westcoastgrandnational
Member
- Joined
- May 28, 2014
exhaust leak has already been fixed and made no difference either in how the car runs
87 GN at idle
- Thread starter westcoastgrandnational
- Start date
If fixing the exhaust leak didn't change the way the car runs, it's in a very bad state of tune. An exhaust leak at low load will trick the 02 into thinking you're lean, and the ECM will respond by dumping in more fuel than you actually need (high BLMs on a scantool). When you kick it, (after the cloud of black smoke clears out the tail pipe) the boost will suffer because you're venting exhaust pressure instead of driving the turbo.
When you replaced the IAC did you clean out the passages in the throttlebody and make sure there was no crud on the seating area where the IAC seals?
Grab the the throttle blade with your hand (engine off) and let it snap shut a few times. Does it stick shut?
If you have an old laptop that has a car charger or a good battery, there's a cheap way to scan the car with an ALDL converter and see what's going on. It's not as convenient as a scanmaster for everyday driving, but it might save your engine today.
When you replaced the IAC did you clean out the passages in the throttlebody and make sure there was no crud on the seating area where the IAC seals?
Grab the the throttle blade with your hand (engine off) and let it snap shut a few times. Does it stick shut?
If you have an old laptop that has a car charger or a good battery, there's a cheap way to scan the car with an ALDL converter and see what's going on. It's not as convenient as a scanmaster for everyday driving, but it might save your engine today.
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RmvBfrFlght
Well-Known Member
- Joined
- Sep 28, 2007
The 'slow start' Buick ignition system requires the cam sensor to know when to start firing the coils. Once running the ICM will retain the firing sequence even without the cam sensor input.
Try this, loosen the cam sensor retaining bolt a tad, start the engine, then rotate the cam sensor. Let us know what happens.
You are correct about the SFI fueling, the ECM requires the cam signal to sequence the injectors.
RemoveBeforeFlight
Hmm, looks like we are saying the same thing. I agree the engine won't start without the cam sensor as the ICM needs the initial reference and I have no doubt rotating the cam sensor while running will change the fuel injector timing. Are you saying that the ignition timing will also change after rotating the cam sensor while it is running? If so, then I have learned something new. Also, it's worth noting I'm not trying to be argumentative, just trying to have a solid understanding. Thanks in advance.
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RmvBfrFlght
Well-Known Member
- Joined
- Sep 28, 2007
Yes, dependent upon which way the sensor is rotated the spark will either advance to the next set of cylinders or fall back to the previous set of cylinders. When the cam signal is present the ICM will resync to it on a continual basis. This is why setting it correctly is so important, when it is 'not quite right' the spark can fire on the wrong cylinder. Most of the time this is intermittent and drives the owner crazy.
The change in injector timing would likely not even be noticeable.
RemoveBeforeFlight
No, you can not change ignition timing, at all, by adjusting the cam sensor. This is why the cam sensor fix it plug from Casper's works. Even without a cam sensor at all, you can get the car started but it'll be in batch fire mode. It'll get you home. Again, the cam sensor does NOTHING for ignition timing.
Tweaking the sensor one way or another will allow to start quicker; this is the benefit of better injector timing which the cam sensor DOES control.
From gnttype.org See #1
Cam Sensor Basics
If we're discussing a DIS on a TR, well after 10 years I'm surprised there's still confusion.
1.Setting the cam sensor has NOTHING to do with initial timing.
2.Moving the cam sensor a few degrees does nothing to the ignition timing. If the car runs, (and the 3x trigger on the balancer is mounted correctly by the factory) then your ignition timing will be EXACTLY what's in the spark map of the chip regardless of where the cam sensor is set.
3.I say if the car runs, because for ignition timing, all the cam sensor does is tell us which cylinder is #6. After the cam signal goes LOW, (stock spec is 25 deg ATDC of cylinder #1) the next RISING edge of the CRANK pulse will occur exactly 10 deg BTDC of cylinder #6.
4.Therefore, if the cam signal wasn't there, you would never know which crank pulse signaled #6 (or any other cylinder for that matter).
