HOW TO DO AN ADVANCED SEARCH.

Mon Jul 08, 2013 3:56 pm by Admin


For the benefit of 944Hybrids users there are two search functions available for you to use.
The purpose of this sticky is to explain the "Advanced Search" function because it is much more powerful and is the best choice when researching information.

When you log on to the site a list of options is shown in a line at the top of the page. One option is labelled "Search", use this option (NOT the search box lower down on the right).

After you click on the upper search option, a drop down box appears. At the bottom of this box is a radio button marked "Advanced …

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**FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

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**FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  Porsche951toLS3 on Sat Jul 14, 2018 3:31 am

I do not see this problem in the forums so I need help please.

1986 Porsche 944 Turbo with new crate LS3 motor with the Hot Cam   480hp.  

I just got it out on the road and I have only one problem that I cannot figure out.
While driving at low speeds or while cruising and no acceleration, the car is lightly bucking or jerking
back and forth.  I feel like I need to accelerate just to make it stop.  I have the Drive by Wire pedal.
I do not have any engine light or error codes.

My idea was to brace the transmission like toyota trucks do with there rear end to stop this, but I am
wondering if anyone else has had this problem.   I don't know if this is mechanical or tuning.

I have gone through the whole car and the suspension is all new......very frustrated and I cannot find any mention of this in the forums.  

I appreciate any feedback.

NOTE: ***After you read all the way to the bottom, you can see how I fixed this issue. I am so happy**


Last edited by Porsche951toLS3 on Tue Aug 28, 2018 7:34 pm; edited 2 times in total (Reason for editing : Now fixed and I wanted to change the title to reflect this)
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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  Arthropraxis on Sat Jul 14, 2018 9:24 am

My car had some surging at low speed constant throttle until it was dyno tuned. I also run VSS, some people do not, which is supposed to help smoothness at low speed.
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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  sharkey on Sat Jul 14, 2018 12:10 pm

bracing the transaxle will only make the bucking worse. its not mechanical, its electronic. like mentioned above, if you dont have the vss kit in the car, put one in, the ecm needs it. past that, you need tuning.

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944 with LS3 bucking or jerking while cruising or low speed problem

Post  Porsche951toLS3 on Sat Jul 14, 2018 12:38 pm

Idea
Your feedback is saving me from doing stupid things.


Last edited by Porsche951toLS3 on Sat Jul 14, 2018 12:52 pm; edited 2 times in total
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944 with LS3 bucking or jerking while cruising or low speed problem

Post  Porsche951toLS3 on Sat Jul 14, 2018 12:48 pm

I have a VSS sensor and 40 tooth wheel installed.  Since I do not know if this is correct I am throwing out my gap which was set at .80mm.  I did not have instructions for gap, but I found this setting while reading online.  Is my gap ok or should it be closer.  Additionally I used 16 AWG silicone wire to extend the sensor all the way to the back. Is my wire too large and is my gap too wide?

Maybe the question before going to the tuner is how do I verify the VSS sensor is working?  I can look at the app "Torque" using my phone and an ODBII dongle.  Would seeing the speed of the car come from that sensor?  

I have also noticed that sometimes when coming to a stop it will dip down below idle and then recover but one time it stopped the engine.  As I think about your comments, these all sound like the VSS sensor issue.  Additionally I have my MAF in an Airraid tube in the nose of the car well over 10" from the intake.
I don't know what information someone may ask for.  

I guess I need to do more homework, but ANY FEEDBACK is APPRECIATED.  This is my only little frustrating issue.  Wisdom from others can stop all my endless stupid trials and errors.  

Thank you for the comments so far.  You stopped me from making braces to fix this.


Last edited by Porsche951toLS3 on Sat Jul 14, 2018 2:08 pm; edited 1 time in total
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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  sharkey on Sat Jul 14, 2018 2:05 pm

yea you can use the torque app to monitor the vss signal, see if its working and see if it is anywhere close to actual speed. with the idle dropping and stalling during coast down, it sounds like a vss related issue.

the maf doesnt care where it is in the intake tube, just as long as its in a straight piece of tubing thats the specs from the manual. ive dealt with a few gm crate engine installs and even when the car is put together with everything built to the letter of the manual it still needs tuning. what i find in gm vehicles is anytime you do anything to change the airflow in the air intake (be it a cold air intake, or a crate engine that doesnt use the exact same intake the tune was written for) you will need to calibrate the maf tables to make it right. you will be able to see how far out things are in the fuel trims, your ideal long term fuel trims (ltft bank 1 and 2) should be + or - 4% in a perfect world.

id recommend having a look at things with the torque app, make sure the vss is working and go from there.

