A problem with my 2001 B1500 3.9 just cropped up all of a sudden a couple of weeks ago.

After starting my van stone cold it runs fine until the PCM sends it into either a closed loop or it reaches normal operating temperature.

Symptoms: rough idle, low power (20 mph max up hills floored), rough acceleration. Seems OK under cruise. Kind of feels like a misfire but no OBD II codes of courses. No stalling. Exhaust stinks but doesn't smell rich. No black smoke.

Can't tell if fuel consumption has went up. I did check it at 11 mpg around town which seems normal compared to my slant 6 and 5.7 liter Chevy van.

I replaced the distributor cap and rotor button (looked worn) and the coil.

​​​​​​I Just recently replaced the PCM (no bus error and no start). I replaced the 02 sensor a year ago. The heater was burned out causing backfiring and popping a 1 minute after a hot start.

I'm leaning towards the air intake sensor. My ELM 327 tool is saying the intake temperature is 50F hotter than ambient.

One morning it was 70F and after a cold start said the intake temperature was 77F which isn't that far off but on a 90 degree day the intake temperature is close to 150F.

That leads me to believe the computer thinks it's running hotter than it is.

Is that normal?

I'm thinking about just taking it to a shop that could diagnose this problem. Otherwise I'm just going to be throwing new parts on it until the issue goes away.

Not really sure where to start.

I had to order a shrader valve for my fuel pressure guage off Amazon. Couldn't find one in my town without buying a whole kit. I thought perhaps it could be a bad fuel pump or clogged filter but the van runs perfectly fine when cold.

This is while idling at 90F. Intake hose is connected.

 

IAT isn't the most accurate thing in the world. It's more reading the temp of the intake itself, rather than the air passing thru it. (which is also likely rather warm.)

Try unplugging the front O2 sensor, and drive like that. See if it runs any better. (this WILL set a code.)

 

MAP sensor? Doesn't always throw a code, can lead to rough hot start issues.

 

I tested that and it's going better 0 and 9 volts as I rev the engine so I think it's fine. I just replaced it about 1000 miles ago.

 

I check into this. Thanks.

 

What brand sensor did you install?

 

I can't remember. I think I bought it off eBay.

Here's a shot of the voltage reading while trying the engine up and down. Shows a higher voltage when accelerating down the road so that's normal.


Could the fuel pump motor be at fault when it gets hot? My shrader valve arrived so I could hook a pressure guage to the fuel rail.

I'm going to test the fuel pressure and see what readings I get

 

It's actually switching, but, is it accurate? The dodges are really picky about their sensors..... For the O2, NTK, or Denso sensors only. Bosch sensors *look* like they work, but, they actually don't.... and you get weird behavior. Poor performance, bad gas mileage (worse than normal...), and may even set codes.

 

I'm seriously going to change the recent Bosch O2 sensor I installed because of this.

@HeyYou is a real mechanic with stuff you can't learn in books. Thank you.

 

Something I should mention. But didn't want to confuse anybody thinking I was still running this breather on the throttle body.

I installed one of these breathers. The problem seem to have started not long after. I put the original air cleaner back on with the outside air hose connected but it didn't fix the problem.

I wonder if I cooked something from running this open breather. Thought it sounded "cool" at the time.

I have one of those 4" breathers on my 84 Dodge Slant 6 , 1 barrel and it actually runs OK if not better.

I realize fuel atomization is different between carbed and fuel injected vehicles.