Engine trouble after cam swap
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From: St. Louis, Missouri
Engine trouble after cam swap I just recently installed the G5X4 cam. I had the car tuned and it never really felt like a big cam ls1 car. When i go WOT under 3k it will miss fire. Also running WOT around 5k it will feel as if you loose quite a bit of power.
We discovered that the EVAP was stuck open and was dumping raw fuel into the intake.. My tuner also ran an injector cylinder balance test and showed that cylinder 2 through 8 were pretty weak. Just playing around under the hood, i realized that i could spin each push rod while they were torqued under the rockers. So i have no preload? Im using 7.4 texas speed PR's. My question is, could the lifters be bad? Could the dual springs be too much for the stock lifters? Wrong size PR's?
My tuner assures me that the tune is on and i have trouble in my valvetrain somewhere. I also ran a cranking compression test and everything looked okay. Anyone have any ideas where i can start?
We discovered that the EVAP was stuck open and was dumping raw fuel into the intake.. My tuner also ran an injector cylinder balance test and showed that cylinder 2 through 8 were pretty weak. Just playing around under the hood, i realized that i could spin each push rod while they were torqued under the rockers. So i have no preload? Im using 7.4 texas speed PR's. My question is, could the lifters be bad? Could the dual springs be too much for the stock lifters? Wrong size PR's?
My tuner assures me that the tune is on and i have trouble in my valvetrain somewhere. I also ran a cranking compression test and everything looked okay. Anyone have any ideas where i can start?
Last edited by ws6_bandit; Jul 17, 2008 at 09:30 AM.
My brothers car has these exact symptoms and I've been trying to figure it out forever. I never thought to check the evap system and I'm temped to do so now. I have swapped everything on the car with known good parts from my car to try to diagnose the cause to no avail.
I will be working on it some more this weekend and will be sure to post any thing I think may help. Meanwhile, here is a to the top for you in the hopes that someone may have an answer.
I will be working on it some more this weekend and will be sure to post any thing I think may help. Meanwhile, here is a to the top for you in the hopes that someone may have an answer.
Did you have any of these symptoms BEFORE the cam swap? Did you do the swap or did your tuner do that part too? You say you have no preload. Are you using the OEM rockers and pushrods? If so, they are non-adjustable. When you say you can spin the pushrods you don't mean there is freeplay do you? Do you have a noisy valve train? You should not have pushrod freeplay, but being able to spin the push rod when the cam lobe is on the heel is not necessarily a bad thing. You need to go back over your work especially if you did NOT have these symptoms before the cam swap. What is your experience level? The LS cam swap is not hard. Actually it's one of the easiest since the heads or intake don't have to come off. There is a ton of info on this site that has piled up into a mountain by this time just on cam swaps alone. All of these problems can be avoided if you ask your questions ahead of time. When you work on an LS series be it a cam swap or a new set of CNCed heads the engine should start and work flawlessly the first time the key is turned. That's what the extensive library this site has become over more than 10 years is all about.
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Did you have any of these symptoms BEFORE the cam swap? Did you do the swap or did your tuner do that part too? You say you have no preload. Are you using the OEM rockers and pushrods? If so, they are non-adjustable. When you say you can spin the pushrods you don't mean there is freeplay do you? Do you have a noisy valve train? You should not have pushrod freeplay, but being able to spin the push rod when the cam lobe is on the heel is not necessarily a bad thing. You need to go back over your work especially if you did NOT have these symptoms before the cam swap. What is your experience level? The LS cam swap is not hard. Actually it's one of the easiest since the heads or intake don't have to come off. There is a ton of info on this site that has piled up into a mountain by this time just on cam swaps alone. All of these problems can be avoided if you ask your questions ahead of time. When you work on an LS series be it a cam swap or a new set of CNCed heads the engine should start and work flawlessly the first time the key is turned. That's what the extensive library this site has become over more than 10 years is all about.
Before i did the swap i read the walk through on ls1howto almost every night for a week. Although this was my first cam swap, it was not hard by any means.
The rockers are stock..Pushrods are 7.4 from texas speed. There is no free play in the push rods but it will spin unless the valve is on the open or close ramp. My tuner put a stethoscope on the valve covers and we heard a strong tick from cylinder 2.. We had a feeling it was a broken valve spring but they all checked out fine. On the cylinder balance test, cylinder 2 was weakest so i pulled the valve springs and had them tested.. they were fine. The valvetrain is kinda noisy at cruising speeds.... alot like a sewing machine. Especially when your driving next to a concrete median, but i would assume that is just the dual springs. The cam was installed dot to dot on timing.
Just throwing things around in my mind... the only thing in the swap that was not new was the cam... I bought it from a local LS1 guy. He said the cam had only a few thousand miles on it.