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944 with LS3 bucking or jerking while cruising or low speed problem

Post  Porsche951toLS3 on Sat Jul 14, 2018 2:53 pm

NEW INFO - My Torque app reads the VSS sensor at approx 13mph when I am doing 50mph.  Sounds like my problem.

So now how to fix it please. I will be doing a lot of homework to understand this problem. 

1.  My VSS to ring gap is set to .80mm which may be too wide
2.  I used 16AWG wire to extend the VSS sensor plug......is that too large of wire?

ANY OTHER SUGGESTIONS or do I have a bad sensor?  I am open to everything and excited to
have the possible answer thanks to you guys who answer this stuff.  I am very appreciative.
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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  sharkey on Sat Jul 14, 2018 4:04 pm

im not sure if you can look at data on a graph with the torque app, but if you can look at the graph and see if its a smooth signal. if the graph is smooth id have no reason to suspect the gap is too large. in fact, id suspect the gap may be too tight, .8mm seems a little on the tight side, however that can depend on the tooth depth on the reluctor wheel as well. again, if the signal is smooth id say its just fine. same deal with the wire size, it shouldnt affect it, but if it did you would see a jumpy signal.

my thoughts are its in the calibration. im not sure what they set the crate engine ecm with for a vss trigger wheel.

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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  sharkey on Sat Jul 14, 2018 4:21 pm

it just dawned on me i have an e67 gm crate engine base calibration from a car we built at our shop. i had a look and it shows the vss and it does indeed show a 40 tooth trigger wheel, however it also has a gear ratio of 3.91. the difference here is the calibration is assuming the speed sensor is on the transmission output shaft in a normal vehicle, essentially between the trans and differential. our vss setup is after the final drive, and is at wheel speed, not driveshaft speed. the ecm is using the rear end ratio setting as a divisor for the speedo. if you work backwards,

50 mph / 3.91 (the gear ratio setting in the ecm) = 12.8 mph, round it to 13mph.

the answer, your going to have to find someone to go into the ecm with HP Tuners and change the setting. its as simple as changing the gear ratio box from 3.91 to 1 and flash the calibration in.

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944 with LS3 bucking or jerking while cruising or low speed problem

Post  Porsche951toLS3 on Sat Jul 14, 2018 10:08 pm

I think you hit the nail on the head. While you figured this out, I went out to the car and:

1. Double checked my gap - no problem.
2. Ran the car using "Torque" in graph mode - No Noise
3. Everything reads approximately 25% of my actual speed
4. Your calculations are dead on to my problem.

Thank you............I have my answer to get a tuner to set my VSS correctly.
I will write back on this forum after I am done to confirm results.

**YOU HAVE FIXED MY PROBLEM. I AM HUMBLED AND APPRECIATIVE FOR YOUR GENIUS***
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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  sharkey on Sun Jul 15, 2018 1:14 am

im just glad i can be of some help.

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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  superman22x on Mon Jul 16, 2018 9:24 pm

It does not matter if you are reading 13mph or 50mph, the software only really cares if you are in neutral or drive, and with the manual transmission it estimates this by looking at vehicle speed. And even still, if you are on the pedal at all, it doesn't matter. It's really only for coast mode.  

Do you have a 4" intake?  I also run an LS3 and had the same problem.  I had originally ran a 3" intake, and had the problem before I changed a cal around the MAF.  There is a cal that converts frequency seen by the MAF to airflow.  The card style MAF takes a tiny sample of air and assumes you are flowing the same amount of air through a 4" diameter pipe.  I'm not sure what is available in HPTuners or EFILive for this, but I imagine there is something along these lines.  This is all for a Gen IV controller.

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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  sharkey on Mon Jul 16, 2018 10:34 pm

looking at the ls3 crate tune i have, the ecm doesnt increase the "idle speed" till 8mph. with the gear ratio settings in the ecm that 8 mph is 31 mph actual speed. this may not be the whole issue, but its for sure a problem.

the air intake is for sure another issue, and this is why i recommend tuning. like i said above, the tune for the crate engine is based on a specific air intake design and any deviation from that design will cause the tune to be out. same with headers and exhaust design, it wont change things as much as the intake side, but it needs to be adjusted for. it would be like slapping a holley carb on a small block chevy crate engine and expecting it to be 100%, its just not gonna happen. ive yet to hear of an ls crate engine that was tuned and didnt see gains in power and driveability.

either find a local tuner thats familiar with the gen 4 ls stuff, or take this as an opportunity to purchase hp tuners and learn how a modern efi control system works. the gen 4 controllers are very advanced and complex to tune, and it takes hours upon hours of reading and learning to get into. however all you need to do right now is sort out the vss settings, and recalibrating the maf vs frequency tables, and thats not all that difficult as far as things go. being able to tune your own car is very rewarding.

