Hi guys. I just bought this 3.0L 1998 Ranger 4x4 with manual transmission. I love the truck. There are a few issues though of course, one of which is this thing that happens sometimes when I downshift to pull a long grade. I downshift, lets say into 3rd, bringing the RPMs up to about 3500, and then SOMETIMES after a few seconds at that RPM I get this huge, obvious jolt, that feels like one of the cylinders in the engine just pre-detonated badly. That's what I imagine is happening anyways, I could be totally wrong. There is a strong jolt that no one could miss, accompanied by an audible "thud" sound. What he hell is going on there? If it is detonation I feel like if that keeps happening one of these times I'm going to bend a rod or something really bad. I haven't done seafoam yet but I was thinking about it. The truck has 183,000 miles on it. Thanks for your help.

 

You should be running the 3.0l at 3,500RPM most of the time thats its peak power range

I would check motor mounts and transmission mount

Open the hood
Set park brake or block a tire on BOTH sides
Start engine
Put in 1st gear and watch the engine as you let out the clutch a bit, it will lift up on one side but not too much
Then push in the clutch quickly and listen for a "thud" shouldn't be one

Now do the same test using Reverse

That tests engine mounts

You will have to get under the truck to check trans mount, just push on transfer case, side to side and up.

If you have an extended cab then you will have a two piece drive shaft and a carrier bearing, you will see it a foot or so behind transfer case.
Carrier bearings wear out, push on drive shaft shouldn't move side to side and rubber inside bearing case should not be cracked.
Behind carrier bearing is the Slip Joint, has a rubber sleeve over it, this can may a clunking noise if the get dry, there is a special Blue Lube to use on them, but you have to drop drive shaft


Engine could have a misfire but no clunk or thud noise

 

Thanks for those tips on checking the mounts! That is great, useful info and I will try that. However I don't think the thud/jolt is from bad mounts because the jolt happens several seconds after I have let the clutch out, after the drive train has been under load and settled back down again after the shift. I could imagine free play at the motor/transmission mounts causing an upset right when power is added or taken away, but not like several seconds (maybe 10 seconds even) after the change in torque caused by shifting. I was doing some research online and found people talking about a similar problem (that might be the same thing exactly) that had to do with a gunked-up MAF. I think I'll buy some MAF cleaner and clean that puppy out, as well as a Seafoam treatment and I'll bet that'll get rid of it. The thud/jolt only happens sometimes though too, it's not consistent at all.

 

Yes, you should clean MAF every few years
And I use seafoam in the gas tank once a year on all my fuel injected engines, does smooth out the idle noticeably on my 1994 Ranger, after 1/2 tank or so

Its better to take the possible mechanical issues off the table first then move on to the possible electronic issues, thats because the electronics are monitored and rarely break.
90% of sensors or controls that are replaced were working fine, sometimes just the act of unplugging and plugging back in the connector cleans it up enough for the device to work better, which is why "new" sensor fixed the problem, lol.

 

Huh that's interesting, and makes sense. Great advice thanks. Did I mention I love the internet? Nobody better take my Information Superhighway away