Me and my dad just rebulit a 1985 corvette we had bought that had a blown head gasket.
When we tore into the project we realized it had: Long tube headers, Accel base, Aluminum heads, Different non OE unknown cam, different valves, and 1.6 rocker arms.
This is a 4+3 manual.
Anyways once we got it put together with no leaks it starts up and runs a little rough. Once coolant temp reaches 100 it idles good. It runs good from about 1200-2500 Rpm's after that it runs really ******!
The timing is set at 6 degrees.
thanks!
I need help because this is my dd

 

I think the first thing I would do is to pull the computer out under the dash on the passenger side of the car and check to see if it has the standard GM chip. If it has a cam, it might need a custom tune. Since this is a unknown it needs to be check out. Can you data log the car with a laptop?

Are there any codes?

Do you have a fuel pressure gauge? Attached it to the schrader valve and let the car warm up. Then bring up your RPM to the point you start having issues and watch the gauge. Is your fuel pressure staying constant or is it dropping as you get the the higher RPM's?

 

Look for vacuum leaks.

 

Some info in the following links may help. The second link contains a multitude of info..... just click on 'home' page for access to specific areas of concern:

http://tech.corvettecentral.com/2011...trouble-codes/

http://www.corvettebuyers.com/c4vettes/ecm.htm

 

I would check for vac leaks and then check fuel pressure....is the check engine light on? Check for codes if it is.....

 

Thanks a bunch guys I will look into all of these. We shouldve checked out the cam while the motor was apart....
Do the stock injectors have a green ring around them?
What should my fuel pressure be for all my "mods"?

 

I was also wondering who you guys would recommend to get a chip burned from?
Whats a good price?
Also is a 40gph pump good enough or do I need a bigger one?
thanks,

 

The stock injectors from my 85 were metal and were rated for 24#/Hr. There were no stripes. It sounds like you have aftermarket injectors. The question is what size. All injectors are rated at 43psi. So as long as you have pressure in the 40-43 psi range it will be OK for getting started. If it has the stock fuel pressure regulator there is no adjustment.

 

It's hard to find a tuner for the 85. The 85 was a unique year and has a different ECM than the later years. Getting a chip burned is going to be tough if you don't know the build of the engine. I would do as previously suggested. Remove the ECM, carefully remove the chip and see if it is stock. I'm guessing it is not. But if it was burned by a professional tuner it could have a label to tell who did it. If you're that lucky, the tuner will likely have a record of the build.

 

I have an 85 and I wouldn't bother with getting a chip burned. The 85 will tolerate a lot of changes without needing to get a new chip.

 

@cumbercr
Thanks for injector info. The car did come with an afpr, I believe im around 45 psi. It seemed to run better the more i turned it up.
Were probably gonna swap out the ecm for an 86 and newer one so we can find a guy to tune it.
I was wondering who the easiest to work with and best tuner would be?
Also, how do i datalog my car and what is that?
thanks you guys are awesome!

 

Were you able to find if your chip has been modified? The problem you have now is that you don't know enough about the engine build to know where to start. There's some basic information any tuner needs. Cubic inches, compression, cam specs, heads, injector size and intake.

I'm also planning an ECM swap in the future. I plan to use PCMforLess to do my initial program. Their site is www.pcmofnc.com.

Data logging is pretty easy. You can download the Tuner Pro RT software for free. You will need to buy a cable that adapts your ALDL connector under the dash to a USB. You can find the cable on Moates website. Tuner Pro allows you to save files in Excel. That's helpful when exchanging files with your tuner.

 

Start at the basics

Do a base idle setup, the ecm needs this to be correct to run the engine properly.

Set your car to a base idle (as per my shop manual)
when hot.

Connect a paper clip, to your diagnostic terminal under your dash connect to terminal A and B (the top right two pins).
Turn on ignition but don't run the engine.
wait at least 30 seconds and then remove the idle air valve connector (IAC) (the square plug) then turn of ignition and unplug the paperclip.
Now remove the timing connector a single wire near the fuel pump relay.
Start your vette and set the idle speed to 400 rpm in neutral (auto trans) 450 rpm (manual trans) then check your throttle position sensor,
the top two wires it should be set to 0.54volts dc, also confirm with engine off that the tps rises to 4.5 volts at full throttle.
Turn of the ignition and reconnect the iac valve connector and timing connecter and start your vette.
it should go to 1200 rpm then drop slowly to 600 rpm, take the car for a 15 minute drive with the usual stop lights.
It is normal for a little hunting while the ecm relearns, also do a few spirited take offs.
All should settle after 15 to 30 mins normal driving and have a stable idle.


Good luck

By the way my 85 has a supercharged engine and the ecm has no ''special'' chip
The fuel pressure is controlled by a vortech FMU that raises fuel pressure per psi boost, to force more fuel thru the injectors increasing fuel flow and keeps the engine from leaning out.

Most mild engine mods should work ok with the standard ECM.

Note a bad injector electrical connector can cause misfiring, they can get pulled from the connector terminals easily. A good simple check all cylinders are running is start the engine from stone cold run for 30 secs and turn it of, then check the exhaust manifold an inch or so from the head if any are cold.

Good luck hopefully just needs a tune, also check the fuel pressure the 85 has around 30 psi standard as they have 24lb injectors. Later c4s run around 38 psi fuel pressure, also good to change fuel filter if you notice the pressure drops as you rev it.

 

I actually hanv't pulled the ECM yet, but I will probably do so tonight. Its under the dash on passenger side correct?
Well this just got a little more confusing now that I have aftermarket injectors with inknown rating.... haha.
I will check all this and report back
thanks guys!