Kentucky Mudhunter

Hey guys, awesome site! This isn't Camaro related but I think you guys will offer the best help. I have 95 LT1 from a Buick Roadmaster in my 85 S10. Everything is stock on the motor except I have an airfoil in the throttle body, a Hypertech programmer, and Granetelli fuel pump. I used the original Roadmaster wiring harness and altered it to fit in the truck. Every wire has been soldered with heatshrink. The truck runs awesome (even thought it weighs over 5000 lbs), except it runs rich all the time (therefore poor fuel mileage). You can smell the raw fuel just standing near the back of the truck. Also after driving the interstate for a while then pulling off and sitting at a traffic light at idle it will throw a left bank lean code (I can't remember the number at the moment). I have replaced the MAF(with AC Delco), Distributor (with an Accel), both O2 sensors, and Evap purge solenoid. Before the LT1 I had a carbed 350 in the truck and it got better fuel mileage. Anyone have any ideas where to go next? I don't want to keeep throwing money at this thing but with the price of fuel I've got to do something. I had thought about getting the stuff to do a datalog after reading about it on this site. Would that help me find my problem? If you need to know anything else about my setup check out mywebpage or ask. I would really like to get this thing fixed.

Granite00

Check for a leaking fuel pressure regulator. The vacuum hose goes to the manifold and when the diaphram ruptures, they will allow fuel to get pulled right thru the line straight into the intake manifold.

Pull the line off and check for any sign of fuel. Plug the line and start the engine up. It might have to be running to leak. Also try connecting and disconnecting the line with the engine running to see if it leaks.

WS6T3RROR

Left bank lean tells you where to look. Check the exhaust for a leak around the o2 and upstream from it.

Look for a bad plug wire, bad plug or a clogged injector.

Anything that would cause a misfire or put oxygen into the exhaust stream will cause it to add fuel, and when it cant anymore it throws that lean code. You could also switch sides with the o2 sensors to eliminate that as a problem, see if it gives right bank lean after a swap.

Kentucky Mudhunter

I just put new plugs & wires on it about 2 months ago and that did not change anything. It did not change any thing when I replaced both O2 sensors either. I can't find any exhaust leaks. I think I checked the regulator back when I first started trying to figure this out but will check it again. I had wondered if it was the injectors (they are original with 250K on them) but didn't want to go buy a whole set. Is there a way to check if the injector is clogged or leaking?

WS6T3RROR

Take em to somebody and have them flow tested.

What trips the code you keep getting, is that the o2 sensor keeps reporting oxygen in the exhaust. So the computer adds to the long term fuel trims until it hits the limit there, then the short term fuel trims swing up and add more fuel. When the computer has hit both limits it freaks out and says ok I have added all the fuel I can and its still not enough.

The only things that will do that is a misfire, an injector that is barely working, or oxygen getting in the system from a leak. I guess if there was a substantial vacuum leak somewhere, or a leak between the maf and the tb that was pretty bad if you're running one, then that would do it to. In order for a leak after the maf to do it though you'd have to have split blm's. Maybe if you found somebody with a scanner and could log it it'd be easier, until then you're just going to have to eyeball it and try to find out why it thinks theres air.

You might also check out the harness and make sure the wires to the left bank o2 arent chewed up. You could also check out the voltage supplied to the injectors on that side too. You may even be able to tell which cylinder it is if theres a problem by using an infrared temp gun to see where they're all running at for exhaust temps.

Kentucky Mudhunter

No leaks between the MAF and TB. Also couldn't find any vacuum leaks. I'll double check the wires going to the O2 and see about getting an infrared temp gun (I think they have one here at work). Thanks for the help guys and I'll let you know what I find out.

Kentucky Mudhunter

Wires to the O2 sensor are fine. I bought the infrared temp sensor and here are the temps for each cylinder. (I measured these on the exhaust manifold as close to the block as possible).

#1 - 290° #2 - 300°
#3 - 340° #4 - 490°
#5 - 350° #6 - 320°
#7 - 310° #8 - 290°

Do these temps look normal. Obviously #4 has a problem. Is it most likely an injector?

Thanks for all your help guys.

TobyZ28

I would check the plug on #4. Also look for arcing around it.
It does sound reasonable to suspect the injector

Kentucky Mudhunter

I just recently replaced all the plugs and wires with no change to my fuel mileage but I will check it out tonight to verify. I kind of suspect the injectors because they have 250K + on them and are still factory as far as I know. Thanks.

Jazsun

A bad coolant temp sensor reading low and hurt MPG and cause a rich condition...check the post I have in LT1-Tech

Kentucky Mudhunter

Thanks but I replaced the collant temp sensor as well with no change. Wiring checked good for the sensor also.

edman

A lean left or right bank code means the computer thinks it's lean, even if it is only a vacuum leak, exhaust leak, or a periodic missfire due to either a bad plug, ignition wire, or the vacuum causing a slight missfire at only one spark plug. In any event, the 02 sensor is reading excess oxygen on the left side, and is sending that info to the computer, which is correcting by richening the fuel for the whole engine. Look for a loose or damaged vacuum line, leak at exhaust manifold, or damaged ignition wire on the left side. Check the charcoal cannister purge vacuum lines and cannister too.