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About a year ago, my kids and I were on a road trip from california to missouri. When I got through SLC, Utah the truck rpms shot up to around 5000 and the temperature gauge was showing hot. I quickly got off the road at my first opportunity to check it out. This is going uphill, btw. When I couldn’t find anything, I gave the key a few turns to see if I could pull up any codes, nothing. I basically nursed the truck the rest of the way without getting on the throttle for fear of messing something up. Ever since that incident, it’s been sluggish getting up to speed, feeling like it’s not shifting when it should and causing it to hit around 3000 rpms just to get up to highway speeds (65 mph here) but even then, it’s only wanting to level out around 55-60. Took it to a transmission place, they couldnt pull up any codes. They say “its driving and shifting” fine. I disagree. Today, I had to push it to 4000 rpms just so I could get up to 55 and merge before the lane ended. And after that, it didnt want to go below 2000 rpms. It usually settles on 18-1900 rpms at 65-70 mph. This is a 2001 4.7 4×4. Can someone please help me narrow down the issues I’m having here?
If there’s no codes being thrown up then start with the obvious things first as there’s that many sensors in cars now something should have thrown a code up, check for routine service parts like air filter plugs oil filter, check EGR and DPF if its diesel, just to rule out any blockages that may be causing it before you start taking apart your engine or transmission. also if the temperature shot up double check the thermostat, I know this wouldn’t cause high idle but check its in good condition as there cheap to replace. bad timing issues would cause lower than normal MPG, burn oil, loss of performance, noisier engine especially if its got a timing chain, it may struggle to start or randomly stall, misfire, rough idling high or low or fluctuating. if its your transmission the your issues would include loud whining and clunking noises, lack or response, maybe a burning smell from overheating fluid or leaking fluid, transmission is noisier than usual in neutral. I think your car has a timing chain rather than belt so there usually isn’t a service interval for replacement but would be worth checking with a garage to see if they can check the condition of it anyway as its a costly repair if it goes wrong, if its stretched or jumped a tooth then it could cause some of these issues but not usually revving high as that. guessing its an automatic transmission, check for any common issues or see if owners are having to service parts around the same time. try taking it to another garage and get a second opinion if you still think it may be the transmission, by the sound of the symptoms your explaining I would be swaying more towards gearbox/clutch issues as this is what’s happened to me in the past and its always turned out to be them. not sure about the temperature spike though, has that only happened the once when the revs shot up that high? is the clutch slipping at all?
Check coolant system, such as the thermostat mentioned above. The thermostat wouldn’t cause high rpms directly but it will cause high internal temperatures and high engine temps can cause the motor to work extra hard to perform the way it supposed to. Check for proper compression. Check each cylinder for proper compression. Check for leaks in the air intake, air filter housing, vacuum lines, and exhaust. Check the timing. Belt/chain, spark plug gaps, distributor if you have one, possibly the trucks computer. I’ve seen cars run poorly just because the computer hadn’t been reset after a battery change. The computer was stopping the ignition sequence because it thought the battery was still bad. Reset the code and the car started up. Get a second, third, fourth opinion. Go to a Dodge certified mechanic. Pick a shop that deals with these trucks all the time. They’ll know these engines and it’s systems better then they know their wives. Good luck.
