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I am working on a 94 Chevy Silverado with a 5.7L. The engine

Customer Question
is new and has about...
I am working on a 94 Chevy Silverado with a 5.7L. The engine is new and has about 1.2k on it. Customer complaint is that it is running too rich to the point where he could only drive about 75 miles on a set of plugs before the plugs would be so fouled they would barely spark. After over looking and checking every single thing i.e. Fuel Pressure, compression test, etc. (which where all normal), I hooked up a vacuum gauge. Now here is the tricky part I have never seen, the truck starts right up, idles horribly at about 13in of Hg vac. When given throttle it runs fine at 20 in Hg vac, even when revved it recovers right back to 20 in. Hg vac and instantly drops back to 13 in of Hg vac and idles horribly. I have checked for leaks, used ether etc. and nothing. There is an aftermarket chrome intake which I would assume would be the problem however; why would it run fine for 1200 miles and then just all of a sudden start running terrible? My brain is rattled, could use some input.. Thanks
Submitted: 3 months ago.Category: Chevy
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7/28/2017
Chevy Mechanic: K. Wiggins, ASE Certified Technician replied 3 months ago
K. Wiggins
K. Wiggins, ASE Certified Technician
Category: Chevy
Satisfied Customers: 3,031
Experience: ASE Certified Technician, Associates Degree in Automotive Technology, 15+ years in the trade
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Hello, have you checked the timing? Retarded timing can cause the low vac at idle and fuel consumption issues.

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Customer reply replied 3 months ago
Yep, that was the first thing I did
Chevy Mechanic: K. Wiggins, ASE Certified Technician replied 3 months ago

Good, next things to check would be intake air leak and valve lash, valves being too tight will do this as well.

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Customer reply replied 3 months ago
Checked all of that.
Customer reply replied 3 months ago
re-adjusted the valves ( I do half turn), still doing it.
Customer reply replied 3 months ago
No collapsed lifters either
Chevy Mechanic: K. Wiggins, ASE Certified Technician replied 3 months ago

OK, looks like you're on it. how's the injector pattern look? Also is the throttle body clean and have you checked the pintle on the idle air control valve for wear

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Customer reply replied 3 months ago
Yea, I even used a whole entire spare; Throttle body, ECM (switched the PROM of course), all sensors etc. Still does it.
Chevy Mechanic: K. Wiggins, ASE Certified Technician replied 3 months ago

OK, the engine itself was it assembled by someone or bought as a assembly? It's possible the cam/crank timing is off at the timing chain.

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Customer reply replied 3 months ago
Haha, replaced that too. You can understand why I am frustrated.
Customer reply replied 3 months ago
Plus, it never would have ran fine to begin with if that were the problem
Chevy Mechanic: K. Wiggins, ASE Certified Technician replied 3 months ago

I see where you're coming from for sure. Let me open this back up to the other experts. I've pretty much went through all I know to check in this case.

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Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago
Tim's Auto Repair
Category: Chevy
Satisfied Customers: 16,082
Experience: Have owned a repair shop for 25 yrs.
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Hi, My name is ***** ***** for the delay.

I will do my best to assist you

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Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

do you get any trouble codes?

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Customer reply replied 3 months ago
No, I did get the Map code and running rich but, that should go off when the pressure is low
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

so you did get a map sensor code?

did you replace the map?

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Customer reply replied 3 months ago
Even replaced it with three other ones to make triple sure
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

you cant go by a vacuum test gauge..it wont tell you anything sense the vacuum will go up and down depending on how the engine is running

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Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

what 3 other ones?

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Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

does it run well when the engine is cold?

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Customer reply replied 3 months ago
3 other Map sensors, just in case the new one was faulty. it runs all the time, just the same whether hot or cold until the plugs get too fouled out than it will barely start
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

ok.

have you removed the egr valve?

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Customer reply replied 3 months ago
Yea, the new chrome intake doesn't have the EGR valve port on it so they just bypassed it.
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

ok.

replace the ect[engine coolant temperature sensor

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Customer reply replied 3 months ago
Did that
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

there isnt many things on this engine to cause this

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Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

how much regulated fuel pressure does it have?

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Customer reply replied 3 months ago
I checked it last week, it was 12-13psi
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

how did you test it?>

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Customer reply replied 3 months ago
yea
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

how did you test it? how did you test the fuel pressure?

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Customer reply replied 3 months ago
put it inline between the pressure line and throttle body
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

ok

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Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

there is just only a coupleof more things that would cause this problem

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Customer reply replied 3 months ago
like
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

1-remove the fuel return line a blow through it to make sure it isnt clogged or has a kink somewhere.

2-a bad coil can cause this slimier problem.

3- the ecm is bad.

there is nothing else

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Customer reply replied 3 months ago
1-did that. 2- Replaced that. 3- replaced that
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

and the compression is good on all 8 cylinders?

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Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

there just isnt anything left on this one

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Customer reply replied 3 months ago
You see my frustration
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

the compression..is it good on all 8..?

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Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

the cam may not have broken in correctly and is worn out

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Customer reply replied 3 months ago
I took it out, it looked ok
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

make sure the compression is right on all 8 now

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Customer reply replied 3 months ago
I did like 2 hours ago, I am sure it hasn't changed
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

should be 100psi+ on the first stroke

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Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

did you check the distributor for wear/play?

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Customer reply replied 3 months ago
yea, even used an extra just to check
Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

and you do have 100psi+ on the first compression stroke of the engine?

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Chevy Mechanic: Tim's Auto Repair, mechanic replied 3 months ago

please stand by..perhaps one of the other guys has a better idea of what is going on here

\

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