Engine Stuttering and RPM Dives...

[jmc1997ck]

1997 Chevy C1500 RCSB 5.7L auto: Applying brake to slow to a stop, right after truck comes to a stop engine loses rpm's and stutters then idles normally. Accelerating from stop, engine stutters again then gets back on track once past 5 to 10mph. Problem has been getting worse for about three weeks and today the "service engine soon" light came on. Stuttering and rpm loss only seems to happen when in gear and there is a load on the engine. Side note, last fill up I added a bottle of gas treatment and now I'm at the tail end of this tank of gas. Bad gas treatment product? Either fuel delivery issue or spark issue? Looking for some insight, methods of troubleshooting, and parts/pieces to either clean or replace. Thanks guys!

 

[SAATR]

The first thing I would do is get a fuel pressure gauge hooked up and check KOEO and KOER fuel pressure to verify that it's in spec. Should be 60 psi with KOEO and between 55 and 60 psi with the engine running, preferably at operating temp. I don't suspect you will find an issue here as the truck runs fine with the exception of the things you mentioned.

Once you have this baseline, I would run the gauge between the hood and the cowl and tape it to the windshield were it can easily be seen from the driver's seat, but not interfere with your vision. Take it for a drive and try to reproduce your problem. Monitor the fuel pressure while accelerating and braking and see what happens. I think what you're seeing may be an issue with the pump's power or ground that's causing your pressure to drop off momentarily when you accelerate or brake. It's easy and nearly free to check.

 

[twomanymontes]

What code was set? That would help diagnose the problem.

 

[RHamill]

In for the code, ready to figure this out

 

[SAATR]

I'm betting on at least a P0300.

 

[jmc1997ck]

Haven't taken it to anyone to see what code is being thrown. Could be unrelated, but who knows. The truck is going to the shop today, as I am tight on time and patience to tweak with it myself. Thanks guys!

 

[twomanymontes]

Please let us know what they find

 

[jmc1997ck]

A couple vacuum leaks and a severed PCV hose. Double face-palming myself for not seeing it, or even listening for it. PCV hose had split so perfectly the tech could only see the damage while the engine was running. Tech didn't document engine code, but the truck runs great again. Stupid problem, easy fix.

 

[twomanymontes]

Glad it was an easy fix. And don't beat yourself up over it. I do this for a living and there has been plenty of times that I miss something simple like that.

 

[SAATR]

Surprised you didn't see an idle RPM issue or more serious misfiring with that. Just another example of the KISS principle in action . Glad it was an easy fix!