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94 Idle low and smokes

 
Old 02-03-2019, 04:49 PM
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h1duck
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Default 94 Idle low and smokes

I am new here and will try to put all info in. I have a 1994 vin P that idles low ( under 400 ) and will stall times and it starts to smoke ( smells like oil and fuel mix ). I have not driven this vette as I bought it in a box so to speak. I have ohmed the injectors ( 12.3 - 12.4 ) I did compression test ( 150 - 175 ) and there is no more than 4 psi bleed down. I have checked the MAP and it shows good. I did the noid test and all injectors flash. I have spark at plugs and plugs 1,2,3,4 are black and 5,6,7,8 are clean. All the plugs are on the wet side when pulled out and it seems to be oil and gas.
Here is the history that I have been told. They had roller rockers installed and the computer done ( I do not know as to what ) and he drove for about two weeks and it would barely run and he sold it to the guy I bought it from. I was told when the guy I bought it from bought it it had a noise in the engine. I found the noise to be loose rockers on cylinder 8.
The car sets a MAP code circuit reading high and after starting it many times it set O2 and I think it was #2 right side lean.
Fuel pressure is 42-48 and holds at 42 not running. Yes I did drain fuel tank and put fresh fuel in.
I hope someone has had same problem and can guide me in the right direction.
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Old 02-03-2019, 06:47 PM
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93Rubie
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How does it run with the MAF unplugged? Located in the intake boot after the air filter before the throttle body.
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Old 02-05-2019, 07:32 AM
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I don't know I will try that and see. I do know at idle I have no vacuum reading
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Old 02-09-2019, 10:18 PM
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How do you know you have no vacuum at idle?
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Old 02-10-2019, 02:03 AM
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Default 94 Idle low and smokes



Animated diagram showing the operation of a tuned circuit (LC circuit). The capacitor C stores energy in its electric fieldE and the inductor L stores energy in its magnetic fieldB(green). The animation shows the circuit at progressive points in the oscillation. The oscillations are slowed down; in an actual tuned circuit the charge may oscillate back and forth thousands to billions of times per second.


My 90 Vette has a similar problem it smelled bad and ran bad after it warmed up. I tracked it to the capacitor.

The ignition system has a capacitor and a coil, they form a tuned circuit, or a resonant circuit, which means the generate an oscillation. The oscillation how the coil generates the high output, if the capacitor's value or the value of the inductance in the coil changes enough you tuned circuit may not bust the coil voltage enough to get a decent spark.

I used a spark gap tester to verify the problem. Spark gap testers are cheap only about $10.00.

Ray
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Old 02-10-2019, 08:20 PM
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The 94's run a speed density system so they have a MAP not a MAF. I would start with checking your MAP sensor voltage. If it is too high under low vacuum that will confuse the computer and it will add fuel to the mix up to the point of flooding it out. Do you know what having the computer done means? If the previous owners replaced the computer because it wouldn't run they may have been having the same problem you are. It could be as simple as a bad MAP sensor or a bad vacuum line to the MAP.
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Old 02-13-2019, 07:46 AM
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Default Vacuum

Originally Posted by 93Rubie View Post
How do you know you have no vacuum at idle?
I put a vacuum gauge on the intake and it read zero until I raised the RPM. I did not pay close attention to where the vacuum went above ten ( I know I should have )
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Old 02-13-2019, 07:51 AM
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My car does it right from start up ( low idle ) and smoking takes about 2-3 minutes
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Old 02-13-2019, 08:02 AM
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I do believe the 94 used the speed density as a back up unless you have a ZR1. I have both a MAP and a MAF.
The previous owner installed 1.6-1 roller rockers and I believe that is why he had the computer done but it is the same computer. I was told that it ran great for a couple weeks after and than had a noise in motor and was running bad. I found noise to be two loose rockers on #8 cylinder and fixed them
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Old 02-13-2019, 11:45 AM
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Default Unpluge MAF

Originally Posted by 93Rubie View Post
How does it run with the MAF unplugged? Located in the intake boot after the air filter before the throttle body.
93Rubie I unplugged the MAF and the car idles up and down by it's self. I did not run it but about a minute and smoke smells like raw fuel.
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Old 02-13-2019, 03:27 PM
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93Rubie
I gave you false info in my last reply so I have found out. I had a vacuum leak that I had created when I broke a connector so when I started the car after unhooking the MAF the idle went up and down. I fixed the leak and tried again the car would not start until I pressed the gas peddle to the floor than it started and a lot of smoke came out and when I let off peddle the car stalled. I re hooked the MAF and the car did not want to start and when I let off key it backfired. I tried again and it backfired again while cranking and blew out the valve cover gaskets. I would say it was flooded or out of time if it were a carb engine.
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Old 02-13-2019, 03:35 PM
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Originally Posted by h1duck View Post
I would say it was flooded or out of time if it were a carb engine.
Or the computer is making the fuel mixture way to rich when engine is warmed up.
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Old 02-13-2019, 03:45 PM
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The engine is cold as it only ran less than a minute
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Old 02-17-2019, 07:53 PM
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Originally Posted by slow-vette View Post
The 94's run a speed density system so they have a MAP not a MAF. I would start with checking your MAP sensor voltage. If it is too high under low vacuum that will confuse the computer and it will add fuel to the mix up to the point of flooding it out. Do you know what having the computer done means? If the previous owners replaced the computer because it wouldn't run they may have been having the same problem you are. It could be as simple as a bad MAP sensor or a bad vacuum line to the MAP.
This right here is why I hate the internet. Your FLAT wrong. 94's are MAF. MAP/Speed Density is back up but with a CEL on all the time.
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Old 02-17-2019, 08:00 PM
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So you don't have vacuum in the manifold at idle? Correct?

Will the engine rev up at all?

Is the cat (or cats) plugged? I would crack open the pipes are the manifold connections and see what happens?

Which bank of cylinders is wet? You listed them but NO SBC in history has a firing order or cylinder layout like that.
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Old 02-18-2019, 09:23 AM
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Yes the is no vacuum or so little my gauge will not read it. The idle is very low but does rev up on it's own from time to time and did rev up and down when I had a vacuum leak and the MAF was unplugged.
Yes I can rev the engine it does have a slight (very slight) lag when I hit the gas.
I did have the exhaust partially open and made no difference.
I know there is firing order fits my black or white plugs. 1 thru 4 are black and wet and 5 thru 8 are white and wet.
I did have a lot of back firing after i fixed the broken vacuum fitting ( I broke it just before I unplugged the MAF and forgot to fix ) and tried to start the engine. I have to replace valve cover gaskets as it backfired and blew them out. I have never seen this happen before.
I am thinking that I may have bad injector or several flooding engine as part of problem.
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