95 4.3 TBI spark table info

Hello,

I have a 95 4.3 TBI engine with a 01227747 that for a very long time have had an idle hunting problem. After years of research I couldn't find a solution to straighten out the idle. People then advised me that that firmware in the ecm was out of date.

Then I was introduced to megasquirt. I have since replaced my ecm with megasquirt II, v3.0 and have regretted it for a while.

I am just trying to get this stock engine and it has plenty of power in stock configuration for what I am using it for.

I am using tunerstudioMS (I know there are probably not a lot of people familiar with that) but I am trying to create a spark table and I have no idea where to get started. Does anyone have or know how to create or where to get a spark advance table for this engine?

I can get it to idle, but the idle is around 1500 rpm and according to the spark advance table this is where it should be. Can anyone give me a target idle RPM for this engine?

I am greatly appreciative of any information that I can get and thank you very much in advance for your time.

Will

first off i don't claim to have any knowledge of the tbi 4.3s, i do have a 95 blazer (CPI) which runs 7427. did the 95 tbi motors have the "vortec" heads? the cpi motors did.(completely different spark requirements from the prevortec heads......) i played around with several different bins for mine, found that the astro cpi tunes had quite a bit more aggressive spark tables than the blazer. made a "bastard child" bin.really woke my blazer up. maybe you could look at some different bins and see how they handled the spark. you cant take the 7427 tables copy and paste, but they should point you in the right direction......
either way, your gonna want to do some data logging to see what your truck really wants. sooner or later somebody with some knowledge will chime in............

have you checked out tunerprort? i believe most of the folks on here will be more familiar with it.....

Thanks for the response and clear information.
No I have not checked out tunerprort yet. I just found this site today.
My engine is from a 95 s-10 blazer (or so I am told from the junk yard I bought it at). It is indeed a TBI, according to the research I have done it is a vortec technology and it has the vortec valve covers.

Right now I am stuck with the generic 12x12 spark advance table that megasquirt produces generically. I can only get my idle to go down by retarding the spark with the distributor. Then it does not like to start. Megasquirts information and forum is really quite terrible and I am kind of regretting getting it. I have been trying to get this damn engine to run right for 4 years now. At this point I do not think that the 12x12 table is really even big enough for the table that I need.

I have read online and set my base timing to 0 degrees at TDC, however, with the timing wire unconnected I can't even get the engine to start. Is this really the correct way to set timing?

Is it really possible that there was something wrong with my factory ecm? I question that because I have two of them and the idle used to surge on both of them.

I have been logging a lot of stuff but, right now I am at a point where I don't even know were the advance should be at idle.

Thanks for your response. I will check out that other site too.

Will

my std trans idle vareys with different bin files some files 550 most are 600 a couple 750 they are all set different. I had a 95 engine like yours that I replaced it idled good at 600, but I was running a 161288 ecm that is what is in my 1991 truck. the heads are different than swill port but the combustion chamber look the same its not heart shaped like the true vortec heads.12-18.5 degrezz with timming set to 0 should give you smooth idle if everthing else is right with a stock engine. I run 20 at idle with that engine but I do a lot of dirt road driving.here is one file you can open with tuner pro $ao an see what I run in the main spark table.

Awesome thanks for the info, I am now learning how to use tuner pro so I can open it and see it. What would I use to connect my ecm to my computer to use tuner pro?

that engine was really worn out the balance shaft and cam gears caused a lot of knocks at a steady speed so you could probly add some timming , you need a ald cable I think is what it .isd key board not working. is called. get on moatse web sight they have all kinds of things for data logging and chip tunning.

Thanks,
I figured out how to read your bin in tunerpro. To be honest with you it left me a little astonished. Either I am not correct on how I am reading the table or your numbers are way off from what megasquirt created for me. I am not sure if your table is representing total advance but you have much lower numbers then I do.
Here is what my table looks like with the megasquirt running a 2.5 bar Map sensor:
Attachment 10877
I am starting to feel like the megasquirt was a bad idea. From what I have seem most gm tables are bigger then the 12x12 table you can create in megasquirt and tunerpro has a lot more parameters and a lot easier navigation of software then megasquirt. I don't know if it is smart to switch back. I was thinking today about creating some connections in the harness so that way I can hook up either the megasquirt or a gm ecm with tunerpro. Does this sound like a good idea?

I set my base timing to 0 degrees, pulled the valve cover and distributor cap as I rotated the engine by hand (underneath from the flywheel) and verified the valves as they opened and closed and the distributer as it went all the way around. For some reason it will not start when I disconnect the bypass wire. Is this common?

Also my fuel injectors 52355209 but I can't find any solid information on the internet about flow rate. Right now I have it set for 60#.

I am really excited about learning all this.

this bin is one iam playing with in my truck now with a new engine I pick up 2-3 knocks whin shifting gears. I don't know about megasqwirt.i would think it would start with the wire un hooked, might be something wrong with yore limp home mode.i think nasty z has mesed with you set up before maybe he will chpme pn. do ing a lot of misspelling and my delete botton wont work.

Sorry to read about your key board ony. Not sure if my typing would be readable if my delete button did not work. Thank you for the effort.

Tried some new stuff tonight and got some interesting results.

