interpreting compression results?
10-11-2014, 12:08 PM
#1
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interpreting compression results?
In my seemingly never ending quest to find a cause for my P0420 I did a compression test.
#1= 180 psi
#2= 180 psi
#3= 178 psi
#4= 200 psi
So, I understand 180 psi is spec. What do you think the 200 psi is all about?
Since they all checked out good I did not bother with a leakdown.
And just to doom myself again, The code has cleared and passed the catalyst monitor 3 times again. I am beginning to suspect an intermittent problem with the MAF or MAP sensors.
#1= 180 psi
#2= 180 psi
#3= 178 psi
#4= 200 psi
So, I understand 180 psi is spec. What do you think the 200 psi is all about?
Since they all checked out good I did not bother with a leakdown.
And just to doom myself again, The code has cleared and passed the catalyst monitor 3 times again. I am beginning to suspect an intermittent problem with the MAF or MAP sensors.
10-11-2014, 03:16 PM
#3
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H'mmm, maybe that has been the problem. I noticed a lot more carbon on that injector mount when I replaced the injectors a couple of weeks ago and the plug was slightly blacker than the rest. Mayhaps that was the offending injector. It was cheaper to buy 4 new ones than to take 4 for testing.
While the plugs were out I poured a bit of SeaFoam into each cylinder and let it sit for 15-20 minutes before driving.
While the plugs were out I poured a bit of SeaFoam into each cylinder and let it sit for 15-20 minutes before driving.
10-11-2014, 08:50 PM
#5
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1,2 & 3 all popped out with the plastic insert, #4 insert was stuck in the hole. I did not even try cleaning anything up good, just wiped the holes and stuck everything back together.
That may be why it's taking some time to show up in performance, as I gather the suction in the cylinder has a lot to do with the final seal of the injectors. They just slide in easily, but take a lot of coaxing to get back out after running.
10-12-2014, 12:22 AM
#6
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I'm with db on this one Don, carbon buildup can cause a high compression reading if that particular cylinder has been loading up due to a bad injector.
I'd not lose any sleep over it, in time the excess carbon deposits will burn off, or you could hasten things with a good fuel system cleaner.
I use Chevron Techron Concentrate "Plus" fuel system and injector cleaner, but there are plenty of alternatives like SeaFoam.
I'd not lose any sleep over it, in time the excess carbon deposits will burn off, or you could hasten things with a good fuel system cleaner.
I use Chevron Techron Concentrate "Plus" fuel system and injector cleaner, but there are plenty of alternatives like SeaFoam.
10-12-2014, 01:29 PM
#8
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How did you do the compression test? In the "old days" I used to run the engine to full temp and while that was happening, get every thing ready, I.E. spark plug socket, ratchet, extensions, battery charger, compression gauge, spring to hold open throttle valve and locate the fuse to pull for the fuel pump. Once the engine was hot, shut it off then pull all the plugs and locate them for closer examination later, pull the fuel pump fuse, open and lock the throttle valve with the spring, attach the battery charger and turn on (not needed now usually) insert compression gauge in #1. Have an assistant crank the engine and note how fast the pressure goes up and max value. Stop cranking and move on the #2, then #3, then #4, etc, etc.
What is important here is not only max value but also how fast the pressure goes up. If pressure is too high on one or more cylinder that is generally a carbon build up issue and should show up on the plug for that cylinder.
Check plugs to see if they are all the same color, if not troubleshoot why? Remove throttle spring and reinsert fuel pump fuse. Put old plugs back in or new ones which ever is needed.
What is important here is not only max value but also how fast the pressure goes up. If pressure is too high on one or more cylinder that is generally a carbon build up issue and should show up on the plug for that cylinder.
Check plugs to see if they are all the same color, if not troubleshoot why? Remove throttle spring and reinsert fuel pump fuse. Put old plugs back in or new ones which ever is needed.
10-12-2014, 02:13 PM
#9
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How did you do the compression test? In the "old days" I used to run the engine to full temp and while that was happening, get every thing ready, I.E. spark plug socket, ratchet, extensions, battery charger, compression gauge, spring to hold open throttle valve and locate the fuse to pull for the fuel pump. Once the engine was hot, shut it off then pull all the plugs and locate them for closer examination later, pull the fuel pump fuse, open and lock the throttle valve with the spring, attach the battery charger and turn on (not needed now usually) insert compression gauge in #1. Have an assistant crank the engine and note how fast the pressure goes up and max value. Stop cranking and move on the #2, then #3, then #4, etc, etc.
What is important here is not only max value but also how fast the pressure goes up. If pressure is too high on one or more cylinder that is generally a carbon build up issue and should show up on the plug for that cylinder.
Check plugs to see if they are all the same color, if not troubleshoot why? Remove throttle spring and reinsert fuel pump fuse. Put old plugs back in or new ones which ever is needed.
What is important here is not only max value but also how fast the pressure goes up. If pressure is too high on one or more cylinder that is generally a carbon build up issue and should show up on the plug for that cylinder.
Check plugs to see if they are all the same color, if not troubleshoot why? Remove throttle spring and reinsert fuel pump fuse. Put old plugs back in or new ones which ever is needed.
All built up within a few turns. #4 was just a tiny bit blacker, just enough to notice on close examination.
When I changed the injectors #4 was much harder to pull out and seemed to be more carbon around it.
Today I decided to put the old cat back in with known good sensors and the new injectors. Don't you love messing with exhaust studs on Sunday? Yep, cross threaded the nut on one by hand only! Subbed with a bolt & washer from Tractor Supply until I can get a new stud & nut. At least it wasn't the stud side.
10-12-2014, 03:15 PM
#10
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You know Don, the chances of cross threading something go up exponentially on Sundays, it's the reason I limit my wrench twirling to Saturdays.