yellow73bb

My car is a 1973 Corvette with 454 engine and 747 ECM, with Holley 4 barrel TBI (same as projection 4Di). The car runs quite well now until the water temperature gets up to around 140-150, then it drops off in performance (pretty rough during acceleration). I think it might be too rich because I often get backfiring out the tailpipe under hard acceleration at WOT (not through intake as near as I can tell). What tables should I concentrate on for this? It seems to be the same whether I am in PE mode or not.

My VE table is now pretty good, I get values typoically between 122 and 132 or so. I do get in the low 120s at 90 and 100 MAP. Am I too rich?

funstick

you sure your temp sensor is accurate ?

yellow73bb

I think so. It is close at least. I have a 195 thermostat and the temperature peaks out at about 192.

funstick

verify its whole reading range with a termoeter. if its not reading correctly itll cause alot of problems. is this a new problem or and old one ?? if its new id also look at the output of the ignition module in terms of coil drive. as its heating up its might be dying out.

Dyno Don

iTrader: (7)

Try a different CTS (coolant temp sensor)
The one with the yellow/black wire.

yellow73bb

I don't know if this is a new problem or not, I am only just getting this beast up to run even this good. If the temp sensor is off, do you think it is reading lower than the actual engine temperature and causing the computer to run rich?

Don, what do you mean by yellow and black wire? On mine, there are no wires on the temp sensor, only on the cable going to the temp sensor, which is indeed yellow and black. The sensor is located just below the thermostat housing (on the engine side). I will go get a new one, maybe that will help. It costs all of $7.99 at Autozone.

funstick

yeah if the temp sensor reads low then the engine will run really rich bog back fire and in general run like crap. its a big problem with fords and colds starts as the cold tempature range tend to become non functional i wonder if your high temp rage has become nonm functional. just a question.

V8Astro Captain

iTrader: (1)

Before you do all that, try adding more timing in the cold SA table. Maybe that'll help.

I remember when I first started mine it would run great but as it got warm the engine would start running real bad and the IAC would go to max. When cold the cold SA table was adding enuf timing, but as it got warm the timing went away and it would run real bad.

yellow73bb

I can try that. The table only goes from 0 MAP to 40 MAP though, does it still help at higher MAP like WOT? Mine adds some in at55 but subtracts a bunch out at 65.

Maybe I should put a potentiometer in where my temp sensor is once the engine is warm and then I can adjust it till I get it running good and see what "temperature" the engine likes. From that I could look at the tables to see what the settings are. This would mess with spark and fuel, but might be educational. Have others tried this?

V8Astro Captain

iTrader: (1)

Ahh see that's where they getcha

The cold comp spark table is in VACUUM. Which is basically the inverse of MAP. VAC = BARO - MAP. Since BARO is most likely ~100, then you can roughly assume that VAC = 100 - MAP.

Let's say BARO was read at 100.0 kPa. So if the engine is running at 35 kPa then the VAC = 65.

So the table actually covers somewhere between 60-100 MAP. That's why the table is labeled backwards of the main spark table.

yellow73bb

he he he --- now that you mention it, I remember reading that somewhere. I will try adding a few degrees at all points between 45 and 65 and see what happens.

Low C1500

I would play around with they array "accel pump vs coolant"

The table is cliped @ 138 deg c. So the value for temps higher might be a really small multiplier.

Sounds like your going lean, Are you using winaldl to scan, if so just watch your O2 voltage reading under accel. If its toggling too much force open loop (just raise mine temp for closed loop). High voltage = rich condition, low voltage = lean.

Also if your running stock gains (prop gains vs. o2, etc..) You've got alot of injector for the stock settings. If so your probably going rich under accel.

yellow73bb

Well, some success at last on this. I had earlier asked V8Astro how he solved his off-idle bog. He said he added a bunch of fuel to the 90 and 100 MAP areas of the VE#1 table. So, since I had an off-idle bog, I decided to multiply my 90 and 100 MAP columns by 1.2 and then my 80, 90, and 100 MAP columns by an additional 1.1. Now it pulls smoothly from 500 RPM on up. It runs a whole lot better. My BLMs in those areas are now around 120, but it runs OK for the first time. Next, I guess I need to concentrate a little more on spark advance and see if I can get some more power. I can finally chirp the tires in second, but not in third yet like I could with my Holley Pro-jection system.

It does seem to run rough for a short time during accelerating after running at cruise speed for a while -- maybe I'm too rich and fouling plugs . . . . .

Thanks for all the help.

Grumpy

Seriously investigate data logging.
And maybe a WB.
With Lockers, you can data log and log the WB with it.
Like the posting I did showing what my car runs like.
Makes all this guessing stuff obsolete.

3-4 sessions of 5-6 mins of data logging and I can pretty much start from scratch and nail the fuel stuff now, other then WOT.

On the BBC in my truck they run a very limited amount of advance. And it makes pretty good HP. Don't get caught up in the more is better timing fiasco.

yellow73bb

Grumpy,

What is "Lockers"? I am not familiar with that?

I suspect that the timing is pretty close on my engine. That is why I have been working exclusively on the fuel. I think that any timing changes will be fine tuning.

V8Astro Captain

iTrader: (1)

John, Lockers may be right up your alley. I haven't built it because it's way beyond my abilities right now.

Lockers is a different kind of scanner that consists of a daughter board and some software. If you open up a 7747 you'll see that there is an edge connector inside on the same board that the PROM and CALPAK are on. The Lockers board attaches directly to this edge connector, and from what I understand, gets data as fast as the ECM thinks it up. It then transmits that data at 57k! One of the guys said that the Lockers tach display was as fast as tach in his dash.

I can build some simple ALDL stuff but if I read the instructions right you need a 'scope to figure out timing...or something.

One of the guys from the Corvette forum made a programs to go with the Lockers board that's almost identical to WinALDL, our favorite! "Tuner" also outputs some ram info for inj pw and SA.

I'll e-mail it all to you...