Chevy Uplander 3.9 hesitate when accelerating

In the morning, when i go to pick up my news paper at local convenience store, the van is running rough and hesitate when accelerating.
When i take the van 1 hous later, it will run smoothly and there will be no hesitation and i will be good for the rest of the day.

If i skip the trip to convenience store and the first thing in the morning i do a long trip, let’s say 2 hours trip, the van will run rough all the way during those 2 hours.

When the van is running rough it will stay in this state until it’s turned off, wait and restarted again.

When the van is running soothly, it will stay in this state until next morning.

While driving, it never happened that the smooth running engine became running rough and the opposite is also true. It never hapenned while driving that the rough running engine became smooth.

I suspect that at engine start up, a parameter is stored and kept in memory until the car is turned off, wait and restarted again.

DTC code P0336 and P1174

Any idea? Leaving in a cold climate in Montreal Quebec aera. Thanks

Replace your crankshaft position sensor.

The P1174 is either a O2 sensor or vacuum leak.

The codes seem to indicate a possible problem with the crank sensor and a fuel trim problem. The fuel trim problem might be caused by a faulty spark due to the crank sensor, so focus on verifying the crank sensor is working before worrying about the fuel trim problem. Crank sensors on the fritz are well known to be affected by heat.

This week end, i plugged in my osb2 scanner and i monitored the rpm sensor while the engine was running rough. I was not able to get any signal.
I was getting signal from other gauge like coolant temp, mass sensor but not from RPM.

Am i right to assume the rpm gauge in my obd2 scanner is getting the signal from crank sensor?

RPM gauge in instrument panel cluster (dashboard) was showing correct RPM. Is it related to crank sensor?

Crank sensor just got replaced. Now it always hesitate when accelerating and it always run rough at idle. Intermittent problem became constant.
CKP variation relearn procedure was not done because I don’t have a scan tool for this. Should I bring it to the shop? Can I do it without the scan tool?

Well, you’ve proved the problem is at least related to the CPS. That’s something.

hmmm … have the DTC codes changed after CPS replacement? Missing means there’s a weak or no “bang” in one or more of the cylinders, at the time in the sequence when there should be. So it pretty much has to be a problem with the spark, fuel, or the compression. Doing a fuel pressure reading and compression of all the cylinders might provide a clue, but I doubt it.

My guess it is probably still due to an ignition (spark) problem. It could be a problematic sensor inside the distributor, or on the camshaft. Or a coil or coil pack. Or a spark plug wire. Or a spark plug, etc. Hard to say. I don’t know how your vehicle’s ignition system works, there’s a range of designs out there, but somebody here would probably know once you provide the model year.

So what to do? Well, most shops have some kind of ignition system analyzer, where they can hook up probes and determine if the spark is occurring and at the right time or not, and if not, which cylinder(s) is affected.

Don’t want to do that? If the DTC code says just one cylinder is misfiring, you can swap things around from one cylinder to another, spark plugs, wires, coil packs, etc, and see if the cylinder misfire changes with the swap or not. That provides a good clue as to which part is bad. Another idea is an inexpensive gadget you can hook up in series with the spark plug wire, which flashes a light if there’s a spark or not. There’s a more expensive inductive version which works just by touching it near to the wire too.

What do you mean by CPS

I believe George means crankshaft position sensor

Not one to nitpick, but I don’t blame you for being confused, because CPS is not the acronym for that particular sensor

It’s actually CKP sensor

Let’s follow this for a moment . . . a camshaft position sensor is CMP sensor

Hopefully it’s now clear why CPS is not correct.

Now you guys can pile on me, and explain why I’m making more out of this than I should


Now you guys can pile on me, and explain why I’m making more out of this than I should

Naw, you’re just using the correct name for a specific part on a car. This prevents confusion. By adhering to standards the diagnostic and repair process is streamlined.

This is just SOP.

Yes, by CPS I meant the crank position sensor. And the experts above are correct, the correct acronym for that part is CKP.

When I have acronym trouble, here’s a site I use sometimes.

It lists this sensor both ways, under CKP, or under CPS. But CKP is the correct term.