95 4.3 TBI spark table info

[ironwill11]

Hello,

I recently joined gearhead efi looking for some information for my 95 TBI 4.3

If anyone has any suggestions or help I would greatly appreciate it, even if it is converting back to my stock ecm; here is my story:


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 People then advised me that that firmware in the ecm was out of date.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

[Matrix]

I played with that stuff a long time ago with my 4.3 safari van. What seems strange to me is you were running a 7747 computer on a 1995. Can you describe your application? I can probably find my old info for my van. I ran it with 2 different ECU's - the 1227747 (7747) and the stock 16144288 ECU. If you like I can post up the timing map for that ECU once I dig up my old info.

Let me know

[ironwill11]

I played with that stuff a long time ago with my 4.3 safari van. What seems strange to me is you were running a 7747 computer on a 1995. Can you describe your application? I can probably find my old info for my van. I ran it with 2 different ECU's - the 1227747 (7747) and the stock 16144288 ECU. If you like I can post up the timing map for that ECU once I dig up my old info.

Let me know

Thanks for the reply. My setup has gotten more and more common over the years.

I put the 95 4.3 tbi with a th350 behind it in an 88.5 suzuki samurai. When I started this there weren't too many people out there with information. It was done with a wiring harness from painless performance who are the ones that stated that a 7747 is the way to go. So I went to a local junk yard and pulled one out of a van if memory serves me correct. Misunderstood the problems I had and bought a new 7747 from the dealer. I still have both of them. They ran fine for a while, but I parked the vehicle for a while due to some broken parts.

Got it running again and had a problem with the idle surging. Unplugged the MAP sensor (vacuum or electric gave the same effect) and it would straighten out and run fine (except for a dead spot higher in the rpms). For years people told me it was a vacuum leak. A neighbor had a mechanic friend that "reset the map sensor" and it ran fine again.

Another broken part and another period of time with it sitting. Start it back up again and idle hunting is back. Searched all over the internet to find the same ideas with no resolve. The mechanic who "reset the map sensor was now at the funny farm so there is not much I can do to find out what he did. That is when I decided to megasquirt it so I can see what was going on.

Silver lining out of the whole story: The vacuum is very constant.

Sorry about the length. That is pretty much the sad saga.
Not sure the megasquirt was the right move. Still have both ecm. Not sure if I should convert it back or stick with the megasquirt.

I would love any information you can give me as I am trying to catch up with this stuff.

Will

[Matrix]

I have a few files that are slightly different, but the target idle vs coolant temperature looks like this:

Deg C RPM
55 600
65 600
75 575
85 537.5
95 537.5
100 537.5
115 625
120 650
135 650

Have you ever checked the EGR pipe to ensure it isn't plugged and that the EGR valve is working correctly? I know on my van, the EGR valve was stuck slightly open once and the van wouldn't idle worth a crap. Are you running the EGR valve with Megasquirt?

Also, when you had the 7747 ECU in there did you ever follow these procedures?
http://www.thirdgen.org/forums/tbi/6055 ... -idle.html

If these aren't set correctly, then your idle would be messed up. I suspect the guy that fixed your idle probably set up the IAC as discussed in the post.

[ironwill11]

Thanks for the info. Right now I don't have a way of comparing temp vs. RPM. With the megasquirt they tell me I have to use tunerstudioMS software which is not real helpful and any information about megasquirt references a very out of date tunerstudioMS.

I took the EGR valve off and everything checked out. I don't think I checked the whole pipe though.

Since that is the first time I read about that procedure with the IAC, no I never did that when I was running the 7747. I read that a lot of people were having the idle hunting problem and changed their IAC and got no results.

Also back when I was running the 7747, I did check the fuel pressure and it checked out. I bought an adjustable regulator just to make sure. I even found that if I pinched down on the return line that would increase the pressure and it would straighten out a decent amount but never just idle normally. Plus if you gave it and throttle it would drop to its knees.

No I am not running an EGR. I left it on the engine but it is not hooked up to the megasquirt.

Will

[ironwill11]

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?

[ironwill11]

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