Little Background:
I finally bought my first Vette this fall. It's an '85 4+3 stock everything w/ 65k. (Previously I tinkered with mid 80's Firebirds.) The deeper I get into this car, the more I am realizing that routine maintenance was not likely done. Needless to say, I have a lot of newbie Vette questions. I am absolutely ecstatic that I found the Forum. Your help & reading others' problems has helped me more than I can describe. Thanx!

Now to my question:
I am reading that some folks are getting in the 20's in 4th gear and 31 in OD. I am only getting 21 in OD @ 80mph. Is this too low? What can/should I do to improve this?

I have pulled a plug and it is clearly stock and needs replacement. When the engine is cold, I can smell gas out the pipes. I have not checked/noticed when warm. Last night (in the high 30's), I started it to show a buddy. (It was parked for a week.) When I revved it, it bogged for a second before revving. Normal? Never happened before.

If there is anyone in the Twin Cities area who would be willing to get together over the winter and show a hard-working quick-study newbie a thing or two, I'd be grateful.

-Kyle

 

Sounds a lot like the '85 I rescued from a clod... little/no routine maintenance (gray/black nearly-gone power steering fluid, 1 qt. of oil left in pan, half-off plug wires, etc.).

Mine's an automatic. I was getting 20, 21 MPG when I got it. I did some right-away cheap fixes like enough oil (amazing what that'll do!), some new plugs (Bosch platinum-tips), an air filter (Fram, but the K&N is coming), a non-burned-up coil (Accel HEI works great), and I got the plug wires routed correctly. Highway MPG went up to 21/22. Then I got the exhaust leak fixed and the oxygen sensor stuck back in (it was about to fall out, I found out), and I got the timing set right (6 degrees before TDC -- it was lagging about 10 degrees behind); MPG went up to a solid 23, even though I drive it like I stole it. I also got most of the water out of the gas (over time, 10 bottles of dry-gas and counting), ran three or four bottles of fuel-injector cleaner through it, and the peformance went way up. Fuel filter's next weekend.

It still does a little of that chug/lag/half-stall thing you describe when it's cold -- I suspect that's because it's missing the second oxygen sensor (due to Billy Bob's backyard mechanic putting on what look like homemade exhaust pipes and taking out the cat converter). That fix is still on the horizon, but what's worked best for me so far is the basics -- straghtening out the spark, getting the gas/injectors de-sludged, and then going after the more complicated (read: more expensive) computer-oriented stuff like sensors and modules once the foundation's shored up.

 

I am never a fan of throwing money at a car, however, I always do a complete tune up on any used car I buy and intend to keep for the long haul. Plugs, wires, all filters, throttle body and plenum cleaning and a new o2 sensor do wonders and give you a good starting point. Early c4's had a problem with fuel tank pickups (socks or prefilters, they are sometimes called) I would change the sock and the fuel filter also. If coil is origional, you may want to pop one in while you are in there. They degrade over time.

 

It breaks my heart to see what some people do to cars.

Here is my plan:
-Replace the ignition system from coil-to-plugs.
-Fuel & K&N air filters (done)
-Oil was done by seller. (Might install magnetic filter/plug in Spring.)
-OD fluid & filter change
-Rear diff fluid change (Might install drain plug system.)
-Coolant F&F (Professional due to EPA regs.)
-Swap out injectors
-Adjustable fuel pressure regulator
-Clean TB & plenum
-Check O2 sensors
-Timing (Need Gun)
-Codes (Need Scan Tools)
-Sensor testing (Need Test Harnesses)

I'm afraid to tackle the fuel pickup/pump. I just don't have the facility to swap this out. Quite honestly, I'm not confident in my know-how, either. This might be for a professional.

Thanks for the help, guys.

 

The fuel pump on the C4 is a 20 minute job. You don't have to drop the tank. I changed mine in a parking lot in the dark.

Unscrew the fuel pump door & tray and remove as one piece. Remove the rubber boot. Then remove the rubber lines & clamps, remember which is which. Next, unscrew the 8 or 10 bolts around the flange and the fuel pump assembly comes right out.

 

You can pull the pump and check or change the sock in the same or less time than it takes to change the plugs. Less cuts or scrapes, too. If you don't have a factory service manual, visit www.helminc.com and order one. It will become one of your more valuable tools.

RACE ON!!!

 

According to the Chilton Manual, I'm going to need to pull the entire tank out. ('85 VIN 8) Is this false? I'll check some service manuals.

 

I would not run out and buy sensor testors. A voltmeter and a safety pin work pretty well. No engine codes likely mean no sensor troubles.

 

This is completely false. Follow the steps in the previous post. It truly is a 1/2 hr job. That is why I mentioned it in my post. $5 part and 30 minutes to change.

 

The GM repair books calls for dropping the tank too. A dealership would charge you 2.5 hours in labor for this, even though I'm sure they'd do the 1/2 hour method.

 

-Replace the ignition system from coil-to-plugs.

Good idea. Get the bare bones NGK or AC copper plugs. They'll perform better than all that quadruple platinum crap, but will require shorter change intervals. Consider making your own plug wires from a universal kit for a perfect fit, if you care about cosmetics. You'll need the plug wire crimp tool to do it right.