5.Once we have this info, cylinder #6 and #3 will fire. Remember this is a waste spark system (but I'm sure everyone knows that by now) so #6 will be on compression but #3 on exhaust, whose spark is wasted. It takes very little energy to fire a plug that's not under compression, so it's no big deal.
5a.Note also that the current goes through and fires one plug the "normal" way (center electrode to GND electrode), through the block, and fires the other plug "backwards" (GND electrode to center electrode).
5b.This being the case, if you switch wires on the SAME coil (6&3, 1&4, 2&5) it won't make a bit of difference to the car - the plug that was "backward" firing before will now be "normal" and vice versa.
5c.So you can see, on crank up and during limp-home mode, spark advance is 10 deg BTDC since the rising (active) edge of the crank signal occurs 10 deg BTDC of every cylinder.
6.So, moving the cam sensor within the window where the next rising crank pulse is the #6 cylinder has absolutely NO effect on actual ignition timing. Ignition timing calculations are based off the CRANK sensor, which cannot be adjusted short of modifying the balancer or retapping the crank sensor mounting location!
7.So what happens when you move the cam sensor beyond that window and the next crank pulse is either #1 or #5 (depending on the direction you moved it) and not #6? You guessed it, the #6/3 coil will still fire, but the #6 won't be anywhere near TDC and the engine will either kick back or just not run. Regardless, if you get the cam sensor out of adjustment enough to affect ignition timing, it'll simply be out of sync so much the car won't run. That's why if the car is actually running, you can bet the ignition timing is dead on.
8.This brings up some more points. (Might as well be thorough) What happens if you set the cam sensor 180 degrees out? For ignition, nothing. The plug that was supposed to be on compression will now be on exhaust, and vice versa. The car doesn't care! Ignition will be perfect. Fueling, on the other hand, is a different story. More on that later.
9.What happens if you unplug the cam sensor while the engine is running? Nothing. A malf code will set, but as long as you don't kill the engine it'll keep running perfectly (assuming the crank sensor is good.) Once you kill it though, it won't start again.
10.What happens if you move the cam sensor while the engine is running? Every two revs, the cam sensor info is checked. If the cam sensor signal is present, it updates and resyncs. If not there, a malf code is set and the previous sync is used. See #9. For ignition, moving the cam sensor within that window where it syncs correctly does nothing. Move it outside that window and you'll backfire like never before, as you'll fire the wrong cylinder at the wrong time. Trust me, I had it happen. My cam sensor lost it's tab for the keyway on the shaft and started moving on it's own. Exploded my mufflers. I wrote a note about 2 months back about that.
11.So, I hope everyone's convinced that adjusting the cam sensor has absolutely no effect on ignition timing, but can only cause a no-start or tremendous backfire & stalling if running.
A stretched/slipped timing chain therefore also has no effect on ignition timing.
12.HOWEVER, adjusting the cam sensor has a tremendous effect on FUELING, as the SFI syncs off the cam too. I don't know much (yet) about the fueling specs, but it apparently has a much narrower window than ignition in order to sync to the wrong cylinder. This is why if you have the cam 180 deg out the car will run terribly because the fueling is all messed up. Basically it'll be in a SFI mode where fuel is puddling for 1 rev before being sucked in.
13.This is where any performance gain/losses will occur. MAYBE advancing the cam sensor a bit might help a big cam engine that opens the intake sooner, I don't know.
It definitely affects idle quality having the cam sensor out of adjustment. In my opinion I can't see how advancing the cam will help as you're practically in a batch fire mode at WOT where the injector is on practically the whole time. I can't see how a few msec sooner is going to have a great effect. SFI has it's greatest effect at idle & part throttle, and a misadjusted cam definitely can be felt here.
Actually, the fueling can only sync off the crank signal too, with the cam telling it which crank pulse corresponds to which cylinder, so it you're off, you're off by a whole cylinder. It'll be a step function. Within a certain window, you'll be fueling the same cylinder, adjust some more, and you'll step into another one. I can't believe fueling the wrong cylinder can help performance no matter what cam you have.
