Blazin4x4

I have hit a wall with my blazer... I can't get it to stop dying. I have done alot of reading and tried everything I can think of but nothing I have tried helps it.

The thing will fire up strong as ever and idle real high, about 1500 rpm, for about 20 seconds then it will slowly start to settle down and down until it hits 800 rpm or so and then it sounds like I turned the key off almost like it loses spark... the problem is I have no idea what this could be or where to go. I have played with the ve tables, iac, stall saver, o2 idle err correction, desired c/l idle speed, and none have affected it. It stills dies like the ignition was cut off... but it runs when I give it throttle. I suspect it might be just flooding it'self because it smells and acts like its running very rich.

Kpa goes from 60 to 40 kpa and o2 readings are around .500 mv when it dies.

Oh yeah as a reminder what is the ideal mv in c/l?

Also is there some sort of glossary to the terms that are used in tunerpro? I keep forgeting what some of the abbreviations mean.

dimented24x7

iTrader: (2)

It sounds like its possibly hitting a lean spot in the VE table if it suddenly just craps out. It could also be not enough spark advance, but if it leans out to around 18-20:1, itll crap right out at idle. Same thing if it goes way rich, except there you may have some black smoke to give an indication of what the problem is. If its lean, you may still have a gassy smell in the exhaust as the fuel wont be burning.

You wont see this on the stock O2 sensor, but with a wideband, you'll have a good indication if this is really the problem. If you dont have a wideband O2 sensor and control unit, get one. Even if your running a carb later on down the road, its extremly helpfull in tuning the motor.

Blazin4x4

What table should I change for spark advance? the kpa is all over the place when it dies though sometimes it's 45 sometimes 100. I haven't even gotten a full data log because of this... matter of fact I barely had 1/3 a data log.

dimented24x7

iTrader: (2)

Before adjusting the SA, it would be a good idea to get a wideband O2 and rough in the fueling first. Its best to adjust one thing at a time. At this point, it sounds as though the fueling is off.

ldo_marlin

Any error codes?

V8Astro Captain

iTrader: (1)

With a larger cam it you might try advancing the physical dizzy setting and see if it will run on its own. Then you know you need more timing, which is usually the case with a larger cam and stock calibration.

dimented24x7 mentioned using the WB O2 which is good advice. I never had one back when but the dizzy trick worked for me a bunch of times. Kinda like using a bulldozer to drive a nail in but you gotta start somewhere.

Blazin4x4

hmmm never thought of that... I believe it's 4 degrees advance right now... how far should I advance it? couple of degrees?


I do need a wb... just don't have the dough right now. I was reading one of the stickys on a tech page here that said the stock o2 or a wideband o2 will tell you it's lean when it's way rich due to cam overlap... is this true or is it only certain types of o2 sensors?

Val Snyder

If running flattops I've had decent luck with 8-10 degrees at 4600-5000 ft elevation, drop 1/2 degree for every 1000 ft below.Try 8 all across the map up to 1000 rpm to start with. Could also crack the butterflies open a bit so you are not relying on IAC action for air, How much fuel pressure are you running? I have a bin for the 7747 running a 670 on a 350, 60 over w flattops + plenty of cam that I will send to you if you wish as a starting point. Val

Blazin4x4

not sure about the fuel pressure... I have yet to get a gauge hooked up.

So when you say 8 degrees up to 1000 rpm I'm assuming you mean spark slope-deg/1000 in the constants?

It's funny that you say that about the butterflies. I think I went as far open as they can go and still no idle. But if I give it enough throttle to let it run at 900-1000 it will stay running.

Yes, that .bin would be awesome! Pm when you get a chance.

I'll give the new timing a try and tinker with a few things and see what I come up with. Probably gonna be right back here asking more newb questions but hey thats how you learn I guess.

Thanks man.

Blazin4x4

Well I think I need to play with the r/l thresholds but I'm not sure I understand what they do in a 7747... also when I use the bichty xdf I got from val I see accell enrichment vs map kpa... it increases the usec the injectors are open when kpa goes up therefore when in D kpa goes up and up until it drowns.

Can anyone shed some light?

I tried differenet spark advance manually and tried to use ecm to do it and if it moved at all it wouldn't idle in park.

alvanwie

You need to just stabilize idle before you can start doing any real tuning. I have found the best way to do this is to flatten out the SA and VE fuel tables any where near your idle range so that the ecm does not react to the engine flucuations.

Here is what I would do. Set your dizzy to 10 degrees and set the ecm base timing to the same value. In the main SA table, set all values from 400-1200 rpm and 30-70 kpa to 26 degrees. If you are running BBC injectors (80#) set the injector contsant (BPW) to 90. In the main VE table, set all values from 400-1600 rpm and 30-70 kpa to about 40 or 45. Set your desire idle to 800 or 900 and bump the stall saver numbers into the 600+ range.

