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| bam | Weird timing issue | ||
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Senior Guru
 
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93 LT1, 6 spd (just to remind everyone)
I am doing my own tuning now and have adjusted the "main spark advance vs. RPM vs. Load" tables, I have the timing set at 14 degrees at 800rpm all the way across thru all the KPa from 25 to 100. The weird problem is that when I data log the car at idle I am showing 28 degrees of advance and it is very erratic moving from 25 - 30 while neither the rpm or KPa fluctuates that much. I know from reading the FSM that the opti has nothing to with setting degrees of advance, that is all done by the ECM. So something is going on in the computer right, it can't be anything else? I tried a brand new chip thinking the one I have been using might be corrupted but no difference. I also know that the computer adds timing advance when the engine is cold so I checked the temp showing in data master and it reads 195 so that can't be it either. Any thoughts? I see nothing in the FSM that tells how to diagnose a problem like this. No codes either. Any comments, suggestions? |
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Posted on: 2013/5/26 22:35
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| pianoguy | Re: Weird timing issue | ||
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Guru Emeritus
 
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Do you have an MSD opti in it? They have a gizmo in them to supposedly adjust the timing a bit.
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Posted on: 2013/5/27 16:56
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1996 LT4 �Before you criticize someone, you should walk a mile in their shoes. That way when you criticize them, you are a mile away from them and you have their shoes.�- Jack Handey |
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| djxib | Re: Weird timing issue | ||
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Senior Guru
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I've seen that too. The only things I'm aware of that would cause the actual timing to change for a given RPM are the 'closed TPS advance' (that you'll see if you lift off the throttle between shifts) or spark retard due to knock.
I meant to do some research on this a while back but too many projects.. I have noticed however that at WOT the timing is exactly as described at 100KPa unless I get knock (1992). Assuming your closed TPS advance table maps to your main spark table, 14 degrees at idle sounds very low for your cam, you could try different degrees of advance to get the best vacuum at idle. I run about 30 degrees on mine. Good luck! |
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Posted on: 2013/5/27 17:24
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_________________
Andy 1996 Greenwood Collectors Edition LT4 Previously 1992 Convertible Polo Green. 383 LT1/LT4 forged/balanced. V7-YSi, Alky. 608RWHP... Now sitting at a dismantler with a salvage title. Still runs... |
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| bam | Re: Weird timing issue | ||
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Senior Guru
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Quote:
I do have the MSD but I want to adjust the timing in the computer, why else would you have "main spark advance vs RPM vs load" table if not to make adjustments? Simply does not make sense to me. |
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Posted on: 2013/5/27 23:26
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| bam | Re: Weird timing issue | ||
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Senior Guru
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Quote:
1. Are you saying you have tried to adjust timing in the main spark advance table and it does nothing except at WOT? 2. I will try adjusting the "closed TPS advance" table and see if that does anything. Although I think that must be to use the engine to brake the car when the throttle is closed completely by momentarily bumping the timing up. I notice that is the only time the timing goes down, and that is when I want it to stay the same. 3.It is very hard for me to believe that these LT engines need 30 degrees of advance at idle, that says a very inefficient engine at idle. I know the cam does make a difference but that much?? I can see it at 6000rpm when the dwell of the piston at TDC is split seconds. But at idle why wouldn't you want the timing much closer to TDC. I know when I built a 406 small block with a CC cam it liked 12-14 advance at idle, it would simply not run with stock advance of 8. When I set it I remember it would hardly run with timing over 20 at idle, are LT engines really that much different? |
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Posted on: 2013/5/27 23:40
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| bam | Re: Weird timing issue | ||
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Senior Guru
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Anyway the bucking/cam surge is back with a vengeance. I have been able to get my VE tables almost perfect, so I was thinking it might be timing. The bucking/cam surge was almost completely gone, only slightly felt below 1000rpm. Now it is back again all the way to 2000rpm and very annoying, I think this car is going to put me in the funny farm! If I could simply adjust the timing then I would know for sure if that it is it or if I should go on to something else but as it is I have no way of knowing. How can you make a car that you can't adjust the timing on? Ok rant over.
