I really want to improve how my engine starts up. What will happen is when the engine does fire, it surges up to around 1300 rpm in about a 1/4 of a second, falls like a brick, and is then caught by the ecm and then it stablizes at around 1200 before falling off to the desired idle speed of 700 rpms or so. Ideally, id like it all to be in one smooth motion rather then an abrupt instantanious rev up, drop off, come back up and fall off. Ive played around some with the IAC but that has little effect. I think its probably more likely the timing. Theres a pretty steep ramp up to the portions of the timing curve that the engine operates in and the engine is probably 'climing the hill' sort of speak and then when the timing falls off the engine drops off. Ive also heard some audable knock on start up occasionally as well. Any input on how to get a smoother start?

Heres the timing curve:

 

How about in table form?.

 

Ok, theres the table for those who prefer it. I get more meaning out of the graph but thats just me.

 

One thing thats made it kinda difficult is the fact taht this is an engine that would like to have more gear and more stall instead of the low rpm stock stall and 2.77 gears. I have to give it a good deal of timing early on in jsut the right doses or it just bogs down real bad in 2nd-4th under 1600 rpms. So I have to have those steep changes in the timing.

 

If you're using a lot of throttle and it's bogging in 4th gear, you might have a TCC issue. I think you're using the 88 ecm but in any case, the 89-92 8746 have a table that is based on engine vacuum vs timing retard for tcc lockup. Stock my table has over 4 degrees (I think, might be more) taken out at 0 vac (near wide open throttle) but this might not be your case. I'm just speculating reasons for 4th gear bog because it shouldn't.
I have to go but I'll reply later.

 

My tcc is totally gone. Ive disabled all but the manditory lockup after 80 mph. Not really to lock the tc, but I hear the trans only routes fluid to the cooler when its locked. The edelbrock cam I ahve has something like 280 degrees of advertised duration, and I wonder if that isnt part of the bogging problem. The additional overlap may not sit too well with 8.5:1 compression at low engine speeds. Ive gotten it to work pretty well but it was alot more work then I had to put into the rest of teh table.

 

I don't see where your table is that far off.

Lets see you VE table.

 

ok, heres the VE table.

 

And the other table....
BTW, what is your actual base timing set at, what about the value of 'initial timing' in the chip. What are the 3 bias values (main, temp, tcc), what are your temp tables? If your main is exactly what you're running (base is set with initial in chip) then add some timing down low and disable the PE timing. What is going to be tuff is getting a larger cam to work with a small torque converter AND have low compression. Is EGR still enabled?

 

I never really touched the biases, theyre still at 20 deg. Never could get a clear answer as to whether to adjust them or not. Tuner cats automatically subtracts the biases so i see what the dist. will see as far as timing goes. Hence, I never really bothered with them. The base timing is set to around 2 deg BTDC and the base time in the prom is set to this as well. The base timing doesnt seem to have much impact on start up. It really seems that once the ecm enters the loop, thats when it gets kinda funky. Ive noticed that when i smoothed things out a bit (table above), the start up was a bit smoother. Its almost like as soon as one of the cyl. fires, an unseen force jsut gives the piston an all mighty kick and the engine instantly snaps to around 1200 rpm and then it drops off untill the ecm catches it.

The egr is gone, completly disabled, and tuned to run w/o it. The cam itself only has around 204 degrees @.05 but its a real lazy profile and has lots of advertised duration. That may alow the cylinders to bleed off pressure at low speeds and it certanly seems like it. At low rpms (<500) it lopes real bad and doesnt pull much vacuum. This again may be a problem since the engine will swing cross the tables when it dips down that low. As for the bog, Ive largely eliminated it though, and gotten it to be pretty responsive.

 

As for the bog. I was jsut reminded by another thread that Im still using the stock timing set that came with my engine. Forgot all about this but IIRC, alot of these smog era timing sets came with 5 degrees of retard built in, so in essance im running my cam with one degree of retard, which will shift the power curve over. Goauto center has my 350 with the same cam profile in it. It has a very tpi-esque torque curve. >link<

 

Try taking some fuel out at the 400RPM/100 K/Pa area.
What K/Pa does your engine idle at?.

