Hi all, having an issue with my 2002 Dodge Ram 1500 4.7.
It runs well for 15 to 20 mins, then shuts off, so I'm think it has something to do with a sensor when it goes from open to closed loop. It runs perfect when cold, but when it's warm it shuts off, almost like you turned the key, no sputtering or anything. I can still hear the fuel pump running when this happens. I cannot restart until it cools down.
I'm getting code P0320 (Ignition/Distributor Engine Speed Input Circuit), and then recently P1299 popped up too (Manifold absolute pressure (MAP) sensor/ throttle position (TP) sensor - vacuum leak). I replaced the crankshaft position sensor with an Autozone one, no change in symptoms - check engine lights up once engine dies.
It was much cooler out today (20 deg F less), and was difficult to start the truck (extended crank). But once it started, it was misfiring. No more codes.
Any ideas on diagnosing this or where to look? Many thanks.

 

These engines absolutely HATE aftermarket sensors in critical locations. I would return the crank sensor, and put the old one back in. (as symptoms got worse with the 'new' one....) Code could also be referring to cam position sensor...... Mopar sensors only though please.

 

I would invest in a scan tool that can look at live data. I think you're onto something that your truck is fine in open loop/warmup mode, but doesn't know what to do in closed loop mode. Looking at the live data, you may be able to see something that's super wonky and go from there.

Have you smoked the system to check for vacuum leaks?

 

The original sensor was impossible to remove without damaging it. Rust created a smaller diameter hole so the sensor could not just be pulled out; the outer plastic separated from the metal and had to be removed piecemeal. I guess I have to bite the bullet and buy a genuine Mopar crankshaft sensor.
I was under the impression that the cam sensor is used in just starting the engine, and not to keep it running?

 

Right audiowize, that's what I was saying. I think something is happening going from open to closed loop, but I'm not sure what. I have monitored live data and nothing seems out of whack. I'm getting good readings for the coolant and intake air temps, fuel trims look ok, primary O2 sensors ok, engine rpm reading is constant so I was assuming the aftermarket crankshaft sensor was ok.
I have not smoked tested it yet, do you think that would be beneficial? I was thinking that code just came up as a secondary thing. It didn't want to start and was misfiring before, so I'm not sure how much good that would do.

 

The crank sensor is typically 100% required to get an engine to start. In fact whenever I try to start a modern engine that has been sitting for a long time, no spark generally points me in the direction of a failed crank sensor. The cam sensor is what the ECU uses to tell the fuel injectors and spark plugs when they need to do their thing, as the crank position sensor doesn't give enough info to determine whether a given cylinder is on the compression stroke or exhaust stroke. I have found in general with OBD equipped cars (not speaking of Dodges specifically), a good crank sensor and a bad cam sensor will throw a check engine light or store a code for you, but a bad crank sensor will not. In a V-engine, we expect to see two of these cam sensors to create some redundancy in case one fails, and even on some inline engines with DOHC, you'll see one sensor on each cam and things can still function without one sensor. Rolling the clock back a little bit to what you own, a lot of the time the cam sensor is built into the distributor and a little more sketchy.

 

Yes, I would smoke test it. If you have a serious vacuum leak, everything may look OK with the engine trying to warm up and using a bit more fuel, but when it leans out things go haywire. Smoke testing is also basically free (just costs you a cigar), and I would always suggest starting with the least expensive items first.

You mentioned that your old crank sensor was crusty, how are the connectors?

 

Cam sensor is required at startup, and is also used while engine is running to tell the PCM which injector it needs to fire next. It *can* sorta run without it.... but, it runs a lot better with it.

 

FWIW,
A couple years ago on my '05 Ram 5.7 it took a little persistence scraping rust, some Blaster, and working the crank sensor to remove without damage. I replaced it with the NAPA brand and have not had a problem since.

 

The genuine Mopar crankshaft sensor did NOT change a thing. That's $90 I'm never getting back....
Here's an update:
It started everyday this week but would shut off after about 15 mins. No misfiring.
Today, still with the old Autozone sensor in, ran for 15 mins, shut off. I then replaced the sensor with the Mopar one (engine was still somewhat warm). Started and ran for 15 mins. Throws the same P0320, when restarting it will runs for 30 secs and throw the same code again along with P1299 occasionally. "Check gauges" also comes on, rpm gauge moves crazy. Will not restart until cold.
Wires/connector "looks" good. I can hear the fuel pump run when it shuts off and can smell fuel.
I monitored the open loop/closed loop status and it only takes a few minutes for it to switch from open to closed, no changes when that happens, so that rules out my hypothesis.
So is the smoke test next? Check the cam sensor? If I unplug the cam sensor will it run, maybe getting bad info from that sensor?
Thanks for the input guys.