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95 chevy impala ss stock rebuild on LT1 engine less than 500 mi on rebuild
when driving the car the engine is running lean on the left side as diagnosised by a obd1 scan tool. The coughing & bogging down symptoms get worse the longer you drive the car and it is especially bad when making either a left or right turn. Is this a problem with the oxygen sensors, or with the fuel delivery system? The oxygen sensors are new with less than 300 miles on them,and the fuel injectors were professionally rebuilt by Street Performance in Mena Ark.

Edited by Customer (name blocked for privacy) on September 26 2006 at 3:23 PM

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1995 Chevrolet Impala Lt1 350

Customer (name blocked for privacy)

If it is a lean condition than the first thing you should look into would be a vacuum leak. Either a bad intake gasket or hose or even a sticking EGR valve. Does this vehicle stll have the stock intake and smog equipment on it?

Reply to BOBBY's Post: there are no vacuum leaks on the engine. I used a smoke generating machine to look for leaks on the intake manifold and on the engine in general. The egr valve has been removed and the port sealed. The intake has been changed to a larger (58mm) Eldebrock throttle body. The computer has been reprogrammed to accommodate the larger volume of air. I had a professional mechanic with the computer program reset the computer.

Okay, then if you are not pulling too much air then you are probably not getting enough fuel. You will need to check and see what your fuel pressure is with a fuel pressure gauge. Do you have access to one?

Reply to BOBBY's Post: I have used the fuel pressure gauge and the fuel pressure appears to be normal with pressure running at 44. when I go to WTO the fuel pressure goes up to between 49 and 52. when I let off the gas the pressure returns to the normal range. under normal driving conditions the fuel pressure stays at a normal reading.
By the way Bobby thank you for all of your time and help with this problem so far

Not a problem, I am here to try and help you get this fixed. Those fuel pressure readings actually seem sort of low, especially with bigger injectors. Was an adjustable fuel pressure regulator installed on this engine?

Reply to BOBBY's Post: No i didn't install a new fuel pressure regulator. The injectors are the same all that has changed is the throttle body. I did however install a new fuel filter.

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Your fuel pressure is actually sort of high. It should be more around 43 psi. Does your main fuel line go into the left side of the fuel rail, and the return is on the right side?

Reply to BOBBY's Post: Sorry Bobby I went out of town for the weekend. I believe that the opposite is true that the main fuel line comes into the right side of the fuel rail and the return is on the left side. Again thank you for your time and patience in helping me with my question!!

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Was the engine rebuilt to all stock specs, or were some performance upgrades made?

Reply to BOBBY's Post: There were some minor upgrades made. I went with a corvette cam of the same year and used the equvalient corvette springs. I removed the EGR valve, blocked it off and had it removed from the engine computer program. As I had mentioned before I also upgraded the throttle body to 58mm. I did have the PCM reprogrammed to accommodate these changes by a professional reprogrammer. It was during his reprogramming that we discovered that the left bank was intermittenly running lean. This problem gets worse the longer the car runs and is especially bad when making either a right or left turn.

You may have bad injectors, but in my opinion since you did some minor upgrades you may want to look into getting larger injectors. With the different cam, larger throttle body, and blocked off EGR the engine is probably pulling in even more air than the stock injectors can make up for. Even with reprogramming the injectors may not be able to keep up. You can try moving your injectors from one side of the engine to the other to see if the other side goes lean. In my opinion though the injectors you have may not be able to accomidate the extra air, and if an injector is just border line bad this will magnify it.

Reply to BOBBY's Post: Are there any other possibilites that could cause this problem? Could the O2 sensors be part of the problem? One last question what size are the original injectors for that engine? If I go to bigger injectors do you have a recommendation on the size? Thanks again for all your time and patience in answering my questions. You have been very helpful.

It could be an O2 sensor problem eventhough they were recently replaced. What brand did you use? When they rebuilt your engine did they give you an approximate horsepower rating?

Edited by FIX IT MAN on October 3 2006 at 3:57 PM

Reply to BOBBY's Post: I was the one who rebuilt my engine. I have no idea what the horsepower rating would be. When I replaced the O2 sensors I used Bosch brand replacements. Should I go back to OEM sensors? would disconnecting the sensors help in any way?

If you want to see if the sensor is accurate switch the sensors from one side to the other. As far as the injectors are concerned what I would recommend doing is getting in contact with Holley or Accel or Edelbrock and tell them what parts were enhanced in the engine and see what size injectors they recommend. If you want I can check for you though.

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Reply to BOBBY's Post: I will switch the injectors and let you know the results. Please check for me on the size of the injectors. Thank you for your time.

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I would bump your fuel injectors up to a 19 lb. injector. This should give you the amount of fuel you need for your engine.

Reply to BOBBY's Post: Bobby,
Thank you for all of your help with this problem. I will try your suggestions about the injectors and the O2 sensors. How do I get back in touch with you directly so I can give you the results of these tests? You have been very helpful.

All you need to do is come back to this post for help. If the post happens to close you can just hit the relist even if you have paid and it will open back up. Keep me informed on what happens.

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