Let's see you IAC park table.

Looks like it get a huge gulp of fuel, so I'd about bet the IAC par numbers are high.

If you have to resych them and the crank AFR might take some work, but it'll be worth it.

 

The park position is set to 145 counts

 

So maybe tapering the tables off at around 400 rpm and/or curbing the crank AFR would help? Should I try attacking the very low portions of the VE table first? Or maybe try the crank AFR? The engine pulls around 20 inHg@750 rpm. At 550 its around 17 inHg and form there it drops like a brick. In gear is around 14 inHg with a smooth idle but a somewhat rowdy exaust note.

 

I'd try subtracting 10 from all the park positions.
Then in the 400 and first RPM range above it, and in the 80+ K/Pa area take some fuel out.
Save the crank AFR for a final tune.

 

I think the engine starts off at the park position and then decays to the initial steps in that table but how long does that usually take?

 

Could you post your second VE table. I can't tell what your VE table looks like without it.
Also, if all biases are accounted for then I would still take a look at the temp SA table. Zero it out for tuning. Stock you'll have a swing from 6 to -2 degrees of timing just based on normal operating temps.
Then like grumpy said, take out some fuel and see if the bog is better or worse and then watch your TPS vs mph vs map. The least amount of TPS and MAP to hold a specific mph on a flat road will tell you if you're going the wrong way with your fuel and spark.
FWIW, you might want to disable the IAC all together when doing this fine tuning. The calibrations will spit in extra fuel with rapid IAC openings. I haven't measured it but I don't see why they need the extra fuel. The MAP AE table should cover this....or shouldn't it?

 

Goes like this.
When you turn the key off, the IAC goes thur a reset routine.
And depending on code parks the IAC at like 130 counts.
At key on the ecm reads the CTS, and then moves the IAC to that position.

So actually the IAC goes from the reset position to the Park position as you turn the key on.

Then once the engine is running the IAC should decay down as the now running engine, goes to the commanded idle speed.

Now you have *deadbands*, and some decay rates for the choke, SA, etc that all effect the IAC. If the ecm is detecting what MIGHT be a stall then it overrules all those for that.

Just don't get ahead of yourself on what to play with. Work with what I mentioned, and once you get clear on those three and their interactions, then you can play with all the little tweaks.

Learn, crawl, walk, run, that sort of thing. Learning the start stuff incorrectly, and trying to relearn it would be a royal PITB.

 

Ok, heres teh extended ve tables. Didnt have to du much with it as the 350 seems to be just a larger version of the L03 and has similar VE at high loads. My biggest problem is I have no idea what the VE's are at low rpms so I dont know what the fueling should look like down below 800 rpm. Maybe today ill force the engine to run at low speeds so I can rough it in a bit better down low.

 

Ah, ok... So the IAC goes to those then on start up. Origionally, the stock ones had like 180-210 counts at the cold temps. The engine would do the same thing it does now but idle at the max allowed idle speed untill it warmed up. John, Ive already zeroed out the cool SA adder tables.

 

The IAC at power up & engine start is a bit confusing. One drawback to the '8746 is that there is no crank IAC setting other then the one park steps term (at LD511).

This makes it difficult to get enough IAC for cold start while not having too much IAC on a warm start. The addition of a IAC start position table is an asset. Although it is not an easy code change to make.

I ran some startups on the bench and was suprised at how fast the IAC can increase (cold start) or decrease (hot start) upon the engine entering a run condition (> 400 RPM).

I used a stock ANLU cal, in this case it also matches the hac if one wishes to follow along.

At key on the IAC is at park position, 160 steps. Once the engine speed exceeds 400 RPM the IAC will quickly move to another position. The IAC step speed appears to be 160 steps a second. Hence the rapid movment.

The new position will be defined by several tables. Add together the value at LD50F (40 steps), the value of the baro table at D558 (10 steps @ 100KPa), and the value of the IAC Motor Position vs Coolant table at LD547 (64 steps, 90c startup temp), for a new position of 114 steps.

