Closing in on a problem

[damanx]

I was just curious about the timing. I'm pretty sure that if Mark had worked a BIN file and the timing was changed in it, then he would have told you to verify your base timing to match the BIN file.

Seems odd that you'd have to resort to doing this for something that automatically controlled if all your sensors and ECM is good.

Here is something you might want to read through. (beware that some pages are out of order).

http://igor.chudov.com/manuals/TBI_Fuel_Control.pdf

[1great40]

I was just curious about the timing. I'm pretty sure that if Mark had worked a BIN file and the timing was changed in it, then he would have told you to verify your base timing to match the BIN file.

Seems odd that you'd have to resort to doing this for something that automatically controlled if all your sensors and ECM is good.

Here is something you might want to read through. (beware that some pages are out of order).

http://igor.chudov.com/manuals/TBI_Fuel_Control.pdf

According to the information you just gave me, the engine is idling exactly where it should for a stock configuration. I had Mark make a new PROM because I wanted a higher idle speed. My 4.3 is a pre balance shaft model (1989) and it's in a street rod. My gut feel is that my drivetrain isolation is probably not as good as what they did at the factory and since these engines aren't the smoothest idling in the world, I opted to get a PROM burned that would bump the idle up a little. Mark also changed things in the PROM to reflect the fact that I'm not using EGR, AIR, or purge. So my only problem is that the idle speed is too low for a nice smooth feel. I have played with upping the fuel pressure to compensate for a dual exhaust with turbo mufflers vs a single exhaust with a street muffler and a cat, since the engine was idling too lean. The fuel pressure change really got the engine idling a lot better, probably as good as it ever would. Now I'm just trying to finesse it to the point where I'm happy with it

[1great40]

Well I need to pat myself on the back for doing a great job on the idle stop solenoid install. But have to give an even bigger pat to the General, whos' little '747 has outsmarted me again.

What worked in theory and what worked manually doesn't work when it's automated and the idle speed with the solenoid not actuated keeps climbing.

So, I guess I can try what Fast 355 suggested and let the thing idle with 0 IAC counts when it's hard against the stop screw, or I can let Eaglemark have another shot at frying up a fresh PROM with more speed dialed in, or I need to delay the actuation of the solenoid until after the truck is in gear and the IAC puts the idle where it thinks it should be and then I bump it a little from there.

An old Rochester 2 barrel is looking mighty good about now :)

[steveo]

An old Rochester 2 barrel is looking mighty good about now :)

i know it seems that way, but it's just as easy to get a 'carb quality' idle from fuel injection as it is a carb, which is just fixed idle air. you can just disable the IAC for anything but cold start, disable closed loop, and run 'er a bit rich.

you're trying to achieve something better than what a carb would give you, which takes a bunch of work and experimentation, but is totally rewarding.

in the end, there's nothing wrong with 0 iac steps when it's hot, though?

the only problem with that in a tbi system seems to be that if something is going to cause idle to -increase- (vacuum leak either expected or not... change in the weather..whatever), the computer is helpless to do anything about it.

So my only problem is that the idle speed is too low for a nice smooth feel.

you can usually force pretty smooth n low idle out of any engine with the assistance of electronic timing control.. almost every engine seems to want more fuel, more timing, and repeat, until idle smooths. this can be done completely manually like a carb n points motor, just turning the distributor and jacking around with fuel pressure and the throttle plate. then just set it back to stock and the changes can be placed in the bin?

[ony]

it kindof sounds like the stall saver inable disable needs set to match the rpms you are trying to idle at in your bin file. + 2-4 degree timming increase at idele make a lot of differents on idle smoothnes as stevo said. my 4.3 is a standard trans I have it set to 16.5 in the bin iam running where as it was 12.5 makes it idle a little better an helps taking off from a dead stop.[normal driving] .

[damanx]

it kindof sounds like the stall saver inable disable needs set to match the rpms you are trying to idle at in your bin file. + 2-4 degree timming increase at idele make a lot of differents on idle smoothnes as stevo said. my 4.3 is a standard trans I have it set to 16.5 in the bin iam running where as it was 12.5 makes it idle a little better an helps taking off from a dead stop.[normal driving] .

Ony, you reminded me of my issues when I first started playing with the timing table on my truck. (note that it's a TBI on an engine that was originally a SPFI).

Would advancing the timing in the idle rpm/map areas of the spark table help him?

[lionelhutz]

I've played with a few 7747 tunes and never had one idle 175-200 rpm off of what was programmed. I recall the idle typically varied by 25-50rpm.

