Why does my truck sound like a diesel under load?

[RonD]

Yes, no CKP signal would cause a "no start", but loose or out of position CKP would cause advanced or retarded timing.

O2 sensors are not used until engine warms up, computer uses rich mix based on MAF data and TPS data from a table in memory.

 

[cp2295]

Okay I know the ckp is right, I'll double check with a timing gun. And I'll see if the o2 sensor is working right, shouldn't it be in open loop on startup?

 

[RonD]

Yes, open loop on startup.
If engine is cold it will stay in open loop for 5 to 10 minutes.
If engine is warm it will stay in open loop for 1 to 2 minutes.

 

[cp2295]

Okay what if it goes Into closed loop really quickly or stays in open loop, what would that mean?

 

[RonD]

Closed loops main requirement is that the engine is warmed up, ECT sensor has low ohms.
Once that happens there is a timer that is 60-120 seconds that starts, when done O2 sensors are looked at to see if they are working.
O2 sensors can't work if they are under 650degF, most are heated now but that can't even come close to 650degF, so they rely on exhaust gas temp to bring them up above 650degF, the heaters just allow them to get there faster, which is what the timer is for.
When ECT hits a specific "warmness" the timer starts, so cold start or warm start there is still a delay.
All the other sensors are also tested for connection and "sanity"(data coming in makes sense).
If all is well then closed loop starts.

When computer starts, engine running, there is also a general timer that runs in open loop, closed loop turns off this timer.
If timer expires the CEL will come on, this indicates Open loop is lasting too long, general code for this is p0125, this timer is usually 10-15minutes of engine operation, allowing plenty of time to warm up.


If it goes into Closed Loop right away then computer is broken.
You can put computer into open loop by unplug a main sensor, like the MAF, but as far as I know there is nothing you can do to force a closed loop.

 

[cp2295]

Okay does it really matter if it stays in closed loop at startup? Truck runs fine at startup idles high like it should and then lowers once it warms up a bit, I'm gonna check it's loop status..

 

[RonD]

If idle is high and then comes down as engine warms up it means ECT is working, IAC valve is working and computer is in open loop, it is running pre-set fuel/air mix during this time from data tables in it's memory.

Closed loop just means computer is not running pre-set parameters, it is relying on sensors, like the O2's, to set fuel mix ratios in real time.

 

[cp2295]

Okay cool my iac valve is not very good I think. It's autozone POS, takes forever for the idle to go down and sometimes when I get off the freeway it stays at 1500 rpms for 30 seconds.. Pretty much until I come to a stop then it slowly lowers to 750. It's pretty new couple months but I've noticed that ever since I bought it, makes the idle come down way slower. Gonna return it and buy a motorcraft one off rockauto, $63

And out of curiousity does the computer add more fuel by just holding the injectors open longer?

And if I accidentally wired the o2 sensors wrong would it just blow out a fuse or not show any voltage? They show voltage just fine and I got no codes.

How can I test the egr valve?

 

[RonD]

If you are getting O2 voltage between .1 and .9volts then O2 is working, .4/.5 is the sweet spot of good exhaust.

Yes, computer will set a code if O2 isn't changing or is changing too slow.

Yes, computer extends the dwell of the injectors, opens them longer, when you want to increase and maintain higher RPMs, or to run rich like on a cold engine.
The Cam Position Sensor(CPS) is used for sequential fuel injection(injector sprays fuel only when its intake valve is opening), without a good CPS signal computer will run injectors in Batch Fire mode, Batch Fire on a V6 opens 3 injectors each time, this keeps intake full of fuel vapor, wastes fuel when compared to sequential, but still better than carb system.

With engine idling put a longer vacuum line on EGR valves vacuum port, suck on the vacuum line to open EGR valve, engine should start to stumble and can die if you hold it open long enough.

 

[cp2295]

I did the egr test and the engine starting dying, I couldn't make it die but whatever it was a tiny line anyways. My o2s bounce around from .1-.9 sometimes going to .08.. What should my mass air flow be reading? At idle it's at .59 lb/min, at 2500 rpms (in neutral) it's at 1.71 lbs/min. Sound right?

 

[adsm08]

Don't remember what year your 4.0l is but EGR system usually monitors engine vacuum with a MAP sensor built into the DPFE sensor.
The vacuum tells computer the load and it opens EGR valve accordingly so leaky vacuum line in the EGR system would either throw off the load reading or not open EGR valve enough.

That setup is specific to the Explorer 4.0 SOHC. The Rangers didn't use a MAP sensor after about 1992. They had a 5-wire MAF with integrated BARO sensor.

 

[cp2295]

Mines a 4 wire maf sensor. And it's a weird because my fuel trims for long term are around 15-20% but every time I check the short term they're always around 0-5%. I never see it even close to 20, so whys the long term up there? And that noise I've figured out is replicated every time I give it a good amount of throttle then push in the clutch. It'll do it for a half second (just really quick). So I don't think it's ping.. Just some sort of rattle

 

[cp2295]

I can get it to do it in neutral sometimes too and the clutch, slave, and throw out bearing are all new so can't be that

Belt tensioner?