In this case the IAC moved from 160 steps to 114 steps in about 360 msec. This decrease in steps started immediately upon the engine reaching 400 RPM.

After about 1 second the kickdown delay expired (table at D560) and the IAC further extended (steps decreased). The ANLU kickdown steps are at LD527 (65 steps) and are decayed out according to the filter term at D53C (64, smaller number is slower). This took about 3 seconds.


In the case of a cold start (-5c) the IAC increased from the park position (160 steps) to 191 steps (max IAC). Again this was a rapid increase which took about 300 msec.

Without a crank IAC position it becomes a balancing act for both a cold and hot startup. It can still be improved upon. The park and run steps along with the kickdown steps and kickdown delay can be adjusted. Increasing the throttle opening (idle screw) decreases the amount of IAC required and lessens the impact of the IAC steps and motion.

RBob.

 

Thought id try something. Did a cold start with no IAC. Fully extended. It still does that same instant to 1000 rpm bit. Cranks over about one revolution and as soon as the gas makes its way into the cyl, it immediatly fires once or twice, and without the IAC, it promptly stops dead in its tracks. Its jsut like, crank..crank...crank... FIRE!!!, and then the sound of the starter motor winding down. Its that sudden. Come to think of it, the car has done this since the day I bought it. Even with teh stock L03 it would do that same thing, crank, fire, die when its cold out. Is this maybe a base timing issue or maybe too much fuel on cold start and possibly not as much of an IAC thing?

 

<sigh>
Ah, Grasshopper,
you just jumped right past everything.
Remember my advise of one step at a time.
Once you have the basics down, then you can move on.

Now that you have two entirely ways to handle it, you might get to the stage of having a real problem, rethinking too many things that aren't applicable. Trust me, I know how this goes..

 

Jsut want to relay some things. I found out today that below 800 rpm its crazy rich. I remidied that so at least up to around 50 kpa its tuned closer to where it should be. Another interesting thing is that the motor flooded and the plugs fouled out after the nostart and it wouldnt even fire. Cleared it out and did some more low speed tuning. This really isnt to remedy the cold start issue as much as to remedy the fact that when the engine gets a taste of all that fuel it gets a bit upset and the rpms dip. To be as specific as possible, the engine seems to, for all intensive purposes, snap up to around 1200 and then immediatly cuts out. The computer does manage to catch it 99.8% of the time. If it does cut out and stall, its next to impossible to refire it. Thats the issue that I have. The whole event happens over less then half a second. Not drawing any conclusions, just want to make sure im not being ambiguous in any way.

After the cars had a chance to sit over a cold night, I'll go out and try again. Ill also make some adjustments to the IAC table as suggested. Maybe even record a short clip of what it sounds like.

 

Had to take the car out for a minute and the reduction in IAC counts as per grumpys sugestion combinded with me getting the fuel closer to where it needs to be really seems to help eliminate that sudden pulse that it has on start up and the engine comes up much more uniformly. It definatly aint no Bently or a Rolls-Royce but its alot better. The acid test will be the cold startup tommorow after its been sitting awhile.

 

I was having a similar issue

I started by taking away spark from the closed spark table. Grumpy then caught me and saved me much frustration when I had entered zero's in the table. My park position seems to be adequate. I need to check my rpms the next time I start it and see what it is flairing up too now. I think it is close to 1200 - 1500 rpms, then right to idle.

I then went and ran VE master, and had to go back and start adding spark to keep it idling when I came to a stop.

Listen, read and reread

small changes and keep track of them. I create a copy of my current bin, then rename that copy to what I am changing, then edit. Makes it easy to back up a step

 

Yeah, hopefully the steep reduction in fuel and less counts will do the trick. I had set my min blm to 96 and at low speeds both it and the integrater where completly bottomed out.

As for archives, every 3-4 bins, I save a backup to the archives, and I have around 80 bins so I have a good idea of how things have chaged if I want to look.

 

The cold start is definatly better, there isnt that sudden spike that it had before. Still peaks a bit for a moment when it finally catches. The peak pretty much absent on a warm start after then car has been sitting for a bit but on hot starts and cold starts its there, but at least it doesnt crater after it catches and almost die each time I try to start it.