14.I think that's it. Sorry, didn't mean to write a book. Isn't this info in the FAQ list or something? If not it needs to be. Too much misinformation out there. I should copyright this and charge! Now that it's posted on the list, everyone will be an expert on this and can claim "Oh yeah, I knew that stuff 10 years ago!" Yeah, right. But that's what this list is for, to educate Buick owners and admirers about their cars, so that they don't get ripped off by mechanics and such, right Scott?
Cam Sensor Basics
If we're discussing a DIS on a TR, well after 10 years I'm surprised there's still confusion.
1.Setting the cam sensor has NOTHING to do with initial timing.
2.Moving the cam sensor a few degrees does nothing to the ignition timing. If the car runs, (and the 3x trigger on the balancer is mounted correctly by the factory) then your ignition timing will be EXACTLY what's in the spark map of the chip regardless of where the cam sensor is set.
3.I say if the car runs, because for ignition timing, all the cam sensor does is tell us which cylinder is #6. After the cam signal goes LOW, (stock spec is 25 deg ATDC of cylinder #1) the next RISING edge of the CRANK pulse will occur exactly 10 deg BTDC of cylinder #6.
4.Therefore, if the cam signal wasn't there, you would never know which crank pulse signaled #6 (or any other cylinder for that matter).
5.Once we have this info, cylinder #6 and #3 will fire. Remember this is a waste spark system (but I'm sure everyone knows that by now) so #6 will be on compression but #3 on exhaust, whose spark is wasted. It takes very little energy to fire a plug that's not under compression, so it's no big deal.
5a.Note also that the current goes through and fires one plug the "normal" way (center electrode to GND electrode), through the block, and fires the other plug "backwards" (GND electrode to center electrode).
5b.This being the case, if you switch wires on the SAME coil (6&3, 1&4, 2&5) it won't make a bit of difference to the car - the plug that was "backward" firing before will now be "normal" and vice versa.
5c.So you can see, on crank up and during limp-home mode, spark advance is 10 deg BTDC since the rising (active) edge of the crank signal occurs 10 deg BTDC of every cylinder.
6.So, moving the cam sensor within the window where the next rising crank pulse is the #6 cylinder has absolutely NO effect on actual ignition timing. Ignition timing calculations are based off the CRANK sensor, which cannot be adjusted short of modifying the balancer or retapping the crank sensor mounting location!
7.So what happens when you move the cam sensor beyond that window and the next crank pulse is either #1 or #5 (depending on the direction you moved it) and not #6? You guessed it, the #6/3 coil will still fire, but the #6 won't be anywhere near TDC and the engine will either kick back or just not run. Regardless, if you get the cam sensor out of adjustment enough to affect ignition timing, it'll simply be out of sync so much the car won't run. That's why if the car is actually running, you can bet the ignition timing is dead on.
8.This brings up some more points. (Might as well be thorough) What happens if you set the cam sensor 180 degrees out? For ignition, nothing. The plug that was supposed to be on compression will now be on exhaust, and vice versa. The car doesn't care! Ignition will be perfect. Fueling, on the other hand, is a different story. More on that later.
9.What happens if you unplug the cam sensor while the engine is running? Nothing. A malf code will set, but as long as you don't kill the engine it'll keep running perfectly (assuming the crank sensor is good.) Once you kill it though, it won't start again.
10.What happens if you move the cam sensor while the engine is running? Every two revs, the cam sensor info is checked. If the cam sensor signal is present, it updates and resyncs. If not there, a malf code is set and the previous sync is used. See #9. For ignition, moving the cam sensor within that window where it syncs correctly does nothing. Move it outside that window and you'll backfire like never before, as you'll fire the wrong cylinder at the wrong time. Trust me, I had it happen. My cam sensor lost it's tab for the keyway on the shaft and started moving on it's own. Exploded my mufflers. I wrote a note about 2 months back about that.
11.So, I hope everyone's convinced that adjusting the cam sensor has absolutely no effect on ignition timing, but can only cause a no-start or tremendous backfire & stalling if running.
A stretched/slipped timing chain therefore also has no effect on ignition timing.
