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Old 08-21-2011, 07:55 PM
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Vortec stumbling under load.

My 98 Suburban has the 5.7 Vortec. It has just started running rough- mostly uphill. Today I replaced the Fuel Filter and removed and cleaned the throttle body. I am on my way to change the plugs next.

The gas has been running with either lucas or techron on alternate fills. All fluids are in check, no vacuum leaks- none at the TBI base either.

No experience with Fuel injection... if the plugs don't bring her out of the funk, is it likely dirty injectors?

Clean or replace them?

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Old 08-21-2011, 07:57 PM
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How many miles are on it?
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Old 08-21-2011, 08:04 PM
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200K just rolled over yesterday
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Old 08-21-2011, 10:34 PM
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Check fuel pressure first. If the vehicle is tuned up, and the pressure checks out, I would suspect the poppet injectors. Delphi makes a mpfi upgrade kit for our L31 engines. They go bad and cause hard starting, rough running/idle, poor fuel economy/performance. I would look into it. Well worth it!
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Old 08-22-2011, 09:58 AM
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Have you noticed any loss of coolant, I would also pull the distributor cap check for alot of play in the ditributor, these engine are bad about 2 things, intake gaskets leaking, and chewing up distributor gears. these are not TBI engines.
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Old 08-22-2011, 01:14 PM
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Check the rotor real close, those are famous for burnning a hole through right under the tang that hits the coil button. This is assuming it is a large cap HEI.
Any misfire codes.
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Old 08-22-2011, 01:32 PM
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Might be time to check/replace the cat-con(s). This was recently brought up in another thread where a 3500 series Chevy van w/the Vortec engine was cracking exhaust manifolds, presumably because of heat.
EDIT- I'm not saying YOUR cracking exhaust manifolds, just that a plugged up cat-con will make the engine run poorly. Sorry for any confusion.

Any stored codes?

Believe it or not, it's not inconceivable that the original plugs are still in it, or on only its second set- so plugs would be a definite maybe.

T-bucket23 mentioned the rotor. That and the cap, wires, EGR valve, PCV system could all stand a careful inspection. That cap is one of those "correct-a-cap" type affairs where the wires are routed out each side towards the bank where they go. You can see the way the terminals are routed by the way the cap's molded. But the advice still applies to check for any burnt spots or carbon tracking, cracks and the like.



Edit- I see T-buck already treed me on the codes...

Last edited by cobalt327; 08-22-2011 at 01:49 PM.
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Old 08-23-2011, 11:07 AM
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Do a tune up 1st, cap/rotor, wires, plugs. These coils are pretty hot for a cap/rotor setup and the caps rotors can go pretty quickly.
Fuel pressure should be 60-66 psi, key on engine off.

Here is some CSFI cleaning instructions and some MPFI upgrade injection info.

http://members.shaw.ca/betterthanyou...g%20Poppet.htm

peace
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Old 08-23-2011, 04:50 PM
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The CSFI poppets are an issue on these when it comes to any kind of miles. also I have heard of rough running due to the Plastic distributor wearing. The poppets would be my first guess is they are stock.
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Old 03-27-2012, 07:43 AM
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Quote:
Originally Posted by chucksrt
The CSFI poppets are an issue on these when it comes to any kind of miles. also I have heard of rough running due to the Plastic distributor wearing. The poppets would be my first guess is they are stock.
I have the same promlem on a low mileage engine in a 96 k2500 , new intake gaskets and a new set of MPFI setup in place of the poppets , and I have a new filter and fuel pump, so I am pretty sure its not the injectors...
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