1992 5.2 truck stumbles at steady speed on highway?

Recently I bought a 1992 Dodge with the 318/NV4500 combo. ( I knows his should go in truck section but seems to be more traffic here.)
If you hold a steady speed, it stumbles or bucks. If you either apply more or less throttle it instantly goes away. Fresh tune-up. No vacuum leaks. Tested sensors with scan tool ( OTC ) TPS reads smoothly. No dead spots. Any help is is appreciated.

I would check to see if the 1992-1995 style dual valve EGR system is working properly.

It is very common on older OBD-I system Ram pickups for the seat sealing surface of the EGR pintle valve to corrode away badly and allow extra gas flow all the time.

Since the EGR valve on the intake manifold and the loose EGR modulating valve are both hard to get at in their positions in the rear I would just buy new ones and install if the ones there are old. Check for brittle plastic vacuum lines too.

Do not just disconnect the electrical plug to the EGR modulating valve or the separate EGR valve, doing either of those turns the EGR flow onto maximum causing stalling.... this was an EPA "fail safe" rule.

You could disconnect and plug the hot gas line from passenger side exhaust manifold up to the EGR valve to see if the steady speed bucking goes away. Both threaded connections are likely to be corroded so use Mopar oxygen sensor thread spray, Kroil, or your favorite penetrent. Just cutting the steel tube and using hi temp silicone hose to rejoin is an option.

Below the throttle body butterflys is a cast in EGR passageway with dual outlets aiming right and left. One of these two holes can plug with carbon deposits, causing all the flow to go to 4 cylinders.

Dirty fuel injectors causing multiple cylinder misfire from lean a/f is also possible.

Good luck

I had the very same style truck years ago with the exact problem. I couldn't figure it out, so I took it to the dealership. They said it was the distributor drive bushing was worn. If that's what they replaced, it fixed the problem. Ran perfect afterwards.

^^^ I wonder if a sloppy t chain could cause the same type of "spark scatter" symptoms?

Another thing that can cause that exact problem is a faulty throttle position sensor. I had that issue on a Durango/5.9. The sensor is easy to change and not crazy expensive.

On the distributor drive bushing... I believe MOPAR tried to replace the tried and true bronze piece with aluminum. It did not work and there was a service bulletin and I believe free replacement with bronze. I would be surprised if there are many aluminum bushings left on the road.

THIS Real common on the OBD1 magnum engine trucks , And its really common on a 3.9 V6.



MAYBE, but not likely.

This week I plan to do both of the things suggested. EGR and distributor bushing while I am working in that part of the engine. One question, what tool do I use to remove the bushing?

We had the Mopar tool at the dealer as they have a tool to remove the bushing and to install and burnish it. But I dont remember the part # off top of my head as its a Miller tool. The dealer should be able to give you the # or it should be in the service manual. Ron

For the MOPAR tool... I borrowed it from a MOPAR dealer I traded with for my BB.

Same tool as the Magnum. It can also be purchased but a bit spendy. Getting the old bushing out w/o tool is not too hard. The tool is pretty important for install and burnish.

Are you sure it is the bushing and not the TPS?

CONFIRM the firing order, it could be as simple as a crossed plug wire

Firing order and (very odd looking) officially revised ignition wire routing to prevent cross-fire between cylinders 5 and 7

http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm

Note that the ignition wire routing for cylinders 6 and 8 looks exactly opposite of what you would think it should be.

I have double checked the firing order. everything is great there. The T.P.S. reads smoothly also. I will probably change it just for good measure though. Going to check for slop in the distributor to verify the bad bushing. I may just pay the dealer to perform the bushing R&R as I don't need to buy the tools to do this.

yes push the bushing sideways & see how much radial play it has. EDIT meant to say push the shaft sideways to see how much play the bushing is allowing it to have.