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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Uh oh, loss of power, weird noise and motor shaking
+3
Lemming
Rich L.
docwyte
7 posters
944Hybrids: 924/944/968 and 928 V8 Conversions :: Technical Stuff (other than motors) :: General Mechanical
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Uh oh, loss of power, weird noise and motor shaking
On my way home from the track yesterday the car started to shake. There was a loud harmonic resonance and I pretty much lost all power on the motor.
Since I was close to home I kept going. When I got off the freeway and ran it through the gears from a stop, the motor seemed fine. Normal power, no weird noises and no vibration.
WTF? I did notice I didn't have the power I normally had on track this past weekend, but I chalked it up to having the cats back in the car. I also saw that the car was running a bit rich, with AFR's around 12 vs the normal 12.6-12.8 I usually see....
Besides a compression test, what should I be looking for and doing?
Since I was close to home I kept going. When I got off the freeway and ran it through the gears from a stop, the motor seemed fine. Normal power, no weird noises and no vibration.
WTF? I did notice I didn't have the power I normally had on track this past weekend, but I chalked it up to having the cats back in the car. I also saw that the car was running a bit rich, with AFR's around 12 vs the normal 12.6-12.8 I usually see....
Besides a compression test, what should I be looking for and doing?
docwyte- Posts : 1393
Join date : 2010-07-18
Re: Uh oh, loss of power, weird noise and motor shaking
Bummer Doc. It sounds great and seemed strong in the vid you posted. How were the water temps? First thing I'd do is pull the plugs and have a look at them. I had a popping and power loss at WOT that turned out to be a plug wire that had rubbed on the header and split. Good luck with it.
Rich
Rich
Rich L.- Posts : 928
Join date : 2011-05-30
Location : Seattle
Re: Uh oh, loss of power, weird noise and motor shaking
I usually pull on that yellow GT3 and it was walking away from me. It's just weird, I'm about 3-5 seconds off the pace from last year. When I dynoed the car this year it was 20rwhp down from last year too...
Water temps were better with the bigger radiator, around 230-240, but I still need them lower. Looks like I'll be opening up the front bumper where the license plate mounts and see how much that helps.
I'll check the plugs and see what they look like. How do you do a compression test on a coil pack car? With a dizzy you'd just pull the coil wire, but you can't do that with coil packs...
Water temps were better with the bigger radiator, around 230-240, but I still need them lower. Looks like I'll be opening up the front bumper where the license plate mounts and see how much that helps.
I'll check the plugs and see what they look like. How do you do a compression test on a coil pack car? With a dizzy you'd just pull the coil wire, but you can't do that with coil packs...
docwyte- Posts : 1393
Join date : 2010-07-18
Re: Uh oh, loss of power, weird noise and motor shaking
Unplugging the white connector at each row of coils does the same thing.
Rich L.- Posts : 928
Join date : 2011-05-30
Location : Seattle
Re: Uh oh, loss of power, weird noise and motor shaking
Ok, easy enough. I'll have to pull the plugs for a compression test anyways...
docwyte- Posts : 1393
Join date : 2010-07-18
Re: Uh oh, loss of power, weird noise and motor shaking
Yes, I burned through a plug wire on one of the first test days and it killed the power. I'm still learning the LS motor and trouble shooting, so can't be of much help here.
Wait on cutting the front bumper up, I'll be testing mine this weekend at Barber and will let you know if it helps.
Wait on cutting the front bumper up, I'll be testing mine this weekend at Barber and will let you know if it helps.
Lemming- Posts : 855
Join date : 2011-05-30
Location : B'ham
Re: Uh oh, loss of power, weird noise and motor shaking
I would moitor misfires while running the car under load, just because it doesnt set a code doesnt mean its not misfiring. Does HPT give you a power balance test? it might be called cylinder balance test. I would suspect fuel, when was the last time you filled up? Normal gas station? Is it a national chain? I typically only get fuel from BP/Shell i see too many people come in with shitty gas.
Marky522- Posts : 175
Join date : 2009-06-29
Re: Uh oh, loss of power, weird noise and motor shaking
Sounds like an O2 sensor might have gone south. Check plugs and see if one side of the engine looks fat or if you have a scanner check 02 readings and see if one is lazy or dead.
968LS3RS- Posts : 10
Join date : 2012-05-17
Re: Uh oh, loss of power, weird noise and motor shaking
I recently replaced both pre cat O2 sensors, so I doubt that's it. I know u had a cylinder imbalance due to an exhaust leak on the drivers side, but only at idle. I fixed that tonight.
docwyte- Posts : 1393
Join date : 2010-07-18
Re: Uh oh, loss of power, weird noise and motor shaking
Just because they are new does not mean one could not fail prematurely.
968LS3RS- Posts : 10
Join date : 2012-05-17
Re: Uh oh, loss of power, weird noise and motor shaking
I just had the same issue. It turned out to be bad vacuum leak.
zeusrotty- Posts : 444
Join date : 2010-07-30
Re: Uh oh, loss of power, weird noise and motor shaking
Hmm, wonder if replacing that smog valve will clear this up then...
docwyte- Posts : 1393
Join date : 2010-07-18
Re: Uh oh, loss of power, weird noise and motor shaking
docwyte wrote:Hmm, wonder if replacing that smog valve will clear this up then...
My issue was the throttle body has a block off on the side of it that wore through, and I am pretty sure is what caused a backfire and stall that blew the block-off for the brake booster on the back of the intake manifold. Are you getting any codes?
zeusrotty- Posts : 444
Join date : 2010-07-30
Re: Uh oh, loss of power, weird noise and motor shaking
Nope,no codes, but I do have a bank imbalance at idle. One of the nubs had broken off my smog pump valve that led to the fitting on the drivers side header...
docwyte- Posts : 1393
Join date : 2010-07-18
Re: Uh oh, loss of power, weird noise and motor shaking
docwyte wrote:Nope,no codes, but I do have a bank imbalance at idle. One of the nubs had broken off my smog pump valve that led to the fitting on the drivers side header...
Ah, we don't have to have smog in Illinois for cars this old.
zeusrotty- Posts : 444
Join date : 2010-07-30
Re: Uh oh, loss of power, weird noise and motor shaking
Please don't tell me you are running the same tune as before. There is CAT protection built into the ECU that can be turned on and off that would save the CATs from wearing quickly. The car should be retuned as well, and the AFRs should be dialed in closer now compared to running without CATs. All the O2 sensors should be turned back on as well.
robstah- Posts : 352
Join date : 2009-08-28
Age : 38
Location : Athens, GA
944Hybrids: 924/944/968 and 928 V8 Conversions :: Technical Stuff (other than motors) :: General Mechanical
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