 

Here is a little visual of the IAC after the engine stops running. Notice the IAC reset, it's the big red line.

 

I hear it sweep through its range of motion to calibrate each time I shut the engine off, but I didnt know it could actually move that quickly.

 

At the graph point of ca 13368 where the IAC line goes straight up is not movement. What is happening is that the ECM sets the IAC counts to 200 without moving the IAC. This is done to get the IAC counts high in order to step to a fully closed position as the first step of the power off reset.

The IAC is then commanded to move to zero (the downward slope), then once it reaches zero it is commanded to the park position (the upward slope). The IAC stepping rate is 160 steps per second.

RBob.

 

(Hannibal Lecter)
(Silence of the Lambs)

Clorise, I love your graphical Lockers.

(Hannibal)

 

That's not the half of it. I'm just having trouble getting a clean binary input with visual basic. I know it's just me because I can't seem to figure out how the data is stored in a byte array. So I have it as text input which is a string, and then I convert the ascii character to hex for EVERY byte recieved. This is a royal PITA.
I have the ability to read in log files from lockers and display the data in the plotter. Very user friendly and full of features. I'm just trying to get it to work with the dynamic data as of late.
If you want the plotter I'll send it over, just e-mail me.

 

Is that plotter a custom OCX that you bought or is it something you built?

 

I didn't make it, it was bought by some graduate student before he switched to using LabView, so it's mine and I can't release the ocx. The product is activex IOComp plot pack.

 

While in the past I've mentioned closing down the max and park IAC counts, I've recently seen when doing the opposite, can work.

On my car, I installed a bored engine, and the startup routine has been driving me bonkers. Well turns out I had an couple electrical gremlins, that were making it all just too much fun, but anyway. I wound up opening the max position from 175 to 231, and the park start position from 150 to 230. And then have the normal warm-up start park positions. With no real engine vac, from the big cam it takes a large slug of air to get things to light off.

 

In that case why not just reduce the startup enrichment? I guess both work ... either use more air or less fuel (or a combo of both). Just curious why you took the more air approach instead of the less fuel approach?

I honestly think that doing a combination of both is probably the best bet. Big cams just need less fuel at idle. Thus, they also need less fuel at startup. But, just like you said - since the vacuum is lower we should try to let more air into the motor in order to get things moving. Thoughts on the combo approach?

Tim

 

I tried both, the more air worked better.

 

Awesome. That actually makes a LOT of sense the more I think about it - and with the testing I did today. You still want to fire off with approximately the same fuel to get that thing spinning up fast. You just need lots of air.

I decreased the startup fuel by 20% and the same thing happened. On my first try to start the engine spun up and then died. On the second try to start the motor spun up, started to die, and then the ECM caught it and all was well. This time I had the wide band hooked up and the AFR was around 15:1. Obviously, decreasing the startup fueling didn't help.

I then tried putting the startup fueling back to stock and increasing the park position to 220. The same thing happened. HOWEVER, review of the data shows that the park position was 160 and not 220. I reviewed the anht_hac and sure enough ... there is a max IAC step setting at 160. This constant currently is not in the TunerCat TDF. I just added it. The address is at 66A. I'll test whenever it cools down again. I'll also ask TunerCat to add the max IAC setting to the TDF. You guys working a Super $8D ECU should add this.

Tim

 

Something to the same effect; on our engine dyno we're able to motor the engine and have found that you can NOT just limit the air or else the motor will shut off. We tried holding the throttle open at a very small amount and it ran flawlessly at 14:1 below 8000rpm and then at 20% throttle and around 8500rpm the engine shut off from not enough air (negative torque is a sign of engine off).
In a way, our little 4 banger is an extream engine. It's making over 140hp/L. On startup I found a technique that starts even the most stuborn of engines, you crack the throttle open a bunch and slowely close the throttle to richen up the mixture. Sound familiar?
Then when I get to tune the cold start (once a day usually) I richen it up and crack the throttle, fires right up.