Laughably Low Power

[AidanBotham]

Hi all, first post here but been watching for a while. My 99 ram with the Magnum 5.9 has always been a dog (it has 270k miles) but recently I went up to the mountains with 2 dirtbikes and it could barely pull itself along.

I was only at 8000 ft with 1000lbs of bikes/gear/people, and it was at 4k rpm in first gear to get up a mild paved grade at 30mph.

I just did a compression test, here they are
Passenger Bank: 138, 142, 140, 130
Driver Bank: 132, 150, 122, 118

These don't seem super great (as you would expect for mileage) but to me, they should be more than enough to haul some little dirtbikes up a hill.

Does anyone have suggestions for what to check next? Thanks guys

Probably worth noting that I do have the dealer emissions writing on my core support so it's probably been detuned. Also the spark plugs are new, and it's on its 2nd trans, but it shifts good so I don't think that's my problem.

 

[tron67j]

You could retest the 118 cylinder after putting a small amount of oil in the cylinder first. If compression goes up then worn components. But low compression on multiple cylinders is certainly taking power away. The combination of extra weight in truck, high altitude, and other factors (i.e. if you have over-sized tires, push bar on front, big tool box in bed, etc) all can explain the lack of performance. May be time for an engine rebuild and hopefully others can offer some alternatives. Good luck.

 

[Yeret]

Got the exact same year with the exact same engine. Dealt with plenty of things that hogged 'er down...

-The so-called "death flash," which pretty much every OBD2 second-gen Ram has. Not gonna go into detail as I'm pretty sure there's a thread or two around here regarding it, but a canned aftermarket tune made a BIG difference in how the engine responded.

-Clogged catalytic converter. Easy test is to pull out the upstream O2 sensor and note any difference in engine performance. If it does run stronger, your cat is scat. Problem here is if it's the original cat, the O2 sensors are probably seized in place and can be a real SOB to extract. Alternatively, just let the engine warm up, put the transmission in neutral, then rev the engine. If it won't go past 3,000 RPM no matter how much throttle you give it, the converter is backed up harder than a fiber-deficient ********.

-Going with the previous, faulty O2 sensors, mainly the upstream one, can cause the engine, once warm, to run excessively rich or excessively lean. I've never experienced this one myself, but it seems common enough to warrant mentioning.

-Blown intake plenum gasket. VERY common with second gen Rams. Read here for everything you could want to know about this problem. This particular problem will also result in fouled O2 sensors, plugged catalytic converters, and fouled spark plugs (don't even get me started on THAT one...). When I pulled mine apart, the factory gasket came out in numerous, hard pieces.

 

[zrock]

I could be wrong but i thought the spec was if there is 10% difference between holes its time for a rebuild.. Most of the holes are falling into that..

 

[1998RamMan]

Dont know if this was already mentioned, but I would check your plenum gasket if you haven't already. I know those going bad can make a negative impact on performance.