1998 Dodge Ram 1500 Starting/idle/driving issues

[Mike Heimes]

Hey all! I currently own a 1998 Dodge Ram 5.9 Liter with a few issues I feel are all connected.

It started with cold starting taking about 5-7 seconds for the engine to turn over and the idle was rough when at a stop. When I would take off from a red light it would jump until I got to around 15MPH and then it would pickup and have smooth acceleration the rest of the way through. Wasn’t bad enough not to drive so I went ahead and changed plugs/checked wires, new air filter, ran some sea foam. After all of that didn’t get any change out of anything.

One day leaving a parking lot after shopping I pulled out into traffic and it wouldn’t go above 40 miles an hour and quickly went to 35,30,25,20 all the way down to 10mph and it would go a hair over..pulled into an auto parts store since it was close..took a quick look over of the engine, topped off oil and started it back up..left the parking lot and took back roads home at about 15mph where it’s sat since. Did a little research and have since changed the idle air control valve and Map sensor.

As of right now it takes about 10 seconds to start and the idle is really bad to the point that it just shuts off or just idles terribly. Switching from gear to gear doesn’t change the idle at all.It will only drive about 5mph. I also noticed that when the engine starts I don’t get that loud throaty dodge startup, I honestly can’t even hear the engine running.Only way I can tell half the time is checking the RPM’s or the truck shaking from the idle.

Was thinking of changing the coil, checking for clogged cat, but I don’t want to keep shotgunning parts if I’m not sure it will fix or not.

Any guidance is very much appreciated.Thank y’all so much!

 

[Hero6]

How many miles on it? Could be a clogged cat or bad fuel pump. You can check the cat by pulling the front O2 sensor completely out of the pipe and see how it runs. I am sure others will chime in as well.

 

[Mike Heimes]

Thanks for the reply Hero

It has 79,000 miles on it. I will definitely try pulling the front O2 sensor and see if that makes a difference..was kind of thinking either O2 sensor or clogged cat at this point.Thanks again!

 

[SportRam00]

If you don't fix it by doing the O2 sensor pull then it sounds like you need to start with a full tune up.... Not very expensive and with 79K on the clock and age, it's time.

I would do the following:
1. Test for spark across all cylinders with a spark tester. If you get good consistent spark the ignition system is in good shape. If not...
2. If you haven't changed this these out recently, I would install a new cap and rotor on the distributor and wires. Looks like you already changed the plugs. See how it runs. Still running bad?
3. Test the ignition coil. You can find various test procedures for this out there somewhere. If bad, replace. Still running bad?
3. Check Fuel pressure at the rail should be right around 49-50psi at idle. (If it low, the fuel pump might be going out.) Still running bad?
4. Perform a compression test on all cylinders. Compression should be at or above 120psi on the cylinders and should not vary between cylinders more than 15%. You can find the procedure for performing this test online as well

If the cat does turn out to be the issue, then definitely check the intake plenum gasket. If your engine has been sucking oil from the engine valley, that will clog your cat and foul your O2 sensors.

Good luck.

 

[Yeret]

Sounds like a plugged cat to me. When mine plugged up, I had every single symptom you just listed.

If the cat is plugged, removing the upstream O2 sensor will provide a small pathway for the exhaust flow and allow the engine to run a tad better. Otherwise, another good test it to let the engine warm up, which will also warm up the cat, and then put the tranny in neutral and try revving the engine. If it hits a wall around 3,000 RPM and won't increase no matter how much throttle you give it, the cat's plugged.

79,000 miles sounds a tad light for a modern cat to plug. As Sport Ram said, you'll definitely want to check the intake plenum for leaks because burning oil will foul the cat in a hurry.