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Loren Champlain Sr
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Mar 5, 2009, 3:56 PM
Post #26 of 49
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Re: Sentra misfire compression test results
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Don't want to sound stupid, but make sure you don't have #3 & #4 plug wires and/or injectors crossed. Compression readings are a bit low, but enough that they should at least fire.
Loren
SW Washington
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Tom Greenleaf
Ultimate Carjunky
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Mar 6, 2009, 5:09 AM
Post #27 of 49
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Re: Sentra misfire compression test results
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Excellent point Loren. It should still fire and help with engine operation even if truly low side. In fact if they have been weak for a while because of crossed up wires those cylinders might read low because of that and snap out of it when corrected. Totally worth a double check of firing order as said,
T
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Anonymous Poster
Mar 7, 2009, 10:21 AM
Post #28 of 49
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Re: Sentra misfire back to square one
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This morning my wife and did a cold compression test. each cylinder had an initial burst of 90 psi, number 1 and 2 built up to 150, 3 and 4 built up to 120.
looking down into the spark plug holes number 4 had a puddle of gas on top of the piston and number 3 was very wet. we blew then out with air and got them dry and then added a few squirts of motor oil to them both and conpression tested them again. Both gave an initial burst of 90 and built up to over 160.
We also got number 3 and 4 individualy at TDC and blew in 60 psi of air pressure, air did not come out the tailpipe or the intake but we could slightly hear it going someplace, unknown. When putting air into one plug hole we listened carefully at the adjoining plug hole to see it air was going from one cylinder to the other. it was not.
At this moment we have the valve cover off and are scratching our heads. I have had motors. run with only 40 or 50 psi
Is it possible the distributer internally can be directing spark incorrectly? We have the model with an internal crank angle sensor. 5 or 6 months ago the car started to misfire or run very rough, we pulled the distributer cap and the sealed cover under the rotor and saw a buildup of grease under the sealed cover and I suspected the seal was bad. I cleaned the mess up and the car ran fine again. My Haynes manual says that no replacement parts are available and the distributer must be replaced as a unit.
We are desperate to find what is wrong. I even checked the EGR and it moves with just a little finger pressure.
As an added note when we looked in the spark plug holes after the compression test and right after we blew each of them out with air we could see fuel running across the top of #3 piston coming from the area of the fuel rail.
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Anonymous Poster
Mar 7, 2009, 10:28 AM
Post #29 of 49
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Re: Sentra misfire back to square one
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I forgot to metion that we rechecked the plug wires, that was one of my initial thoughts, they are correct, and the injector wires cannot be connected wrong.
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Tom Greenleaf
Ultimate Carjunky
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Mar 7, 2009, 10:42 AM
Post #30 of 49
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Re: Sentra misfire back to square one
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Bill - Note that firing order depends on how you count, where you start, and the direction of rotation of distributor. Check it by watching rotor spin if needed but should look like this and the order shown,
That means 1-3-4-2 but it's easy to mix #2 and #3 as shown if you counted clockwise on this distributor. Do you see what I mean? If you counted clockwise starting at #1 the next would have #3 where #2 should have been - easy mistake.
Double check that so it's at least NOT part of this situation,
T
(This post was edited by Tom Greenleaf on Mar 7, 2009, 10:43 AM)
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Loren Champlain Sr
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Mar 7, 2009, 6:33 PM
Post #31 of 49
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Re: Sentra misfire back to square one
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Okay; I think it may be time to drop back and punt. Originally, you said that #4 was not firing. Now, #3 is flooding. Is #4 firing, now? Have you done a fuel pressure test? I'm beginning to wonder if the fuel pressure regulator is allowing too much pressure, so much that it is overcoming the injectors....or...the PCM is toast. (which I doubt). The compression readings sound fine. Can you tell by looking, where the EGR valve mounts? To which intake runner? Could it be stuck open? This doesn't sound like a distributor/secondary problem to me. Just some thoughts.
Loren
SW Washington
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Anonymous Poster
Mar 8, 2009, 9:46 AM
Post #32 of 49
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Re: Sentra misfire back to square one
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We just checked and doublechecked the wiring and the firing order and the wires and even checked the direction of the rotor to make sure it was going the right way and it is correct.
I was looking down at that thin film of liquid on top of number 3 and figured a way to attach a Q-tip to a mechanical finger to go in and dab some up and see what it was, it smelled like gas, but felt like oil, and we had put some oil in there for the wet compression test. But when I blow it out with air pressure and look down in the hole the thin layer of Liquid seems to be seeping back in on top of the piston
To answer the last question yes it was number 4 not firing and the other day it was both 3 and 4 not firing but when I drove it around the block in low gear and let it rev up it seemed to smooth out. That could be just my imagination tho.
