GSL-SE Timing / Idle Issue
GSL-SE Timing / Idle Issue
I must have read a hundread posts via the SEARCH but couldn't find anything on this.\:
Recently I've developed a rough idle on my '85 SE (EFI) - the cars runs great once it's rolling (good power up through the RPM range) but the idle is rough, and I mean very lumpy around 800 RPM. No surging although is does seem to hunt a bit in a slow cycle up and down.
To top it off, I can't pick up the trailing pulley marks when I tried to set the timing. The leading is OK but the trailing is nowhere to be found (and the tach is OK).
The TPS is set correctly and the BAC is new. Plugs are in good shape, wires / cap are a year old. I also changed out the coil to one I had lying around that tested OK. BTW, I running MSD direct fire on the leading but I don't think this has anything to do with my problems.
Can anyone think of anything that I missed or should be looking at? Once again, the problem is only at idle
Recently I've developed a rough idle on my '85 SE (EFI) - the cars runs great once it's rolling (good power up through the RPM range) but the idle is rough, and I mean very lumpy around 800 RPM. No surging although is does seem to hunt a bit in a slow cycle up and down.
To top it off, I can't pick up the trailing pulley marks when I tried to set the timing. The leading is OK but the trailing is nowhere to be found (and the tach is OK).
The TPS is set correctly and the BAC is new. Plugs are in good shape, wires / cap are a year old. I also changed out the coil to one I had lying around that tested OK. BTW, I running MSD direct fire on the leading but I don't think this has anything to do with my problems.
Can anyone think of anything that I missed or should be looking at? Once again, the problem is only at idle
5 inches of Fury!
Joined: Oct 2003
Posts: 47
Likes: 0
From: Livermore, CA
Sounds like the problem I had with mine when I first got it. I found the previous owner had the leading and trailing coil wires backwards on the distributor. I switched the wires and it quit surging and ran smooth.
But, you have the MSD set-up, I guess you could still check it, but it might be a vacuum leak.
But, you have the MSD set-up, I guess you could still check it, but it might be a vacuum leak.
84SE-EGI helpy-helperton
Joined: Oct 2002
Posts: 3,584
Likes: 542
From: Phoenix, AZ
Couple of things - first off; thanks for putting GSL-SE in the post title. I *always* drop in on a thread about SE's!
On the Leading/Trailing coil wires, you'll notice that the coils are mounted front to back, Trailing in Front, Leading in Back, and these will need to coincide with what's marked on the Dist Cap. Once you have that confirmed, then check timing again, but REMOVE the vacuum advance rubber tubes from the dizzy. The FSM outlines that you need to disconnect the vacuum lines to ensure that any slight 'surging' will not affect your timing light's ability to show you the lead/trail marks on the main pulley.
BTW, 'surging' is the name given to what SE's do when one or several things have gone out of adjustment or need cleaning. Surging is when the engine will idle up and down anywhere from 300-2k rpm at what should be a normal, steady idle speed. Some of the causes for 'surging' follow;
Sticky TB rods - these rods get 'spalling' from the steel rods rubbing inside the aluminum TB housing, which causes the rods to stick. As the idle drops, the rods stick shut until the vacuum pressure in the BACV tries to compensate, opening the butterflies. As the butterflies open, the idle increases until the BACV kicks in, closing the butterflies and dropping the idle again - endless cycle.
Dirty BACV valve - driver's side of DEI chamber, remove and spray brake cleaner into the air inlets to clear out any carbon that's preventing the BACV from breathing properly. Reinstall with a good gasket seal.
TPS - sometimes, the TPS adjustment can help contribute to surging, but usually exhibits itself in erratic throttle settings under steady-state driving conditions, or what feels like 'surging' at speed. Adjust TPS using 2-light method or digital voltmeter.
The SE has some quirky things that take place during idle conditions, but not so much that you can't get it to run right. Take a look at these suggestions and then post back, and we can help you get it sorted out. HTH,
On the Leading/Trailing coil wires, you'll notice that the coils are mounted front to back, Trailing in Front, Leading in Back, and these will need to coincide with what's marked on the Dist Cap. Once you have that confirmed, then check timing again, but REMOVE the vacuum advance rubber tubes from the dizzy. The FSM outlines that you need to disconnect the vacuum lines to ensure that any slight 'surging' will not affect your timing light's ability to show you the lead/trail marks on the main pulley.
BTW, 'surging' is the name given to what SE's do when one or several things have gone out of adjustment or need cleaning. Surging is when the engine will idle up and down anywhere from 300-2k rpm at what should be a normal, steady idle speed. Some of the causes for 'surging' follow;
Sticky TB rods - these rods get 'spalling' from the steel rods rubbing inside the aluminum TB housing, which causes the rods to stick. As the idle drops, the rods stick shut until the vacuum pressure in the BACV tries to compensate, opening the butterflies. As the butterflies open, the idle increases until the BACV kicks in, closing the butterflies and dropping the idle again - endless cycle.
