I have a 1999 Ram Van 3500, Roadtrek camper conversion (so it's heavy) with the 5.2L engine. Recently when under heavy load (e.g. loaded down and driving uphill on the freeway), the CEL will sometimes start blinking. Thankfully it's rare, but it has happened twice in the past few months. From what I've read online, a blinking CEL is BAD NEWS and is warning of potential engine damage, so it's got me a little freaked out. When I got home and hooked up my code reader, I found that no codes were stored or pending.

Google search results suggested severe misfiring as a cause of the blinking CEL, but it doesn't feel like that's happening (no noticeable power loss, etc.). After the first time this happened, I replaced the cap, rotor, plugs, and wires. The van runs great, but the blinking CEL has happened twice more after the tune-up.

At this point, if the cause is the ignition system, the only other thing I can think of is maybe the coil is borderline and struggles when the engine is under heavy load. But that seems like a stretch to me.

Any ideas what could be going on here?

 

Well, there's this similar situation that seems to have been a clogged cat.
https://dodgeforum.com/forum/dodge-r...ml#post2279741

 

Since the issue is directly related to loading the engine, yes, it is either a misfire due to a weak spark (one you might not even feel), a leaking valve, or a failing/leaking fuel injector. Your Google search was correct, in that a flashing CEL means there is sufficient raw fuel (due to a misfire) entering the catalytic converter to cause it permanent damage.

Using a scan tool that reads live data is the easiest way to diagnose this. Connect the scan tool, set it to watch live data, then go for an uphill drive to see which cylinder is misfiring.

 

Update: I've checked fuel pressure (exactly at spec) and replaced the ignition coil. I had already replaced the spark plugs, wires (following the new routing in the service bulletin), cap, and rotor. On this weekend's trip, the blinking CEL happened again a couple of times, but the last time it stayed on solid before I could pull over. Scan tool showed misfire on cylinder 3, plus pending codes for misfire on cylinder 2 and multiple cylinder misfire.

I'm at a bit of a loss here. What else could be causing this? It only happens when the van is working REALLY hard, struggling up a steep hill. But if what I've already done didn't fix it, what else could it be?

 

What spark plugs are in there?

 

Champion copper plugs

 

Last time it had a tuneup?

When my 96 2500 (truck) was doing that, it was a failing crank sensor.... under normal conditions, it worked fine, but, under heavy load, the CEL would be flashing..... It's a shot in the dark..... and not a cheap part to just throw at it.. but if you do, use ONLY a GENUINE mopar sensor.

 

Last tune up was earlier this year. Interesting what you're saying about the crank sensor. My crank sensor failed a couple of years ago while I was traveling, and was replaced by a shop in Las Vegas. No idea what brand they used.

Is there a way to check if the crank sensor is working right under heavy load? Maybe watching some kind of live data?

 

I think you would need an oscilloscope to monitor the wave form under load.

Another member here, (GDStock, hasn't been around for quite a while though) Did a test on his with an o-scope.... he was having unstable idle issues. O-scope showed that the wave form was inconsistent.... installed a new mopar crank sensor, wave form looked MUCH better, and unstable idle issues disappeared...

I was actually rather surprised by that..... I mean, the signal from the crank sensor just tells the PCM where the crank is in it's rotation, I didn't think that the strength of that signal would have any effect whatsoever on the actual spark. Color me surprised.

 

Thanks, I appreciate the clarification. The thing is, I have no issues at idle. In fact, the van still feels and sounds like it's running great, even when the CEL tells me it's misfiring.

I've got PCM Scan installed on an old laptop. I guess it's time to dig into what sort of real-time data it's able to provide.