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Author
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Topic: Got the Leak Down Test Result for #1
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twisted54
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Member # 1981
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posted
 
 
OK...my seemed to be down a bit on power. I finally did a compression test today:
#1 - 140
#2 - 150
#3 - 150
#4 - 170
#5 - 165 (This is the plug that would be wet after a run)
#6 - 165
#7 - 165
#8 - 150
How screwed am I?
Thanks guys...
[ December 08, 2005, 04:41 PM: Message edited by: twisted54 ]
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JohnB
Tech Moderator
Member # 969
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posted
What intake are you running Tony?
I'll be the first to say...blown HG, passenger side.
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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Jdub07
( O Y O )
Member # 2728
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posted
quote:
Originally posted by JohnB:
What intake are you running Tony?
I'll be the first to say...blown HG, passenger side.
what are 'good' numbers?
Posts: 7282 | Registered: Apr 2003
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JohnB
Tech Moderator
Member # 969
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posted
Relatively even across the board, give or take 10%.
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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twisted54
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Member # 1981
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posted
I have the Trick Flow Track Heat U/L on there.
Is there a way to find out for sure if it's blown?
That's seems right though with almost all of the numbers being lower on that side.
Thanks John...
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JohnB
Tech Moderator
Member # 969
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posted
Perform a leakdown test. That will tell you for sure.
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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twisted54
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Member # 1981
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posted
quote:
Originally posted by JohnB:
Perform a leakdown test. That will tell you for sure.
Did you get your leakdown tester back yet?
EDIT: I've also noticed a hissing coming from the engine compartment, possibly the passenger side. I started noticing it after the last backfire. I guess that could be a sign too huh???
[ December 05, 2005, 06:16 PM: Message edited by: twisted54 ]
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95331StrimVert
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Member # 6250
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posted
Bummer Tony,
Looks like both of us will be working on our rides at the same time...
Tony
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95331StrimVert
Posts: 398 | From: Martinez ca | Registered: Nov 2005
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twisted54
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Member # 1981
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posted
Yeah this sucks Tony... these damn mustangs are driving me crazy.
Tony
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93PONY
Mr. Valve Events
Member # 60
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posted
You had a nitrous backfire?
The hissing is most likely a vaccum leak.....which could easily explain the lack of power.
Compression #'s do not indicate a blown HG.
When HG's blow they don't blow across one entire bank. One cylinder typicaly will blow either into the oil or water passage, into the cylinder next to it, into the lifter galley, or out the side of the head.
From the #'s I can say one thing for sure....your valves are sealing....which is a good sign.
Did you perform the compression test with the ignition key turning over the starter? If so, did you disable the fuel system? If not the fuel squirting into the cylinders will give you false results.
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Posts: 4265 | From: Fair Oaks, CA | Registered: Nov 2000
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twisted54
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Member # 1981
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posted
quote:
Originally posted by 93PONY:
You had a nitrous backfire?
The hissing is most likely a vaccum leak.....which could easily explain the lack of power.
Compression #'s do not indicate a blown HG.
When HG's blow they don't blow across one entire bank. One cylinder typicaly will blow either into the oil or water passage, into the cylinder next to it, into the lifter galley, or out the side of the head.
From the #'s I can say one thing for sure....your valves are sealing....which is a good sign.
Did you perform the compression test with the ignition key turning over the starter? If so, did you disable the fuel system? If not the fuel squirting into the cylinders will give you false results.
Yeah I had a nitrous backfire a few months back which blew out my PRO-M. That's when the problems seemed to have started.
I'll have to see if I can find a vacuum leak tomorrow. I did the test with the key turning over the starter and no I didn't disable the fuel system. Can you tell me what I should unplug and were it's located?
I'll give it another try tomorrow.
Thanks Shaun...
Tony
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Blind
2.3L
CAFords OG
Member # 3052
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posted
quote:
Originally posted by twisted54:
quote:
Originally posted by 93PONY:
You had a nitrous backfire?
The hissing is most likely a vaccum leak.....which could easily explain the lack of power.
Compression #'s do not indicate a blown HG.
When HG's blow they don't blow across one entire bank. One cylinder typicaly will blow either into the oil or water passage, into the cylinder next to it, into the lifter galley, or out the side of the head.
From the #'s I can say one thing for sure....your valves are sealing....which is a good sign.
Did you perform the compression test with the ignition key turning over the starter? If so, did you disable the fuel system? If not the fuel squirting into the cylinders will give you false results.
Yeah I had a nitrous backfire a few months back which blew out my PRO-M. That's when the problems seemed to have started.
I'll have to see if I can find a vacuum leak tomorrow. I did the test with the key turning over the starter and no I didn't disable the fuel system. Can you tell me what I should unplug and were it's located?
I'll give it another try tomorrow.
Thanks Shaun...
