Surging, but only under a very specific situation

[BigJ]

I've asked this on a Dakota forum but got nowhere. Thought I might try you very knowledgeable folks :)

My '98 4x4 is rock solid. The 318 is crazy strong, the 44RE tranny shifts like new, NP231 engage/disengage without a hitch, 194 front and 8-1/4 rear are golden... but...

There's this metered onramp to a freeway by my house. This onramp is a 270 degree turn, steadily elevating up to the freeway over its (the onramp's) entrance. Maybe 25feet of elevation?

Every time I take it we're moving at 2ish mph. Stop and go. Its just enough incline to keep the truck stationary when off the brake, so the lightest touch of throttle is required to get it to roll. If I apply that throttle, I can get the thing to surge like crazy. Its like the gearbox cant decide what to do and it sends the motor way up in RPM sometimes, at which time the motor catches itself and comes crashing down to an almost stall. I can get it to do this every time.

What might it be? An early indication of a problem? Again, this is the ONLY time I can get this to happen. And its easily avoided. But when its happening, its pretty violent and the truck seems to be hurting bad. Thoughts?

[DesertDog]

well if its hurting take it to a doctor.......lol

my guess is vaccum for the intake somewhere is leaking ,, even a stiky EGR valve can cause some of the slightest rapid jumps in rpm to almost a stall.. not saying its the egr but you might test it , by taking it off and cleaning it ur-self,,, not hard to do ..

and then again it could be a vaccum line itself has dry rotted and has caused this ??

back to the intake ,, i had a k2500 7.4L 4x4 suburban... that did that very issue u could'nt get it to do it any where else but going up an incline. come to find out my intake manifold had a hair line crack in it.....

so who's to say exactly there jason what it could be

but i know 1 thing i would take a different on ramp till i figured it out ....lol

[BigJ]

but i know 1 thing i would take a different on ramp till i figured it out ....lol
Haha problem solved!

I'll check the valve and all the hoses. Last time I was in there (about 2 months ago?) all looked ok, but I'll check again. Thanks!

[Tbird100636]

Hmmm... there's a few things I can think of here, not sure which you will find. First, you don't have an EGR valve, 98 and up Magnum 3.9L, 5.2L (318) and 5.9L (360) didn't have them. Second, a common issue on the old Magnum Series was the intake manifold runner cover. There's a cover on the bottom of the intake that reveals the inside for casting. The cover gasket cracks, and spits out or sucks in, and starts with high oil consumption. It gradually sucks the oil out of the engine. The worst case is when you have a very high idle, eventually setting a check engine light. How you check it is with the engine running, remove the PCV valve from the valve cover, with the hose still hooked up. Disconnect the breather hose from the throttle body elbow (the one from the left valve cover. Cover the PCV hole with your thumb, and the breather hose also. If you feel vacuum blocking these off then the gasket is going. Block the hole and hose opposite of how I described to make sure. Vacuum, bad gasket. You do not have to remove the distributor to take the intake off.

Just unbolt the accessory bracket with the Alternator and A/C compressor still bolted up and set it aside (I haven't done one in a while, but you should be able to figure it out as you go). You need the intake manifold gaskets, the cover gasket, the intake bolts, the cover bolts, the front and back manifold seals, and the intake-to-water pump hose. Get the thermostat and gasket, best time to do it, it's tighter to do with everything installed.

Another thing to check is the throttle body. Make sure it is clean, remove the IAC valve and see if the tip is dirty. If it is, the throttle body is dirty, remove the throttle body and clean with carb clean. Use an old toothbrush to scrub hard dirt. Remove the TPS and MAP sensor before cleaning. Don't break the MAP sensor rubber elbow!!! I kind of doubt this is the issue.

The last one is the TPS, we had allot of old Magnum TPS's doing wierd things, OD issues, I think some surging issues, be worth a look at the sensor readout with a scan tool when the condition happens.