I have a 95 Suburban with a 16197427 computer with BYJL memcal and have been trying to diagnose a stuttering in the engine under loads.
I have been datalogging with RT v4 with the OD_V102.xdf and it is showing my spark advance dropping almost to TDC as the engine is under load(High MAP around 2k rpm) as I'm trying to accelerate the truck. I'm trying to find out if this is the actual spark advance or just a number that is added to base timing(mine is the stock 0 btdc) and whatever the ignition module in the distributor has. It shows around 20 degrees advanced at idle and down as low as 8 degrees advanced at WOT around 2500 rpm. There is absolutely no knock counts or degrees of knock retard at all when this is happening.
I'm really not sure what to make of this number as my truck is going lean according to the 02 sensor and the MAP is not rebounding as the engine starts to come up on the power curve like I would expect. I'm used to older carbed vehicles where the initial is around 10-14 degrees, vacuum advance adds about 16 degrees and mechanical ideally gives you about 36 degrees at WOT.
I've done the usual tune up items(plugs, wires, cap, and rotor) along with a new cts because the old one was badly corroded and a new distributor because the pickup coil was out of spec when I got the truck. It has a new fuel pump with 10.5 psi at idle and still above 10 psi under load. I thought internal motor at first and did have a stuck valve that I was able to free up with a bit of oil and pressure. I now have good compression over all cylinders(low 145 high 158) and the timing chain slack seems to be ok(about 6-10 degrees before the rotor begins following a change in direction of the crank).
I have datalogs of it running if anyone will think that it will help. Any help would be greatly appreciated.
Spark Advance 0D BYJL confusion
Moderators: robertisaar, dex
-
Cruzer Dood
- Posts: 8
- Joined: Tue Jan 05, 2010 6:27 pm
I'm new to this too, and am using the same system in a EFI swap. I can't answer your problem directly as far as timing goes, but from what I have read, your fuel pressure looks low, should be 12-13 lbs. One thing I have read, is there's a difference between car and truck Ign modules. If I understand it right, the car has a built in retard, and the trucks advance the timing. I did some cut and paste from a bookmark from TGO, maybe you'll find a tidbit of info there. HTH, Al
Poor L05
i did an engine swap over the winter and i have been messing with the motor ever since.... for one when the rpms reach somewhere in the 4500-5000 range the car starts to run like **** and looses power and falls flat on its face until it shifts... i have adjusted the timing and i set it at zero and it runs sluggish compared to advanced timing, with the timing advanced it seems to idle ALOT smoother but misfired alot when it is advanced enough, i was in the engine bay listening to the motor and i advanced the timing off that gauge thing and seems like it idled good there (with the exception of the misfires) but no matter what i do it still seems to run crappy up top... and another thing i have been timing my 0-60 runs and they are in the range of 8-9 secs... (thats not much faster than my L03 completely stock was) i did one a long time ago it was around a late 7 sec run but since then i have been slow... could it be because of my gears? plus i just did the ultimate tbi mods and i feel no difference at all... doesn't make the car differ form how it was at all... any ideas guys? I'm getting frustrated....
__________________
Re: Poor L05
checklist: 350 prom chip/ 350 esc module/ 350 injectors
egr valve hooked up/ vacum lines?
does it pop and backfire alot?
Re: Poor L05
it does pop sometimes when its up high in the rpms... up to 4500 its fine.... it has the Blazer Computer in it, along with the 350 injectors... egr valve should be hooked up fine...vacuum lines are ok i think,
Re: Poor L05
I did the o2 sensor tuning thing... it read between .87-.9 and when it started running crappy it would either read .90 or .91 and one time i got a .92 too.
Poor L05
I got it so it doesn't do the dieing thing anymore but i'm getting 9-10 sec 0-60s.... very dissappointed with this motor if thats all it can do with ultimate TBI mods, headers, exhaust, and open element. Anyone have any idea? and i messed with fuel pressure alot and the timing and nothing changes anything......