Tony
I have a kill switch installed on my fuel pump, so if you want a nice permanent way to turn off the fuel pump find the fuel pump relay and install a switch on that so you can manually turn the relay on/off.
I'm not sure where it is on a 94/95 but if you have a chiltons for your car I'm sure you can find it, or find some location where you can splice a switch in-line with the power to the fuel pump.
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89 LX Notchback ex 4cyl, 14psi
02 Harley F150, 15psi
Posts: 8521 | From: Fairfield | Registered: Jul 2003
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66 AC COBRA
Nitrous King
Member # 904
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posted
or just pull the fuel pump relay ![[Big Grin]](biggrin.gif)
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72 Vega - WCHRA Extreme 10.5
Posts: 6280 | From: Winters | Registered: Feb 2002
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93PONY
Mr. Valve Events
Member # 60
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posted
I just 'pop' the inertia switch that's in the trunk. Typically a blow with your fist will make the buttom pop up....which disables the fuel pump. Pushing the button down again enables the pump. The inertia switch is located on the drivers side of the trunk right behind the tail lights.
Make sure when you're doing the test that you count the revolutions of the motor & duplicate it on each cylinder. EI, if you turn over the motor 5 times on the #1 cylinder......repeat the 5 times on every cylinder to get a more accurate test.
If you can, hold the TB wide open. (jam it open with something).
Also, have all 8 sparkplugs removed.....most people do this. However, some will remove 1 plug, test that cylinder, install the plug & go to the next cylinder.
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Dynotuning
(916)715-7569
Posts: 4265 | From: Fair Oaks, CA | Registered: Nov 2000
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JohnB
Tech Moderator
Member # 969
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posted
quote:
Originally posted by 93PONY:
Compression #'s do not indicate a blown HG.
When HG's blow they don't blow across one entire bank. One cylinder typicaly will blow either into the oil or water passage, into the cylinder next to it, into the lifter galley, or out the side of the head.
So, say #2 blew out side to side...you don't think the numbers would be like this?
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1965 Shelby Cobra
1993 Cobra
2012 F150 Raptor
2020 GT500
Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002
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twisted54
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Member # 1981
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posted
Found the leak...
 vacuum line going to FPR...
How much would this hurt performance?
Could this have caused the car to be really lean when I first put it on the dyno to have JeffS tune it? If so, he adjusted the A/F...is it probably way rich now?
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93PONY
Mr. Valve Events
Member # 60
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posted
A leak of that size is most noticed at idle.... The un-metered air itself would cause the motor to run a little lean, but the lack of a vacuum signal to the FPR would make the motor run rich.
At WOT the FPR should see zero vacuum just like having the vacuum line to it disconnected.
Hard to say whether it affects the tune significantly or not.
The small vacuum leak you have at WOT should have minimal impacts on WOT since the way Jeff tunes is through the Mass-air.....so bypassing the mass-air will make the car run lean (vacuum leak) & fixing the leak should bring A/F back into spec.
However, if Jeff dialed in the mass-air WITH the vaccum leak then most likely the mass-airflow curve is off slightly.
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
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Posts: 4265 | From: Fair Oaks, CA | Registered: Nov 2000
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166 Merlo
FELONY
MOTORSPORTS
Member # 1549
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posted
What if you just jump it from the starter solenoid? then u don't have to beat your inertia switch, dig for the pump relay, and stay under the hood the entire time without going back and forth or needing a buddy.
Would this be the winner as to how to turn the motor over, or is there something flawed here that I failed to see?
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Posts: 3954 | From: Thebay | Registered: Jul 2002
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twisted54
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Member # 1981
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posted
quote:
Originally posted by 93PONY:
A leak of that size is most noticed at idle.... The un-metered air itself would cause the motor to run a little lean, but the lack of a vacuum signal to the FPR would make the motor run rich.
At WOT the FPR should see zero vacuum just like having the vacuum line to it disconnected.
Hard to say whether it affects the tune significantly or not.
The small vacuum leak you have at WOT should have minimal impacts on WOT since the way Jeff tunes is through the Mass-air.....so bypassing the mass-air will make the car run lean (vacuum leak) & fixing the leak should bring A/F back into spec.
However, if Jeff dialed in the mass-air WITH the vaccum leak then most likely the mass-airflow curve is off slightly.
Yeah I have to bring it back to Jeff but before I do, I want to do a leak down test. Shaun how much do you guys charge for that?
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2013 Black on Black 5.0 with Boost N Things - CORN FED 🌽
Posts: 3421 | From: ebay | Registered: Oct 2002
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95331StrimVert
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Member # 6250
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posted
Tony, Your vert sounds real nice pulling away... very loud;-) see you soon, as im about ready to pull the exhaust, the car is in the air....
Talk later,
Tony
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95331StrimVert
Posts: 398 | From: Martinez ca | Registered: Nov 2005
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twisted54
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Member # 1981
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posted
Thanks Tony...