Dirty BACV valve - driver's side of DEI chamber, remove and spray brake cleaner into the air inlets to clear out any carbon that's preventing the BACV from breathing properly. Reinstall with a good gasket seal.
TPS - sometimes, the TPS adjustment can help contribute to surging, but usually exhibits itself in erratic throttle settings under steady-state driving conditions, or what feels like 'surging' at speed. Adjust TPS using 2-light method or digital voltmeter.
The SE has some quirky things that take place during idle conditions, but not so much that you can't get it to run right. Take a look at these suggestions and then post back, and we can help you get it sorted out. HTH,
Last edited by LongDuck; Apr 12, 2004 at 01:28 PM.
Longduck - glad you dropped in.... I've added some info to your quote
I'm going to do a more thorough exam on vac leaks - I might be missing a small one somewhere. My emmedialte concern was why I wasn't picking up the pulley marking on the trainling and I thnk you have answered that. I'll post back once I've had a chance to dig some some.
Originally posted by LongDuck
Couple of things - first off; thanks for putting GSL-SE in the post title. I *always* drop in on a thread about SE's!
On the Leading/Trailing coil wires, you'll notice that the coils are mounted front to back, Trailing in Front, Leading in Back, and these will need to coincide with what's marked on the Dist Cap. Once you have that confirmed, then check timing again, but REMOVE the vacuum advance rubber tubes from the dizzy. The FSM outlines that you need to disconnect the vacuum lines to ensure that any slight 'surging' will not affect your timing light's ability to show you the lead/trail marks on the main pulley.
I'm running direct fire so this is not an issue (2 coils on the leading, one on the trailing - looks good)
Good note on disconecting the vac lines - I'll try that
BTW, 'surging' is the name given to what SE's do when one or several things have gone out of adjustment or need cleaning. Surging is when the engine will idle up and down anywhere from 300-2k rpm at what should be a normal, steady idle speed. Some of the causes for 'surging' follow;
Sticky TB rods - these rods get 'spalling' from the steel rods rubbing inside the aluminum TB housing, which causes the rods to stick. As the idle drops, the rods stick shut until the vacuum pressure in the BACV tries to compensate, opening the butterflies. As the butterflies open, the idle increases until the BACV kicks in, closing the butterflies and dropping the idle again - endless cycle.
All components of the TB look good - very clean and well lubed. Everything moves freely with no binding
Dirty BACV valve - driver's side of DEI chamber, remove and spray brake cleaner into the air inlets to clear out any carbon that's preventing the BACV from breathing properly. Reinstall with a good gasket seal.
BAC is new
TPS - sometimes, the TPS adjustment can help contribute to surging, but usually exhibits itself in erratic throttle settings under steady-state driving conditions, or what feels like 'surging' at speed. Adjust TPS using 2-light method or digital voltmeter.
This was done - TPS is reading correctly
The SE has some quirky things that take place during idle conditions, but not so much that you can't get it to run right. Take a look at these suggestions and then post back, and we can help you get it sorted out. HTH,
Couple of things - first off; thanks for putting GSL-SE in the post title. I *always* drop in on a thread about SE's!
On the Leading/Trailing coil wires, you'll notice that the coils are mounted front to back, Trailing in Front, Leading in Back, and these will need to coincide with what's marked on the Dist Cap. Once you have that confirmed, then check timing again, but REMOVE the vacuum advance rubber tubes from the dizzy. The FSM outlines that you need to disconnect the vacuum lines to ensure that any slight 'surging' will not affect your timing light's ability to show you the lead/trail marks on the main pulley.
I'm running direct fire so this is not an issue (2 coils on the leading, one on the trailing - looks good)
Good note on disconecting the vac lines - I'll try that
BTW, 'surging' is the name given to what SE's do when one or several things have gone out of adjustment or need cleaning. Surging is when the engine will idle up and down anywhere from 300-2k rpm at what should be a normal, steady idle speed. Some of the causes for 'surging' follow;
Sticky TB rods - these rods get 'spalling' from the steel rods rubbing inside the aluminum TB housing, which causes the rods to stick. As the idle drops, the rods stick shut until the vacuum pressure in the BACV tries to compensate, opening the butterflies. As the butterflies open, the idle increases until the BACV kicks in, closing the butterflies and dropping the idle again - endless cycle.
All components of the TB look good - very clean and well lubed. Everything moves freely with no binding
Dirty BACV valve - driver's side of DEI chamber, remove and spray brake cleaner into the air inlets to clear out any carbon that's preventing the BACV from breathing properly. Reinstall with a good gasket seal.
BAC is new
TPS - sometimes, the TPS adjustment can help contribute to surging, but usually exhibits itself in erratic throttle settings under steady-state driving conditions, or what feels like 'surging' at speed. Adjust TPS using 2-light method or digital voltmeter.
This was done - TPS is reading correctly
The SE has some quirky things that take place during idle conditions, but not so much that you can't get it to run right. Take a look at these suggestions and then post back, and we can help you get it sorted out. HTH,
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