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Verdad Gallardo That's a good idea. Do you have a good scan tool. You turner certainly does. Do you have any DTCs? Monitor the STFTs to see if you're lean. That will show up as a negative percentage or some value less than 128(when using the binary coded decimal number system) or a decimal number like 1.15 with 1.0 being perfect AFR when using Lambda). If your STFTs are low maybe you left a rubber hose disconnected and you have a vacuum leak sending you LEAN. Can you(or an assistant) monitor the STFTs while spraying the top end? If you see the STFTs jump RICH at some point while spraying look for a cracked rubber hose or one that is not connected properly in the area you were spraying at the moment the STFTs went RICH. Of course there are other things. Go back over your work. If this is new to you need a system. Use a checklist if necessary.
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That's a good idea. Do you have a good scan tool. You turner certainly does. Do you have any DTCs? Monitor the STFTs to see if you're lean. That will show up as a negative percentage or some value less than 128(when using the binary coded decimal number system) or a decimal number like 1.15 with 1.0 being perfect AFR when using Lambda). If your STFTs are low maybe you left a rubber hose disconnected and you have a vacuum leak sending you LEAN. Can you(or an assistant) monitor the STFTs while spraying the top end? If you see the STFTs jump RICH at some point while spraying look for a cracked rubber hose or one that is not connected properly in the area you were spraying at the moment the STFTs went RICH. Of course there are other things. Go back over your work. If this is new to you need a system. Use a checklist if necessary.
You're sure you didn't miss a tooth when putting the chain back on? It would usually set a check engine light, but ive seen it before where it didn't. That could be your problem. I wouldn't think it would be a lifter problem.
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If it was off a tooth would is have that bad of a miss? PTV is soo close with this cam i would figure being off a tooth would be devastating. Posting tune info in just a sec....
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LTFT's are sitting between -2 and +1 throughout the entire range. The O2's were stuck at .850mV... we determined the EVAP was stuck open. After deleting the EVAP, the O2's went back to switching properly and the trims returned to normal.
Here are some snap shots from my dyno runs..
http://i109.photobucket.com/albums/n...ndit/dyno1.jpg
http://i109.photobucket.com/albums/n...ndit/dyno2.jpg
http://i109.photobucket.com/albums/n...ndit/dyno3.jpg
http://i109.photobucket.com/albums/n...ndit/dyno4.jpg
And here is the A/F graph...http://i109.photobucket.com/albums/n...dit/dyno-2.jpg
By the way, i am just relaying info from my tuner, Keith McCord.
Here are some snap shots from my dyno runs..
http://i109.photobucket.com/albums/n...ndit/dyno1.jpg
http://i109.photobucket.com/albums/n...ndit/dyno2.jpg
http://i109.photobucket.com/albums/n...ndit/dyno3.jpg
http://i109.photobucket.com/albums/n...ndit/dyno4.jpg
And here is the A/F graph...http://i109.photobucket.com/albums/n...dit/dyno-2.jpg
By the way, i am just relaying info from my tuner, Keith McCord.
Last edited by ws6_bandit; Jul 19, 2008 at 06:56 PM.
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From: St. Louis, Mazarah
Here are his dyno charts. The first pull (lesser) was made with his cutouts closed and the wideband in the tailpipe. The second run was made with the cutouts open while the wideband was left in the tailpipe (glory run), thus you are seeing a significant lean reading from it. Tune was left unchanged between runs, it was mainly to see if his stock WS6 exhaust was holding him back.
Fuel trims during transitional driving range between -2 and +1 and zero out upon transition to wide open throttle. O2s are switching as expected. There is significant noise coming from the front lifter(s) which is very audible when using a stethoscope. The o-ring was not replaced when doing the camshaft swap. We've seen in the past where the ring was rolled and we were not getting adequate volume of oil to the top end and causing a lifter pump up issue even though the oil pressure seemed ok. I'm begining to wonder if this is the case, especially with his springs being roughly 406# at the nose.
Fuel trims during transitional driving range between -2 and +1 and zero out upon transition to wide open throttle. O2s are switching as expected. There is significant noise coming from the front lifter(s) which is very audible when using a stethoscope. The o-ring was not replaced when doing the camshaft swap. We've seen in the past where the ring was rolled and we were not getting adequate volume of oil to the top end and causing a lifter pump up issue even though the oil pressure seemed ok. I'm begining to wonder if this is the case, especially with his springs being roughly 406# at the nose.
Did he pull the pump off or just swap the cam? If he didn't have a oil supply problem before the cam swap and the pump was not disturbed the "O" ring should be in tact. He's trying to isolate a problem that he didn't have before the swap. He has to go back over his steps.
Teching In
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From: St. Louis, Mazarah
Did he pull the pump off or just swap the cam? If he didn't have a oil supply problem before the cam swap and the pump was not disturbed the "O" ring should be in tact. He's trying to isolate a problem that he didn't have before the swap. He has to go back over his steps.
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Did he pull the pump off or just swap the cam? If he didn't have a oil supply problem before the cam swap and the pump was not disturbed the "O" ring should be in tact. He's trying to isolate a problem that he didn't have before the swap. He has to go back over his steps.
The cam sensor is used by the PCM to adjust the injector timing. It will affect more than just start up. It will be difficult for the car to start w/o one, b/c it will use the crank sensor once it realizes it is not receiving the cam sensor signal(usually backfiring and failing to start on the first crank). The fueling will not be accurate with a faulty CMP.