My 1996 camaro seems to have a low rpm miss that I can not figure out. I have a lt4 hotcam with headers, cat back, highflow cats, electric waterpump, 1.6rr's, stock stall and a 3:42 geared ws6 rear end. I get 18mpg on the highway and only about 7mpg on the street. The highway millage is not too bad but the street millage is way off. I filled the tank last weak and went streets for the whole tank and I am at 70mi with about 2 gallons in the tank now; that is 12 gallons and 70mi. What kind of mpg should I get with this car; I know it should be substantially better.

 

Did it ever run good since you either worked it or bought it?

Have you ever scanned it to see if it's showing a misfire attributable to any particular cylinder(s)? Or at least pulled the plugs to look at them?

 

pull the vacuum line off your fuel pressure regulator and see if theres fuel on that side of it. There shouldn't be, I'm guessing there is. that will cause low rpm roughness and kill your milage.

 

It ran great for a short period of time last May through June. Then it started to run like crap and dump fuel, missing really bad up top. It got to the point where it would not idle. So I I replaced the opti and that did not help. I took it to GM and found the fuel pump was bad. I changed the pump with a walbro 255lph and the car seemed to run fine; but it was not. It had a slight miss down low. I have been working on it since July, changing the fuelpump twice, injectors, plugs, wires, tps, IAC, MAF, ICM, Coil, opti's and caps and rotors. The problem with showing misfire is that I installed a double chain with the cam swap and the crank sensor has been tuned out by madz28. The fuel pressure regulator was also changed. Do you think a dyno tune will help point the problem out? Should I do a compression test; that would be a pain.

 

In order for compression to be a problem it would produce a dead cylinder. So check for a dead cylinder.

And look at the plugs.

 

Last time I checked the plugs they all looked good on the driver side but the passanger side had a orange kind of rust look to them. I have pulled a couple passenger side plugs since and they looked fine, but they only had 40mi on them. Maybe 40mi was not enough to show a problem; I am going to pull a couple tomorrow. I was thinking rust looking plugs means water in the cylender; but I am not burning or loosing water.

 

So why don't you check for a dead cylinder?

Plug analysis
Plug analysis

Rust color on plugs doesn't mean water. If it did, you would have a lot worse problem than that. Your cylinder and rings would be "rusty". Correct?

How old is the fuel ?

Check for dead cylinders.

 

Ok thanks I will do that today, the plugs should have enough mi on them to show a problem now. If I can not figure it out soon I think I might go to the dark side and buy a supercharged ls1; if everything checks out on it.

 

if a spark plug condition looks diffrent than all the others, u Definitely have a problem there. do a ompresion test and findout

 

Ok I checked the plugs and they all look about the same. None are totally black. They look normal except a few looked to be running rich. They seemed to get a little black the further back in the firing order. #1-4 looked 100% good then from #5-8 the plugs got a little black (carbon build up). Could a bad opti cause this? I am starting to think opti. Could it be the Autolite 106 plugs?

 

imo, before u change the opti, first do the spark plug wires and see how it will go, if not then change the opti

 

Why do you keep avoiding the search for dead cylinders?

 

I pulled all the plugs out and they look like it was running really good. Just a little black on a couple of them. It runs so rich that it will burn my eye's at idle. I did do a compression test on a couple cylinders. I got 170-155 psi on every cylinder tested. The tester I have will not work in some cylinders unless I remove the headers. I changed the plugs and wires again today and the problem remains. I am really leaning towards the opti; it is a autozone opti. Only thing stopping from taking it apart is it does not miss at high rpms at wot, it only has a problem at idle and light throttle. I can really feel it at 45mph in overdrive when I try to accelerate. It is like a slug until I get to 3/4 throttle.

 

I have a similar problem going on with mine and its looking like a bad o2 sensor. Going to replace it next week and see what happens.

 

You might be on to something here. How can I rule out the
O2's with out changing them. I do have a scanner, what kind of numbers are normal for the O2's.