Would pushrods which are too long make a stock car sound cammed?
03-06-2012, 03:40 PM
#1
Would pushrods which are too long make a stock car sound cammed? A friend has a rebuilt ls1 in his Trans Am which sounds like it has a cam even though it is just a stock 98 ls1 cam.
The heads were requested to be milled .010" and the block had at least a cleanup pass maybe a little more off.
Stock pushrods, lifters, 98 cam (car was an 02) and headers. On first start it sounded normal but had zero oil pressure so he killed it and fixed a damaged o-ring. Started it back up with oil pressure and it has a lope like sound to it. I'm wondering if the lifters pumping up is what triggered it to start happening.
It has run this way for years trying to track down the cause. Changed several sensors, intake gaskets, all rubber hoses, etc. Last weekend the thought of pushrod length occurred to me when I was messing with mine and noticed too short of pushrods caused my cams lope to go away.
The car throws no codes but scans show misfires at idle on all cylinders and sometimes tosses codes for o2 sensors (replacing sensors doesn't help). Gets a little smoke on cold start. Has no vacuum leaks that can be found anywhere. It runs fairly strong and on par with other similar modded fbodies in the area.
We are planning to pull a valve cover and check preload this week, just curious if this could be the culprit or just coincidence.
The heads were requested to be milled .010" and the block had at least a cleanup pass maybe a little more off.
Stock pushrods, lifters, 98 cam (car was an 02) and headers. On first start it sounded normal but had zero oil pressure so he killed it and fixed a damaged o-ring. Started it back up with oil pressure and it has a lope like sound to it. I'm wondering if the lifters pumping up is what triggered it to start happening.
It has run this way for years trying to track down the cause. Changed several sensors, intake gaskets, all rubber hoses, etc. Last weekend the thought of pushrod length occurred to me when I was messing with mine and noticed too short of pushrods caused my cams lope to go away.
The car throws no codes but scans show misfires at idle on all cylinders and sometimes tosses codes for o2 sensors (replacing sensors doesn't help). Gets a little smoke on cold start. Has no vacuum leaks that can be found anywhere. It runs fairly strong and on par with other similar modded fbodies in the area.
We are planning to pull a valve cover and check preload this week, just curious if this could be the culprit or just coincidence.
03-06-2012, 04:59 PM
#4
Well that is assuming the machine shop only milled .010", the work was not checked. Also it is unknown how much was taken off the block.
I know it's a stretch, but with this never ending diagnosis we try not to overlook any possibility.
The fact it started once oil pressure was achieved would make it a possibility in my mind. Always open to other ideas and criticism as well. That's why I asked instead of just telling him to throw some 7.375" in it
I know it's a stretch, but with this never ending diagnosis we try not to overlook any possibility.
The fact it started once oil pressure was achieved would make it a possibility in my mind. Always open to other ideas and criticism as well. That's why I asked instead of just telling him to throw some 7.375" in it
03-06-2012, 11:59 PM
#5
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You pulled the valve covers to check for any mechanical failure?! Could be a broken valvespring causing it to missfire. Seen this happen on numerous occasions.
03-07-2012, 08:20 AM
#7
No mechanical issues are visible and the tune was stock for the 02 when it first started and since then the VE tables and timing tables for the 98 cam were pasted in with no results.
It runs fine other than the constant misfires at idle, the cammed sound, and the fuel trims are high (more likely a consequence than a symptom of the root cause).
Idle is normal RPM.
It runs fine other than the constant misfires at idle, the cammed sound, and the fuel trims are high (more likely a consequence than a symptom of the root cause).
Idle is normal RPM.
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03-11-2012, 04:29 PM
#10
Pulled a cover and checked the preload. Using stock 02 ls1 lifters, he had .115+ preload.
We checked it with the 7.35" pushrods and it was down to .060" so we went on a limb and tossed the rest of them in.
On first start the "lope" type sound was already severely reduced. Exhaust note was slightly quieter too. Went for a drive to make sure it wasn't down on power or throttle response and it drove excellent.
When we got back he pulled the battery cable to let the pcm reset. On the next startup after that it seemed to run even more smoothe. So far it likes like that could indeed have been the problem. Will report back if anything changes.
We checked it with the 7.35" pushrods and it was down to .060" so we went on a limb and tossed the rest of them in.
On first start the "lope" type sound was already severely reduced. Exhaust note was slightly quieter too. Went for a drive to make sure it wasn't down on power or throttle response and it drove excellent.
When we got back he pulled the battery cable to let the pcm reset. On the next startup after that it seemed to run even more smoothe. So far it likes like that could indeed have been the problem. Will report back if anything changes.