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Posted on: 2013/5/28 14:31
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| Schrade | Re: Weird timing issue | ||
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Elite Guru
 
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Thomas - maybe get forum bosses to merge this thread with the 'Tuning' thread.
Best help (which is most of the guys on guru boards), comes when all the info is in the same thread - easier to scroll back for some detail. Any luck getting data saved in another format? Maybe a camera snappic of the screen even? |
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Posted on: 2013/5/28 18:01
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LT5, Marc Haibeck ECM module, AUTOMATIC!!! 
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| pianoguy | Re: Weird timing issue | ||
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Guru Emeritus
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Quote:
I should've been more clear - I meant to suggest that maybe something is afoul with the MSD's timing adjustment mechanism. |
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Posted on: 2013/5/28 18:14
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_________________
1996 LT4 �Before you criticize someone, you should walk a mile in their shoes. That way when you criticize them, you are a mile away from them and you have their shoes.�- Jack Handey |
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| bam | Re: Weird timing issue | ||
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Senior Guru
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Ok I remembered there are two data logs in with the data master program when you download it. So I took a look at them. Both are Y car's (93 Corvette) one auto the other stick. When I scroll back to areas where the motor is idling, say 700-800 rpm I am seeing 18-22 degree of advance, never any more. That is 10 degrees less than what I am showing, this makes me think something is fishy with the computer, Opti or the prom. I assume these two cars are stock because they both end the WOT runs at 5500 rpm. I have looked back over some of my past data logs and am seeing 20 degrees of advance at idle, now I am at 28 when I went thru the whole table and reduced timing except at WOT and the timing moves up? This is really a mystery.
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Posted on: 2013/5/28 22:55
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| bam | Re: Weird timing issue | ||
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Senior Guru
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Quote:
I'd be glad to do a camera shot, which part would you like to see, timing at idle where the problem is? I'll give it a try. |
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Posted on: 2013/5/28 22:58
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| bam | Re: Weird timing issue | ||
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Senior Guru
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Here are a couple of screen shots from data master, one from my car, the other was included with the program, you can see the differences in the timing.
http://s1113.photobucket.com/user/pho ... alog_zps5c03a47c.png.html http://s1113.photobucket.com/user/pho ... ster_zps1e75370e.png.html |
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Posted on: 2013/5/28 23:50
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| Schrade | Re: Weird timing issue | ||
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Elite Guru
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Short Term fuel is not right - too low??? Burn is lean.
Someone else has got to see something else here............... |
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Posted on: 2013/5/29 2:03
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| bam | Re: Weird timing issue | ||
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Senior Guru
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Blade, thanks for taking a look. You are looking at my log right and not the one from data master? What do you mean when you say "short term fuel is not right-too low??" What is short term fuel? Is that the "short term counts" right under the BLM's? On my data log they are 114/115 isn't that rich? Notice the BLM's are 128/125 I have worked really hard to get those suckers at close to 128 and no longer split. They were running 140's/ 108's typically and all over the place. I don't think this is a fueling issue any longer but let me know more what you see here that I don't. thanks again.
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Posted on: 2013/5/29 13:08
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| djxib | Re: Weird timing issue | ||
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Senior Guru
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Quote:
That's the mother of all split BLM's in the datamaster sample! Yours looks pretty good, slightly rich but OK. The O2 MV's are both 800+ which arguably means it's still slightly rich, especially if they stay up in the 800's constantly (you should see them dance up and down constantly with 450 being the mid point). The short term counts are the 'right now' measure of the fueling, and below 128 show's they are detecting rich and therefore pulling fuel. The long terms will be incremented or decrement based on various algorithms but they are very close to 128 so if I were you I'd leave the VE at idle alone at this point. As for the spark, all I can see is 29 degrees. Send me the .uni file and your $DA2 BIN (you have my email) and I'll take a look at the datalog and correlate with the spark table. I'll also promise to post my opinions back on the forum. Cheers |
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Posted on: 2013/5/30 2:21
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_________________
Andy 1996 Greenwood Collectors Edition LT4 Previously 1992 Convertible Polo Green. 383 LT1/LT4 forged/balanced. V7-YSi, Alky. 608RWHP... Now sitting at a dismantler with a salvage title. Still runs... |
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| bam | Re: Weird timing issue | ||
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Senior Guru
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Yea those splits are horrible!!! I am really happy with my BLM's now, there are a few lean spots in the data log I sent but I have already added a little fuel in those spots. I really think the timing is making the car buck. It must be pretty obvious that if timing is too advanced (don't know for sure if mine is or not) it would cause the motor to buck.
