Mark_ZZ3

Am I chasing the impossible?

I've been trying to tune a setup for some time - without much luck. The challenge is startup. Seems to need LOTS of fuel and you need to open the throttle a bit to help. I can't seem to find a config that makes this any better ... So is this just the way it needs to be?

350 (rebuilt), Edelbrock RPM heads, 3/4 headers, unknown BIG cam - idles with 10-12 inches of vacuum. 1989 TPI setup on top, 22lb injectors, AFPR set to stock, timing set to 8 btdc. No emission stuff.

When it does run, I can get the VE tables to work ... seems to need them set to the 40's at 50kpa which is where it idles. BLMs work here. Throttle is crisp to jump up ... but need some smoothing in the tables. So far ... runs well.

The startup is still a mystery. I can't seem to get it to start "nice". Needs help. Sometimes needs two tries. Sometimes feels like no fuel at all. So weird.

I've run it with the fuel pump ON, pressure stable, checked and swapped sensors, check grounds, wiring, all the usual stuff. The engine simply has low vac on startup ... seems to want lots of fuel in order to start. Then smells rich for the first 10 seconds.

Anyone have a similar issue with a low vac cam? Was there a way around it, or is it simply the case you need to help it?

(I've search and search forums looking for similar cases. Found one waaaay back, but wasn't able to help).

My best setup so far ...

- removed all the delay in the Crank Fuel Delivery Delay
- Changed the crank pulse multiplier to be "1" in pulse 1-6, and then .25 there after. (The engine seems to try and start if you crank it long enough)
- richened up the crank pulse with at the current temp ... 3 and 4 times! But if FEELS like I need to just go crazy on this number.
- Startup enrichment is stock

I've tried various configs to see if any difference. Not really. Tried a bit more spark and less spark. No help.

Observation ... on the Vac gauge ... there is nothing during crank ... usually I see the needle move. Maybe engine issue with valve overlap. Unsure.

Sorry for the brain dump. I've spent so much time tweaking this setup ... but maybe its untunable.

Mark.

cpalmaccio1@gma

I was in this boat as well. Big cam for my computer. You have 2 choices..... Get a chip burnt. Scott hansen of tuned performance and really knows his ****. You can get a safe start mail order chip from him. Be advised though if you want the car to run optimum you will have to data log with scott and go through several chips. He will get it running right but will take some time. I went this route at first and he burnt me a really good safe start chip. I however wanted more control and also to learn myself. On the advice of great guys on here i went with rbobs ebl p4. I couldn't be happier. At first it was fustrating because i know nothing but our forum guys and rbob walked me through it. Rbob has great customer service .What i ended up doing was taking scotts scotts tables and using them with the ebl. The ve learn capability if the ebl along with a wb 02 are a necessity for tuning what you have unless your a seasoned tuner like scott.

cpalmaccio1@gma

Also.... Don't foul your plugs like i did 3 times.

Orr89RocZ

iTrader: (20)

ULTM8Z

how's your IAC motor? I was getting some rough starts a while ago and chased it to a bad IAC (even though once it was running the "bad" IAC held the idle stable).

replacing the IAC solved the problem.

Mark_ZZ3

VE once running is ok. I got those numbers Ok range. Seem to be in the 50-60 KPA range. Had to adjust to 40-ish VE to get BLM in order. At idle vac is only 10 inches.

I've started from stock a few times and have not found the best combo yet. So far crank pulse width is 3X over any sock config which still might not be enough. Crank pulse multiplier is modified over stock. Removed Crank fuel delivery delay.

Startup Enrichment ... that is used AFTER crank? Ok ... have not adjusted that one ... might explain the times when it started to fire, but quickly died off. If I had to adjust the crank pulse 3X over stock numbers, then the same could be true for startup enrichment. I need to look at the HAC file and see where it uses that.

So ... with larger cam ... it is achievable to have it start on it's own without having to crack open the throttle? Good to work towards.

Mark.

Mark_ZZ3

I'm doing my own chips. I live the MAF world mostly (and 12p code). The 7730 SD is new for me. Need to learn the tables and such. Perhaps starting with an engine that was never run with a TPI before wasn't a great plan ... but that is how I learn.

Mark.

Mark_ZZ3

Tried a different TB, as well as different TPS, ICM, and IAC. Same results. Could still be something mechanical ... but might be my code.

Mark.

Orr89RocZ

iTrader: (20)

84Elky

You're going to think this is totally crazy, but had same hard to start issue. So questions: Does it start easier when you let off the key? Is it harder to start when it's hot?

If either answer is yes, check your coil wire for continuity and proper resistance. Wiggle each end around while checking. I had a brand new wire set that had a defective factory connection. Was worse when it got hot. Would run great, but always hard to start.

Also agree with Orr89RocZ that idling at 40-50 kpa is not a big cam and should provide 14-16 in Hg unless a wild overlap grind (unlikely), but 10 in Hg at that kpa seems low. Vacuum leaks?

Mark_ZZ3

An update ... traced an issue down to bad wiring on the fuze for the injectors. was not fully connected during crank ... all the time. Hence odd problems. After trying to tweak and tweak, I finally said something is wrong with the engine. It's not tuning. Once that was fixed ... THEN it was tuneable. And yes ... it will start on it's own. Whew!

