Hello everyone, I wanted to see if I could get a little advise about a truck problem that Ive been working on for the past week.

I have a 95 1500, 318, with 245,000 miles. Engine is a jasper rebuild with now probably 130k of that.

Last week, on the interstate, the truck began shuddering when it dropped into low rpms in overdrive. I was able to get it home the rest of the 15 miles or so, driving with both feet and keeping the rpms up but it would kill if I let the rpms drop. It ran rough, especially in idle, but also not great at speed.

I unplugged the battery, and left it for the night like that, next day I began trying what I knew to do.

Check the compression, mostly around 115-133, but one cylinder was about 100 (the 2nd from the front, passenger side).

Replaced plugs, wires cap and rotor.

Checked oil, not low, dark brown, kinda cruddy.

No oil in radiator.

I pulled the fuel rail because I have had clogged injectors before, shot them off with carb cleaner, there was a bit of red gas towards the rear one as if it was a little rust in there, but I sprayed everything pretty good. Theres pressure at the shrader valve, don't know how much exactly.

The truck had sat for a few weeks prior to this drive, although in made it about 140 miles on the interstate that day before the problem. Gas level is low.

Seemed like it was struggling with the air intake with the filter off...cleaned the throttle body, replaced the IAC motor - which actually might have helped the barest little bit. Looked for vacuum leaks but found nothing as of yet, that would have been one of my first guesses...never had carb cleaner work for that. If I unplug a vacuum line idle actually improves, or maybe that's because it increases the rpms.

I just did an oil change, and the oil was very dark, no water. Running a magnet through it, I did find the smallest shaving, maybe the size of a sesame seed. Maybe a few smaller shaving, half a dozen very small.

It still runs rough, not really driveable except in the barest pinch. What should I try next?

 

Getting any codes? Check engine light flashing? How's the plenum? (see stickied thread at the top of this forum....)

Sounds a LOT like an engine miss. That *should* generate some codes. You have already taken care of the obvious stuff... So, that leaves a blown plenum, (which gives you a lovely vacuum leak) or a failing sensor somewhere.

Does it run ok the first couple minutes, and then start running crappy? Or does it run crappy right away?

 

Crappy right away.

I looked down the intake when I had the throttlebody off, it looked oily, not like a puddle, but its certainly gummy....that reminds me, I replaced the pcv valve too.

I last had the intake off about 10 years ago, and I put a new gasket on the plenum...but it wasn't the aluminum upgrade pan. Would a blown plenum cause it to run like total crap, or is it just an oil loss thing? Would there be a way to confirm that its the plenum in addition to the flashlight test, something concrete...cause I'm a little unsure how much oil down there is evidence of plenum, and how much is just my neglect.

Only code I got the other day was for the IAC, when I was fiddling with it.

I kinda suspected that the rear passenger cylinder was missing, cause misting the manifold there took longer to evaporate, but it still runs the same with that plug wire disconnected.

 

The PCV system will put some in there. Best thing is to look toward the back of the intake, and see if any oil is pooling back there.

Another test would be to disable the PCV system, (disconnect and plug hoses/vacuum port) pull the oil fill cap, and start the engine. You should feel a breeze coming OUT of the fill hole. If you have vacuum there, plenum is most certainly blown.

The plenum, by itself, probably won't make it run as bad as it sounds like it is, that would more likely be a sensor problem. Cam, or crank position sensor. Can you read codes? There may be something pending, that hasn't turned on the light yet.

Also, since you have EGR, a stuck valve could cause it as well.

 

Code 12, no others.

Do I just plug the pcv vacuum for that test, or all vacuum ports?

I remember fiddling the egr long time ago, maybe thinking the tube had been plugged. All I really remember was what a bear it was to get back there.

 

Yeah, they stashed it nicely, didn't they.......

Nah, just unplug the PCV valve from the manifold, and plug that port, pull the hose off the air box, and plug the HOSE. That will leave the oil fill hole as the only inlet/outlet from the crankcase.

 

Not much of a breeze coming from the oil change fill hole, but air is obviously exiting the valve cover as I can see a light smoke emanating from the hole. If not that I couldn't tell if it were positive or negative.

 

That's actually a good sign.....

Likely a failing sensor then.

 

Is there an order I should proceed with regarding the sensors? In the alternative, should I drive around a bit when traffic is low and see if I get a code?

 

Wouldn't hurt to drive it a bit, and see what turns up. Trouble is, I don't think the 95 computers differentiate between cam and crank sensor failures. Cam sensor is certainly cheaper...... but, I suspect crank sensor is your issue. (Get them at the dealer, they actually work right, not a claim the aftermarket fellers can make.)