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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  superman22x on Mon Jul 16, 2018 11:51 pm

I assume you are cruising above idle speed. Idle speed will only matter when in speed control when you are coasting, unless there are some really high values in that table (like if you have an engine cal for an auto trans).

The gen IV stuff is complex, it's very model based. A lot of tuners don't understand it well really, even the ones that say they do.

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944 with LS3 bucking or jerking while cruising or low speed problem

Post  Porsche951toLS3 on Tue Jul 17, 2018 12:44 am

I contacted three tuners and picked one who actually addressed the issues you all have stated in these forums. I am now fully understanding why I definitely need this tune. I have the 4" intake all the way with no restriction, but the MAF is in the nose so much further away from it's intended location. I also have the headers from Renegade Hybrids which I am sure changes things as well as my incorrect VSS sensor ratio that sharkey figured out.

I now fully understand with everyone's help why this tune will fix my problems. The person I picked just tuned a Porsche 944 with the 525hp LS3 for a guy across town so he is already familiar with what I need and he has 12 years of tuning experience.

He comes over next Monday. I will update this forum for future readers on this topic. I hope to have a great write up on my results.

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944 with LS3 bucking or jerking while cruising or low speed problem

Post  Porsche951toLS3 on Sun Aug 19, 2018 1:40 am

Ok. I am at a loss, but this is where I am at with the tuning. I just put 500 miles on the car and have the engine fully broken in with no issues in the oil. Very happy, and now on to the tuning.

The bucking and jerking at cruising with just a touch of pedal is still here after the tune. The tuner stated this is coming from my LS3 hot cam and sometimes it will not program out. Should I check with yet another tuner? He set my timing to 24 from 20 and at the higher end made the mixture slightly richer. Nothing is a problem except for this bucking at cruise.

It seems that whenever a gain is made with any of the tune, there is a side effect that affects something else. Do I need another tuner?

I only feel frustrated since I thought that this bucking should be able to be fixed, but I don't have the knowledge to know if I just don't have the right tuner or if this is something I have to live with since I have the hot cam for this LS3. BTW, this car screams in an awesome way when accelerating. Wow, very impressed and the car is very tight.

Would there be anyone else out there that has tuned an LS3/480 with good results that could send me their mappings or whatever it is called. Maybe I could show it to my tuner to steer him in the right direction. I don't know what to ask for here, but I trying to replicate a good tune for this same engine please. Any help is appreciated.
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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  sharkey on Sun Aug 19, 2018 2:06 am

with a modern efi engine when making changes on the tune you shouldnt be having negatives in another area, you should be able to refine it all over.

where did he change the timing from 24 to 20 degrees? if he did that under cruise, find a new tuner. under cruise conditions i would expect to be running 30+ degrees. im gonna have a look through some tunes and see what i can come up with, but without seeing data logs and your tune its really hard to make suggestions.

what sort of rpm are you trying to cruise at? with the cam thats in it, its not a stretch to think this isnt going to like cruising at 1500rpm like you would do with a stock ls engine.

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944 with LS3 bucking or jerking while cruising or low speed problem

Post  Porsche951toLS3 on Mon Aug 20, 2018 2:07 am

Actually the timing was from 20 to 24, but either way...........I am looking for another tuner.  I have a retired friend who has been into cars for 50 years owning shops and hot rods.  I am taking it over to him and his shop buddies this week.  We are going to find a person who can fix this problem once and for all.  

The cruising is at about 2200 rpm in that range.  I was told that I may need to have the mixture slightly richer in the range where I am holding the cruise speed which is just touching the pedal.  Either way, I know that there are those who can fix this, I just need to do my homework before putting out another 300-400 dollars.  If the end result fixes it all, I do not mind the costs since this will be for the life of the car.  

I appreciate all who have given input on this quest.  I will post my final results when it is all done.  
I am almost there.  The car gets so many compliments on the build......now to just finish the computer settings.  There are times when I want to put down a thousand dollars and learn to tune this engine myself.  At least I would have the knowledge to talk in this forum and would have a new skill in my bag.
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**FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  Porsche951toLS3 on Mon Aug 27, 2018 11:58 pm

I want to share how I fixed my surging or jerking while cruising.  Here is my story.

