4 cylinders rich, 4 cylinders L-jet: Fixed! (Cam timing)
01-09-2018, 08:24 AM
#76
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Thread Starter
Hi Dave,
The interesting question is whether the symptoms are explicable. As the cam timing is advanced it should favour low/mid rpm range performance at the expense of top end. To perform better it needs more air flow and fuel to match but if the mix was rich at low/mid range that possibly suggests less air flow. I am not too familiar with the engine management system on your model year but it would be interesting to see if anyone can explain how your symptoms came about because of the cam error.
I suspect the 32VR cam timing tool does not work on your model given its name but for the 32 valve models it is a must for DIY enthusiasts. No idea if there is an equivalent device for your model year but if there is I bet you might consider buying one!
Either way well done albeit it took some time to get there. One cam tooth out is 15 crank degrees- folks playing around with cam timing tend to vary about 10 degrees retard tops looking for more top end so your error factor should be significant.
The interesting question is whether the symptoms are explicable. As the cam timing is advanced it should favour low/mid rpm range performance at the expense of top end. To perform better it needs more air flow and fuel to match but if the mix was rich at low/mid range that possibly suggests less air flow. I am not too familiar with the engine management system on your model year but it would be interesting to see if anyone can explain how your symptoms came about because of the cam error.
I suspect the 32VR cam timing tool does not work on your model given its name but for the 32 valve models it is a must for DIY enthusiasts. No idea if there is an equivalent device for your model year but if there is I bet you might consider buying one!
Either way well done albeit it took some time to get there. One cam tooth out is 15 crank degrees- folks playing around with cam timing tend to vary about 10 degrees retard tops looking for more top end so your error factor should be significant.
I've heard of people tweaking their cam timing, but since I have no controlled way to do it, I just never tried to understand it. I would have guessed they would adjust both cams, not just one, but I don't know. I was looking for something different on one side of my engine, I thought I had found a bad injector. Finally I rechecked my cam gear timing marks and found the DS one tooth advanced. Totally my fault, just didn't see the error.
Thanks,
Dave
01-09-2018, 10:30 AM
#77
Rennlist Member
Hi Fred,
I've heard of people tweaking their cam timing, but since I have no controlled way to do it, I just never tried to understand it. I would have guessed they would adjust both cams, not just one, but I don't know. I was looking for something different on one side of my engine, I thought I had found a bad injector. Finally I rechecked my cam gear timing marks and found the DS one tooth advanced. Totally my fault, just didn't see the error.
Thanks,
Dave
I've heard of people tweaking their cam timing, but since I have no controlled way to do it, I just never tried to understand it. I would have guessed they would adjust both cams, not just one, but I don't know. I was looking for something different on one side of my engine, I thought I had found a bad injector. Finally I rechecked my cam gear timing marks and found the DS one tooth advanced. Totally my fault, just didn't see the error.
Thanks,
Dave
On the 32V models we can tweak the cam timing within a limited range of about 15 crank degrees or plus minus 7.5 degrees of the factory timing thanks to the adjustment range available. One tooth is the equivalent of 15 crank degrees and presumably the adjustment range is a bit more than the tooth to tooth range. Needless to say one should set the same adjustment offset to both banks. There is no way to adjust the exhaust cam relative to the inlet cam but the cam envelope relative to the crank position can be adjusted on both banks.
Your case is interesting in that in so far as I can tell none of our brains trust actually recognised your symptoms as indicative of the eventual root cause [apologies if I missed anything in the thread]. What I would like to understand is the logic as to why your symptoms occurred the way they did. I am not too surprised something like this happened but I do not understand the physics of why at the moment. Maybe someone from within our midst does
01-09-2018, 10:46 AM
#78
Administrator - "Tyson"
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Once he was able to eliminate the possibility of any single (or multiple) cylinders being the culprit, the primary suspect of two banks being consistently off like this is cam timing.
The thread started out with him thinking an O2 sensor was bad, it wasn't initially seen or known the problem was the two banks being consistently off in air / fuel.
However, he did discover an injector wasn't in the best shape which could have caused bigger issues down the road.
01-09-2018, 10:59 AM
#79
Rennlist Member
Indeed once it has been established that the problem is pertaining to 4 cylinders on one bank the indicator is cam timing. However what I was trying to allude to is the specific symptoms and of specific interest to me, why such symptoms actually occur. I can well understand folks being thrown off by other factors but as I could interpret, the symptoms were pretty specific from the initial post but it took until post 47 to arrive at that conclusion if that makes sense.
