2005 Ram 1500 4.7 intermittent P0308 on cold startup only

[JustCummin]

Hey All,

I've read tons of similar scenarios to mine but nothing quite exact and wondering what to check next.

Recently purchased truck for son's first vehicle with 128k. The truck runs great after it's fired up. smooth throttle response, good power. But almost immediately after buying it truck started giving a p0308 code on cold start ups. Erased 1st one, 2nd one came on as p0300, but since then have almost all been p0308. After 2nd one I replaced #8 coil, no change, then all new spark plugs (all gapped .044), no change. Spark plugs looked relatively similar and normal. Definitely no major discoloration with #8 plug.

Then I went to compression, cylinders 2, 4, 6 at about 150, 8 is 135. Obviously still decent but something going on with 8. Listened close to valve cover, no ticking or knocking from the rocker.

Every time code hits, its between 100-350rpm. Once truck is warmed, code does not repeat until next day's cold start again.

I wouldn't think I would be seeing 135psi with a blown head gasket or broken valve seat, but who knows.

Where do the smarter minds than mine feel would be the best approach next? TIA

 

[jws123]

I would swap the valve lifters on that cylinder while the valve cover is off will give you a idea how sludged up it is. Also check the timing guides to you can see them with the cover off at 128k if the timing chains/tensioenrs have not been done its due. tipically if they have been changed the guides will be white in color another thing to check is fuel pressure can and crank sensors.

 

[JustCummin]

Will check all of those. Thanks Jws123

 

[JustCummin]

Update: pulled off valve covers, replaced all lifters. Engine had very little sludge. Replaced timing chain tension guides. Put back together, engine ran good for about 1 week then p0308 returned. Then replaced all fuel injectors, engine ran good for about 2 weeks then p0308 returned.

I guess headgasket would be next?

 

[3pedals]

good idea to get a spare pcm and tipm for troubleshooting, as they aren’t very expensive. I just had a similar issue on my ‘08 4.7 (intemittent p0302) that was worse when cold. Had a spare pcm laying around from diagnosis of a problem a few years ago, and sure enuf the pcm was the issue.

 

[Bills86e]

I was about to say to you to replace PCM. Been there, done that.

 

[JustCummin]

Thanks guys. Reliable company to order pcms from?

 

[JustCummin]

Well PCM replaced, light stayed off for about 3 days then came back with p0308, p0300 and now a p0700 and p0740 as well. So to summarize:

Coils replaced
Spark plugs replaced
Lifters replaced
Fuel injectors replaced
Timing chain tensioner replaced
Engine had very minimal sludge
PCM replaced

Each time light goes out for about 2-3 days, then cold start and light comes on. Usually it's just the p0308.

Any tips where to go next?

 

[3pedals]

Next I would check wiring. Several years ago when my truck was around 250k miles, had an issue where it would cut out over a bump (or reversing up a hill), but only when ambient temps were 90+. Long story short ended up being a broken wire in middle of main harness. It took my mechanic having his coworker drive the truck on a lift while he wiggled wires under the hood to find the issue.