Piston Slap: The Importance of Enlightened Diagnoses

Geoff writes:

Sajeev, I enjoy your TTAC contributions very much. I have a 2002 Dodge Ram with a 5.9 liter V8. Starts every time and idles fine initially. But just when it transitions over from the cold start sequence to Normal running it starts to act as if it is gasping for air.

If I give it a stab of WOT or if I shut it off and restart everything is fine for the rest of the time I drive it which makes me think O2 sensor. But looking at the O2 output it remains high when the engine is stumbling but after the WOT or restart the O2 sensor signal begins cycling up and down as it should. It will throw a CEL if I let it keep going once the stumble starts – but I can’t remember the code at the moment.

Since I know how to replace a starter the restart is my “fix” but any pointers on where to go next? After it throws the light the engine stops sputtering and the idle returns to normal.

Sajeev answers:

Writing to an automotive help column without posting the CEL code is like dating a gal/guy that’s a total jerk, but not pretty/handsome enough to justify the psycho jerk-i-tude. You never do this, unless you know your audience both loves you and knows your vehicle like the back of their hand.

Since you asked for pointers, here’s my short list to anyone posting on Piston Slap or some forum where noobs get flamed:

• Year, Make, Model and relevant options (completed)
• Mileage (needed)
• Previous, relevant service history (kinda needed)
• Engine Codes scanned with your scan tool or the free service at a parts store (mandatory)
• Research the code here. (definitely appreciated)
• Ask about your next step on the diagnostic tree after giving us a good slice of the branch.

Without following the above pointers, I can only guess. So what the hell: there’s a problem with the EGR system, as it happens after warmup. Maybe it’s a bad sensor/actuator, or some vacuum lines are toast. Maybe the intake manifold and the EGR need a good cleaning. But I’ll go with the EGR valve itself, because there’s zero accountability on my side!

Off to you, Best and Brightest!

[Image: Dodge/Fiat Chrysler Automobiles]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.