In general you are trying find a set of parameter that will allow the engine to idle but prevent the computer from changing SA or Fuel in response to what the engine is doing. Once you find the parameters that allow it to idle, then you can start logging data to see what it will really need as engine operating conditions change.

ULTM8Z

Unless you changed the closed loop delay timer, in the first 20 seconds of running, you're still in open loop. Messing with the O2 centering voltage isn't going to do anything.

If the 7747 is anything similar to a 7730, you may want to play around with the open loop fuel tables.

BTW, I've run that L79 cam on a carbed car way back when, and the vacuum is quite low at idle. IIRC, it's very old design out of the mid-sixties 327/360hp Corvettes. The ECM may be just dumping boat loads of fuel in according to the airflow reading. Damn thing made awesome mid-range power though!!!

Fast355

iTrader: (2)

I ran basically the same cam in my 305 (Mellings C-410-P / GM L82, 224/224 @ .050, .450/.461" lift, 115* LSA, 107 ICL, 4* advanced) for some time on the stock 7747 ecm with tuning. Got it to run very well. The L82 cam that I was running only makes like 14 in/hg of vacuum @ 700 rpm and about 8 in/hg when loaded against the converter and A/C compressor. Made tuning a challange. He definately wants the throttle plates open enough to get 700 rpm in Park/Neutral with 0-5 IAC counts, the second he drops it into gear the counts are going to jump up to about 50. He basically needs to transfer the 20-40 KPA region of his VE table down to the 40-60 KPA region, as well as make sure he has about 24* of idle timing in the 40-60 KPA region at idle. That should help.

The cam DOES make awesome mid-upper rpm HP and sounds sweet.

Blazin4x4

Thats good stuff right there. I will try that out this weekend and see how she reacts. Never thought of transfering low kpa for high kpa numbers and I remember a guy at a hot rod shop telling me to take all the advance out to get a baseling idle.

So I'm in o/l? I thought it is set to idle in c/l unless you change it. Can you elaborate?

I'm wondering why my kpa is so high though. I am at the high side of 63 kpa at 850 rpm or so. Is this normal?

I got a high map flag and I also got a Prom error flag. What would cause those flags?


Hey fast, do you have any .bins from that motor? I remember you sent me some .bins but I still don't know what to do to get them to work in my 7747. I think I still have the .bins. Can you explain how to make them work?


Thank you... you guys are the farkin masters. Where's the bow down smiley?

ULTM8Z

Everytime you start the engine (not matter hot or cold), you're in open loop for some specified period of time. In the constants area (at least in the 7730), there are three parameters for this: Closed loop delay timer for cold, warm, and hot. The cold is the longest of course, and hot being the shortest.

One thing I forgot to ask is that if this problem clears up after a few minutes of running? Or does it continue indefinitely? That piece of data would probably make or break my suggestion here...

Blazin4x4

It's a problem at 70 degrees and at 180 so yes it is indefinite... What really puzzled me is how it dies exactly 5.5 seconds after going into drive.

Blazin4x4

Hey fast, wouldn't transferring 20-40 kpa numbers to 40-60 kpa richen it up?

So maybe I'm lean when it dies... the smell seems decent. I'm heading to my storage unit in a few so I'll surely have more questions.

Thanks for the help guys.

Ronny

iTrader: (1)

not sure of your truck but mine can burn and idle at a very rich mixture. when i swapped FP reg springs i in error set to very high fuel pressure. black smoke out the pipes.

so, i would assume you are lean. i dont think spark is the problem. i idle at 20 deg and all cells around where i idle are also 20 should it meander into another cell. i see no reason why it wont idle at 20 deg. or 16 or 24 for that matter. i would up the idle speed with throttle stop screw until it does not die. and log there. adjust fuel for reasonable BLM. move fueling around that cell to match. i bet it will be a high BLM. then gradually drop idle speed 100 rpms at a time till you note a change in idle quality. then adjust the fueling at that point for that rpm/map. a trend may develop of lean. as stated first tune is the idle.

other option is to run OL at idle (especially large cam)but that might need a WB to dial in.

Blazin4x4

Yeah it seemed a little too finicky even for a noobie tuner on a modified motor. Funny thing is rich or lean it dies every time when put in D. I'm using my nose to tell rich or lean because I haven't logged enough to get some usable numbers. 7747 is damn slow... I want an ebl.

I've been mentioning that I had a high map malf flag and rrob just showed me how to fix is. Could the ecm going into n-alfa cause these problems?

Fast355

iTrader: (2)

Sure can, because the ECM reverts to a fixed VE number. You should not be seeing 80+ KPA though.

Blazin4x4

What could cause 80+ kpa #'s. Bad sensor?

RBob

iTrader: (1)

When the engine starts to sputter and/or drop the idle down the MAP will increase. This is a prime area for getting MAP high errors.

Once the tune is better this issue goes away. Until then it is better to set the trip point high enough that the ECM doesn't revert to n-alpha mode.

RBob.