-OD fluid & filter change

Must do, it's probably never been done, leading cause of 4+3 failures IMO. Get 2 or 3 qts of ATF, and "The right stuff" gasket maker, do not use a pan gasket. The filter you need is any of these part numbers...
AC-Delco #: TF184
Fram #: FT1024
Napa #: ATP14717
It's listed as a 69 Ford Ranchero FMX filter. Same exact filter, throw out the ford gasket. GM part number is not in the computer. Try and reuse your stock grommet, otherwise post on where to get one. (Don't use the ecklers/midamerica filter grommets)

-Rear diff fluid change (Might install drain plug system.)

A $12 plastic fluid pump will get almost everything out of there, if you attach a longer tube to the suck side. Buy (2) qts 75w90 oil or something close, and 8oz of limited slip additive.

-Swap out injectors
Send your injectors to Rich at Cruzin Performance. $90-100 and they'll come back good as new. The 85 bosch injectors are definitely worth keeping. Goto cruzinperformance.com

-Adjustable fuel pressure regulator

Unnecessary if you are close to stock. Only do this if your stock diaphram is torn, or fuel pressure isn't close to spec. I don't know what spec is off hand, but it's lower for 85s than for 86s. (32psi at idle I think?)

-Clean TB & plenum

Runners too. Will need a steel bottle brush and maybe a parts washer. Brake cleaner probably won't cut it.

-Check O2 sensors
Not sure how to check these. You could wire brush them off I guess. The sensing element is not accessible however. I've always been told checking the resistance of one will damage it.

-Timing (Need Gun)

-Codes (Need Scan Tools)
Very expensive item, hope you're sitting down. j/k! Take paperclip from drawer, bend paper clip into U shape, stick in upper right ports of ALDL port under the drivers side dash where your right knee goes. Count morse code type flashes. 12 12 12, code1 code1 code1, code2 code2 code2, 12 12 12. "12" is just an ecm test, not a trouble code.

-Sensor testing (Need Test Harnesses)

As mentioned, a voltmeter is fine. I found alligator clips to work better than having to hold the pins on the connector.

 

Absolutely false.

 

Wow! Thanx, CC. That should save a few bucks.

I was thinking of the Adj. FPReg. because I'll have the fuel/intake system exposed anyhow. Sometime I plan on tweaking the exhaust and intakes, so I thought I might as well prepare.

Someone suggested that I replace the OD & diff fluid and run around for several miles, THEN replace them again with new filter/additives/etc. This seems a reasonable way to wash out the inside. Not too pricey, either. Thoughts? Maybe wait and see how ugly the fluids are.

After I get the maintenance issues cleaned up and make sure I have no codes to deal with, I'm planning on replacing the POS radio and restoring the brakes/suspension. The suspension is quite greasy and showing signs of wear in the bushings & shocks. Plus the fittings in the lower arms are recessed, telling me it's time to replace them. Plus, I just cleaned a few ounces of grease off the front rims. That's a bad sign. Steering still seems tight, so I won't need the complete front end done. Might as well check the bearings, huh?

 

Fuel pump changed. It took me about an hour. I was being extra careful pulling the hoses & such plus I had to solder the black wire. That's the point where I thought it best to have a fire extinguisher handy.

Thanx for the tips everyone!

I might be making it up in my head, but it seemed to have a smoother overall feel to it on the test drive. It could be the 40 degree dry air, or maybe this actually helped some?

 

A weak pump basically acts like a rev limiter. I got a big difference over 4000rpms after changing mine, 15hp worth, if I recall.

 

That'll probably work since the first time you seal your o/d pan on, it's gonna leak anyways. You have to get it 100% dry, or atf will keep dribbling onto the gasketmaker while it's setting up.

As for the brakes, a good flushing, maybe new pads, and turned rotors are in order. Clean and lube the caliper pins well. Don't let anyone sell you on upgrading them till you give em a chance. I was very pleased with my 85's brakes, 99% of the time (exception being when I pretended I was mario andretti for an hour.)



Tip on refilling the o/d to capacity.... Put the rear end on jackstands, (block front tire on both sides) and put the car in gear while you pump it in. Basically, it's full when it comes out of the fill hole AND the cooler lines to the radiator are full, which is why you've gotta run the car.

 

20s in 4th and 31 in o/d is unrealistic for your 85.

If you have the 3.07 rear end, you have the same setup as me. Remember, later L98s had better heads and roller cams (and .50 overdrive manual trans), and thus were slightly more fuel efficient.

I averaged about 24mpg in stock trim, at 75mph in o/d. The biggest improvement for my mileage was the SLP cold air intake, bumped me up to an average 26mpg on the highway (and even higher on colder days). The automatics get better highway mileage in my experience, or at least the ones with taller rear end gears.

Dirty injectors will give you unbalanced A/F ratio to your cylinders, and will burn more gas. A new O2 sensor will probably help too. Don't buy one that's made in taiwan either. I noticed from your profile you're an engineer, what do yo do for a living?

 

Other than pulling the injectors (all 9 of them) and sending them off to Rich at Cruzinperformance, I would use a paper clip across pins A&B of the ALDL to pull any stored codes. This will help to isolate any sensor problems.

Indeed an AFPR would be a good addition in preparation for doing some air flow mods. First check fuel pressure at idle with the vacuum hose disconnected, then set the AFPR to that value as the starting point for tuning.

When you have the intake off it's time to do the TB coolant bypass mod. This will make future work under the plenum much easier not having to deal with cooant.

BTW, my '88 with a .7 OD and 2.59s out back pulls 30mpg on flat highway at 60-70mph with the top on. Even with 3.07s you should be able to get mid-high 20s with a good tune on.

 

Doesn't that just make you want to smack the person(s) that wrote the Chilton's manual in the back of the head, for telling you that you have to drop the whole tank?