Jeff1904

Any advice on this, with a full tank it seems to run fine the first quarter of the tank but then the last 3 quarters drain out of the engine it seems i get 110 to 120 miles on a full tank of gas. Car has been threw some new parts just recently changed the spark plugs and spark plug connectors the icm, water pump, optispark, and harmonic-balancer probbley about a month ago. But i also cut off the cat and straight piped it which i think is messing with the o2 sensors maybe i dont know, i need advice on how to fix this thanks guys

Injuneer

There is no after-cat O2 sensor on an OBD-1 1994 LT1, so cutting off the cat will not affect fuel usage or the way the engine runs.

How old are the two pre-cat O2 sensors? Have you scanned it for codes? Have you checked the fuel pressure? Have you checked for a leaking fuel pressure regulator? Any exhaust leaks before the O2 sensors?

The fuel gauge is notorious for faulty calibration.... top 1/2 of the gauge represents about 10 gallons, leaving about 5 usable gallons below the 1/2 mark, and only 1 or 2 gallons at the 1/4 mark. "Miles per tank" is not an accurate way to measure fuel consumption. Record the odometer miles at each fill up, and divide the miles driven between fills by the number of gallons required to fill the tank.

Best way to solve problems like this is to get the free download of Scan9495, buy or build an ALDL cable, and use the software to pull codes and run a data log of the sensors and PCM parameters while driving the car. One of us can help you interpret the data log.

Check the top "sticky" thread at the top of the "Computer Diagnostics and Programming" forum for info on Scan9495.

IDriveA95Z28

I was getting really bad gas millage in my 1995 z28. so come to find out i have a vacumm leak and a exahust leak so that is what i have to fix. so maybe check your mainfolds or air hoses running from your air intake maybe. thats what found to be the problem.

Injuneer

Unfortunately "Jeff1904" had not signed into this site since he posted his original question.

Jeff1904

Thanks for the advice my straight pipe does have an exhaust leak we are trying to get rid when we get another welder but that's after the O2 sensors. okay how do you build the cable?

Injuneer

Start with the first post in the "sticky" on the "Computer Diagnostics....." forum, and work your way through the first page or two of posts. Tells you how to build the cable, and where to buy ready-made cables.

https://www.camaroz28.com/forums/com...95-lt1-874306/

Jeff1904

Thanks, ordered the stuff should be here soon, hopefully I will reply back with some results.

GaryDoug

If you are using the instructions to build a cable: Pay particular attention to the paragraph describing how to set the pc to NOT download and install new device drivers. You want to install older device drivers (before plugging in the cable) like the ones on the web site with Scan9495... and then never update them. Some newer updates can render the cable unusable.

Jeff1904

Thank you guys all for your help, I made this cable if that makes a difference, also I saw in the instructions of Scan9495 you wanted information on manual cars? I could help if still needed? Anyways is this what you need I'm not entirely sure let me know?

GaryDoug

Data file looks good. The bank 1 long term (driver side) fuel trim is maxed out at 160 most of the time, meaning the pcm is adding a lot of fuel to that side. Confirmed by the injector pulse widths being about 30% higher on that side. Right side looks fairly normal. Might be a skewed sensor or exhaust design issue but wait until the real expert, Fred, takes a look.

p.s. I assume you are at an altitude of about 4000 feet. If not, the MAP sensor may need attention.

Injuneer

Is the AIR pump functioning?

Jeff1904

I'm not sure honestly how do I check I tried taking the fuse out and relay to hear a different sound but I dont, how do I check for sure?

Jeff1904

Cool thanks for your help and making this great scan software and yeah my elevation is about 4200

Injuneer

Haven't had more than a few minutes to look at the data log. The driver's side O2 sensor readings are certainly suspect. Always seems to read lower than the passenger side. It does cylce as required, but then, while driving, it just nosedives and stays at a very lean reading for a long time. I just need to look for what is causing that.

The AIR pump only runs for a couple minutes at startup. The data log has a "flag" that indicates it is commanding the pump on when it is supposed to be on. But that doesn't mean it is running. The PCM only monitors the relay control circuit, and as long as the fuse in the circuit and the relay are good, no code is set. The pump can be disconnected and/or removed in OBD-1 and it won't set a code.

I'm looking for signs that the pump is working. As the O2 sensors hear up, they should read extremely lean if the pump is working. Doesn't seem to be happening. Are the check valves for the exhaust manifolds in place?

http://shbox.com/1/diverters.jpg

Jeff1904

Yes they are in place my drivers side one is bent tho could this be the problem or no? My dad did this to get the valve cover off a long time ago he said it was ok? I didn't believe him but anyways here a picture.

If this is the problem the air pump or the air value because i do not have a cat is the air pump necessary anymore would removing the whole thing fix the problem? Unless the pump still helps the car let me know what you think.