Have not checked fuel pressure, do not have a gauge to do that any suggestions.
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Tom Greenleaf
Ultimate Carjunky
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Mar 8, 2009, 10:14 AM
Post #33 of 49
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Re: Sentra misfire back to square one
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If you were blowing out something in the cylinder with common air you really don't get a total clean out easily that way as air in must come out the same hole if on TDC.
About now it may be good to take this out for a run with known ok oil in crankcase NOT full of gas or anything in oil and blow this out a bit. You can play around with stuff so long that with a running vehicle a good run gives you clearer info and better testing. The run around the block idea OR if it runs worth a damn at all really give it a ride to fully warm up - highway speeds and let the oils and whatevers burn out real good. Converter will unless overwhelmed burn up the excess fuel if any if not just being overwhelmed while trying of course.
I've seen "flooding" be more issue that just spark plugs and needs a good run and warm up. Just maybe things will start behaving or make future tests more accurate,
T
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Anonymous Poster
Mar 8, 2009, 10:22 AM
Post #34 of 49
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Re: Sentra misfire back to square one
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Sounds like a good idea, Sorta nervous about taking a ride with only two cyclinders but what the heck more can I do to it now. Will do a compression check as soon as we get back from a drive.
Thanks for all your advice lets just hope we can get this thing fixed,. I had a vacuum gauge/fuel pump tester once but cannot find it anywhere.
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Tom Greenleaf
Ultimate Carjunky
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Mar 8, 2009, 10:27 AM
Post #35 of 49
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Re: Sentra misfire back to square one
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I hear you. If it can't smooth out it will just overload the converter(s) so don't overdo it like that. Perhaps take known working plugs now and put those in the suspect cylinders before the ride if easy enough,
T
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Anonymous Poster
Mar 8, 2009, 11:33 AM
Post #36 of 49
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Re: Sentra misfire back to square one
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I did what you suggested with the plugs and took about 5 trips around the block. At idle it barely runs, give it a little gas and it revs up and smooths out a little,
It developed a nice oil leak somewhere, it drips when it runs now, is not coming from the valve cover. will look into that later.
It seemed to have plenty of pep driving in low gear around the block at 25 to 30 mph. take my foot of the gas and it almost quits.
Pulled into carport and immediatly pulled the plugs. one and two clear and working fine, 3 not as clear some black carbon sooting, 4 not firing at all and full of black soot
Neighbor said he could smell gas in the exhaust
Did a quick compression check 1 and 2 good pressure, 3 and 4 worse then before, 3 initialy 40 psi and pumped up to 120, 4 initially 30 and pumped up to 120
Every time I check the compression I get different readings,
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bill k
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Mar 8, 2009, 4:50 PM
Post #37 of 49
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Re: Sentra misfire back to square one
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Hi Guys, I found the following on "How Stuff Works" do you think it is possible that one or two of the new injectors I installed are leaking and causing the problems I am having.
Leaky Fuel Injectors
Wear in the injector orifice and/or accumulated deposits can sometimes prevent the pintle valve inside an injector from seating, allowing fuel to dribble out the nozzle. The extra fuel causes a rich fuel condition, which can foul spark plugs, increase emissions and cause a rough idle. A carbon-fouled spark plug in one cylinder of a multi-port EFI engine usually indicates a leaky injector. If cleaning fails to eliminate the leak (which it can if dirt or varnish are responsible), replacement will be necessary.
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Loren Champlain Sr
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Mar 8, 2009, 5:59 PM
Post #38 of 49
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Re: Sentra misfire back to square one
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It is entirely possible that you have faulty injectors, but the odds of the faulty one(s) ending up on the same cylinder as before you replaced them.......Not likely. I'm leaning towards thinking the low compression is the result of excess fuel, washing the lubrication from the cylinder walls. The head gasket theory is possible, a break in the gasket between those two (3&4) cylinders. The resulting loss of compression could cause the overfueling. This has been going on for so long, now, I've forgotten some of the q & a. (old phart syndrome). Low engine vacuum, due to cylinder wash or head gasket, or any number of things, would cause the MAP sensor to tell the 'puter to go full rich, but that should cause all four to overfuel. Same with the CTS. So, it is puzzling why just #4? I'm pretty sure, by now, that you've checked valve clearances, looking for tight valves? And, vacuum leaks that would affect that cylinder? (EGR, vacuum hoses, ect). Again, I really don't think this is a secondary (dist., plugs, wires) problem. As Tom mentioned many posts ago, a leakdown test would be very helpful. A noid light installed on #4 and live data on a scanner would be helpful.
