My father has a 1993 Corvette CE. The car is in very good condition. It has just 50k miles on it but it has a few issues. It has the LT4 cam, cut lid with K&N filter, MSD coil, MSD wires, NGK plugs, and an MSD Opti-Spark. We are going to put on an MSD box that lets you adjust rev limiters etc...... The tranny was completely gone through and we had the shifting stiffened up but nothign major.

Well anyway it doesnt throw any codes but it is running rich as hell. Checked the fuel pressure and the local GM garage said it was "within spec" at idle and under load. The freaking this has 60 psi for heavens sake! When we took it to them they were to check it and they spent HOURS trying to adjust it. They were not even smart enough to use that little screw on the throttle body to jack up the idle from 700rpm to 900rpm. They are freaking dumb as hell and I cant wait to chew them out because they charge for a few hours to work on it and adjust it. Plan to get my pop back some money. They couldnt even adjust the throttle cable, its slightly loose so we wanted to tighten it up.

Is there any other issues that there may be that could cause it to run really rich other than the fuel pressure? After changing to another regulator that is between 30-40psi it runs almost like it should. Because of the GM garage though saying it was as best as it could be there is an issue. The 02 sensor needs cleaned up or replaced and 3 of the plugs are junk and we have to replace all of them.

What do you guys think? What else could it be? Think it could be the ECM? Just not sure what else to do at this point.

Oh, and what do you think the GM garage is going to say when I show them that the best tech guy they have is a freaking retard.

They said that the reason it would shift right in the upper rpms is because of the ASR button being on....lol The other thing was it was my dad and I who figured out the stock coil was junk. Idiots I tell you!

Down the road this thing runs like a champ. Even though its a D36 with the wussy gears.....lol

 

Is it the stock LT4 cam, or the LT4 Hot cam?

Does the car have a "tune" for the new cam?

 

Was told it is the "hot cam" but with just the stock 1.5 rockers. Is the lift not .525 on the Hot Cam with 1.6 rockers? If so the lift iwth the 1.5 rockers is around .492ish. I never could understand why people wouldnt just put 1.6 rockers on the stock cam and get more lift that way rather than changing the cam and leaving the stock rockers.

I dont think it has a proper tune.

 

There is alot more to a camshaft than just lift. A stock LT1 camshaft with 1.6 rockers won't compare to a Hot Cam with 1.5 rockers.

Also, changing the tune would really help with the rich condition.

 

Did you check for vac leaks. Also take some readings with an ohm meter on your injectors could be dumping fuel

 

Injectors check out. Please show me what the LT4 cam with 1.5 rockers is compared to the stock cam. I thought the stock cam with the 1.5s would get a little more duration or something as well.

Another thing, if the larger cam needs more fuel (assuming so) woudlnt it be a safe assumption that it would run lean not rich, as it is now.

Thanks!

 

You definately should get a tune done if you've done a cam mod. You also might want to download DataMaster and purchase/make and ALDL cable. I've been able to isolate several issues with the data collected.

http://www.ttspowersystems.com/DataMaster.html

 

Stock 93 cam specs: 202/207 duration at .050, .450/.460 lift, 116 LSA. LT4 Hot Cam specs: 218/228, .492/.492, 112.

 

I have a place to do a tune with that cable. At the last ditch effort if this place cant figure it out I will go that route.

Thanks guys!

 

Your 93 has speed density fuel injection, not mass air flow. Since the Hotcam decreases engine vacuum at idle the MAP sensor views the lower reading as an open throttle and signals the ECM to increase pulse width.

 

I knew the 93 was speed density and my 94 was mass air flow.

What do you mean by pulse width? So the larger cam would "trick" the ecm in to giving it more fuel than it needs?

 

Pulse width is injector on time, the longer the injectors remain open the more fuel flows. There is no trick to the equation, it is just that mass air flow cars are somewhat more adaptable to cam change than speed density because they measure air flow directly to determine load.
Speed density systems use the MAP reading to calculate load based on manifold pressure. A typical stock engine produces 20 to 21" of vacuum at idle, as the throttle is opened manifold vacuum drops, (at WOT it is zero).
The stock fuel "program" in the ECM views 21" of manifold vacuum as "idle" and adjusts fuel flow accordingly, your engine with hotcam probably has around 16 or 17" of vacuum at idle so the ECM adjusts pulse width for a throttle that is farther open.
As others have mentioned you need a tune to correct the fuel program to match the mechanical changes caused by the hotcam.

 

I have a 1993 LT1 ECM for sale. please email me at
carl_bruer@yahoo.com if interested, thx.

 

You need to have a new PROM burned with all the upgrades.