Now the enjoyment of tuning a working engine!!! Lots of smiles in the garage once it ran. Now to sort out the VE tables in cruise and such ... idle seems to jump to 1700RPM at times with the throttle closed. Need to datalog. Long bunch of days.

Mark.

1MeanZ

iTrader: (9)

Subscribing to this. I fought with a "larger cammed" speed density 350 TPI last spring for hours and hours and could not eliminate an idle surge. Car started and ran really well except the idle. Curious to see what works for you.

ULTM8Z

I'd recommend going open loop at idle with the S_AUJP. That pretty much solved all my idle and tip-in issues with my Miniram.

Orr89RocZ

iTrader: (20)

x2. But if you want to try closed loop have you messed with the o2 volts parameters? I think there are some rich lean offset tables or values for idle and such. Try swinging them up some to account for overlap oxygen much like how AIR diverts 100 mv offset

ULTM8Z

I played around with those for years trying to take the Miniram beast.... but I never quite got it right until I went open loop idle.

Orr89RocZ

iTrader: (20)

Yeah. The miniram just suffers from low plenum volume and air distribution issue. Gm had offset fueling cyl to cyl for the lt1 to help that issue

ULTM8Z

I'm just continually very thankful for the folks who put in the time and effort to decode all this stuff and generate the tools like Tunerpro and the SAUJP stuff... RBob, 84Elky, JP86SS, off the top of my head..... and the others (forgive me for not mentioning them by name).

I literally would not be running the Miniram right now if it weren't for the capabilities those tools gave me.

Mark_ZZ3

Surprizingly the idle was the easiest part of this setup. At first it surged and was super rich. Once I sorted our "where" the idle was in the sense of the Kpa, I adjusted the VE waaaay down. This engine was in the 50-60 Kpa range where the VE table had 70-ish. I had to reduce that down to 40-ish and the BLM sits around 128. From that area, I smoothed the numbers so as to avoid a big step. I still need to plot out the cruise zone and coast zone as these are now at different vac settings compared to stock setup.

The startup is much improved. Consistent I would say. Always starts if you just tap the gas pedal a bit on start up. Otherwise it will start up after a second or two of cranking. I could not seem to get the right combo to make this stock like. Too much time spent on it ... needed to get the driving settings in line.

The base config is AUJP, but with a few settings pulled from the vette. I like the base line vette for lock up convertor stuff.

I need to run around in open look with a wideband on it and set the VE tables yet.

Mark.

84Elky

Some things to help big cam (or really any) TPI idle. Lean out the idle area in the VE table to achieve 136+ BLM. Won't hurt anything at <1000 RPM because only 6+% lean and no load. Heck, highway fuel mode does same thing at much higher RPMs. Set Spark in RPM idle range to the same value for every kPa.

Here's a trick to optimize idle spark by using a vacuum gauge and dial-back timing light. Set Spark Table idle RPM range to same values (for example 22 degrees for all kPa values 400 to 800 RPM). To minimize idle spark fluctuation, zero out the "Idle SA .vs. RPM Error" table.

At operating temp, idle car with EST Bypass CONNECTED (yes "connected"). Turn distributor until maximum vacuum achieved. Lock-down distributor. Spark is now where idling engine is the happiest. Using dial-back timing light, determine Total TDC timing at idle. Say it's 26 degrees BTDC. Assume ECM Base Distributor setting is 6 deg. That means 16 degrees of reference spark is essentially running the engine [ECM TDC(22) - ECM Base(6) = REF(16)]. That's what the engine wants because of highest manifold vacuum.

Next, disconnect EST Bypass line and check timing. Assume physical distributor location is now providing 10 deg BTDC. Change the BIN Base setting to 10 deg and increase idle spark everywhere by 4 deg to achieve the same reference spark. Now [ECM TDC(22+4=26) - ECM BASE(6+4=10) = REF(16)]. Optimal idle spark now set. No more guessing! Don't forget to renter values in the "Idle SA .vs. RPM Error" table.

If for some reason 10 deg is too much Base for startup, change it say to 8 and increase Spark Table at idle 2 degrees where now [ECM TDC(22+2=24) - ECM BASE(8) = REF(16)], etc. Not the most desirable because BIN not equal dist. setting, but optimal spark is still being provided at idle. Engine is now as happy as it can get.

moneyman380

Following. I've been fighting my setup for awhile now as well. Big cam superramed 355 on 730 ecm. I have start up issues and idle issues. Using a ostrich 2.0 for tuning on tunerpro.

Orr89RocZ

iTrader: (20)

I know my 400” with a 246/252 cam wouldnt stay running with est disconnected with timing less than 12 deg. It wouldnt start well without total timing atleast 28 deg, i believe i had near 30 at idle cells.

Definitely like staying open loop at idle to let overlap do its thing and not worry about o2 correction. Read plugs to get idle mix right but wideband helps just tune it leaner like mid 15’s. Try that.

ULTM8Z

SAUJP with open loop idle would be my suggestion as well.

Even with a mild cam, it worked wonders for my Miniramed 350...