Is it accurate to check your timing with a timing light while it is cranking?
I unplugged the bypass wire from the megasquirt so there should be no timing advance; however, I can't get it to start and run like that so I put the timing light on it while it is cranking and trying to start. If this is accurate then it means I am about 15-20 degrees retarded. The other night I took the valve cover off and distrib. cap off and rotated the flywheel twice to go through all 4 strokes. I verified that the distrib. was pointing in the right direction for when the valves were working and the timing marks were lined up. However, I don't know if that is specific enough.
Does anyone know a good way to get this timing lined up? The only way I can think requires three people. One to crank, one to hold the timing light, and one to turn the distributor.

Deciding to throw caution to the wind (being a frustrated newbie at this), I changed the spark table so it would have radically different advance seeing as it was normally reading 20 degrees I set it so 800 rpm would be the 20 degrees instead of its 1200. Well all the megasquirt did was increase the advance to 33 degrees and it started at 1200 rpm again. Thinking that the base timing is not correct, the only other issue I can see is my required fuel may be too high.

Thank makes me wonder about my injectors and try to figure out what their flow rate is.

Megasquirt is really frustrating me and I am thinking about converting the harness back to using the 7477 ecm.

Sorry for the long post, any thoughts?

Although there is differences between ms and extra it shouldn't be hard to get it idle. When you talk about bypass I will assume you are using a hei 7 or 8 module. With the bypass disconected set your initial to 10 advance. If everything else is correct it should run and idle. Once that is working you can proceed with setting the reference angle and that is done differently for different firmware but in extra go to fixed timing and do reference until it matches. This is from memory. I have two cars running ms and the setting can be different. I mostly fool with gm 6395 and 7427 although one of my cars has both gm and ms.

are you positive the idle problem is in the tune? have you checked for vacuum leaks? a spray bottle of soapy water can save a lot of headaches. a bad diaphram in the brake booster can drive a man crazy chasing idle problems...... still seems the ms should run with the bypass disconnected, maybe have the ignition module tested, check voltage at the module........ they do some funny things if ya get one that is a little flaky or the voltage is off...... i have seen factory modules with 20-30 degrees difference to one identical to it............

i don't believe the timing light will tell you much during cranking, too much variation due to compression,starter and other stuff......

Quote:

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Originally Posted by myburb

Although there is differences between ms and extra it shouldn't be hard to get it idle. When you talk about bypass I will assume you are using a hei 7 or 8 module. With the bypass disconected set your initial to 10 advance. If everything else is correct it should run and idle. Once that is working you can proceed with setting the reference angle and that is done differently for different firmware but in extra go to fixed timing and do reference until it matches. This is from memory. I have two cars running ms and the setting can be different. I mostly fool with gm 6395 and 7427 although one of my cars has both gm and ms.

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myburb,

Thanks for the info. I have the hei 8 module. My engine does not have degrees of advance on the timing belt cover. It only has the one slot to line up.
My biggest problem with megasquirt is that there have been numerous updates to tunerstudioMS which major changes and after searching the internet, the manual only references the older version of tunerstudioMS. For example, the tool bar is different on my version and I can not find the location to set the reference angle or fixed timing. I appreciate the info. I am at the very beginning of the tuning process and have no way of know if my timing is accurate other then pulling the valve cover and turning the engine by hand.

Quote:

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Originally Posted by skandolis

are you positive the idle problem is in the tune? have you checked for vacuum leaks? a spray bottle of soapy water can save a lot of headaches. a bad diaphram in the brake booster can drive a man crazy chasing idle problems...... still seems the ms should run with the bypass disconnected, maybe have the ignition module tested, check voltage at the module........ they do some funny things if ya get one that is a little flaky or the voltage is off...... i have seen factory modules with 20-30 degrees difference to one identical to it............

i don't believe the timing light will tell you much during cranking, too much variation due to compression,starter and other stuff......

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skandolis,

I am not sure if the idle problem is in the tune. The idle used to hunt prior to megasquirt. The folks at diyautotune told me it megasquirt would help me out. The MS does try to run with the bypass disconnected. It cranks and stumbles once or twice, but can't stay running.

As far as vacuum leaks, I spent a year looking for them. I found a number of people online that had the same idle hunting as I had and replaced many parts looking for vacuum leaks to no resolve. The most damning evidence that suggests there is no vacuum leak is that when hooked up to my laptop my MAP is very constant.

I am at the very beginning of the tuning process. All my tables were generic tables created by tunerstudioMS (Very difficult software to used since all the material in the manual references a tunerstudioMS version that does not exist anymore. I have no idea how to set it to fixed advance. I know that if I increase the trigger offset the idle will come down a little (up to around 28).

I do know that as it warms up it tends to gradually increase the idle. Only once did it act like it should and start around 1200 rpms and come down to 800 rpms. Then the next day it would not start at all unless I increased the advance.

I have played around with the timing so much that I wanted to make sure I had my timing marks aligned properly but I could only do it by hand.

Will

Hello everyone,

Did not get a lot of work done due to a nasty sinus infection, but it gave me time to think.
Since there is very little information on getting started with megasquirt, I have decided to hook up the GM wiring harness.

First question: I have the two 7477 ecus. Any recommendation on another ecu that I should use for a relatively stock 95 4.3l TBI from an s-10 blazer?

Follow up question: Can anyone point me in the right direction to getting started with tuning whatever the recommended ECU might be?

All help is appreciated.

Will