My filter is located in the nose of the car where the turbo intercooler used to be.  Air comes in from the two long holes at the bumper level.  There is an area about the size of my hand that is open from the air filter to the engine side.  As I am messing around, I put metal tape over this hole "thinking" that I did not want any heat to enter the filter from the hot engine area.  Sounds like a good idea and I would have more cool air from the outside, except the bucking or surging was now far worse than before.......so I removed it and it was now back to the original surging and bucking that I have been so pissed off about.  

I started reading about Corvettes having this surging problem when they would put a cold air aftermarket product on their car.  During this reading I learned that the MAF or mass air flow sensor for the GM LS3 engine is crazy over sensitive to ANYTHING.  Some have had problems with just the air from the radiator fan causing the MAF to behave badly.  They talked about turbulence with the after market products that could not be tuned out and it all went away when putting the stock airbox back in place.  

The word that stuck with me was "TURBULENCE".  I got to thinking that since the air was entering my bumper area or rather ramming air into the air filter area, this would cause turbulence.  So I took some dense foam and plugged up the driver's side hole which was directly in front of the air filter.  This caused all of the air to be pulled from the other hole without the ram air or turbulent effect.  BAM..........my jerking all went away.  I was so amazed at this simple fix, I was driving the car at 3am in the morning and testing every possible method to get the jerking back and it was all smooth.  I drove it again today and again all smooth (except for the BMW that got in the way causing me to spin tires at a rolling 40 mph).  The car continued to have extreme power with all the smoothness of my original 4 cylinder engine.  I could not be happier.  I have been on this quest thinking that it could all be tuned out.  It could not be tuned out, but once the turbulent air was addressed, BAM..........problem solved.

Additionally in my research with the Corvette group, there were many opinions about an oiled or non oiled air cleaner.  I have the K&N oiled air cleaner..........so I ordered a reusable non oiled air cleaner to address every possible issue stated in those forums and stay on the safe side of the arguments.

Hopefully this will help others solve this jerking problem that drove me nuts.

**Note, there is still a ever so slight parking lot speed surging......but very easy to deal with***
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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  Rich L. on Sat Sep 01, 2018 1:11 pm

Nice! Thanks for sharing.

I did noticed while doing my build how the MAF doesn't have an "air straightener" attached. My previous build was an Audi 5 cylinder turbo and the MAF had a 2 inch plastic bit ahead of the hot strip with longitudinal vanes. And the airbox had an air horn. I incorporated both in that build, perhaps that would help with the Chevy MAF as well.

Rich
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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  turbobob924 on Mon Sep 03, 2018 8:25 pm

watching.

We should all share our HP tuner files somewhere?

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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  charger440 on Fri Nov 02, 2018 11:43 pm

Wow! Someone with the same problems I've been hiding from! I too am using the ls3 hot cam, drive by wire with the ls376 480 controller kit. I too found the speed sensor is not reading correctly but ignored it due to the fact that it is reading something and does go into fuel shut off..

My MAF is also in the nose of the car, behind a dry filter though. I will need to look at this! As driving the car normally makes it very difficult and frustrating.. it feels like a driveline slack issue, yet everything is tight.

Thanks for the post!

Do you have any pictures of your air intake and fix?

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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  Porsche951toLS3 on Thu Nov 08, 2018 10:05 pm

This is the picture of my intake.  The red is what I fabricated to keep my hood latch.  I can go to 6600 RPM with no choking.  The heavy foam was jammed into the bumper slot just in front of the air cleaner.  Hope that makes sense.[You must be registered and logged in to see this image.][You must be registered and logged in to see this image.]
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Last edited by Porsche951toLS3 on Thu Nov 08, 2018 10:11 pm; edited 1 time in total (Reason for editing : Additional Pictures)
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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  charger440 on Thu Nov 08, 2018 11:55 pm

Thanks for the pics, I have a very similar air intake.
After doing a little research, i found a lot of LS guys buy the honeycomb air flow straighteners for their aftermarket air intakes to smooth out the airflow past the MAF.

I just ordered one from [You must be registered and logged in to see this link.]

I'm hoping that will fix the issue.. if not I'll be blocking the air duct to reduce the "ram air" effect.
Have you looked into the airflow straightener? could fix your issue off idle / low speeds?

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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

Post  Porsche951toLS3 on Sun Nov 11, 2018 10:15 pm

I did not use that, but now you have my attention.  I will see what your results are and then purchase one if you like the results.  I am curious if they have a 4" version.  I suppose the 103mm is close enough, but I would love to hear your results.


Last edited by Porsche951toLS3 on Sun Nov 11, 2018 10:15 pm; edited 1 time in total (Reason for editing : spelling)
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Re: **FIXED** 944 with LS3 bucking or jerking while cruising or low speed problem

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