Taking a little time to thank all of you who helped me make progress on tuning the PCM on my 94 Corvette 4.8LS conversion. I started posting on July 1. The progress I made so far would have been impossible without all of your help. As a way of paying it forward, I am posting this report and am open to questions about what I have learned and help in the tasks yet to be completed.

In Summary:

I bought the car on Ebay, knowing that it had some tuning issues. Primarily a very high idle. I discovered that there was no XDF file available for the OS (1273010), which I later found out was a custom tune from HPTuners.

Based on advice given in this forum, I downloaded PCM hammer and TunerPro RT. I also bought an OBDX interface.

I had a friend with an HPTuner read the existing file and can now examine it on my laptop. With this, I also discovered that the injectors were 36lb and the transmission (700R4) was set to non-electric in the existing tune.

I discovered that the idle was set way too high. Because I can't modify that OS without using HPT credits, I am taking a stock 5.3 tune and a used PCM to tune my Corvette.

Also based on help received on this forum, I made a bench testing setup so I can modify the tune on my kitchen table instead of on the car.

I transferred the injector settings from the 1273010 tune to the new PCM, disabled VATS, reset Tach pulses and a few other minor settings

Where I am Now:

The car is running on the new PCM. The idle problem is solved. I will run it a while longer to see how the PCM adapts to the engine.

What's Next:

Tuning the VE Table for performance. I am planning on installing a wideband 02 sensor to help with this part. The plan of the original owner was going to turbo this car. I will leave it normally aspirated.

Trying to find out if the Previous owner installed a cam, and if so which one. The engine does have trunions installed on the rocker arms.

Finding out if the Torque Converter Lockup is working and fixing it if necessary.

Finding out how to disable the Transmission DTCs since the PCM still thinks it's 4L60E

Adjusting the cable from the TB to the transmission to eliminate a very hard 1-2 shift and if that doesn't work, finding out why.

Adapting a wiper motor and installing it.


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cool project. what are you doing for the gauges? At this point, I'd say most people are going termX on these setups and getting out of the business of buying credits and all the stuff that goes with it. you may be able to drive it faster that way sooner?

 

Other than the wipers, the car is drivable now. The previous owner described it as follows:

The 1-2 shift is neck jarring, so I have to work on that.

The car has a freshly built 4.8 engine, see receipt for $3600.00 worth of work just on the engine, the 700R4 trans was also recently rebuilt according to the previous owner, it shifts nice and firm. LS1 intake, Holley fuel rails, new injectors,and fuel pressure regulator, it has a wiring harness by Jolt Systems which is integrated into the factory wiring so most of the factory gauges still work. The FX3 adjustable ride control also works or so i am told. it has long tube headers, dual exhaust with muffler deletes, yes its loud and raspy! the tune could use some tweaking as it idles high for my liking but to each is own, just know that it may still need some tweaking. the interior is pretty nice, not all torn up, some wear on drivers seat but overall quite presentable. there is no heat or A/C, and there is no wiper motor installed so obviously no wipers! It has 4 like new Nitto tires on nice chrome Z06 wheels (missing one center cap) brakes look recently new also with painted calipers to match.

 

I just communicated with the previous owner and found out some more details. It has a Lunati cam P/N 20540713. and upgraded valve springs. The torque converter lockup is not connected. It also has a new Northern Radiator. I am going to work on the Torque converter lock up first and then the windshield wipers.

 

If you continue having issues with the tranny, you might consider putting a 4L60E back in. The TV cable can be a real PITA if not adjusted JUST RIGHT.

 

I agree, but this is a built 700R4 and I don't have a 4L60E so I will work on the cable and install something for the torque converter lockup. I know that the 700R4 uses a ground signal for Torque Converter lockup and the PCM sends a +12V. I can fix this with a relay, but am unsure under what conditions the PCM emits the signal. If the 700R4 is a late model (I think it is) I doesn't have an external 4th gear pressure port so I may not be able to use an external pressure swith and will have to open the transmission. Any help in this area will be greatly appreciated.