Loren
SW Washington
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Anonymous Poster
Mar 8, 2009, 7:16 PM
Post #39 of 49
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Re: Sentra misfire back to square one
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This is a puzzel, that's for sure, After the drive today and all the things I tried, I went in, had a beer and watched TV for a few hours trying to get this off my mind, Any way I went back out and looked in all the plug holes and sure enough, numer 4 had a puddle on top of the cylinder. I was curious if it was gas or water, so out came the mchanical finger with a q tip and down it went and got soaked, when I pulled it up my wife flicked a bic and poof up in flames it went like a torch in an Indiana Jones cave movie. gas is passing that injector even when the motor is off, must be the residual pressure in the fuel rail. Anyway tomorrow I will buy a new vacuum gauge and a fuel pressure tester, be nice to have them anyway abd see what I can see.
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Loren Champlain Sr
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Mar 8, 2009, 7:41 PM
Post #40 of 49
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Re: Sentra misfire back to square one
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I find that a beer is always a good fix to a bad day.
Loren
SW Washington
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Tom Greenleaf
Ultimate Carjunky
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Mar 9, 2009, 2:49 AM
Post #41 of 49
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Re: Sentra misfire back to square one
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Kitty will second that motion!
T & K
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Anonymous Poster
Mar 10, 2009, 5:55 AM
Post #42 of 49
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Re: Sentra misfire back to square one
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Kitty and me drink the same beverage
back to the motor
installed my brand new fuel injector pressure gauge between the fuel filter and the fuel rail according to the Haynes manual
Turn the key and get 45 psi but dropping???? start the motor and it runs at 36PSI almost steady, pull the vaccum line off the fuel pressure regulator pressure jumps up to 45 psi, turn the motor off and with 15 to 20 seconds the pressure drops to ZERO and I can not find no leaks anywhere, also there is no evidence of fuel in that vacuum line. that is what I have done so far today...
the book says the system should hold 30 to 40 psi for 5 minutes
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Tom Greenleaf
Ultimate Carjunky
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Mar 10, 2009, 6:38 AM
Post #43 of 49
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Re: Sentra misfire back to square one
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Suggests leaking backward or thru injectors if that fast and you have evidence at the injectors - right?
Hey - this thread is long enough to make a coat by now. Bill - you may want to summarize this to exactly what is and isn't known and already been done and start a new thread on this,
T
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Anonymous Poster
Mar 10, 2009, 7:18 AM
Post #44 of 49
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Re: Sentra misfire back to square one
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the evidence is a Q-tip from the top of the piston soaked in fuel and pressure that will not hold, for kicks I am gonna turn the key on and see what happenes down in the spark plug hole, if it fills with gas then I am sure the injector is KAPUT
this will happen right after lunch I am certainly glad that you guys have stuck with me thru this
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Anonymous Poster
Mar 10, 2009, 9:51 AM
Post #45 of 49
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Re: Sentra misfire back to square one
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Some Success
Changed the number 4 injector, no small feat working alone and once I put the new one in I Just had to pressurize the system to see what happened hooked the battery back and turned the key on for a second and WOW pressure right up to 40 and after 3 minutes it is still holding 15 PSI. I could see the gauge slowly going down so I guess that number 3 is leaking and has got to be changed as well.
Film at 11
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Anonymous Poster
Mar 10, 2009, 10:17 AM
Post #46 of 49
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Re: Sentra misfire back to square one
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Another what tha....... changed the number 3 injector, turned the key to pressurize system, heard a hissing sound and looked pressure was rapidly dropping to Zero and once again gas was on top of the piston, with no electric connected to the injector they should not let any fuel pass. what is happening??? could I have received a bad set of injectors????
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Anonymous Poster
Mar 10, 2009, 11:36 AM
Post #47 of 49
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Re: Sentra misfire back to square one
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The problem appears to be solved and the cause of the problem was ME. I called the injector warehouse and they were more then helkpful and friendly and asked me to check the bottom O ring of the two onjectors I removed and sure enough both were damaged by Me not installing then carefully enough. Both had a small piece of the O ring damaged, one worse then the other and the one I just put in was also damaged. I changed them again with New O rings and the system has been holding 30 psi for about 20 minutes now. When I get it all back together I will let you know how it runs.
The injector warehouse people told me that when there is a problem with replacement injectors 9 times out of ten when new injecters are installed the bottom O ring gets damaged letting them flood the cylinder.
Looks like another tip to put in our collective back pockets when dealing with injectors.
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Anonymous Poster
Mar 11, 2009, 11:37 AM
Post #48 of 49
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Re: Sentra misfire back to square one
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Tom, can you please check my new thread "Engine Surging" and see if you can help me .
Bill
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Tom Greenleaf
Ultimate Carjunky
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Mar 11, 2009, 1:43 PM
Post #49 of 49
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Re: Sentra misfire back to square one
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I saw it - just don't have any ideas just yet.\,
T
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