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"Jerking" over 50mph

 
 
 
 
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Old 08-28-2006, 02:45 PM
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Default "Jerking" over 50mph

First true post here, awesome that there's a great forum for Blazers.

A couple of months ago I started experiencing issues with starting up my '01 LS 4x4. It might struggle for a couple of turns then eventually would start up sounding like a lawn mower. Took it in to the shop and they said that my catalytic converter was clogged but to take it to a Chevy dealership since it was covered by the 8y/80k mile Federal Emissions warranty. Took it to the local Chevy dealer and they informed me that it wasn't the converter but the fuel pump and promptly charged me $700 to replace (I'm not a mechanic by ANY means). So that's replaced and it starts doing the same thing a month later. Take it in to have the converter replaced since they ordered it anyway. They tell me they can't replace the converter since who ever installed the muffler (Flowmaster) welded the muffler pipe to the flange. If they replaced the converter they wouldn't get their money back since it would be butchered from cutting through the pipes. They suggest that I take it to the muffler shop that installed my Flowmaster. Did so and after two weeks of my muffler guy and the Chevy place going at it, my muffler guy generously ate the cost and replaced my converter. While he did this, he showed me the converter that was crystal clear, no clogs, no bent threading of the screen, see perfectly well through the other side. I'm thinking that I may have a computer issue since my truck has started to jerk again while I'm going at a constant speed. It feels as though my truck does not want to stay at an even idle while I'm at a steady 50-65 mph on the highway. I'm not getting a check engine light which is what I have been told would happen if something was wrong with the computer system.

Any thoughts or suggestions out there? I have too many people telling me to trade in the Blazer and I'm resisting with all my might.
 
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Old 08-28-2006, 02:57 PM
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Default RE: "Jerking" over 50mph

Ok, I'll start with the obvious. How many miles are on the truck? Has it ever had an aftermarket oiled air filter installed (K&N)? When was the last tune up (plugs, wires, cap, rotor, pcv valve)?
 
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Old 08-28-2006, 03:02 PM
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Default RE: "Jerking" over 50mph

It just turned to 73k miles on it, and I had a K&N FIPK put on after the initial jerking and start up problems started. The last tune up was in October of 2005 (at 60k miles). Not completely sure off hand what all was done with the tune up and please don't shoot me that I took it to Goodyear to have the oil changed and the tune up performed. I'm learning to trust the smaller, family owned/operated mechanics.
 
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Old 08-28-2006, 03:08 PM
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Default RE: "Jerking" over 50mph

how come you dont do ur own oil changes and tune-ups? very easy and can save you money. But anyway, id check the plugs if i were you. they may be bad or not gapped right.
 
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Old 08-28-2006, 03:10 PM
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Default RE: "Jerking" over 50mph

Well, if you don't know what was done as part of the tune-up, I would suggest atleast pulling off the distributor cap and having a look at the terminals inside the cap as well as the rotor tip. If you see any kind of buildup on these components, replace them.

Now, my question about the oiled air filter is because of this oil's tendancy to coat the MAF (mass air flow) sensor and change it's measuring characteristics. Even if the symptoms were there before the K&N filter, I would recommend pulling off the MAF sensor, removing the 4 outside socket headed screws and CAREFULLY cleaning the heating elements (little resistor lookin' things). To clean them, start off with either an electronics part cleaner (aerosol) or some sensor safe throttlebody or MAF sensor cleaner. If the elements do not return to their off-white color, you may have to use a q-tip soaked in cleaning fluid and LIGHTLY rub the elements on all sides. Be aware, this sensor is $250+ to replace, so be carefull!
 
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Old 08-28-2006, 03:11 PM
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Default RE: "Jerking" over 50mph

Since it wasn't te "Cat" and the tune-up may be good your next step would be to check the "EGR" valve
 
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Old 08-29-2006, 12:58 AM
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Default RE: "Jerking" over 50mph

what was mentioned above and I would like to add, what kind of spark plugs were installed? Yes, it makes a huge difference.
 
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Old 08-29-2006, 10:41 AM
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Default RE: "Jerking" over 50mph

Not sure, I am assuming AC Delco, but I could be wrong, I have a mechanic friend here at work that will look over the plugs and connections and let me know if there is something fishy going on there. Let y'all know what's going on this afternoon. Thank you all for you suggestions and advice.
 
 
 
 
 
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