Re: Poor L05
if you play with the throttle at the throttle body, try snapping it open quicky and see what happens, see if it hesitates, if the fuel pressure cuts out and or if it backfires, i had similar problems with mine but found out my timing was off and wouldnt hold because my cam walked.
Re: Poor L05
i don't have a fuel pressure guage on it, but when i snap it open it would (for the first few times) would kinda sputter for a second then the motor ran for a min and it would just rev up after that.
1st, the 700r4s in the TBI trucks were calibrated to upshift by 4,200 rpm or so. The injector pulsewidth is pretty much maxed out by about 4,000 rpm. Running much over the WOT Upshift RPM of a TBI truck will make the injectors run static.
2nd, the ignition control modules used in the cars and some trucks have a built-in spark latency change as the rpms increase. This was done purposely to limit the maximum rpm of the engine. What happens is as the engine runs over 4,300 rpm, the timing starts to retard until around 5,000 rpm it peaks around 9* retard from the latest entry in the spark table.
3rd the camshaft and valvetrain in your L05 unless upgraded were designed to run with the 4,300 rpm WOT upshift in mind. The cam was a very mild grind and the factory engineers wanted it to live a good long life. Being a hydraulic flat-tappet cam the engineers used valve springs better suited for childrens slinkys. The later model TBI trucks even had a 4,800 rpm fuel shut-off programmed into their PCMs.
.
A word of caution - NBO's are not very accurate at fuel mixtures away from 14.7:1. WBO is the next best thing to dial in WOT performance.
That sounds like the exact problem... when the rpms get high it runs like crap and looses all power. How can i get around that? My next mods are cam and heads. I was gonna have my ECM "reflashed" by some guy where you send in your ECM and he reflashes them for $50. Then sends it back. Any ideas? and how hard is it to change a camshaft?
To fix the module problem is pretty simple, just grab a 369 marked module from a 5.0/5.7 TBI fullsize van. Rbob recently did some testing with the 369 and 048 marked modules. I had noticed a high rpm power drop-off when I installed my replacement module in my van. After reading this post, I went and grabbed a "369" module from a 1993 fullsize G20 Van. My power over 4,000 immediately increased.
Have some interesting information to add this this thread.
First item to note is that in the opening post of this thread, the table shown as for AUJP is not. It is the latency table used for AXCN & ANHT. Which are Corvette large cap distributors. The poster in the thread that liquidH8 linked switched the two tables in his post.
AUJP uses table 2 in the following:
Code:
Table 1 Table 2
RPM usec usec
6375 137.34 305.2
6000 137.34 305.2
5600 137.34 305.2
5200 137.34 305.2
4800 137.34 305.2
4400 152.6 305.2
4000 152.6 289.94
3600 137.34 320.46
3200 167.86 305.2
2800 183.12 244.16
2400 137.34 274.68
2000 137.34 244.16
1600 106.82 305.2
1200 45.78 274.68
800 0 213.64
400 0 0
0 0 0
I have been able to identify two different ignition modules for the small cap distributors. They are the 048 and the 369. Check out the picture of the modules. It is the first 3 digits.
I ran 2 each of the 048 & 369 along with a Holley module through some tests. This was done on a live engine using a marked balancer, timing light, and the What's Up Display to show the commanded SA timing and the engine RPM. The EBL Flash had 5 calibrations banks set up for testing.
Bank 0 was the stock calibration to start up the engine and let it settle in.
The other four banks all had the main & extended timing tables set to 20 BTDC. Temperature comp, PE, launch mode, and whatever else was zero'd out.
Then each of the four banks had different latency tables. Banks 1 & 2 had the two tables shown above. Then banks 3 & 4 had the same tables with the low RPM latency values of 0 filled in with the first value greater then 0 from above it.