12.HOWEVER, adjusting the cam sensor has a tremendous effect on FUELING, as the SFI syncs off the cam too. I don't know much (yet) about the fueling specs, but it apparently has a much narrower window than ignition in order to sync to the wrong cylinder. This is why if you have the cam 180 deg out the car will run terribly because the fueling is all messed up. Basically it'll be in a SFI mode where fuel is puddling for 1 rev before being sucked in.
13.This is where any performance gain/losses will occur. MAYBE advancing the cam sensor a bit might help a big cam engine that opens the intake sooner, I don't know.
It definitely affects idle quality having the cam sensor out of adjustment. In my opinion I can't see how advancing the cam will help as you're practically in a batch fire mode at WOT where the injector is on practically the whole time. I can't see how a few msec sooner is going to have a great effect. SFI has it's greatest effect at idle & part throttle, and a misadjusted cam definitely can be felt here.
Actually, the fueling can only sync off the crank signal too, with the cam telling it which crank pulse corresponds to which cylinder, so it you're off, you're off by a whole cylinder. It'll be a step function. Within a certain window, you'll be fueling the same cylinder, adjust some more, and you'll step into another one. I can't believe fueling the wrong cylinder can help performance no matter what cam you have.
14.I think that's it. Sorry, didn't mean to write a book. Isn't this info in the FAQ list or something? If not it needs to be. Too much misinformation out there. I should copyright this and charge! Now that it's posted on the list, everyone will be an expert on this and can claim "Oh yeah, I knew that stuff 10 years ago!" Yeah, right. But that's what this list is for, to educate Buick owners and admirers about their cars, so that they don't get ripped off by mechanics and such, right Scott?
And there will likely always be !Seems there is still confusion after 25 years.
Buick Mark
Active Member
- Joined
- Sep 12, 2001
Buick Mark
Active Member
- Joined
- Sep 12, 2001
WOW, I haven't read that in years! It was a good re-read tho
RmvBfrFlght
Well-Known Member
- Joined
- Sep 28, 2007
OK, so when is someone going to do what I suggested earlier. That is rotate the cam sensor while the engine is running. Rotate it enough and the ICM will skip forward or backwards as to which two cylinders get spark. I guarantee that the engine will stop running.
You are correct that it doesn't affect the ignition timing per se, I never said that, but it will affect which pair of cylinders get spark. In this case it will affect the spark advance by 120 degrees.
I would do this myself and post a video. But running the Buick Quick Start system, it doesn't use the cam sensor at all for spark set up. I can unplug the cam sensor and the engine will still crank to start and run. I did it to see that it would, it did, and the ECM set the cam sensor malfunction code. So someone with the 'slow start' ignition set up has to step up to the plate...
Or, just read we4Mateo's last post, the #7 & # 10 entries describes EXACTLY what I have been posting.
RemoveBeforeFlight
You are correct that it doesn't affect the ignition timing per se, I never said that, but it will affect which pair of cylinders get spark. In this case it will affect the spark advance by 120 degrees.
I would do this myself and post a video. But running the Buick Quick Start system, it doesn't use the cam sensor at all for spark set up. I can unplug the cam sensor and the engine will still crank to start and run. I did it to see that it would, it did, and the ECM set the cam sensor malfunction code. So someone with the 'slow start' ignition set up has to step up to the plate...
Or, just read we4Mateo's last post, the #7 & # 10 entries describes EXACTLY what I have been posting.
RemoveBeforeFlight
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RmvBfrFlght
Well-Known Member
- Joined
- Sep 28, 2007
RmvBfrFlght
Well-Known Member
- Joined
- Sep 28, 2007
I wouldn't want too, it just seems to be the only way to convince folks that the cam sensor does affect the ignition timing. I'm with you earl, it just seems it may be easier to convince folks that they know what makes a women tick. As it was, this guy was walking along the beach one bright sunny afternoon and stubbed his toe on something in the sand.
He found that it was a magic lamp, and rubbed it three times to bring the genie out for his wish. The genie asked him what he wished for, he responded that it would be nice to have a bridge from California to Hawaii to drive across.
