Twilightoptics

7747 Ecm, $42 mask from Moate's site, Vortec heads, 4.3L.

Once it does start, it idles just dandy. Idles at 40kpa Park, 60kpa drive. Spark table is it. Everything else I could find is zeroed out. Doesn't have a startup spark in this ecu. Base timing at 0-2deg BTDC (0 Initial in the chip) Adjusted the timing based on a Vacuum gauge and the highest I got was 18hg with that timing table and dizzy position.

If I retard the timing (implying an intake valve was open while firing) I get flames, and it really doesn't want to start or idle well.
I added more fuel pressure and it seemed to make it worse too!

Any ideas?

Grumpy

When I was using the 747, it really liked 8d intial timing. Less then that and the engine would just windmill, and not start, and more then that didn't like to crank when hot.

Might try some GM injector cleaner, and see if that helps, a poor injector pattern can do that also.

Twilightoptics

Replaced the pickup in the dizzy. Still backfires.
Advance or retard 1 deg at a time untill it's hard to crank... still backfires.

Tried adding and subtracting in intervals of 2, 20degs of timing in the 100KPA area. Also tried zeroing the cool compensation and doing the same. Still backfires.

Backfires less cold?

injector pattern looks good.
plugs look sooty, porcelain is black. But they aren't wet right after cranking with backfires.

rechecked valve lash = good.

Idles well, no surging, tip in okay.

Crank AFR went from 1 to 10 at the given temp, and it still backfires. There are some open loop AFR tables in this XDF, but open loop runs fine when it starts.

What all does the 7747 look at while cranking?!

Loosing my whits. May go for a carb and use the ecm for timing!

RednGold86Z

iTrader: (1)

Incuctive crossfire (spark is jumping from one wire to the next), or just plain ol' got them wires mixed up, or an intake valve is hanging open. That's about all it possibly could be, in my mind.

JPrevost

You do know that the open loop AFR is calculated by the CTS lookup + Vac lookup. So your tables are showing me lean.
Go back to the stock open loop AFR tables.
Also, do you think your choke AFR table looks normal? Because that is subtracted from the calculated open loop (cts vac added).

RBob

iTrader: (1)

The black sooty plugs, is this after running for a while and warmed up? Or after a few minutes of cold start? If warmed up then a problem, if after a few minutes of cold running, then it may be OK. Depends upon how bad they are. You may still be a little rich in open loop running.

During cranking the ECM does this:

Spark timing is at the initial setting (physical distributor location).
Commanded AFR is from the crank AFR table (unless open loop is richer, then it uses that).
The VE tables are also used: 400 RPM row in main table, 0 RPM in adder table. Usually the 90-100 KPa area. Too low a value and very little fuel will be added.
Inverse temperature term is from the coolant sensor. This is an important sensor and should be checked with a scan tool. Basically, is it reporting the correct value.

If the ECM is in limp mode then the crank signal is used for crank enrichment.

Any chance the vehicle still has summer gas in it? If so that can cause issues.

XDF file? Does it have the main 3D VE table defined correctly? There is a bunch of pivoted definition files out there.

RBob.

Twilightoptics

-Open Loop AFR vs Coolant temp is the factory table:
-AFR at Startup is .5 leaner in the warm temps
-Open Loop AFR vs Map is stock
-Choke AFR modifier is stock
-Crank AFR Is also the factory table.
-BPW set factory 181

Accoding to the ABUL bin I've downloaded, aswell as the one I pulled from my chip.

I'm not sure about the main VE table being pivoted or not. Not sure on what that means. It was the definition file from Moate's site. I will start using the 7747-mine.ecu that you posted in another post as to be the best.

Not summer gas, only pulled the heads off 4 weeks ago. Also, hit the gas station and filled up a few days ago.

The ecm's CTS reads what I feel is correct. There is no error, it does not read -39. Falls right in line with warming up. Using Winaldl.

The plugs were black this time... from the engine starting and warming up. Shut off. Then tried to start with 5 different crank afr settings.

Twilightoptics

Lots of values changed when I put in the 7747-mine.ecu. Could this be from the old bins I was using? Possibly the import feature in Tunerpro v4.00?

Think I'll replace the plugs, find a good $42 6 cyl bin, and start over.

ABUL 42 bin from moate's site.

Thanks for all the help and knowledge guys!

DM91RS

I believe RBob is saying that the tables have the values in the wrong cells. I found that depending on which xdf/ecu I used comparing to Tunercat's fuel #1 table the numbers were going either across instead of up and down or at a diagonal. I just have found one that seems to have the values in the correct cells. Finally getting to use TPRT.

The next ECU I hope try should be RBob's UTBI