Code:
Instead of this:
1600 106.82 305.2
1200 45.78 274.68
800 0 213.64
400 0 0
0 0 0
It was:
1600 106.82 305.2
1200 45.78 274.68
800 45.78 213.64
400 45.78 213.64
0 45.78 213.64
The reason for this was that it was found that the at-crank timing dropped off with the stock table values of 0. The was still latency at the low RPM's that needed to be accounted for.
With this change running the RPM from 800 through 3200 had each module with the appropriate table holding a steady SA. Switch the table and the advance moved around as the RPM changed.
The Holley module (part # 891-103) matched table 2. This was from 800 through 3200 RPM. Did not test past this RPM.
You may be thinking that 3200 is a low RPM. However, look at the engines/vehicles the ignition modes are used in. None of these engines are high RPM. Trucks, Vans, TBI 3rd gens, Caprices, Wagons, even the TPI engines aren't high RPM engines. Note what happens in the following tests. . .
Another test: while checking the timing as the RPM was increased, both the 048 & 369 modules held steady until a particular RPM. This was with 048 & table 1, then 369 with table 2.
The 048 module, it held steady timing until about 3800 RPM where it retarded 4 degrees. Then by 5000 RPM the retard had increased to 6 degrees.
The 369 module, it held steady timing until about 3200 where it gained 2 degrees of advance. This held steady to 5000 RPM, which is the highest RPM it was checked at.
If we could get a sampling of the ignition module in various 3rd gen engines it would be helpful. Under the cap check the 3 digit number and post back. Along with whether it is TPI or TBI. If you know the stock BCC that too would be helpful.
Conjecture:
I know that the latest f-body TBI calibrations use table 2. This matches module 369. Same as the AUJP TPI calibration. I wonder if the 048 modules are for performance limiting, and are set up to limit the engine RPM. With the timing retarded, the power drops off, and most people either up-shift or lift.
Where the 369 modules (the ones I have are from 5.7l full size vans) are more performance oriented. What is interesting is that the 369 modules I have are newer then the 048's. Some even look to be replacements (too new for the age of the vehicle). Maybe a GM upgrade?
A camshaft swap is fairly easy, but takes some mechanical knowledge and lots of time. Its not something that you would want to do in a single weekend.
I doubt that a mail order tune is going to help you any. You really need a larger camshaft, better valvesprings, and a non-mail order retune of the ECM.
Another question for cam experts out there. I am going to be going Vortec heads, i already have flowtech headers 2 1/2" y-pipe into 3" Flowmaster cat back. It will have the SUM-226018 intake with the Carb to TBI intake adapter. along with the ultimate TBI mods with open element and soon i will be going to 3.73's in the rear. Any idea on a cam cause thats my weak point. Thanks a lot!
(also if i picked bad parts let me know and i will probably change what i buy, also keep in mind I'm trying to save money) And all this will be on the L05(which is completely stock right now except for open element and headers and exhaust.)
----------
Check out comp cams web site. locate computer controled cams. i assume the Blazer is hy flat tappet. You will see LSA's at 112-114 range. my first cam was 210/216 @ .05 113 LSA. small cam easier to tune.
Well i swapped out the Truck ECM for a buick roadmaster ECM and my top end power is back it pulls all the way to 5500 rpm, But to really gain the benefits from that particular ECM i have to get bigger injectors right? B/c the roadmaster L05 used bigger fuel injectors than the truck L05's right?
The RM LO5 was rated at 180 fwhp during 1991-1993; truck LO5 were at 195 or 210 fwhp (not sure). The trucks had a different (flat) tappet cam that was slightly warmer than the peanut cam used on the RM 350 (same peanut roller as used on 3rd gen Fcar 305), and a better exhaust, so they were rated higher and MAY have used something higher than 61 #/hr.
So IMO they either used the same (flow rating) injectors, or the trucks got slightly larger ones.
Most of the Cadillac/Buick/Chevy Caprice 180 HP 350 engines that I have come across had 55# 305 injectors in the TBI.
When in doubt go back to the basics. The engine requires several things to run properly. Adequate compression, a good air/fuel mixture, and a properly timed spark. Partially deprive it of any of the preceding and the engine will still run, but will run poorly.
