I brought home a shiny "new" 93 Polo green vette yesterday, and I feel a need to learn it's language so we can have some meaningful discussions.

My only experience with PCM tuning is with a Holley commander 950, so I'm a lil spoiled as far as what can be done and how it can be displayed.

I have a laptop, it has USB, not serial. I don't mind spending a lil money for a sophosticated program that is easy to use.

So...

Does my PCM use flashrom (program on the fly) or EPROM?
If it's an eprom, can it be converted to flashrom?
What program and cables are recommended?

The first thing I need to address is idle speed compensation. I seem to have some issues.
It idles too high, particularly in gear. It really pulls against the brakes at a stop light. If I pop it into neutral, it goes to just over 1000 rpm, and takes several seconds to settle back down to 700. If the air is on, and I turn it off AND put it into neutral, it goes to 1500, and again, takes a good number of seconds to settle back down to 700.

Sitting at a stop light, it sometimes seems to be hunting around for the idle speed it wants.

Yesterday on the way home from the dealer once it got good and hot it was doing some spitting and popping, along with power lose, when I gave the throttle a stab. A couple of times I heard some brief fairly loud pinging just before she sagged. On the assumption that the dealer may have put low octane gas in, I filled up from half with 93 octane last night, that seems to have helped a lot, didn't hear anymore pings or get any more sags last night.

That improvement could be temp related tho... mid-afternoon temps were in the low 90's, early evening a cold front came thru and it droped to low 70's in a matter of an hour!

Last issue for now is temp. Driving her home after purchase, she got hot enough to turn the "check gauges" light on. Digital display showed 248! At the time, outside temp was 92, A/C was on full, and I was crawling in traffic behind someone towing a car hauler. I turned the heater on full blast and she cooled to 225 pretty quickly.
I did not pull off the road to check the cooling fans.

On my evening run (outside temp low 70's and no traffic, 30 miles on country 2 lanes) she never got over 200 degrees.

Plan for now: check and perhaps change spark plugs. Check and perhaps change plug wires. Wondering about o2 sensors. Fuel injector cleaner? (wondering about product / hose kit to use) Thinking about running some seafoam thru the motor (will it hurt the O2 sensors, or should I assume will be replacing them anyway?)

I've had a few vette's before, but they were bought new and dealer serviced. This one will be 100% DIY.

Sorry for the long post, trying to cover everything. Any and all help appreciated!

 

Hi Jim,

I'll try an answer a few of your questions.
--------------------------------------------------------
Does my PCM use flashrom (program on the fly) or EPROM?
If it's an eprom, can it be converted to flashrom?
What program and cables are recommended?

I bought the Romultor (EPROM to flash) and run it always. There are others like the Prominator (?) that are smaller and fit into the computer more compactly. Last time I checked you can get it through the Thirdgen.org site.


The first thing I need to address is idle speed compensation. I seem to have some issues.
It idles too high, particularly in gear. It really pulls against the brakes at a stop light. If I pop it into neutral, it goes to just over 1000 rpm, and takes several seconds to settle back down to 700. If the air is on, and I turn it off AND put it into neutral, it goes to 1500, and again, takes a good number of seconds to settle back down to 700.

Sitting at a stop light, it sometimes seems to be hunting around for the idle speed it wants.

I'm not sure about this one, but it may be the IAC. It's probably never been cleaned. You should get a good shop manual...like the official Chevy Corvette Service Manual set. It's well worth it.

Yesterday on the way home from the dealer once it got good and hot it was doing some spitting and popping, along with power lose, when I gave the throttle a stab. A couple of times I heard some brief fairly loud pinging just before she sagged. On the assumption that the dealer may have put low octane gas in, I filled up from half with 93 octane last night, that seems to have helped a lot, didn't hear anymore pings or get any more sags last night.

That improvement could be temp related tho... mid-afternoon temps were in the low 90's, early evening a cold front came thru and it droped to low 70's in a matter of an hour!

If yours is a Speed Density system like mine temperature makes a big difference.

Last issue for now is temp. Driving her home after purchase, she got hot enough to turn the "check gauges" light on. Digital display showed 248! At the time, outside temp was 92, A/C was on full, and I was crawling in traffic behind someone towing a car hauler. I turned the heater on full blast and she cooled to 225 pretty quickly.
I did not pull off the road to check the cooling fans.

On my evening run (outside temp low 70's and no traffic, 30 miles on country 2 lanes) she never got over 200 degrees.

