I apologize in advance for the long post....

So I got a strange situation. I have an '03 Dodge Ram 1500 Quad Cab with the 5.9L engine. About 6 months ago, the check engine light start popping on every time I'd get to a stop light. It would come on, then go off, come on 5 seconds later, go off, etc. Sometimes it would stay on the entire time until the light turned green and I started moving again. I knew I had issues already because I had been having to put about 2 qts of oil in every week and I was blowing blue smoke out the tail pipe if I really got on the accelerator. I knew I was both leaking and burning oil.

I got it checked out at a really reputable mechanic shop in town. They confirmed what I had feared: I needed a new engine. The existing engine was not able to maintain compression, valve guide seals were leaking and other leaks.

So I replaced the engine. I did my research. Found a reputable company in town who specializes in engine rebuilds. Bought a full long block from them and had this same mechanic replace the engine. That was 45 days ago.

I wasn't happy about spending $5,000 on an engine, especially at 145k miles. But whatever. That's life sometimes.

From there, everything started off fine. The mechanic shop switched out about everything you would switch out on an engine replacement with all new stuff. They put in the special break-in oil and the engine rebuilders specified that had to be changed out for regular oil at 500 miles, which I did at just about exactly 500 miles.

Everything continued fine until about 2 weeks ago. At that point, I had put on about 1,800 miles on the new engine. I went to stop one day and the check engine light came on suddenly. It went off about as soon as it came on. So I couldn't see what the issue was. And it didn't happen again for a few days.

Next time it happened, same thing. I was breaking a little quickly at a stop sign and it went off again. This time I noticed that the oil pressure gauge went down to zero for about 1 second and then came back up to full pressure, as the check engine light turned off.

This started happening more and more frequently. I drive around all day for a living. About 100-250 city miles per day. So it started occurring maybe 5 times a day. At this point, I took it back to my mechanic and had them take a look. They verified with me that the oil pressure sensor was one of the items they replaced when they switched out the engine. So that was a new part. They test drove it and it happened once during their test drive. So they checked it out at their shop and said everything looked fine. No leaks. Oil is still totally full. Sensor appears to be working well.

They said if it continues they'd have to take some mechanical oil pressure gauge and hook it up there and drive it around for a few hours to see what it measures and records. Then they'd know more. They said it could just be an "instrument cluster" issue.

So it's been increasing in frequency. Today probably happened 30 times at stop lights (just really briefly, for 1 second, when I stopped). And it started happening when I was taking a tight curve as well (momentum shifting to the left side of the truck as I went around the curve). It happened at least 3 times while going around curves today. The problem is obviously getting worse. But it never happens when I am just driving straight down the road. Only when stopping quickly or when going around a sharp curve.

Any clue as to what's happening here? Could this be a bad engine? And if so, why does it only happen in these specific conditions? Or could this be an instrument problem?

 

Same symptoms with two engines could indicate the problem lies in what wasn't replaced. Those long blocks wont come with new sensors, so it's entirely possible you've got a bad sending unit or loose connection somewhere.

Did they show you evidence of leaking valve seals and lack of compression? Was the engine running rough before you took it in? Low compression will cause other performance problems that you would notice. Leaky valve seals will cause smoky exhaust. Leaking valve seals and low compression won't cause low oil pressure, as those two areas aren't provided with high oil pressure.

 

Right. I was considering that too. Except for several things that would sort of rule that out. First, the check engine light/oil pressure situation was immediately eliminated first day I got the truck back after the new engine was installed. It went from coming on 200 times a day to zero. So that's the first indicator.....

I'm hoping that's all it is.

Yes. Definitely. Aside from the fact that I was losing oil like a sieve and their tests were showing poor compression all around, the real proof was one day when I tried to haul one of our landscape trailers down the road. This was a basic 6'x10' open ended trailer. It was an easy, flat road. And I've hauled those trailers lots of times before, no problem. The trailer only had half a ton of gravel in it; a typical load. Nothing super heavy. I've hauled that trailer with much bigger loads dozens of times over the years. But normally I do not haul a trailer around most days. Once ever few months, maybe. But this time, my truck could barely get over 30 mph and it took FOREVER to get to that speed. It was just totally gutless once I added the weight of the trailer on it. Then I tried to go up a hill - wouldn't even make it 50 feet. I just had no power. I had to pull over and call one of my crews and we moved the trailer to their truck. It was that day I realized my engine was much more far gone than I thought it was.

The low oil pressure was also related to the fact that I was constantly running out of oil. I'd put 2 qts of oil in it and several days to a week later it would be 2-3 quarts low.

The charged me for a new sending unit. But I didn't see the old one, no. So unless they're lying to me, I think the oil sending unit is new.

 

Did they change the pump and pickup with the rebuild?