o5 RAM 128k 2 wheel drive, 4.7. The idle will be very erratic at cold starts almost every time, like a vacuum leak, but can't track down anything leaking. It almost always is high at cold startup until I put into D or R, and frequently when putting into park after driving after full warm up.. its always worse in warmer weather

After doing a search I have changed plugs, EGR, PCV, IAC sensor, cleaned throttle body but still does it. I gave up and got a diagnostic from the dealer of the PCM being bad. I am not really buying that its bad, anyone have any thoughts on this?

 

I have seen a lot of Dodge 4.7 blown heads, and or knocking crank at 75000 to 100000. I didn't see very many 318 with that low of mileage bad. I for one am a little scared of them. Hopeful Dodge will make improvements on it. I was told at the Dodge garage the 4.7 is a 243 block that Dodge had out back in the 60's and 70's It wasn't a great engine then.

You might check the plugs on the PCM I have seen the corroded, if so clean them and apply a apply a small amount of dielectric grease befor putting electrical plugs back on.

Di-electric Grease, is Translucent, -70 to 400 Degree F, Flash Point Less Than 20 F, Silicone Base, Non-Curing Silicone Paste, Specific Gravity 0.646, Non-curing silicone compound, For Electrical Sealing, Lubricating, Protecting and Insulating, Standards Meets FDA Regulation CFR 21-175.300 and CFR 21-178.3570

Some auto parts stores call it spark plug boot grease.

 

Josh, check the exhaust manifold for broken bolts/leaks before conceding on the PCM. I suppose a bad PCM could cause your issue, but the exhaust manifold leak can as well and is MUCH more common.

Worked on more than a couple of these. Mileage isn't the big factor with the 4.7, I've seen the heads blow at 35k miles, I've also personally been in two vehicles with this engine with over 200,000 miles on them and no head/gasket issues.

The inherent problem with this engine is the head gasket/heads do NOT hold up well to an overheat situation AT ALL. Get it just a little hot and you're probably looking at head work, head gasket if you're VERY lucky.
The 4.7-liter is in danger of cracking a head if the driver continues to drive it when the engine is running in excess of 250 degrees A diagnostic of the radiator, thermostat, water pump and gauge should been done at the first sign of overheating and will pinpoint the problem. 250* is NOT commonly considered a major over-heat BUT IT IS in this engine, so there is just not much room for error here!
Engine failure is caused in the 4.7-liter engine with such a mild over-heat because it has abnormally thin engine block walls. The thin walls cause excessive heat buildup. The OTHER PROBLEM these thin walls that allow heat buildup cause is that if you run the truck with weak anti-freeze and allow it to run at about 235 degrees, over a relatively short period of time it causes oil to become gummy. Continued operation over time will cause the heads to crack. Only strictly following the factory recommended maintenance schedule can minimize the exposure to heat related engine failure!!! I would strongly suggest the use of a synthetic oil or at least a high mileage oil along with changing the PCV valve MORE often than the manufacturer recommends.

But aside from an overheat, whether caused by a cooling system failure or a lack of maintenance, I haven't really seen where this engine is any more susceptible to failure than any of the venerable LA series engines (LA318, LA340, LA360) that preceded it, which WERE 1960s designs. It's downfall is that it simply requires a MUCH HIGHER level of care. Unlike the 318, 360 or even the Hemi, which seem to last just fine with even marginal care, this is NOT a good engine purchase for someone who slacks on maintenance.

The 4.7 (287 CI) engine was actually the first V8 completely designed from the bottom up by Daimler/Chrysler and actually shares most of it's roots with Mercedes engines. Almost all of the engineering and design was done in Germany. With the exception of the 2.5 I4 & the 4.0 I6, which were AMC engines, this was the first engine NOT designed at Mack Avanue (the Chrysler engine complex in Detroit, MI) in decades...

 

Hey guys, I only have a little time to make another quick note. Thanks for the replies, but I have changed the plugs last week and the engine does make a tick tick tick that just started until it warms up. I have never had ANY cooling issues, the things runs great in that area. Oh, I do use synthetic oil

 

If your only experiencing this issue AFTER the plug change, I have to ask if you gapped them or just stuck them in? Are you sure they are all in snug?

 

This was going on WAY before the plug change. In fact, I think they were the original plugs, they had hardly any tip left on them at all! Never seen anything like it. I figured they changed it at the dealer at 70k when I bought it..aparently not

 

Dealers are cheap!

The question remains though if you set the gap yourself?

 

It is either a leak at the exhaust manifold that seals after it heats and swells or the timing chain tensioners which I have read is a common, but not fatal issue.

As for durability, a friend of mine owns a 97 1500. It was a 5.2L (318). He overheated it a couple of times and blew the head gaskets. I replaced them. It later overheated again, cooked the motor this time. I installed a junkyard 5.9L and drove the truck enough to figure out that around town, it ran cool. On the highway, the temp would continue to creep up and up.
I made him buy a radiator before I would release the truck back to him. Never had a bit of trouble since.

Any engine will eventually fail if repeatedly abused. The 4.7L just just a little more fragile than most in the overheating department.

 

Sorry for the late reply guys..I had PRK lasik done last Sat and holy hell it hurt way more than they said it would. Today is the first day I can actually see the screen.

The plugs came pre-gapped at Oreilly at .40 and I checked one in the box to be certain. I am pretty sure they are in tight. The overheating has never been an issue in my truck, its never even gotten over the halfway point that I remember.

The idle issue is still kicking my rear. I replaced the plastic intake crap with a straight aluminum CAI mainly to rid the clutter so I can find the possible vacuum leak but it still does it.

I will check the connections at the computer tomorrow now that I can actually see and its easier to get at. How exactly can an exhaust leak cause erratic idle? Which side is it common for the manifold to be loose on?

 

It seems like the passenger side manifold seems to have issues more than the driver side for some reason. Look for signs of carbon around a port from a leak and for broken bolts/studs.

As for locating a vacuum leak, I use an unlit propane touch and go around the intake, throttlebody, to see if the idle changes. If so, you have found your leak.
I am guessing you gave unhooked the battery for awhile to reset the PCM so it can relearn driving habits? While it is unhooked, remove each of the plugs on the pcm under the hood ans look for any loose pins or corrosion.