setting L98 base ignition timing
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Joined: Jan 2001
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From: Newton (Wichita Area) Kansas
setting L98 base ignition timing
Searched for an answer in the archives and didn't find it so here goes:
When you disconnect the ESC wire it should remove all advance/retard capabilities from the ECM right? So shouldn't the timing mark be in the same place all the time regardless of rpm when you have the timing light on?
If I rev mine past about 1500 rpm the timing retards. Shouldn't it stay put since the ESC wire is disconnected? I've readjusted the timing in a few other EFI equipped vehicles, admittedly Fords, and the timing never changed.
I'm confident I have the correct wire because I'll get an ESC error code if I disconnect it. It's just inside of the power brake booster, brown in color, and has a single prong Weatherpac connector.
[Modified by jmr302, 4:08 PM 6/4/2002]
When you disconnect the ESC wire it should remove all advance/retard capabilities from the ECM right? So shouldn't the timing mark be in the same place all the time regardless of rpm when you have the timing light on?
If I rev mine past about 1500 rpm the timing retards. Shouldn't it stay put since the ESC wire is disconnected? I've readjusted the timing in a few other EFI equipped vehicles, admittedly Fords, and the timing never changed.
I'm confident I have the correct wire because I'll get an ESC error code if I disconnect it. It's just inside of the power brake booster, brown in color, and has a single prong Weatherpac connector.
[Modified by jmr302, 4:08 PM 6/4/2002]
Drifting
Joined: Mar 2001
Posts: 1,636
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From: Lafayette IN
Re: setting L98 base ignition timing (jmr302)
I think there is a little bit of confusion here.
There is an ESC circuit and an EST circuit.
ESC-Electronic spark control. This takes out timing when your knock sensor is triggered.
EST-Electronic spark timing. This curcuit controls normal spark advance and retard (as you would see with a timing light) under all conditions.
Now, the set-timing connector bypasses the EST circuit, not the ESC circuit. With the set-timing connector unplugged, the ECM will not advance the timing at all. BUT but but, there is spark advance built into the module itself, so a slight amount of advance WILL be shown as the RPMs increase (if you used a timing light, this would be the advance you saw).
And I think the code you get when you disconnect the EST set-timing wire is going to be a code 42. An ESC code is code 43.
Good luck, -Matt-
There is an ESC circuit and an EST circuit.
ESC-Electronic spark control. This takes out timing when your knock sensor is triggered.
EST-Electronic spark timing. This curcuit controls normal spark advance and retard (as you would see with a timing light) under all conditions.
Now, the set-timing connector bypasses the EST circuit, not the ESC circuit. With the set-timing connector unplugged, the ECM will not advance the timing at all. BUT but but, there is spark advance built into the module itself, so a slight amount of advance WILL be shown as the RPMs increase (if you used a timing light, this would be the advance you saw).
And I think the code you get when you disconnect the EST set-timing wire is going to be a code 42. An ESC code is code 43.
Good luck, -Matt-
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From: Newton (Wichita Area) Kansas
Re: setting L98 base ignition timing (HighHopes85)
I meant EST. Thanks for setting me straight, Matt. :bb
I had no idea the HEI module had built-in advance. That's definitely the only explanation.
Don't know what I'd do without this forum...
I had no idea the HEI module had built-in advance. That's definitely the only explanation.
Don't know what I'd do without this forum...
Melting Slicks
Joined: May 2000
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From: Chandler AZ
Re: setting L98 base ignition timing (HighHopes85)
there is spark advance built into the module itself, so a slight amount of advance WILL be shown as the RPMs increase (if you used a timing light, this would be the advance you saw
I'm not sure what the prob is but something else is going on. Maybe slipping balancer ring, loose distributor hold down, worn gears, tired module or coil (can't cycle fast enough as rpm's rise)?
Drifting
Joined: Mar 2001
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From: Lafayette IN
Re: setting L98 base ignition timing (gcrouse)
My Helms manual fails me again :rolleyes: Add that to the other 20 some odd electrical errors I have spotted in it and I think I should get my $100 back :mad
Now I am interested to try it out one I get my engine back in. I do know that in limp home mode (different than fail soft mode) that there is advance in the final timing and it does not come from the EST at all. It might come from the network resistors on the MEMCAL...lemme look to see what I find and I will let you know what I am thinking about. Good thing you pointed out the discrepancy.
Now I am interested to try it out one I get my engine back in. I do know that in limp home mode (different than fail soft mode) that there is advance in the final timing and it does not come from the EST at all. It might come from the network resistors on the MEMCAL...lemme look to see what I find and I will let you know what I am thinking about. Good thing you pointed out the discrepancy.
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Drifting
Joined: Mar 2001
Posts: 1,636
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From: Lafayette IN
Re: setting L98 base ignition timing (HighHopes85)
OK, found it! It still could be wrong though.
Page 6E3-104 in 85 Helms manual.
"*Bypass (terminal C)
At about 400RPM, the ECM applies 5 bolts to this circuit to switch spark timing control from the HEI module to the ECM. The wire goes (blah blah) to the ECM. This is disconnected to set base timing. The connector is located as shown in figure XX An open or grounded bypass circuit will set a code 42 and the engine will run at base timing, plus a small amount of advance built into the HEI module."
I knew I wasn't losing my mind! :D
Page 6E3-104 in 85 Helms manual.
