1999 5.9L 360 won't go over 60

[Justin Anaya]

Just like the title my truck won't go over 60

 

[Roadhouse71]

So what happens at 60. Please explain in detail. Then we might have an idea on what direction you might need to go.

 

[Justin Anaya]

At 60 is stays there and I'll try to go back up to speed but then it goes back down to 60 and then when I put my whole foot down it makes a screeching noise and the weird part is that no lights went off like battery or the check engine light

 

[dudeman2009]

Does it rev past 3000RPM in neutral?

 

[Justin Anaya]

My model doesn't have a rpm gage is only speedometer and a big gas gage

 

[Yeret]

A plugged cat could certainly cause this problem. When my original one acutely crapped the bed, I had to drive home at something like 50 on a 65 highway. If I tried to accelerate harder, nothing happened.

As dudeman implied, a plugged cat won't allow our engines to rev beyond 3,000 RPM. Since you don't have a tach, this test will be a little trickier to perform. If you have, or know someone, with a live-data-capable scanner, you can read engine RPM that way.

You noted a screeching noise when you try to accelerate around 60. Does clicking off the overdrive make any difference? Also, does your engine use oil? As I found, when the plenum gasket basically goes "critical," it causes very nasty performance losses. In my case, if I tried to accelerate hard, the CEL would start flashing until I let off the throttle. As a result, I was stuck cruising 60, maybe 65 tops and any attempts to push harder would make the CEL start flickering.

 

[dudeman2009]

Yeret makes a good point, a plenum gasket that has crapped the bed it can cause various issues and lead to exhaust issues as well. A code reader that does live data will be able to read RPM. Another option is to drive it a bit, then when you stop check the cat, if its glowing, thats an issue, it shouldn't be radiating heat all over under the vehicle, it should just be a bit hot from a foot or two away, not scalding at that distance.

 

[mondo]

I second the plugged cat. I had a 99 and had the same symptoms. Although iirc, it didnt want to idle too well either

 

[Justin Anaya]

Ok if it is the cat how can I unclog it at home

 

[crazykid1994]

You can check the cat by pulling the pre cat o2 sensor and seeing if it responds better. It’ll most likely run slightly rich and/or throw an o2 sensor code but you’ll be fine under short drive


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