A.) Check the Compression
B.) Check the cylinder leakdown
C.) Check for proper valve action
D.) Check the ignition timing
E.) Ensure that you have 61# 350 injectors in the TBI unit
F.) Test the fuel pressure to make sure you have atleast 12 psi (Spec is 9-13)
G.) Measure the backpressure on the exhaust system during a WOT 2nd gear pull (should be less than 3 psi)
The cam in that engine is VERY small and does not respond well to minor bolt-ons. I mean the intake valve is only bumped off the seat .350" and the exhaust valve .385", it is also not at peak valve lift for any time and the ramps are not all that aggressive. A LT1 cam, a full exhaust, and a properly tuned ECM will wake this engine up incredibly. I ran a LT1 cammed L03 (added flat-top pistons) truck engine on the stock 1992 Van ECM in my van with the only other additions being headers and a 2 1/2" dual exhaust system. The van HAULED BUTT! Easily ran 0-60 in 8-9 seconds despite 3.08 gears and the stock 1,600 rpm torque converter.
Poor L05
i did an engine swap over the winter and i have been messing with the motor ever since.... for one when the rpms reach somewhere in the 4500-5000 range the car starts to run like **** and looses power and falls flat on its face until it shifts... i have adjusted the timing and i set it at zero and it runs sluggish compared to advanced timing, with the timing advanced it seems to idle ALOT smoother but misfired alot when it is advanced enough, i was in the engine bay listening to the motor and i advanced the timing off that gauge thing and seems like it idled good there (with the exception of the misfires) but no matter what i do it still seems to run crappy up top... and another thing i have been timing my 0-60 runs and they are in the range of 8-9 secs... (thats not much faster than my L03 completely stock was) i did one a long time ago it was around a late 7 sec run but since then i have been slow... could it be because of my gears? plus i just did the ultimate tbi mods and i feel no difference at all... doesn't make the car differ form how it was at all... any ideas guys? I'm getting frustrated....
__________________
Re: Poor L05
checklist: 350 prom chip/ 350 esc module/ 350 injectors
egr valve hooked up/ vacum lines?
does it pop and backfire alot?
Re: Poor L05
it does pop sometimes when its up high in the rpms... up to 4500 its fine.... it has the Blazer Computer in it, along with the 350 injectors... egr valve should be hooked up fine...vacuum lines are ok i think,
Re: Poor L05
I did the o2 sensor tuning thing... it read between .87-.9 and when it started running crappy it would either read .90 or .91 and one time i got a .92 too.
Poor L05
I got it so it doesn't do the dieing thing anymore but i'm getting 9-10 sec 0-60s.... very dissappointed with this motor if thats all it can do with ultimate TBI mods, headers, exhaust, and open element. Anyone have any idea? and i messed with fuel pressure alot and the timing and nothing changes anything......
Re: Poor L05
if you play with the throttle at the throttle body, try snapping it open quicky and see what happens, see if it hesitates, if the fuel pressure cuts out and or if it backfires, i had similar problems with mine but found out my timing was off and wouldnt hold because my cam walked.
Re: Poor L05
i don't have a fuel pressure guage on it, but when i snap it open it would (for the first few times) would kinda sputter for a second then the motor ran for a min and it would just rev up after that.
1st, the 700r4s in the TBI trucks were calibrated to upshift by 4,200 rpm or so. The injector pulsewidth is pretty much maxed out by about 4,000 rpm. Running much over the WOT Upshift RPM of a TBI truck will make the injectors run static.
2nd, the ignition control modules used in the cars and some trucks have a built-in spark latency change as the rpms increase. This was done purposely to limit the maximum rpm of the engine. What happens is as the engine runs over 4,300 rpm, the timing starts to retard until around 5,000 rpm it peaks around 9* retard from the latest entry in the spark table.