My process engineering brain likes to understand why specific phenomena occur irrespective of whether it is of any use or not.
01-09-2018, 11:09 AM
#80
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"I thought I had a bad O2 sensor, but my passenger side engine bank is running much leaner than the drivers side."
That tidbit of information wasn't initially part of the opening post (it was originally "Having trouble with my NB O2 sensor").
That's part of the issue with web forums, often times items added to OP's are missed by people only following the thread. I also changed the thread title for him once the primary culprit was discovered.
That tidbit of information wasn't initially part of the opening post (it was originally "Having trouble with my NB O2 sensor").
That's part of the issue with web forums, often times items added to OP's are missed by people only following the thread. I also changed the thread title for him once the primary culprit was discovered.
01-09-2018, 11:59 AM
#81
Rennlist Member
"I thought I had a bad O2 sensor, but my passenger side engine bank is running much leaner than the drivers side."
That tidbit of information wasn't initially part of the opening post (it was originally "Having trouble with my NB O2 sensor").
That's part of the issue with web forums, often times items added to OP's are missed by people only following the thread. I also changed the thread title for him once the primary culprit was discovered.
That tidbit of information wasn't initially part of the opening post (it was originally "Having trouble with my NB O2 sensor").
That's part of the issue with web forums, often times items added to OP's are missed by people only following the thread. I also changed the thread title for him once the primary culprit was discovered.
No idea why the first post was changed given the chronological sequence of subsequent posts should tell the full story albeit it is a good idea to change the title once the root cause of the problem has been ascertained. I suppose the learning here is that if a post is going to be edited it make sense to add a word or two to explain what the essence of the change was given the facility to do so.
Why the OP's motor experienced the specific symptoms it did remains the focus of my interest
01-09-2018, 12:05 PM
#82
Rennlist Member
Thread Starter
Eric,
Indeed once it has been established that the problem is pertaining to 4 cylinders on one bank the indicator is cam timing. However what I was trying to allude to is the specific symptoms and of specific interest to me, why such symptoms actually occur. I can well understand folks being thrown off by other factors but as I could interpret, the symptoms were pretty specific from the initial post but it took until post 47 to arrive at that conclusion if that makes sense.
My process engineering brain likes to understand why specific phenomena occur irrespective of whether it is of any use or not.
Indeed once it has been established that the problem is pertaining to 4 cylinders on one bank the indicator is cam timing. However what I was trying to allude to is the specific symptoms and of specific interest to me, why such symptoms actually occur. I can well understand folks being thrown off by other factors but as I could interpret, the symptoms were pretty specific from the initial post but it took until post 47 to arrive at that conclusion if that makes sense.
My process engineering brain likes to understand why specific phenomena occur irrespective of whether it is of any use or not.
At the very beginning of this thread I started off doubting my instruments, when they seemed to indicate different AFR on each cylinder bank. Only after verifying the results, did we start to look at asymmetrical conditions in the system. Bad plug, bad injector, bad fuel pressure regulator, etc. I dismissed cam timing, when I thought I could see it was correct. When I double checked, the cam timing was indeed wrong. Because I have a supercharger, it was not that easy to get a good view of the cam sprockets.
My fault, but with your help I think we figured it out.
Thanks
Dave
Last edited by j.kenzie@sbcglobal.net; 01-10-2018 at 08:51 AM.
01-29-2018, 12:07 PM
#83
Rennlist Member
Thread Starter
Good morning,
This is a follow up on my cam timing error and its return to proper timing. I finished my motor mounts and OPG before I could take the car for a test drive.
All I can say is Wow!
AFR's are right on the money and throttle response and power is awesome. I mean 911 Turbo awesome. The roads were temporarily clean and dry in Chicago, but it's going back inside, probably until Spring. I learned that cam timing is very important, (maybe errors are magnified with supercharging.) I also learned that attention to detail is critical on all motor work. I should have known better.
Thanks again,
Dave
This is a follow up on my cam timing error and its return to proper timing. I finished my motor mounts and OPG before I could take the car for a test drive.
All I can say is Wow!
AFR's are right on the money and throttle response and power is awesome. I mean 911 Turbo awesome. The roads were temporarily clean and dry in Chicago, but it's going back inside, probably until Spring. I learned that cam timing is very important, (maybe errors are magnified with supercharging.) I also learned that attention to detail is critical on all motor work. I should have known better.
Thanks again,
Dave