"*Bypass (terminal C)
At about 400RPM, the ECM applies 5 bolts to this circuit to switch spark timing control from the HEI module to the ECM. The wire goes (blah blah) to the ECM. This is disconnected to set base timing. The connector is located as shown in figure XX An open or grounded bypass circuit will set a code 42 and the engine will run at base timing, plus a small amount of advance built into the HEI module."
I knew I wasn't losing my mind! :D
Melting Slicks
Joined: May 2000
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From: Chandler AZ
Re: setting L98 base ignition timing (HighHopes85)
plus a small amount of advance built into the HEI module
Curious problem though in that his timing seems to retard?
JMR you're saying you see base timing at 6 BTDC or so at idle; then above 1500rpm it drops back to 0 or even ATDC? Is it at all possible that you're reading it backwards and it's actually advancing like Matt thinks the HEI module can do?
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From: Newton (Wichita Area) Kansas
Re: setting L98 base ignition timing (gcrouse)
Thanks for the replies.
No, I'm confident in the readings. The balancer is brand new as is the inductive pickup timing light. The scale is stamped into the aftermarket balancer (manufactured that way, I didn't do it) and I have an adjustable pointer on the timing cover. I verified that it points to TDC on the balancer when the #1 piston is at TDC.
With the EST disconnected and the car idling at 1000 rpm I can set the base timing to 6 degrees BTDC and tighten the distributor clamp. The distributor is definitely not moving. Then if I rev the engine past about 1500 rpm the timing retards. The longblock is new but the DUI HEI distributor came off my old engine. I don't know how many miles are on it since it was on the car when I bought it. I'm also running an MSD 6AL but I didn't think that could affect ignition timing in anyway.
The strange thing is the car seems to run normally. It doesn't lose power or go nuts when it's revved. There are no driveability problems above idle.
No, I'm confident in the readings. The balancer is brand new as is the inductive pickup timing light. The scale is stamped into the aftermarket balancer (manufactured that way, I didn't do it) and I have an adjustable pointer on the timing cover. I verified that it points to TDC on the balancer when the #1 piston is at TDC.
With the EST disconnected and the car idling at 1000 rpm I can set the base timing to 6 degrees BTDC and tighten the distributor clamp. The distributor is definitely not moving. Then if I rev the engine past about 1500 rpm the timing retards. The longblock is new but the DUI HEI distributor came off my old engine. I don't know how many miles are on it since it was on the car when I bought it. I'm also running an MSD 6AL but I didn't think that could affect ignition timing in anyway.
The strange thing is the car seems to run normally. It doesn't lose power or go nuts when it's revved. There are no driveability problems above idle.
Melting Slicks
Joined: May 2000
Posts: 2,148
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From: Chandler AZ
Re: setting L98 base ignition timing (jmr302)
Just an obvious check- you don't have a Boost Timing Master or nitrous retard or anything plugged into your MSD?
Here's a bizarre idea: the MSD does multiple sparks (8-10) below 3000rpm; above that it's one big fat spark. Is it possible that at higher rpm's those sparks are getting closer together and your timing light maybe triggering off different spark; i.e. not always the first one of the series? That could make the timing appear to retard when in fact it isn't. Which would also explain why the car still runs good. But does it run good with the ECM advancing the timing? You could still be retarding but the ECM advance compensates.
Out of curiosity, see if you can trigger off the module output to the MSD, or maybe the MSD's TACH output; or try bypassing it back to stock for a test, if you didn't hack up the wiring harness.
The fact that it runs properly kindof excludes the bad stuff: twisted distributor shaft, excessive play between cam/dist gears. Only other thing I can think of is a weak HEI module or MSD box. Good Luck!
Here's a bizarre idea: the MSD does multiple sparks (8-10) below 3000rpm; above that it's one big fat spark. Is it possible that at higher rpm's those sparks are getting closer together and your timing light maybe triggering off different spark; i.e. not always the first one of the series? That could make the timing appear to retard when in fact it isn't. Which would also explain why the car still runs good. But does it run good with the ECM advancing the timing? You could still be retarding but the ECM advance compensates.
Out of curiosity, see if you can trigger off the module output to the MSD, or maybe the MSD's TACH output; or try bypassing it back to stock for a test, if you didn't hack up the wiring harness.
The fact that it runs properly kindof excludes the bad stuff: twisted distributor shaft, excessive play between cam/dist gears. Only other thing I can think of is a weak HEI module or MSD box. Good Luck!
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From: Newton (Wichita Area) Kansas
Re: setting L98 base ignition timing (gcrouse)
Good ideas, G.C.
Answers to a few of your Q's:
Just a regular MSD6AL, nothing added to it.
The car does run well with the ECM controlling the advance.
I'm using Craig Moates diagnostic software and it keeps track of spark advance. I'll log some new data at idle and etc with the EST connected/disconnected and the MSD connected/disconnected. I'll also try to trigger the timing light in several different locations. Your theory about the Multiple Spark Discharge affecting the timing light may be correct. We'll see!
I'll make a follow up post later this weekend. Won't have time to run the car until then.
Answers to a few of your Q's:
Just a regular MSD6AL, nothing added to it.
The car does run well with the ECM controlling the advance.
I'm using Craig Moates diagnostic software and it keeps track of spark advance. I'll log some new data at idle and etc with the EST connected/disconnected and the MSD connected/disconnected. I'll also try to trigger the timing light in several different locations. Your theory about the Multiple Spark Discharge affecting the timing light may be correct. We'll see!
I'll make a follow up post later this weekend. Won't have time to run the car until then.
