for a few days. Its only happened under 32*F.