[ony]

that is what mine does 50-75 rpms ,I think he had it change to a higher rpm and the disable inable may need adjusted in his bin . damanx the smoothest idle that I ever got on my 4.3 was a 747 with a modified apab bin timming at idle was 9 degrezz idle rpm 600 but its a std trans and I didn't like the way it took off from a stop.

[1great40]

Needless to say I hit the sack somewhat defeated but hopefully optimistic for a fix. The next morning I fired the truck up to head to church and it ran the way I expected it to. Fast idle when cold, 600-650 in park and about 700 in drive. Put it back in park and it goes. back to 600-650.

the next step is to drop my idle in drive just a hair more so it's right between smooth and making the truck creep in gear. We'll see how this goes.

[Fast355]

Needless to say I hit the sack somewhat defeated but hopefully optimistic for a fix. The next morning I fired the truck up to head to church and it ran the way I expected it to. Fast idle when cold, 600-650 in park and about 700 in drive. Put it back in park and it goes. back to 600-650.

the next step is to drop my idle in drive just a hair more so it's right between smooth and making the truck creep in gear. We'll see how this goes.

Sounds like your P/N switch might be inverted if you are using one. Park idle should be higher than Drive idle.

[1great40]

Sounds like your P/N switch might be inverted if you are using one. Park idle should be higher than Drive idle.

Good observation Fast 355 but that's part of the plan! My problem was that even though I had a pretty good idle in park, when the engine loaded by putting it in drive, the vibration or should I say resonance was annoying. I added the solenoid to just kick up the idle a bit in drive. Right now it's idling at 700 in drive but returns to 600-650 in park because the solenoid deactivates in park. I'm going to bring the idle in drive down a little more so it's about the same as the unloaded idle in park.

My IAC counts are about 10-12 in park but only hop up to 19 in drive so the engine is running slower in drive than in park without the kick up solenoid

[1great40]

Hello all, I have been away from the board for a bit. Just reporting back that the solenoid fix is not reliable. I'm guessing it has something to do with when the ECM looks at the TPS voltage for it's baseline. What I'm thinking is that if I put the truck in gear too soon after starting, the ECM reads the voltage from the TPS but the TPS voltage is elevated by virtue of the fact that the solenoid as moved the throttle slightly and this screws things up. When it does work, The engine idles about 650 or so RPM in park and then kicks up slightly by the solenoid when in drive. When it doesn't work, the engine idles at about 900 rpm and drops down to about 750 or so in drive. So my attempt to fool the ECM isn't working. I'm guessing I will need another PROM with the idle set up a little higher than the last one EagleMark made for me.

I might try the suggestion about running 0 IAC counts at idle by messing with the minimum air setting again, just letting the engine run at about 800 RPM in park and letting it drop down from there in Drive.

For a while I thought I knew what was going on with this engine but now I'm more baffled than ever :)

[telecasterfool]

Hello all, I am very new to tuning, but I have a 4.3 v6- now running a 1227747 ecm with a AMTU 5.0L $42 bin. I went through the stock $AO bin and transferred all the pertinent data to a $42 4.3auto bin, but it was ASYNCH, and now I've transferred to a Synch bin. My point here is though- there is an RPM for Drive setting, and one for Park/N. My truck idles at the correct settings for both with 10 degrees timing. It has a very mild Comp Cams 260AHR camshaft. Hope this helps

[ony]

you may have better luck idling with an acyn bin till you learn tunning a little more.what are the spec. on your cam compared to a stock cam, I have a v6 also and was thinking of a rebuild and a light cam up grade.

[telecasterfool]

Hi Ony- here is the spec:
COMP Cams 249-CL09-412-8

Exhaust Valve Lift (in.)
0.5
Intake Valve Lift (in.)
0.500
RPM Range
1000-7000
Int. Duration @ .050 in. (Deg)
206
Exh. Duration @ .050 in. (Deg)
210
Int. Duration Advertised (Deg)
260
Exh. Duration Advertised (Deg)
266
Lifter Type
Hydraulic Roller
Usage
Street/Performance
Engine Make/Size
Chevy 200-262 (90 Degree)



I was mistaken on the timing: it's about 26 degrees at idle. So far the idle hasn't been too bad- only been a couple days. I was able to emulate and tune the open loop idle last night. This cam is very mild, but I was just looking for a slight step up from stock with good low end torque. I used the GM performance corvette beehive valvesprings and the Comp Cams magnum roller rocker arms. No head work required if you go this route.

I still have all the info if you need it. This site has been such a big help, I'd love to help someone else.