# 2000 Chevy 2500 5.7L Bogs down at half throttle only when engine is warm



## Brichard (Mar 5, 2013)

My 2000 Chevy 2500 with 5.7L bogs down at half throttle. It does well till it warms up tp about 150 degrees. Then it blubbers and misses when I continue to increas the throttle. I have changed the cap, rotor, and plugs. The lower intake gaskets have been replaced. I have replaced the fuel filter. The distributor was removed to replace the gaskets of course. I feel that it was put back in right. The timing could be off some, but I believe that it is close enough fot he computer to handle. I had the codes read. There is a cam sensor code and a oxygen sensor code. Which one of these should I attempt first? I'm not fully convinced that either would end my problems. I can't go over 60 mph on flat road when it's warmed up.


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## crete5245 (Aug 24, 2006)

The cam sensor I believe is in the distrubtor. So with that said it is very important that the distrubtor is set exact. I know we have done several here at the school I work at and the students have had to set them 2-3 times to get them correct. 

As far as the O2 code, if it is a lean code, you need to track it. Have you checked fuel pump pressure? Low fuel pressure can give you a O2 sensor code lean. should be around 60 psi.


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## jb1390 (Sep 23, 2008)

You could have the distributor off by a full tooth......though I think it would still run like crap when cold. 

Any correlation between changing the gaskets and other work, and when the problem started? If it was fine before, then you did the work, and now it isn't right, then something wasn't put back together correctly.


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## Brichard (Mar 5, 2013)

It is worse after reassembling. I believe that the distributor may not be turned exactly right, but don't think that it is a full tooth off. When put back in, the rotor pointed straight back, just as it had when we pulled it. I was wondering about a vacuum leak, but it runs strong till 150 degrees.


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## Brichard (Mar 5, 2013)

It had been doing this to some degree before the intake gasket leak was fixed. It didn't seem to be temperature related at that time. With the new cap, rotor and plugs, I had been expecting much better performance rather than worse. Thank you all for the help. Hoping for additional ideas. I will take all into consideration.


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## jb1390 (Sep 23, 2008)

I lost a significant amount of power when my catalytic converters plugged up on my 98 with a 5.7. 

Never ran good even when cold though, but it did lose power gradually over time, it was tough to notice at first. They plugged because of a leaking exhaust valve causing bad compression and leaking unburned fuel into the exhaust. Have you checked your compression?


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## Brichard (Mar 5, 2013)

Haven't yet checked conpression or fuel pressure. How do I check the cat?


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## antsrcool (Mar 5, 2013)

easiest way to check cat is to unbolt the upstream 02 sensors and go for a ride.


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## jb1390 (Sep 23, 2008)

There is a quieter way to do it with a vacuum gauge, can reply in more detail tomorrow unless someone else beats me to it


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## 32vld (Feb 4, 2011)

Years ago I gutted out an old O2 sensor leaving just the threaded hex nut base. Picture removing the porcelain center electrode from a spark plug.

Then welded in a metal tube into the center of the O2 sensor base.

Install this custom tool in place of the O2 sensor.

Then if you have an old compound vacuum/pressure gauge, you connect the gauges's rubber hose to the end of the metal tube.

Start engine test for excessive back pressure.

Do they sell an adapter to connect the gauge? Maybe though 30 years ago the did not.

I do not remember what the back pressure reading should be to indicate if the exhaust is blocked or not.

Though what I do remember is when a cat was clogged the car would slowly lose it's top end speed, eventually deteriorating only top out at 40 mph. The engine would idle, though as you would try to give it more gas the engine would not be able to take it. Then bad enough the engine would not even idle then stop running.

This makes me not think it is a cat problem. Though I do not work on cars everyday any more. And have not seen everything. Keep us posted.


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## brad96z28 (Aug 21, 2005)

To see if the dist is off, you need to look at the cmp ****** on the scan tool. I have also changed a ton of ecms on these due to corrosion if the ecm looks like a corroded mess It might be bad. And dont throw parts at diagnose it and fix it.


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## brad96z28 (Aug 21, 2005)

32vld;1615579 said:


> Years ago I gutted out an old O2 sensor leaving just the threaded hex nut base. Picture removing the porcelain center electrode from a spark plug.
> 
> Then welded in a metal tube into the center of the O2 sensor base.
> 
> ...


Or you do it the easy way in 5 seconds and leave the sensor out and see if it runs better.


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## 32vld (Feb 4, 2011)

brad96z28;1616947 said:


> Or you do it the easy way in 5 seconds and leave the sensor out and see if it runs better.


Yes and I have done that as well. When a cat is plugged bad, removing the O2 will cause the engine to run much better.

When a cat is slightly plugged, removing the O2 may not bring about enough improvement to indicate the cat is bad.

Knowing the normal back pressure specification will indicate that BP is going out of spec and the cat is going bad.


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