5.2 not running well all of a sudden
 

Hi all! Been awhile since I've posted. I've got a '95 Ram 1500 5.2, 4x4. It's always ran as smooth as any car I have. But all of a sudden, it started running rough and doesn't have full power. It literally happened overnight. I filled it up with gas, towed a trailer about 150 miles, ran great. Next morning, it idled funny, and when I went to drive away, it shuddered and shook. Feels like a misfire. But there are no codes being flashed.

So I checked the plugs (good), put new plug wires on, replaced the cap and rotor, cleaned the throttle body, checked the fuel pump pressure (good), checked the injector (had power), checked the o2 sensor, checked the TPS and the IAC sensor, and called the gas station to see if they got some bad gas (good). I put an emissions machine on the tailpipe and the hydrocarbons are off the scale. So I figured the problem must still be electrical. I then replaced the front coil, and that made it run better, but still not perfect. I'm really scratching my head on this one! Any guesses on what else this problem could be?
Thanks guys.

Running rich... so, maybe a temp sensor, maybe a failing crank sensor. Have an O'scope you can put on it, and see what coil output looks like?

How old are the o2 sensors?

You checking the O2 sensor but I would replace it. Cheap and easy.

They are two years old. Look good.

Replacing the coil is what made it run better, but it's still not running perfect yet.

That is certainly cheap and easy. But wouldn't a bad O2 sensor throw a code?

I had one that was bad and didn't throw a code for a long time (that's a whole long story in itself). What brand sensor is in it?

You can test the O2 sensors by simply unplugging them. If the engine runs better, sensors are bad, if it still runs the same, your problem is elsewhere.

Not necessarily. I had put in a bwd sensor and it worked a couple years then acted funny. Never got a code. Replaced it with ntk oem. These trucks have very broad parameters and rarely throw codes for anything. Only one I ever had was for speed sensor. I'm at 238k.

I'll have to look tomorrow. I dropped it off at a shop.

I will try that tomorrow. Thanks.

Good to know. Thank you.

Well, got the truck back. I'm not sure what led to what, but it appears by crank position sensor is bad. But, it's replaced and the truck still runs rough at idle and feels a bit weak. The mechanic put a compression gauge on each cylinder and found all were at 100 psi except for cylinder 3 and cylinder 5. They came out 25 and 55. So, it appears that is the problem, but I don't know why bad compression would literally happen overnight....?
And what's next? Move to a thicker oil and see if helps, or is this engine done?

Do a wet test as well. If pressure comes up significantly, that's rings. If it does not, its likely valves.

Also, keep in mind, 100 is the MINIMUM spec for compression, so, the engine is marginal even without taking into consideration two dead cylinders.

Leak down test is next for sure. If it turns out to be the rings, can I just put new rings in or is it new engine time? What about trying some RESTORE in it?

Also, since all the bad cylinders are on one side, could this be a bad head gasket letting air past?

Could be rings, head gasket, or even valves. You aren't going to find a 'fix in a bottle'....... maybe if you had been using it for the last couple years, it would help, but, I suspect it's too late now. (if rings are even the problem.) You might be able to get away with re-ring job. (assuming that is actually the problem.) but, need to check cylinder bores for out of round, and taper. If they are too far out of spec, just doing rings won't help.

So here's an update on the situation. The wet compression test didn't change the reading much, so we are thinking it's valves. Took the valve cover off and there are no bad valve springs, pushrods all look good and move freely and with full travel. So it looks like the low compression is due to worn valves. My mechanic thinks I should just buy a used engine with lower miles and drop it in rather than tear this engine apart to do new valves. What would you do?
I think the engine is worth new valves. This engine has been pretty babied. I've run full synthetic oil and premium filters in it since day one. I did 3,000 mile intervals until last year when I decided to go to 5,000. I've never run it low on oil, never abused it, and I've never taken it over 3,000 rpms. It ran beautifully until all this started to happen a couple weeks ago. I've always heard that these 318 Magnums are near bullet-proof, so is there sense in dumping it and getting a newer used one?

Don't bother doing anything with the stock heads, just replace them. Get NEW castings. They are thicker, and less prone to cracking. (like the stockers do...) You can pick up a pair, ready to bolt on, for around 600 bucks. Or, if you are feeling froggy, you can even upgrade to the EQ heads....... Either way, just scrap the stock heads.

Poor engine never got broke in! Never run over 3k? Never worked? Never anything but synthetic? How many miles does it have?

I have pushed mine so hard and far that it should have blown many times if it weren't built so tough. Yeah, it's wimpy, but it just keeps on going. Have to tow and hit redline a few times on these work horses. Keeps them healthy. Who lives longer? A guy who lifts weights and runs once a week or a guy who never leaves the house and just sits on the couch?

The old man from Grumpy Old Men that smoked 2 packs of Camels, had bacon for breakfast, a bacon sandwich for lunch, and drank his dinner !!

Do the valves still need to be lapped in on the new bolt-ons?
Do you have a link for them?

New. They are new. So, take 'em out of the box, bolt them on.

Check ebay sellers Odessa cylinder head, or Clearwater cylinder head.

Well I checked with three different shops today, and they all told me that if I bolt on new heads and valves, I will probably throw a rod or burn oil excessively afterwards. They all said the heads are notorious for cracking, and they said I should just find a lower mileage engine and drop it in. Seems odd that three bad exhaust valves could wipe out an otherwise a good running engine.......
Now I'm really confused. Seems odd that three bad exhaust valves could wipe out an otherwise good running engine.......

How do your cylinder walls look? Can you still see a bit of the crosshatch pattern? If so, put new heads on it, and call it a day. NUMEROUS other members have done the same, and are still driving their trucks.

How many miles do you have on your engine?

I can't see my cylinder walls. Only the valve covers have been removed.
Engine has 305,000 miles. Full synthetic oil and tofl filters changed every 3,000 miles.

Ouch. Yeah, I would be tempted just to toss in another motor.

Yep, got one on the way. It's coming out of a Ram Van. I hope it's the same engine as mine. They say it will work. I guess I'll find out!