Have fun and hope all goes well with it too. You've got a big job ahead of you.
Yep, see you soon...Tony
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93PONY
Mr. Valve Events
Member # 60
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posted
Leakdown tests have their place.....but are over rated IMO.
Piston rings are not designed to seal untill they are pressurized from the top (during the power stroke). A static leak down test does not put enough pressure on the piston to make the rings seal the way they would in a running engine.
Super low drag race rings have TONS of blowby untill WOT where they seal up great. It's not uncomon to see 10+% leakdown on a good running engine. But at WOT leakdown is virtually gone.
Depending on where the piston is in the bore (TDC, BDC, or in between) the leakdown #'s will be different. More accurate #'s will be had by performing the test while the piston is ~60 degrees past TDC....however, putting 100psi pressure to a piston at this point will force the piston down turning the motor over.
Which brings me to the next problem....you have an auto....how can you hold the piston at 60 degrees past TDC & perform the test? You must physically stop the motor from turning over while you test each cylinder. Let the motor turn over & the test results will not be accurate....which is why most test leak down at TDC or BDC because the motor is less likely to turn over....but the #'s will be higher at either TDC or BDC...especially at BDC as the piston skirt is actually out of the bore & the piston is allowed to rock...losing ring seal.
I have a leakdown tester at home....which I've used a few times. When engine falures have happened (blown HG, bent valves, etc) the leak down told me NOTHING more then a static compression test told me.
I do a compression test first to find the problem cylinder, then if I can not nail down the problem I'll use a leakdown on that one cylinder to narrow down the problem.....yet very rarely does it come down to using the leak down. If compression is extremely low on one cylinder....I already know I'll be removing the heads.
Now...back to your particular issue. I'm guessing you're worried about the bottom end being damaged. Well, lets say you have had severe detonation & compressed the top ringland onto the top ring. The ring is now locked up in the piston creating smoke out the tail pipe. This senario would show up on a compression test. At best you'd have 1/2 the compression on that cylinder as the others. Lets say you broke a ring in half.... Again, not a good seal & smoke out the exhaust would be occuring. Compression would be down significantly from cylinder to cylinder.....although this senario would be harder to detect.
It's my opinion that the original test results are squewed due to fuel wetting the cylinders & giving false #'s. Particularly if you started with the #1 cylinder....it would be the lowest since it'd have less wet fuel in there to help seal things. The next cylinders tested would read higher.
Re-do the compression test disabling the fuel system...simply to varify the #'s. I'd hate to see you tear into a motor that doesn't have a sealing problem.
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SCT dealer
Dynotuning
(916)715-7569
Posts: 4265 | From: Fair Oaks, CA | Registered: Nov 2000
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twisted54
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Member # 1981
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posted
Got it...I think.
I'll redo the comp test today with the fuel system disabled.
Thanks Shaun
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twisted54
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Member # 1981
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posted
Ok...I just finished doing the comp test with the fuel pump disconnected. I verified tht I couldn't hear the pump switching on when I turned the ignition key.
Here are the old and new numbers:
OLD: NEW:
#1 - 140 #1 - 145 (started here)
#2 - 150 #2 - 160
#3 - 150 #3 - 160
#4 - 170 #4 - 170
#5 - 165 #5 - 175
#6 - 165 #6 - 170
#7 - 165 #7 - 170
#8 - 150 #8 - 160
I took the car for a spin after I fixed the vacuum leak and the car would die everytime I stopped. When I pulled the plugs to redo the test, they were all fouled...I'll post a pic later tonight.
Thanks guys.
EDIT: No smoke (white or black) coming out of the tail pipes.
[ December 07, 2005, 06:59 PM: Message edited by: twisted54 ]
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93PONY
Mr. Valve Events
Member # 60
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posted
Those #'s are more consistant...
There is something going on with the #1 cylinder.
It would not be a bad idea to do a leak down on that one cylinder. (although you'll still have to figure out something to keep the motor from turning over during the test.) No need to do the rest...compression #'s look great on all the rest.
It may be that the #1 cylinder intake valve was open during the nitrous backfire.....which could have caused minor damage to the valve (burned the valve, or perhaps slightly bent it). If the leakdown shows the intake valve to have a slight leak there is something you can do without removing the heads or tearing down the motor.
Odd though it may sound, you can 'lap' the valve to get it to reseal on the valveseat. It's quite simple really. Remove the valvespring, re-install the retainer & locks. Pull up hard on the retainer with your hand & rotate the valve. Feel for loose/tight spots. Do this for a few minutes or untill the tight spot (if any) is gone. Re-install the valvespring & re-test compression on that cylinder. The #'s should come up. I'd do this before tearing down the motor.
Your plugs are fuel fouled? Looks like the tune is way off now.
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Dynotuning
(916)715-7569
Posts: 4265 | From: Fair Oaks, CA | Registered: Nov 2000
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