03-15-2012, 09:03 AM
#11
He drove the car around a lot Tuesday. He left the a/c on the whole time since the car used to be worse and often even die with the a/c on.
Never had a bit of a problem with it and it still sounds pretty well smooth. It's been so long since either of us really listened to a stock ls1 cam that wasn't having his issue that we don't have a good comparison on that end.
But at least his stock cam doesn't lope harder than my 230/238 or old 230/224 any more.
Never had a bit of a problem with it and it still sounds pretty well smooth. It's been so long since either of us really listened to a stock ls1 cam that wasn't having his issue that we don't have a good comparison on that end.
But at least his stock cam doesn't lope harder than my 230/238 or old 230/224 any more.
03-15-2012, 10:26 AM
#14
I have not had an opportunity to do a scan for him yet. I was busy switching to a 85mm MAF on my car and retuning for it.
The car is running really well btw, thanks again for your help with tuning it!
We joked he had the "ghost cam" after hearing about the tunes for the 2011 5.0 GTs with the fake cam sound.
It was not subtle. Every person who heard the car run asked him what cam he was running and he would get that frustrated look. I am not exaggerating when I say it sounded like it loped harder than my car, but I'm sure the LM1 and longtubes helped exaggerate the sound.
I will keep the thread updated if there are any changes. I will try to get some logs and see how the PCM reads now.
The car is running really well btw, thanks again for your help with tuning it!
It was not subtle. Every person who heard the car run asked him what cam he was running and he would get that frustrated look. I am not exaggerating when I say it sounded like it loped harder than my car, but I'm sure the LM1 and longtubes helped exaggerate the sound.
I will keep the thread updated if there are any changes. I will try to get some logs and see how the PCM reads now.
03-15-2012, 10:52 AM
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03-15-2012, 02:01 PM
#16
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I have not had an opportunity to do a scan for him yet. I was busy switching to a 85mm MAF on my car and retuning for it.
The car is running really well btw, thanks again for your help with tuning it!
We joked he had the "ghost cam" after hearing about the tunes for the 2011 5.0 GTs with the fake cam sound.
It was not subtle. Every person who heard the car run asked him what cam he was running and he would get that frustrated look. I am not exaggerating when I say it sounded like it loped harder than my car, but I'm sure the LM1 and longtubes helped exaggerate the sound.
Oh and btw, I have LM1 and LT's/OR Y and my car kind of lopes on stock cam and tune. I have been asked if it's cammed. But its not overly agressive at all.
I will keep the thread updated if there are any changes. I will try to get some logs and see how the PCM reads now.
The car is running really well btw, thanks again for your help with tuning it!
We joked he had the "ghost cam" after hearing about the tunes for the 2011 5.0 GTs with the fake cam sound.
It was not subtle. Every person who heard the car run asked him what cam he was running and he would get that frustrated look. I am not exaggerating when I say it sounded like it loped harder than my car, but I'm sure the LM1 and longtubes helped exaggerate the sound.
Oh and btw, I have LM1 and LT's/OR Y and my car kind of lopes on stock cam and tune. I have been asked if it's cammed. But its not overly agressive at all.
I will keep the thread updated if there are any changes. I will try to get some logs and see how the PCM reads now.
03-19-2012, 09:49 AM
#17
Had some nice weather yesterday and I had my Snap On Scanner in the truck so we plugged his car in and went for a drive.
At idle sitting in the driveway we let everything warm up and the trims stayed at 0% for a while. Started driving and they would get -2% up to -5% at light throttle (20-30mph). Did a pull through first and second and the car pulled really well but afterwards the fuel trims were up to around -8% for a minute then leveled back out under 5. Some tuning would clear up what's left I think.
I would say that is a hell of an improvement over having them pegged at 25%. Throttle response is staying extremely crisp and responsive and he reports the car is much more "on edge" to drive and less lazy feeling.
The scanner was picking up some random misfires but at a very low rate. Maybe 2-3 every 30 seconds at idle only. Before it was basically registering every hit as a misfire. Might need a crank relearn to clean up the rest.
At idle sitting in the driveway we let everything warm up and the trims stayed at 0% for a while. Started driving and they would get -2% up to -5% at light throttle (20-30mph). Did a pull through first and second and the car pulled really well but afterwards the fuel trims were up to around -8% for a minute then leveled back out under 5. Some tuning would clear up what's left I think.
I would say that is a hell of an improvement over having them pegged at 25%. Throttle response is staying extremely crisp and responsive and he reports the car is much more "on edge" to drive and less lazy feeling.
The scanner was picking up some random misfires but at a very low rate. Maybe 2-3 every 30 seconds at idle only. Before it was basically registering every hit as a misfire. Might need a crank relearn to clean up the rest.
