It happens both cold and warm.

Also, I just put a new upstream O2 sensor (NGK) in there 2 months ago.

I did a compression test about 6 months ago and 170 across the board except one was at 135 and one was at 155 (#3 and #5 respectively). According to Dodge, this is within spec (within 40 psi) so I was not too worried.

Is this enough of a difference to cause what feels like a slight intermittent miss at idle?

I suspect it might be the common crack in the head between valves.

It never loses coolant, but I can't seem to burp the coolant system. I have parked on a hill and burped it hot, but it still gurgles the first time I step on the gas after firing it up. This has gone on for a couple months now. As far as I know this is unrelated to my miss. I had the miss before I had air in the cooling system.

 

Try this:

Start the truck, let it warm up, and settle down. Get yourself a spray bottle, like for glass cleaner, or something similar, (something that puts out a mist-like spray pattern, but, just have water in it.....) spray your plug wires down. See what happens. (this is best done when it is getting dark out... or, IS dark out. You can SEE the light show if the wires are arcing.)

 

Ah yes, I think I have heard of that trick before, but never tried it.

I will give it a go this weekend.

Thanks HeyYou!

 

Chris,

Spec says ± 0.1 volt. So, when we ask, "what does the spec say" and, we compare that to the results of 0.3 volts, we need to ask to what degree is there a possibility of error in the measurement / DMM / and / or probes used? That is very close to spec and, I would hesitate on tossing it until you've verified the degree of accuracy the meter is capable of.

Now, what kind of hiccup at idle do you feel? If you had to put that into words, how would you describe the feel?

This is VERY common on these heads and, you WILL NOT lose any coolant if it's a DRY CRACK between valve seats. My old heads had this in fact. It also may be a failing lifter- same symptom. Lumpy idle and, very erratic. A failing or very worn lifter fails to hold pressure and, as a result, the valve fails to open when it should thus resulting in sporadic idling.

NOTE: I advise against the use of Champion plugs 100%. While they WERE very good, some lame person decided to save money and cut out quality on those things thus resulting in lower quality and poor performance. I recommend using nothing but NGK V-powers if your looking to run stock type plugs. Cu works fine as does Iridium- do not use platinum plugs in these motors.

I've used those, Bosch (rubbish), autolites and champs and hi performance plugs and, NGKs seemed to be the most consistent in my experience.

CM

 

You've already had lots of good suggestions. Especially worry less about Reference input and paying attention to sensor signal. That is the one that needs to stay under 5v.

It is possible you have a failing voltage regulator in the PCM, but you're not getting any codes, so I wouldn't sweat it. If the PCM thinks MAP voltage is too high, it will set a P0108.

I'd be making sure it's not an ignition issue first. The overwhelming majority of misfires, including the lighter ones that present infrequently as a hesitation or stumble and do not set a P03XX code, are ignition related. This is especially true of vehicles that still use a conventional distributor and wires.

Your compression numbers, assuming they havn't changed, are fine. Honestly, in my experience, the magnum and LA engines need to be down considerably (like, well under 100 PSI), to cause a misfire.

Do the soapy water test for spark leak first. If you see nothing there, pop the cap. If cap and rotor look OK, jerk the plugs out and examine them carefully. You may have obligatory plenum leak fouling up one or more plugs.

And while I haven't had the experience that cmckenna has with Champion plugs dropping in quality, the NGK V-power coppers he mentions or AC Delco Rapid Fire are acceptable substitutes. I would steer clear of Autolites outside of Ford applications, and I wouldn't put Bosch's in my lawnmower. I have yet to use Denso's in a Mopar.

 

Thanks for the tips guys.

HeyYou, I did the spray test, and saw no sparks or arcing. It was dark in my garage (so dark I couldn't see the wires at first), and I definitely sprayed the wires down with a fine mist of water, and saw nothing.

cmckenna and Sixtysixdeuce, I pulled the plugs (they were bosch plugs... chalk that up to my thriftyness), and they all looked pretty healthy. A nice light brown colour. The gaps were pretty good too. Supposed to be 0.035, and they were all between 0.035 and 0.040. But since I didn't find anything wrong with the wires (and since I had new NGK's sitting on my bench), I replaced them with NGK v-powers. The truck might have idled a little better, but the real test will be during my commute of the next week (lots of idling).

cmckenna, I don't think it would be a lifter as I just replaced them all and did the plenum gasket about 4 months ago (I had 1 lifter that wasn't pumping oil, I verified they all were after doing the job).

To describe my miss, it feels like it is idling fine, and then the engine will shake violently for a split second and then go back to normal. Sometimes I get two in a row, sometimes not. Some days it may only do it once while sitting at a light for 1 minute, some days it will do it 3-4 times per light. Some days it may do it only once (and I think the problem may have fixed it self). I am a commuter and spend alot of time idling. I wondered if this may be the cause, but all my old plugs looked pretty good after pulling them.

Sixtysixdeuce, I will wait until I have driven on the new plugs for a week to see if there is a difference, then will look under the dist cap next week. The cap and rotor are only a year old, so they should be pretty good I think, shouldn't they?

When I was playing with the vacuum pump, MAP, and multi-meter, the MAP output voltage never went over 5.0 V as I cycled the MAP from 0-25 in Hg of vacuum.

FYI, checked my PCM connection (was not aware it was pins... I had more of a card connection in mind), pins looked clean, connections were tight. Found the death flash sticker on my PCM.

Also took another crack at burping my rad, I will find out if it worked tommorrow morning.

Any other suggestions besides the cap and rotor (which I will check after driving on the new plugs a little while longer)?

This miss/hiccup has been the most infuriating thing to try to diagnose.

Thanks again for all the help guys.

Cheers,
Chris