Just did the math. I seem to be only getting three miles to the gallon with my 85 vette with the L98 and 700R4 transblack . that is not good at all. If I drove like my brother it would be ok I would expect that.But I don't stand on it unless I have too. OE replaced injector's original HEI dist. Stock exhaust. new o2 sensor new MAF sensor. new plugs and 93 octane fuel. noticed black suute around exhaust tips.I haven't had a chance too check fuel pressure yet. I need to purchase a pressure gauge. the fuel regulator might be adjustable but havent messed with it. It usually starts pretty easy.doesnt runn on when you shut it off. I could really use some suggestions here please. It should be getting a lot more mpg than that thats the reason for the 700r4.PLEASE HELP? Thanks for you time and knowledge.

Something is throwing the computer out of whack and I'm surprised you're not getting codes. The fuel trims must be way off trying to compensate for something. Based on what you've changed, I'd still be looking at the MAF and O2 sensors or the wiring to them but you really need to get plugged in to see what's going on. A program like Autotap is a big help when these things happen since you can look at a bunch of the parameters and codes.

3MPG?!?!? I sure hope that is a typo, and you really meant 13 mpg...
At 3 mpg, you should have raw fuel pouring out the tailpipes, and the engine would be runnin pretty rough! I can't see it having that kind of actual mileage and NOT set codes.
You sure you don't have a LEAK somewhere?

Teh reason I changed all the sensor's was because of the fuel milage I'm getting. with the new stuff I'm getting right at 3.765 m.p.g. no fuel leaks. I just bought the car in Feb. It has some upgrades already. the fuel regulator has an adjustment screww in the top of it. it has a twenty gallon tank and I wanted to test it so I drove it till it sputtered. refueled with 19.5 gallons of gas. I use only 93 octane with injector cleaner every third fill up.only got 68 miles on that tank. I have a white 85 vette and where the exaust tip's are there is black soot and the whole rear of care has specks all over it. I have never seen the check engine light come on since I got the car. it is not burnt out. it comes on at start up. It was a barn find. the car did not run when I bought it. I had to get it running. got it pretty cheap but she needs some love. this vette is very powerful and fast so I'm not sure what has been done to it before I got her. I love this car and am so glad I got her. but this has got me stumped. I've been a mechanic for thirty years and I'm only 43. the fuel problem is why I decided to do the distributer upgrade to maybe burn all the fuel in the cylinder but if there is that much in there I  will try some things like test fuel pressure before and after filter. if it is a adjustable regulator I will adjust it when I have the pressure tester. thing right now is if I can get the fuel all burned up I won't be able to keep tires on it.LOL

This just don't make no sense. That kind of fuel mileage.....engine should be runnin rough, and plugs would be fouled. If the O2 sensor is working, a vacuum leak could cause the ECM to command a richer fuel mixture, but...the engine would still be rough.
I agree you need to find some way(scanner) to plug in to the ECM, and check the data....something's out of whack....but what?

I had a similar problem with my 87.  I found the O2 sensor and the temp sensor defective.

Good point about the coolant temp sensor. That would certainly make the fuel run rich....but it should still also run rough. It's gonna be interesting to find out what the culprit is...

fuel pressure tester is on backorder so decided to check temp sensor. and guess what. According to the shop manual there should be a temp sensor for ecu and one for the gauge the question is niether one is there? one for gauge is located in the head right behind alt. not there plug in head wire gone? the one for the ecu is located above the water pump on the passenger side. there is a plug in that location too. so I searched everywhere that I could see or reach and cannot find any sensor but the oil pressure sending unit in the head at the back of the head on the passenger side in between sparkplugs. I am in the process of finding the wires and where they terminate. I have gone ahead and purchased the sensors and sending units but I will need to find the wires and buy the plugs to attach them. will post when I come up with something.

Any sensor/sending unit in the head itself will be a temp related sensor...there is NO oil going into/thru the head, so there is no oil pressure related sensor located in the head. The oil pressure sensor will be in the oil circuit...either right above the oil filter, on in the top of the block, behind the distributor...maybe both.
The sensor you found on the passenger side head is for the cooling fan control, if I am not mistaken. You are correct on the other two locations, tho... temp guage sensor in the driver side head, and the temp input for the ECM is at the thermostat housing area, and should be a two or three wire connector.

Without ANY ECM temp input, the ECM is gonna default to a -40 degree temp reading....making the engine run REALLY rich! If you have a two-wire temp sensor connector, you can jumper the two wires together, and the temp reading fro the ECM will swing the other way, to extremely hot, and that will change the fuel curve to lean it out quite a bit.
You may have found your problem, anyway!

what about the egr valve.............sticking open......are your plugs fould out.  if the egr sensor was bad it would have a code however the egr valve it self is stuck open when the eng is hot a lot of black smoke out the tail pipes.... check your factory shop manual for your con....