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2004 120,000 miles, will surge

valkman51
0

Asked by valkman51 Oct 20, 2012 at 03:00 PM about the 2004 Chevrolet Silverado 1500 Work Truck Ext Cab Short Bed 2WD

Question type: Maintenance & Repair

When I first start the truck it runs good but then it will surge, run good then surge again. Thought at first it was the transmission but thats not it.  Not sure if there is some sensor going bad or not. No engine light comes on.  Seems ok once the truck gets warmed out.

9 Answers

John Saffrahn
12,825

While driving or at an idle?

2 out of 2 people think this is helpful.
valkman51
0

While driving

John Saffrahn
12,825

Could be a number of things, when was it last tuned up?

valkman51
0

Well, I changed plugs and wires at 100,000 along with cleaning out the injectors. It does seem to run rough when I first start up then it settles down. Thanks

John Saffrahn
12,825

How long does it run like this, is it seconds or minutes. Also did you put the iridium plugs in it or the cheap ones. The newer General Motors ignition systems use an HEI ignition system for a cleaner burn. They used to have HEI on the distributor systems in the late 80s also and the reason those were marked HEI and the new ones aren't is because all the new GMs have it. Point is that instead of 30,000 Volts the new ones are 60,000 to 90,000 Volts and standard plugs are lucky to make it 30,000 miles some crap out as quick as 10,000. It may be starting to need decent plugs and the bad ones just aren't creating the spark needed while the engine is cold and in open loop mode. Let me know what plugs were used and we can go from there.

valkman51
0

John, I'll have to get back with on that. I looked at my idemized bill and it doesn't specify. I know the plugs cost me $48.00. I'll have to pop the hood and check but I have the feeling I may have got the cheaper ones. Thanks for all your help.

John Saffrahn
12,825

What is the spark plug part number on that itemized bill? It should start with a 41-*** if it starts with an R then its just a standard copper plug. Also the plugs alone are approximately $7 which for the 4.8 or 5.3 is 8 plugs. So the plugs alone would be $56 + tax. A shop would be closer to $100 for the same plugs. If they aren't AC Delco then its the wrong brand all together.

valkman51
0

Thanks, I'll check the numbers tomorrow. Silly question but will the bad plugs make the truck hard to start?

John Saffrahn
12,825

Crappy plugs can make it start hard and run crappy while its colder due to the fact that while its cold #1 the air is denser making it thicker and more difficult to pass a good spark through it and #2 when an engine is cold its in what's called open loop mode where most sensors do very little and the rest do nothing. A predetermined amount of fuel is put into the engine depending on where the throttle position sensor reading is and the mas air flow sensor is not payed any attention. This also why your vehicle sometimes smells like gas when its started on a cold and damp morning.

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