I sent you an email with my latest data log. Thanks for taking a look at it, I have spent hours looking at these things! |
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Posted on: 2013/5/30 2:40
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| djxib | Re: Weird timing issue | ||
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Senior Guru
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Quote:
Hi Tom, Sorry it took so long to get to look at your logs - 3 very busy weekends in a row. Anyhow, This afternoon I correlated the datalog and tune that you sent, and as far as I can see Datamaster is reporting a spark advance greater than requested by the tune. It's not far off - most of the time it's showing between 1 and 5 degrees higher. I scanned the other tables (for example temperature correction) and cant see a good reason for it. I'm going to try scanning the forums and asking a couple of folks to see if there's a good reason for it. I'm going to take a look later to see if I can see a reason for the surging problem. |
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Posted on: 2013/6/12 21:53
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_________________
Andy 1996 Greenwood Collectors Edition LT4 Previously 1992 Convertible Polo Green. 383 LT1/LT4 forged/balanced. V7-YSi, Alky. 608RWHP... Now sitting at a dismantler with a salvage title. Still runs... |
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| djxib | Re: Weird timing issue | ||
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Senior Guru
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Further to my last post, the datalog you sent me looks like it was conducted at low speeds and small throttle openings, and my guess is that you experienced a lot of surging throughout the run. I cant see anything obvious, but since your fuel trims are looking pretty good you could try the open loop experiment (set both 'min coolant temperature for closed loop' and 'min coolant temperature for closed loop, cold MAT' to 100 degrees C in the constants table).
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Posted on: 2013/6/12 22:15
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_________________
Andy 1996 Greenwood Collectors Edition LT4 Previously 1992 Convertible Polo Green. 383 LT1/LT4 forged/balanced. V7-YSi, Alky. 608RWHP... Now sitting at a dismantler with a salvage title. Still runs... |
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| bam | Re: Weird timing issue | ||
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Senior Guru
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I am away on business for another week or more. Thanks for looking thru the logs, I know it is time consuming. You are right about there being lots of surging. The funny thing is that for several months it was almost gone, now it is back?? It is making me think it is an intermittent and light miss. I also wonder if it is caused by an injector injecting too much/little fuel or leaking. I checked plugs and the centers look great but around the edge there is a fine black soot. I also omed the wires and the injectors all were fine.
If I do as you suggested above what am I looking for? Should I data log after the above changes? |
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Posted on: 2013/6/19 14:40
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| bam | Re: Weird timing issue | ||
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Senior Guru
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Back to this after a long time! I finally got the timing to change in the ECM, I have no idea why it would not change before this?? Anyway the surging/miss is not the timing being too advanced at idle/lower rpm's. I was able to reset the timing in those ranges to 12-18 and it made no difference. I also ran a leak down test; lowest #8 was 87% highest was #3&6 at 93% so I don't think there is a problem with bad valves. I also omed the plug wires, all very good (almost new taylor wires) and new spark plugs NKG's. No broken valve springs.
I am starting to think this is an intermittent miss because I hooked up a timing light and started the engine and watched for a miss and several times I noticed an intermittent lack of fire from the timing light. My question is this; could this be the almost new MSD opti or the ECM? No codes. How would I check w/o just replacing parts? |
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Posted on: 2013/7/25 17:03
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| Matatk | Re: Weird timing issue | ||
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Webmaster
 
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Could be an intermittent opti as you say since you checked everything else - here are a couple articles:
http://www.underhoodservice.com/Artic ... ng_gm_lt1_v8_engines.aspx http://www.gmhightechperformance.com/ ... _understanding_modifying/ |
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Posted on: 2013/7/26 1:03
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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