turbokinetic

...is kicking my butt!!!

I'm working on a project car that has been in the works for 2 or 3 years. Finally the owner has all the parts for it, and has me attempting to tune it.

It's a 60's Corvette 350, with a Sig Erson 'mystery cam' in it. Nobody knows the cam numbers. The owner has pieced together a TPI setup for it, using a 7730 ECM and $8D speed density program. First 2 days have been troubleshooting the system and wiring. First problem was a TBI throttle sensor which operates backwards from the one needed. Then the TPS wiring harness was pinned wrong. Finally got the TPS reading correct, and engine started for first time with TPI. Then, I found that one of the 2 injector driver circuits was mis-pinned and the engine was running on 4 cylinders.

Finally, after many difficult starts, found that the ECM was getting an IGN ON signal in Run only, but not in Start.

Now that the system is more or less hooked up right, the cam is giving me fits. Due to my inexperience mainly. The owner says it is not a "large" or "radical" cam.

I'm not "new" to tuning, and have wideband, emulator, real-time ALDL program and more hardware to tune this thing without flying blindly. I have tuned some unusual combinations but all my tuning has been boosted engines with stock cams, or 'turbo cams' that still have a very good idle vacuum.

I had the engine idling at 800 RPM (where it idled with the carb) and I get 70 kPa MAP. That is with the best possible idle real-time adjusting the fuel and spark until it idls best. The WB indicates about 13 to 14 and the ALDL indicates about 25 degrees relative to TDC.

The problem is, it wants to stall when I put it in gear. It happens so quickly that I can't see what is happening.

Finally, the distributor started to make a buzzing, screeching noise like the shaft was binding or seizing in the bushing. Once that started, the engine never ran the same again. I know we need a new distributor before continuing.

I would like to ask someone who has tuned a cammed engine a couple things.

First, is a cam that makes 70 kPa at idle going to be usable?
Also, what is a good scientific approach to tuning the VE tables around idle with a setup like this?

Does anyone have a cammed engine lower VE table that they could post so I can look at it and stock side by side?

MANY Thanks in advance!

Sincerely,
David

Six_Shooter

iTrader: (2)

I recently tweaked an Olds that received a very radical cam, at least by EFI standards.

With the old tune, it would start and idle at, I want to say around 900 to 1000 RPM, and around 70 KPA. What the owner did to break in the cam and just get it running and idling decent was to install a resistor on the MAP sensor, to bring the value down, this allowed the engine to start and idle nicely, but wasn't real drive-able this way, understandably.
What I did when I got to tune was reduced fuel at the cell where it would want to idle at, so that it wouldn't load up. I reduced fuel in the 70 KPA range and 800 RPM and below, along with lower KPA and RPM cells, to get the engine to idle down after it started. It now idles around 675 RPM without issue.

I also had to play with the MAP AE to get it to idle going into gear. It looks like I had to reduce it slightly.

Timing didn't change much.

Sometimes getting an engine to idle as it goes into gear can be very difficult. Another friend has a 409 type engine (a smaller version, bored and worked over) that we built a custom short runner large plenum MPFI intake for. Unfortunately it's been way too long since I tuned that one to recall just what I did to get it to stay running as it went into gear, but I do recall it was a PITA to get. I want to say that I also adjusted the AE here, and possibly stall saver parameters. Yeah it looks like I raised the Spark advance Stall saver disable engine speed from 300 to 600 RPM. I don't recall if this made the difference, or if it was someting I tried and didn't change back. It looks like I also reduced some of the IAC idle parameters table vs coolant, in the warmer temps.

71403

Recently dealt with the same thing - bringing up SS helped, combine with adjustments on the IAC parameters (filters & delays), minimum throttle opening helped to get it reasonable.

Don't recall if $8D has parameter for IAC step reduction for park/neutral -> gear transition, if it does reduce it.

If you're dealing with a tight converter, which it sounds like you are, it'll just compound the problem.

turbokinetic

I was frustrated with it yesterday. Day before yesterday it was actually idling OK and I was making good progress on the going into gear issue. Then overnight it all went to pot even though I changed nothing. Now that I am not frustrated anymore, I feel like the faulty distributor HAS TO be the whole reason the engine went from "tune progressing nicely" to "totally random and untunable." Next time I get an opportunity to work on it may be months down the road. I told my friend that we must have a new distributor to continue. Since the fuel, timing, stall-saver, and IAC are ALL dependant on the speed reference - the distributor is critical. And with the shaft vibrating and jumping there's no way it will run right.

YES the converter it pretty tight.

This is a 1933 Dodge truck. It's awesome looking and the TPI engine looks really good in it. The transmission is a stock THM350 from unknown application. When in gear (I can get it in gear by throttling up) idling at 800 RPM, it pulls pretty hard.

Thanks again for the ideas. I'll update here when I get more time to work on it.

This is how the truck is setup. It was wired up before I became involved. As you can see it is a work in progress.

My friend who owns it is very dedicated to keeping it TPI, as I am too. I wish I could continue with it now but got to get back to work.

Sincerely,
David

Six_Shooter

iTrader: (2)

That was supposed to be MAP AE, not VE.