The genie was taken aback a bit, and told the man that that is a lot of work, this would be a huge bridge. Would you have another wish?
After some thought the man replied that he would like to understand women.
The genie immediately replied: two lanes or four...
RemoveBeforeFlight
The cam sensor ONLY tells the car when #6 is close by so the ECM can get on the clock. Once the engine is running and code 12 vanishes the crank sensor is what the car goes buy for spark timing input.
That's why the car goes into batch fire mode if you unplug the cam sensor while running. The ECM has no idea where the intake lobes are, so it just sprays the injectors like a non sequential system.
There's only two common reasons for screwing with cam sensor timing as tuning aid.....
One is the timing tab/balancer mark isn't accurate. For example, if you're 10* retarded and don't know it... "tuning' your cam sensor" advanced will make your car run better. That's not exactly tuning AFAIC. It's more of "tuning around something that needs to be fixed" sorta thing. Back in the old days people used to try to tune a carb around an ignition problem for example.
Second is when you run a big ass cam. That's also made worse when the cam grinder tries to save people from themselves and they grind an advance into the cam.
When the intake valve opens on a sequential port FI system like we have, you have to have an injector cocked and locked and ready to go. (I don't know the relantionship of the injector pulse relative to the stock cam, so bear with me..). If you put a cam in there and the lobe opens 20* sooner than what the ECM expects AND it's ground with 4* advance built in.... What you end up with is the engine sucking plain ole air with no fuel in it for a few degrees. THEN the injector starts spraying the correct amount of fuel for the air that's left. IF that mixture reaches homogenization, the total mixture will be leaner than you want. This is made much worse with forced induction engines as a BUNCH of air will shoot past the valve when it first cracks open.
That's why cars with huge cams run better when you advance the cam sensor from where they belong. The ECM only knows how much air is going past the MAF. It can't know if you're causing the fueling to be tardy. On most cars that lock the BLMs at 128 during WOT, the ECM doesn't pay attention, it just sprays X amount of fuel. If you waste time that could be used for tumble and mixing and stuff, all you've did was kill efficiency and lower the amount of energy the fuel has to offer.
That's why the car goes into batch fire mode if you unplug the cam sensor while running. The ECM has no idea where the intake lobes are, so it just sprays the injectors like a non sequential system.
There's only two common reasons for screwing with cam sensor timing as tuning aid.....
One is the timing tab/balancer mark isn't accurate. For example, if you're 10* retarded and don't know it... "tuning' your cam sensor" advanced will make your car run better. That's not exactly tuning AFAIC. It's more of "tuning around something that needs to be fixed" sorta thing. Back in the old days people used to try to tune a carb around an ignition problem for example.
Second is when you run a big ass cam. That's also made worse when the cam grinder tries to save people from themselves and they grind an advance into the cam.
When the intake valve opens on a sequential port FI system like we have, you have to have an injector cocked and locked and ready to go. (I don't know the relantionship of the injector pulse relative to the stock cam, so bear with me..). If you put a cam in there and the lobe opens 20* sooner than what the ECM expects AND it's ground with 4* advance built in.... What you end up with is the engine sucking plain ole air with no fuel in it for a few degrees. THEN the injector starts spraying the correct amount of fuel for the air that's left. IF that mixture reaches homogenization, the total mixture will be leaner than you want. This is made much worse with forced induction engines as a BUNCH of air will shoot past the valve when it first cracks open.
That's why cars with huge cams run better when you advance the cam sensor from where they belong. The ECM only knows how much air is going past the MAF. It can't know if you're causing the fueling to be tardy. On most cars that lock the BLMs at 128 during WOT, the ECM doesn't pay attention, it just sprays X amount of fuel. If you waste time that could be used for tumble and mixing and stuff, all you've did was kill efficiency and lower the amount of energy the fuel has to offer.
And what part of that post to you dislike, gnjones231?
The true part, or the part where somebody might actually learn how that sensor actauly works?
The true part, or the part where somebody might actually learn how that sensor actauly works?
You know how it is Earl, nay-Sayers everywhere you turn.
