Catalytic Converter causing Hesitation?

Hi all. I am relatively new to the forum and have searched up and down and can't quite pin down my issue. I have a 1999 Tahoe, 5.7 Vortec that I bought a few months ago. Currently 180k. When accelerating, I have a small hiccup/hesitation at around 1800-2000 rpm where power drops but almost immediately picks up again. Most noticeable in 2nd gear. I haven't had the truck long but I have cleaned the MAF, throttle body, new air filter, changed just about all my fluids, all the typical maintenance you do when you buy a used vehicle. The one major issue it has is a rattling catalytic converter, drivers side, no check engine light for it. Ran a scan tool, no codes either. Wondering if this cat-rattle could somehow be linked to my hesitation? Really at a loss here as I'm not as familiar with common L31 problems as I was with my LM7. Thanks for listening, hopefully I can get some insight from y'all!

If the cat is rattling, chances are, the guts inside ( the honeycomb metal inside) is shot, and no longer all together. So, yes, this can cause some flow issues, depending on the situation. If the cat is rattling, it needs to be replaced, and you need to replace both of them.

Yeah, the cat is definitely shot. Do you think the cat is the culprit behind my hesitation problem? Or would it be 2 separate problems, like the TPS? I just find it odd how consistent the problem is, always at about 1800 RPM and most noticeable in 2nd.
Edit: I want to try to solve this hesitation beforehand, since I have to wait a while to blow the big bucks on new cats!

It's really hard to say. Really you need to do a live data code read on the truck. This will tell give you a lot more info, on what's going on. No mater what, you need to replace the cats, anyway. You can always do that, and see if the problem goes away, but a live data code read, will tell you a lot more.

kennythewelder said:

It's really hard to say. Really you need to do a live data code read on the truck. This will tell give you a lot more info, on what's going on. No mater what, you need to replace the cats, anyway. You can always do that, and see if the problem goes away, but a live data code read, will tell you a lot more.

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Got it. Just wanted to see if I could fix my issue beforehand. Gotta save a while to get the new cats. Much appreciated!

jackrabbitZ71 said:

Do you think the cat is the culprit behind my hesitation problem?

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No. If a cat does anything detrimental to performance, it clogs. That won't give you a hesitation, it will give you a power loss that gets worse with engine speed.

But, I'm not sure what the rear O2 sensor will do if the catalyst breaks up. It should just trigger a check engine light. I don't think it affects the tuning.

Erik the Awful said:

No. If a cat does anything detrimental to performance, it clogs. That won't give you a hesitation, it will give you a power loss that gets worse with engine speed.

But, I'm not sure what the rear O2 sensor will do if the catalyst breaks up. It should just trigger a check engine light. I don't think it affects the tuning.

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Ok good to know. The cat definitely rattles but it doesn't sound like tons of little chunks, more like the entire element is sort of loose and wiggles around. No CEL, and I've had the rattling since it was bought but the hesitation is new. Going to clean my MAF and do an ignition tune up soon as I saw corrosion on my distributor cap.

1. Bad Cat likely is not causing hesitation at a specific RPM range. Is it possible yes. Likely no.

1-A.If the cat is rattling. Like you get under the truck and can shake or peck the exhaust while its not running and here stuff moving around it needs to be replaced. If the combs have eroded and exploded chunks could be in the muffler. If its loose and wiggling replace it.

1-B. if the SES light is on for the CAT being bad it will not effect engine fueling. Its just an EPA thing so if you cat is bad you see it so you'll get it fixed.

2. The Code the the ECM that triggers the SES light for a bad CAT doesn't run every time you drive. Just periodically. So if you remove your battery it could be several trips and or miles before the SES light triggers.

3. If your distributor is corroded that could cause hesitation under load at lower RPM. Cylinder pressures are higher under heavy load and weak spark will cause issues more easily. The Distributor is a pain point of the older engines. Good to take the cap off and clean any corrosion off at every oil change.

3-A. If the dizzy is clean. And your getting hesitation under heavy load check your Spark Plugs and coil. Ohm your coil with a multimeter and pull and inspect your plugs.



My truck had a clogged fuel filter once and would not go above 3000 RPM.

Also you should check your fuel pressure. I had almost the same hesitation you do and changing the pump fixed it. My pressure was lower than it was supposed to be but the vehicle still ran and drove.

Grate spark plug chart.