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Alright so I got the air intake out of the way, opened the throttle, and it was too far back into the engine compartment for me to see anything. Even with a flashlight, I just couldn’t get my head at a decent angle to see down in because the hood was in t
It’s worth noting that the truck shook before any evidence of a blown plenum gasket presented itself. (including a complete lack of any warning lights including the CEL). In fact I made a thread about that issue as soon as I could once I was aware of it.
I do have a check engine light now, and have since before the plenum symptoms showed themselves, but not for as long as it shook. In my first post, I explained that the vehicle had a new ECU installed at one point because it went awry and randomly killed
At this point the only assumption I can make is that the shuddering issue is somehow related to my blown plenum gasket discussed in my other thread. I believe its possible that the engine only acts up while under load, and this is why it didn’t shake in neutral or on stands. Also I hauled a relatively heavy wooden picnic table for a friend the other day (it didn’t quite fit into his Prius lol) and the truck didn’t shudder at all the whole time it was carrying the weight.
Yes we have, since going that speed isn’t a problem, but maintaining it for a few seconds is. I also had the rear end on jack stands and it was still doing it. I read on a Jeep forum that someone with a close in year Grand Cherokee with the exact same symptoms as me, and their transfer case ended up being the issue. Both being Chrysler products, (and the transfer cases possibly being the same?) I’m a little bit suspicious of that still. Thanks again for all the help.
Interesting point, I hadn’t considered a resonance problem since we eliminated “death wobble” as a cause. As my physics education reminds me, resonance is a particular pain in the neck to fix when it’s causing a problem. Even a nearly immeasurable shift in any of the rotating parts off center could cause this. I’ll inspect the drive shaft and all u-joints along it tomorrow and look for anything out of order.
I also have a new development: You can’t shift the transfer case into 4L. You can move it from 2WD into Neutal and 4H, and back to 2WD, and they all engage. Regardless of the transmission being in P, D, R, N, or low range, trying to shift into 4L just grinds. Conventional wisdom says that this is probably related. This would suggest to me that there is a gear or clutch in there which isn’t disengaged, and should be. And since the truck wouldn’t be going anywhere near 45 to 60 in 4L, it isn’t playing nicely with those speeds, and may resonate with another part when they are maintained. I can go exactly 30 or 35, or anything under that, all day long any day of the week, and it vibrates as much as a car with a quarter of the mileage.
All signs lead to the engine being fine because it only shudders when maintaining certain speeds. You can rev the engine all you want, whether while moving or not, and it doesn’t shake one bit. I nearly redlined it accelerating from 20 up to 70 and it’s as smooth as you could ask for. I haven’t actually floored it from a full stop before though.
The transmission stuff I added helped a bit, but not as much as I was hoping. I have definitely pinpointed the shuddering as a transmission or transfer case issue though, because when it happens, the 4WD lever oscillates. I unfortunately have nothing else to report.
I’ll get the trans fluid changed when I can, and hopefully it stops then. If not, I’ll have to assume its the transfer case. I guess I could try driving it in 4WD, and see if any new problems make themselves known, which would narrow it down. The 4WD hasn’t been used in a couple years, so I wouldn’t know if there was something wrong with it.
That would deeply sadden me, even more than my dad, and it’s his. I learned to drive on this thing and I’m going to inherit it soon as it stands. I picked up a bottle of injector cleaner, which definitely helped the engine performance a bit, it was sputtering and pinging occasionally, and that’s now fixed. It’s worth mentioning that it also seems to have stopped burning oil. I put in 2 quarts a little over a week ago and it’s all there, and is the right color. I also got a bottle of high mileage transmission treatment, which I just got done applying. Unfortunately I can’t drive it anymore until tomorrow, but by Thursday at the latest I should be able to let you know if that had any effect. In any case, I’m going to drive it until it falls apart.
Yeah, I know. But I figured what the heck, its cheaper than actually having a full tune-up done (which is is very much due for, but funds prohibit it) so it’s worth the possible savings to try it out. I don’t feel qualified enough or comfortable with doing it myself, or I’d happily save the money that way.
The plot thickens… I wasn’t told until now, but yesterday my mother was driving the truck on the freeway at 65 with cruise control. While going up a fairly large hill, it kicked down and revved up to about 3000 like normal… then it kicked down again, with a very rough jolt, revved almost to redline (5k) and the CEL began flashing. After turning the cruise control off, the CEL stayed on but she drove the rest of the way at the same speed and no problems happened. Oil and trans oil are both fine.