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Category: Chevy
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Experience:  ASE certified tech ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
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95 chev 350 in silverado truck..injectors..Throttle body..Engine runs

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95 chev 350 in silverado truck. Duel injectors in Throttle body. Engine runs rich, Black smoke from tail pipe. Engine makes sucking sound through carb. To much fuel making it need more air i would guess. If you pull a vacuam line, engine RPM picks up but still runs rich but is better then when line is on. If I disconnect on of the two injectors, engine runs better. I have check for vacuam leaks, found bad on on EGR value, replace line. I have replace MAP sensor, Fuel Pump, Fuel regulator, rebuilt and replace gaskets in throttle body. Any Ideas on why it's dumping so much fuel. PS, checked voltage on injectors, Got a 2 Volt reading, is that low?

Have you checked the fuel pressure? If so, what is it at?

Are there any codes in the computer?

Do you know what the engine vacuum is at idle?
Customer: replied 5 years ago.

No, fuel pressure not checked. I did rebuild Fuel pressure regulator on carb. Same results. Code on computer, I have a diagnostics reader, but for some reason it keeps telling me that the cord is not connect to vehicle. No check engine light. Vacuum is running about 22.


You should be able to jumper terminal A and B on the diagnostic conenctor, turn the key on and read the codes.

Here is a picture.

Customer: replied 5 years ago.
Amedee, I will not be able to check this until this evening. At work. Would it be okay to pick this back up tommorow. Question I would ask is should voltage be at 3volts on Injectors, also could the throttle positioning sessor cause the excess fuel being pumped in.
You need to have FULL battery voltage at the injectors at all times with the key on and engine running!

YES.. the TPS could very well do this.

YES.. we can certainly pick this back up tomorrow. Please don't forget about me.
Customer: replied 5 years ago.
So, If you check the voltage at the Injectors on the Throttle body, are you saying they should be 12 volts, not 2 volts
YES! But only one wire to each injector will have battery voltage.
Customer: replied 5 years ago.
I will jump the connector to see if I can pull the code. Also will check fuel pressure and Vacuum, and injector voltage. I will contact you tomorrow morning with the info. That will be all for today. Looking forward to resolve issue. Thanks for now.
You bet!

Please dont forget about me.

I will be looking forward to your reply!
Customer: replied 5 years ago.
Okay, follow-up from yesterday. On the 95 chev 1500 silverado, 350 engine, getting to much fuel. I check vacuum, running at 17, if you disconnect one of the 2 injectors, Vacuum goes up to 20 and engine idle increases and smooths out. Pulled code from computer, getting a "33 -maf/map sensor too high". Was unable to check full presure,but i have replaced fuel pump and fuel presure regulator.

Thanks for the update!

You said this engine only has a map sensor..correct?

What is the map sensor voltage at key on engine off?

What about with the engine at idle?
Customer: replied 5 years ago.
yes map sensor
What is the map sensor voltage at key on engine off?

What about with the engine at idle?
Customer: replied 5 years ago.
Unable to check map sensor voltage at this time.
What should they be?
Under 5 volts.

Let me know what you find!
Customer: replied 5 years ago.
From what I have read, Injectors are pulsed by the information received by the EGR and the MAP sensors information provided to the ECM. If I check the MAP sensor and it has 5 volts, i will replace it with a new one.

Is there a check that can be done on the EGR valve? What voltage should it be. Currently if I unplug the EGR, nothing changes on the way the motor is running. Also, where should the fuse be for the EGR, is it under the hood in the fuse bank? I check all fuses there and found none that were burnt out.

I will check voltages this evening. I may stop and pick up a new one on the way home from work. If voltage is 5 volts, I will swap out and put in a new one.

I will be able to answer all of your questions, but we can address one question at a time? I am a bit confused with all of the questions you have just asked me.
Customer: replied 5 years ago.
Sorry about that, I will check MAP sensor voltage this evening. I thought I would check the EGR voltage too if you know what it should be.
Since I am contacting you from work and will not be able to check this until tonight, Though I would check both MAP and EGR voltages. I would like wrap this up tomorrow so that you will get paid. :)
That would be great. Just keep in mind, you are more than welcome to continue to respond back to this thread even after you accept my answer.

As far as the EGR valve goes, this should not affect the way the engine is running unless it is stuck wide open. The EGR valve is for emission purposes only.
Customer: replied 5 years ago.
Amedee, Tested input voltage to MAP sensor. Received reading of 5 volts. I put new MAP sensor in just in case. Still did not fix problem with Load up of fuel on the engine. I check timing, attempted to readjust to 0 degrees BTC which causes the motor to kill. I think timing gear may have jumped on tooth that may be the reason why everything is goofed up. I want to thank you for you help, You really know you stuff. I will Accept your answer when you reply so you will be reembursed for your time. Thanks again and would be more than willig to use your knowledge in the future. Best Regards, Joe

Thanks for the update!

I think you are definitely on to something! I would agree with you that the timing chain could be the cause here.

If you have any further questions, please feel free to ask.

Best regards

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