Is it the original radiator? C4s are know for running hot. I'm in Arizona so I don't even drive my car during the day in the summer. My personal opinon is to spend the money and invest in a good all aluminum slightly over sized radiator and low temp thermostat. Like BeCool radiators.

Plan for now: check and perhaps change spark plugs. Check and perhaps change plug wires. Wondering about o2 sensors. Fuel injector cleaner? (wondering about product / hose kit to use) Thinking about running some seafoam thru the motor (will it hurt the O2 sensors, or should I assume will be replacing them anyway?)

Absolutely, plugs and wires are a given plus you want to get down and personal with the inside of your engine compartment noting the condition of wires, hoses, injector leakage, etc. If you're really serious you might want to think about investing in a wideband (WB) O2 sensor. You can learn so much more about your engine performance this way. Just a WB and a display is all you really need. Data storage isn't really necessary especially if you have it hooked up full time like I do.

I've had a few vette's before, but they were bought new and dealer serviced. This one will be 100% DIY.

Cool! It sounds like you're on the the right track.

 

Thanks for the tips beth!
I'll get started tomorrow.

Any suggestions on software?

The wideband thing is funny. 2 weeks ago, I put a wideband in my 68 camaro... premanently installed of course...lmao.

 

I use DataMaster for logging software and CATS tuner for program editing.

 

You can convert your MEMCAL to be flash programmable, but not while it's in the car. You have a UVEPROM, but you can replace the chip with an Atmel chip that is equivelent, but electrically erasable. Here's what one looks like this:



The only proper way to do it is use a hot air rework station to fully remove the old chip, and then install the replacement (with or without a low-profile socket) in its place. Some people just cut the leads off the old chip, and solder a new one in, but you won't be able to get the cover back on, and the cover holds the MEMCAL in place when the ECM cover plate is installed. By using the right tools, you can get the whole thing back together so it looks stock:



Once you have an eraseable chip, the Moates BURN1 and a Moates Readout header are all you need to reprogram the chip.



I Also use Datamaster for Logging and CATS for my 92. It has the same computer as your 93.

 

Thanks for the tips. I for sure want to convert it to flashrom, burning eproms is nasty!

What about cats RT_Tuner? it claims to be able to flash in real time, or does this only work with PCM's that were born with flashrom?

I did download the (demo) RT_Tuner. It seems to be not finding an "emulator" which I assume is smething it needs to think it is connected to a pcm? Is that a separate downloader?

I can't seem to find a sensor readout... Is it there, or is that what the emulator is for, or? It seems pretty hard for example, to make changes in the fuel curve when you can't monitor live while the engine is running to see what cells need changing?

Bear with me on this, my only real experience with tuning EFI was a Hollet Commander 950 system, totally tunable on the fly.

On my flaky idle, I had a good day. Car just needed some excercise! I've runn her a thousand miles since the purchase Friday, and my idle is now dead stable at 700 rpm's (500 in gear) A/C on or off, works just like it is supposed to!

It sure is nice to drive a vette again...

 

You will not be able to flash in real time unless you buy an EPROM emulator (Moates Osterich) . I had one and never used it. I just pull the MEMCAL out and reburn it, takes about two minutes.

I can't give you any tuning advice because I don't know what I'm doing in that department. I have been using tunes I get from other people based on my log data.

 

Thanks for the tips. I for sure want to convert it to flashrom, burning eproms is nasty!

The Ostrich, romulator, prominator are emulators which is the best hassle free way to reprogram.

What about cats RT_Tuner? it claims to be able to flash in real time, or does this only work with PCM's that were born with flashrom?

I didn't find this program helpful (but you may). Datamaster records the data to be viewed later. As I mentioned before, WB tuning is much easier. Narrow band tuning w/ the stock O2 senor only allows a range (BLM) around 14.7 to be set.

I did download the (demo) RT_Tuner. It seems to be not finding an "emulator" which I assume is smething it needs to think it is connected to a pcm? Is that a separate downloader?

emulators mentioned above

I can't seem to find a sensor readout... Is it there, or is that what the emulator is for, or?

The sensor readout is at the ALDL port. Hook up your ALDL connector to RS-232 laptop port. Run Datamaster and save data run.

The emulator is separate from the monitoring system and is used in place of your EPROM so you don't have to remove the EPROM, program and replace. All you have to do is hook up your programming cable from you laptop to the emulator and reprogram.


It seems pretty hard for example, to make changes in the fuel curve when you can't monitor live while the engine is running to see what cells need changing?

Datamaster is your monitoring software. RT Tuner is a programer only. If you had a WB O2 sensor hooked up while runnning RT tuner you could make adjustments on the fly (w/an emualtor).