fantacmet

So on my other thread some of you might know about this already, but I've done a bit more investigating while driving. While I have done the test and I do have the issue of the intake manifold pan gasket it's not real bad. Yet. This seems like transmission though. This'd **** me off as it's been this way since I got it about a month ago.

So it starts vibrating at about 45 MPH if I'm either accelerating or holding throttle pressure to maintain speed like up a hill or something. If it's holding on flat level ground it will come and go as there is load put on it and removed.

Now if I turn off the OD, it pops into the next gear and drives just DANDY no vibrations whatsoever at all at highway speeds, until I can get up to about 55 then turn OD back on and as long as I stay above 55-60 it's fine.

Now in town with the OD turned off, my oh my, it starts vibrating about 35 MPH, then I turn the OD on and it drops a gear and stops vibrating.

Here's an odd part, at about 45-50 vibrating, I turn off the OD and it stops vibrating about a second before it shifts. Then I turn it back on and it shifts and waits about 3-4 seconds before it starts vibrating again.

Also during the vibration it just seems to be a gutless wonder. Like it will barely hold onto what it's doing. The funny part is pressing on the gas doesn't really do anything, so it's not slipping. I can press it down enough to give it some punch I would think, but not enough to make it downshift and most vehicles will take a steady increase in speed. Nope not on this one, during it's vibrate mode as I've come to call it, it's just sluggish.

I shouldn't have to have the OD on in town and off on the highway to keep it from vibrating, it's like counter intuitive. The OD turns on automatically every time I start it.

Is this transmission or is this the intake gasket issue?

Later this week my ODB2 code reader, writer, and telemetry thing will show up. With a bit more work I can access the non-EPA required stuff and make changes or readings if need be so if there is anything I should be on the lookout for. The first one I'm getting is to connect to my phone and tablet, later on when I fix my laptop I'll get the PC one.

dave1123

First of all, be aware that O/D is fourth gear. You may have a damaged torque convertor. I'm not aware of what controls the lock-up as far as when it's engaged and when it's not. If the springs on the lock-up clutch are broken, they could be causing your chatter or vibration. This out of the smoke in my brain.

If you get a code 37 or a P0740, that's the torque convertor lock-up. Any P07-- code has to do with the trans.

fantacmet

The only codes I've been getting are misfire for cyl 8 misfire.

For the reader I'm thinking of real time telemetry, like injectors dumping too much or too little fuel at a given rpm, or something like that.

dave1123

Sorry, guy. I think this one is for better brains than mine.

sycoglitch

So what year grand cherokee is this and engine

fantacmet

Oh hell, sorry about that I thought I put that in the OP, I knew I was forgetting something.

98 with the 5.2.

I'm pretty sure the Cyl 8 misfire is a phantom caused by the intake gasket issue, as at no point does it really seem like it's misfiring. Running rough sometimes, but not like there's a misfire, and it only does it under load on medium hard acceleration or harder acceleration.

That's what's weird if I just power on through it the vibration isn't there, well it might be but it's so mild you don't even notice it unless you are REALLY paying attention. Same thing with lower speeds.

Any other symptoms that might narrow it down I should look for? It has quite a bit which I wouldn't know where to begin without writing 6 pages to describe it all in detail.

My scanner telemetry thingy came today, I plan to run a log on my way to work or on my way home, and then get that info to the computer if I can and post that.

freegdr

Is vibration happening at same rpms but different speeds when in different gears on tranny ?

fantacmet

Good question, and the answer is sort of complicated. That answer is sort of.

In the same RPM area but it depends on the gear and sometimes the amount of throttle you are giving it. That's how I remember it, I'll check on my way to work and post back for sure when I do in town with OD turned off.

However in a given situation(IE overdrive on or off), it happens only at said speeds when in the average gear for that speed, such as in 4th or OD when the OD is turned on, at between 45 and 55 mph). The interesting thing is, with OD turned on, it will not happen at that RPM in any other gear, though to be fair it usually shifts right before that unless I'm applying heavier throttle, but not always. That's what's so damning about this mess is finding the pattern to it, and the pattern not being consistent like same speed through every RPM range or same RPM through ever speed range, it's not there, as it won't happen in a given RPM range except in one gear, and same thing for a given speed except in one gear.

It does however only happen when under load. Not heavy load either.

fantacmet

So nothing interesting from the telemetry, at least I don't think so. Until I get a baseline for what the fuel trims should be from someone else for an FSM.

It DOES happen in a specific RPM range but ONLY when in the highest gear. So when OD is turned off, it happens about 1400-2200 RPM when in 3rd gear. However when OD is turned on I can count it in 3rd gear and go to that RPM range with the same load and it's fine, but when it's in 4th it will do it in the same RPM range. WTF?

freegdr

Have you checked u joints yet ? Under a load is when there under the most strain.

fantacmet

I'll have to get under and check. Doesn't the fact that it's at 2 different speeds that are not equal multipliers of rotational RPM on the driveshafts kind of rule it out though? I mean when it stops freezing enough for me to be able to get underneath and touch it without my fingers and face going numb before I can get to the driveline I'll check it out, or just take it to a Les Schwabs since out here they mess with it for free, and I make sure that I'm in the Garage underneath it when they are checking it out.

dave1123

A lot of shops won't let you underneath you vehicle while it's up on the lift because of insurance regs. Here in Syracuse, if you get hurt in the shop in any way, they can loose their NYS Repair Shop license.

Hoosier8

Seems to happen under load. Have you replaced your ignition cables or do you have old ones. Under load, the pressure rises and the spark has a harder time jumping the gap. If there is a carbon trail somewhere it may jump there instead of your plug giving the misfire.

dave1123

Check for carbon trailing on the outside of the plug itself. If you have coil packs, check the boot inside it.

fantacmet

I give them an ultimadem, I go in the shop and monitor or I take my business elsewhere, usually they relent, sometimes they ask me to sign a waiver which I am ok with doing. The only other two times I've taken my keys and drove off.

As for the carbon trialing, same issue before and after I did the following.

Plugs, cap, rotor, wires, TPS, IAC Valve. Seafoam in the tank to help clean out the injectors, and each of the above helped a little, pretty much in order of most help to least help there too.

The injector wiring is in good shape not burned is kept away from the hot stuff, and each injector has it's wires loomed to prevent such a happening. I have swapped around the injectors and even replaced one to ensure it's not an injector issue, and each time it's cyl 8 that is misfiring. I have done the est for the intake pan gasket and it failed, with a slight vacuum so that I'm sure isn't helping matters any, but I don't have the time or dough to take care of that right now.