3rd the camshaft and valvetrain in your L05 unless upgraded were designed to run with the 4,300 rpm WOT upshift in mind. The cam was a very mild grind and the factory engineers wanted it to live a good long life. Being a hydraulic flat-tappet cam the engineers used valve springs better suited for childrens slinkys. The later model TBI trucks even had a 4,800 rpm fuel shut-off programmed into their PCMs.
.
A word of caution - NBO's are not very accurate at fuel mixtures away from 14.7:1. WBO is the next best thing to dial in WOT performance.
That sounds like the exact problem... when the rpms get high it runs like crap and looses all power. How can i get around that? My next mods are cam and heads. I was gonna have my ECM "reflashed" by some guy where you send in your ECM and he reflashes them for $50. Then sends it back. Any ideas? and how hard is it to change a camshaft?
To fix the module problem is pretty simple, just grab a 369 marked module from a 5.0/5.7 TBI fullsize van. Rbob recently did some testing with the 369 and 048 marked modules. I had noticed a high rpm power drop-off when I installed my replacement module in my van. After reading this post, I went and grabbed a "369" module from a 1993 fullsize G20 Van. My power over 4,000 immediately increased.
Have some interesting information to add this this thread.
First item to note is that in the opening post of this thread, the table shown as for AUJP is not. It is the latency table used for AXCN & ANHT. Which are Corvette large cap distributors. The poster in the thread that liquidH8 linked switched the two tables in his post.
AUJP uses table 2 in the following:
Code:
Table 1 Table 2
RPM usec usec
6375 137.34 305.2
6000 137.34 305.2
5600 137.34 305.2
5200 137.34 305.2
4800 137.34 305.2
4400 152.6 305.2
4000 152.6 289.94
3600 137.34 320.46
3200 167.86 305.2
2800 183.12 244.16
2400 137.34 274.68
2000 137.34 244.16
1600 106.82 305.2
1200 45.78 274.68
800 0 213.64
400 0 0
0 0 0
I have been able to identify two different ignition modules for the small cap distributors. They are the 048 and the 369. Check out the picture of the modules. It is the first 3 digits.
I ran 2 each of the 048 & 369 along with a Holley module through some tests. This was done on a live engine using a marked balancer, timing light, and the What's Up Display to show the commanded SA timing and the engine RPM. The EBL Flash had 5 calibrations banks set up for testing.
Bank 0 was the stock calibration to start up the engine and let it settle in.
The other four banks all had the main & extended timing tables set to 20 BTDC. Temperature comp, PE, launch mode, and whatever else was zero'd out.
Then each of the four banks had different latency tables. Banks 1 & 2 had the two tables shown above. Then banks 3 & 4 had the same tables with the low RPM latency values of 0 filled in with the first value greater then 0 from above it.
Code:
Instead of this:
1600 106.82 305.2
1200 45.78 274.68
800 0 213.64
400 0 0
0 0 0
It was:
1600 106.82 305.2
1200 45.78 274.68
800 45.78 213.64
400 45.78 213.64
0 45.78 213.64
The reason for this was that it was found that the at-crank timing dropped off with the stock table values of 0. The was still latency at the low RPM's that needed to be accounted for.
With this change running the RPM from 800 through 3200 had each module with the appropriate table holding a steady SA. Switch the table and the advance moved around as the RPM changed.
The Holley module (part # 891-103) matched table 2. This was from 800 through 3200 RPM. Did not test past this RPM.
You may be thinking that 3200 is a low RPM. However, look at the engines/vehicles the ignition modes are used in. None of these engines are high RPM. Trucks, Vans, TBI 3rd gens, Caprices, Wagons, even the TPI engines aren't high RPM engines. Note what happens in the following tests. . .
Another test: while checking the timing as the RPM was increased, both the 048 & 369 modules held steady until a particular RPM. This was with 048 & table 1, then 369 with table 2.
The 048 module, it held steady timing until about 3800 RPM where it retarded 4 degrees. Then by 5000 RPM the retard had increased to 6 degrees.
