Hoping maybe someone can point me in the right direction here. I just finished my miniram conversion this past week. The car starts right up, idles perfect, and revs nice out of gear. When I put it in gear and drive it the car stutters for a couple of seconds off idle and then runs good. Also, when the car shifts into overdrive at slower speed it starts to do the same (45mph at 1600ish RPM). If I take it out of OD and the RPMs go to 2K it's smooth as silk again. Some details below that may help or be important.
- Car has been sitting for 3 years. Gas is not great but it had a full tank of gas. Hoping to drive it a bit and get some fresh gas in it. Can old gas do this?
- New fuel filter was installed and injectors cleaned
- Fuel pressure hold nice and is at aprox 36PSI (this is an 85 with the 24# injectors thus the lower PSI. This matches my service manual)
- New Plugs and wires. Cap and rotor inspected and they looked almost new.
- TPS adjusted according to service manual. If memory is correct I got it right at .5 at idle and almost 5 at WOT
- Base timing set to 6 degrees BTC
- MAT sensor was relocated to air filter housing per TPIS instructions with their kit
- Vacuum was good and steady. No leaks detected with gauge or via ear checks
- 9th injector no longer in play due to Miniram. Also, one of the coolant gauges is no longer hooked up as the miniram only has access for the one and researched showed one was for the 9th injector thus it not being needed. Gauge in cluster reads correct so assumption is I hooked up the correct one but that is also an assumption.
- Car acts the same hot or cold

At this point all I can think of is the gas is that bad but it seemed odd it would only do this at low RPM under load and off idle.

 

Stock chip? If so that may be your problem. You probably need more tip in fuel. Make sure to check basics like plugs, wires cap.

 

Dang, forgot to mention that. It has a TPIS tune. It was tuned for my edlebrock base and Siamesed SLP runners and plenum though. Plugs and wires are new.

Odd thing is it feels like to much fuel as the more throttle I give the worse it is. Very little throttle, it hickups and goes. Medium and it doesn't want to recover. If I floored it I bet it would die.

 

Brian is correct. You need tuning for a miniram. The miniram will want different fuel mapping.

 

You need to determine if it is a lean miss or rich miss. My guess is lean and is probably tip in fuel being too lean. If you hold a steady throttle at 1500 rpm what does it do?

 

Out of gear - Runs perfect

In Gear - It sputters every couple of seconds. Feels almost like a slipping clutch in a manual trans car when you put it in 5th gear going up a hill with a clutch on it's way out. This is an auto car but the best way I can describe it.

I do understand a tune is needed to maximize performance but I know a lot of people have run these with the stock tunes in the interim of getting the tune and just didn't get all it has to offer and they stayed out of WOT. Main goal is to make sure everything is as it should before I start the tune process. Just feels like something is off outside of the tune as well. Ironically enough, I just pulled my air/fuel gauge off the car as I'm trying to get the interior to a more stock look. Maybe I need to temp hook it back up :-(

 

I have never worked on a 1985 C4 Corvette but what you are describing could have something to do with the measuring of air properly going into the engine.

On my 1988 the Mass Air Flow sensor is what is supposed to send data to the ECM so it can calculate fuel metering. Do you have a scanner or something that will show you what is happening inside the system?

The gasoline is too old, I would drain it out and fill the tank with good fresh gas with a bottle of ethanol remover. The old gas is probably not good for running in any car any more. Three years of absorbing moisture in the fuel blocked off my fuel supply line on my 1988 C4. I had to run a new supply line to get mine working properly
One way to remove the gasoline is to disconnect the line feeding the fuel filter and put a hose on it and divert the fuel to a container of some sort. Then let the car pump it for you.
I personally used a siphon hose and then cleaned the tank out with water and used a shop vacuum to remove the water and junk on the bottom of the tank. I was able to stick my hand down the hole into the fuel tank and wipe it clean before refilling it with gas. Please don't try to run that nasty gasoline through your engine.

Definitely hook up the air/fuel ratio and watch what is happening. You might watch the fuel pressure and see what it is doing while you are at it. I would really look at the MAF sensor to be absolutely sure it is working properly....

Good Luck with your Corvette, It will be solved soon with all the experience that is here on the Corvette Forum!

Best regards,
Chris

 

Idle Air Control valve? This would be a good thing to check counts on from a scanner when it's acting up.

 

 

Before I got my 87 tuned for the Mini, I turned the distributor and gave it some more advance. It helped off the line.

 

Appreciate the advise. I'll give that a try and will see if I can get some fresh gas in it. I was planning on a tune but was really hoping to drive it in the interim to make sure everything was working correctly first.

Any suggestions for the tune? I only know about TPIS. Last tune I got wasn't all that great and was really $$$ so if their are anything other or better options I'm all ears.