The 369 module, it held steady timing until about 3200 where it gained 2 degrees of advance. This held steady to 5000 RPM, which is the highest RPM it was checked at.
If we could get a sampling of the ignition module in various 3rd gen engines it would be helpful. Under the cap check the 3 digit number and post back. Along with whether it is TPI or TBI. If you know the stock BCC that too would be helpful.
Conjecture:
I know that the latest f-body TBI calibrations use table 2. This matches module 369. Same as the AUJP TPI calibration. I wonder if the 048 modules are for performance limiting, and are set up to limit the engine RPM. With the timing retarded, the power drops off, and most people either up-shift or lift.
Where the 369 modules (the ones I have are from 5.7l full size vans) are more performance oriented. What is interesting is that the 369 modules I have are newer then the 048's. Some even look to be replacements (too new for the age of the vehicle). Maybe a GM upgrade?
A camshaft swap is fairly easy, but takes some mechanical knowledge and lots of time. Its not something that you would want to do in a single weekend.
I doubt that a mail order tune is going to help you any. You really need a larger camshaft, better valvesprings, and a non-mail order retune of the ECM.
Another question for cam experts out there. I am going to be going Vortec heads, i already have flowtech headers 2 1/2" y-pipe into 3" Flowmaster cat back. It will have the SUM-226018 intake with the Carb to TBI intake adapter. along with the ultimate TBI mods with open element and soon i will be going to 3.73's in the rear. Any idea on a cam cause thats my weak point. Thanks a lot!
(also if i picked bad parts let me know and i will probably change what i buy, also keep in mind I'm trying to save money) And all this will be on the L05(which is completely stock right now except for open element and headers and exhaust.)
----------
Check out comp cams web site. locate computer controled cams. i assume the Blazer is hy flat tappet. You will see LSA's at 112-114 range. my first cam was 210/216 @ .05 113 LSA. small cam easier to tune.
Well i swapped out the Truck ECM for a buick roadmaster ECM and my top end power is back it pulls all the way to 5500 rpm, But to really gain the benefits from that particular ECM i have to get bigger injectors right? B/c the roadmaster L05 used bigger fuel injectors than the truck L05's right?
The RM LO5 was rated at 180 fwhp during 1991-1993; truck LO5 were at 195 or 210 fwhp (not sure). The trucks had a different (flat) tappet cam that was slightly warmer than the peanut cam used on the RM 350 (same peanut roller as used on 3rd gen Fcar 305), and a better exhaust, so they were rated higher and MAY have used something higher than 61 #/hr.
So IMO they either used the same (flow rating) injectors, or the trucks got slightly larger ones.
Most of the Cadillac/Buick/Chevy Caprice 180 HP 350 engines that I have come across had 55# 305 injectors in the TBI.
When in doubt go back to the basics. The engine requires several things to run properly. Adequate compression, a good air/fuel mixture, and a properly timed spark. Partially deprive it of any of the preceding and the engine will still run, but will run poorly.
A.) Check the Compression
B.) Check the cylinder leakdown
C.) Check for proper valve action
D.) Check the ignition timing
E.) Ensure that you have 61# 350 injectors in the TBI unit
F.) Test the fuel pressure to make sure you have atleast 12 psi (Spec is 9-13)
G.) Measure the backpressure on the exhaust system during a WOT 2nd gear pull (should be less than 3 psi)
The cam in that engine is VERY small and does not respond well to minor bolt-ons. I mean the intake valve is only bumped off the seat .350" and the exhaust valve .385", it is also not at peak valve lift for any time and the ramps are not all that aggressive. A LT1 cam, a full exhaust, and a properly tuned ECM will wake this engine up incredibly. I ran a LT1 cammed L03 (added flat-top pistons) truck engine on the stock 1992 Van ECM in my van with the only other additions being headers and a 2 1/2" dual exhaust system. The van HAULED BUTT! Easily ran 0-60 in 8-9 seconds despite 3.08 gears and the stock 1,600 rpm torque converter.