Engine misfire cyl 1 and cyl 5
Hi guys, this mazda has 2 cylinders that are totally misfiring at idle. It seems someone has already replaced plugs and cop's before coming to me. The car dealer brought me the injectors to test and clean and as they were ok I suggested he bring the vehicle to my shop for proper diagnosing, which he did.
Spark good, so carried out a compression test, and I would like so thoughts on what I have found. Cyl 1 has lower compression, but what I want advice on is what is causing the deeper vacuum in the exhaust stroke on Cyl 1?
Cyl 5 is also totally misfiring and yet the compression pattern compared to cyl 3 which is firing is not looking to be obviously all that different to cyl 5 which is not firing so I may have another reason for the misfire which I will further investigate. But for the moment there is some concerns with my captured patterns and I would value some thoughts on cyl 1 differences.
2005 mazda Tribute and ALSO Ford Escape with a 3.0L are very comon that the pcm goes bad internally. I will bet your problem could be your computer. if all your test comes back normal. try to get some captures on your ignition coils and compare to the other known good ones. Also if the conclusion is pcm you most replace coils with OEM ones. Good luck.
Check for your coil driver functionality as Saul stated. Monitor the switched ground at the coil or back probe at the convenient pcm connector
The "deeper vacuum in the exhaust stroke on cyl 1"
The vacuum pocket is not in the exhaust stroke.
The vacuum pocket is the piston moving down during the expansion stroke, or the power stroke.
When the exhaust valve opens, the vacuum pocket is opened to atmospheric pressure.
You should do a cylinder leakage test in cyl 1 because there is a compression leak. Attach a rubber glove over the tailpipe and a balloon over the dipstick tube.
In the cyl 3 cranking waveform, the EVO after the 180 deg Ruler
In the cyl 5 cranking waveform, the EVO before the 180 deg ruler.
Does this engine have 1 or 2 cmp sensors.
Can you post a relative compression with a FLS or WPS in the intake manifold and in the exhaust.
A deeper vacuum pocket is a result of cylinder leakage. The mass of air that is ingested is not the same as when the piston comes back down. Say you took in a certain amount of air. The intake valve closes and seals the cylinder then the piston rises, and compresses that air. A leaking valve will allow that compressed air to escape and when the piston descends again it results in a vacuum. A perfect sealing cylinder, assuming the intake valve closes at 1 psi, will end up with 1 psi after its compressed the air and the piston has descended. But no cylinder is a perfect seal, piston rings must be accounted for. But nonetheless, your answer is cylinder leakage.
For misfires, I always start with a relative compression test, while capturing intake manifold pulses. You might end up moving your pulse probe to the dipstick, and or the exhaust, but always start in the intake. Most times, your problem analysis will stop there.
1 & 5 are companion cylinders.
If you have an intake valve leak on #1, the combustion in #1 can disturb the intake mixture in the plenum and affect other cylinders.
As others have pointed out,Id be scoping the coil drivers. The failures are so common,these vehicles should come with spare PCM.....
Thank you everyone I will carryout more test as you have all recommend and repost these results. I appreciate the advice on the a leaking intake valve causing the deep vacuum in the exhaust pocket that makes sense, one never stops learning in this industry.
It likes like the compression is all over the place, being a car yard vehicle he has declined for me to go any further. So at this present time the car is sitting and awaiting for the car dealer to pick this up. I suspect he will use a back yarder who has a lower labour rate to repair the engine or he may simply action off the car and cut his losses. My thoughts would be, has this had a timing belt failure and the belt was replaced and after which the engine would not run properly due to multiple bent valves? Who knows Dealers never tell us the true story.
I did test one of the coils from the cylinder that was misfiring and the driver is good but the coil current starts to distort on the current ramp when carrying out a WOT, so I believe the replacement coils are cheap Chinese rubbish and while this is not causing the dead misfire at idle it certainly is another issue.
By the way my first look pizzo exhaust sensor I have used in this capture is a home made sensor and I have wired it up wrongly so that when you see a positive pressure it really should be the opposite or inverted, I will fix this up one day, but I though I better mention this so it doesn't confuse you when you see my capture.
Thank you all for your assistance it was much appreciated.
by just looking at your relative compression trace, I see one cam is out of time, in relationship to the other cam.
Albin you have made me look more closely and I think you are right although I am concerned about cyl 2 as it is on the same bank as cyl 4 and 6 and it is definitely lower in comp. all of bank 1 is low and the craning comp to running should represent half but they are all very high when running. I can not easily get to the bank 1 as the manifold is covering the plugs, therefore the reason I have not done a check with my transducer on that bank,
Hi all Albin has made me rethink and learn more as to the possible reason I have such a notable low and uneven relative compression reading on this vehicle. All the low cylinders (except cyl 4) is on the one bank (B1) which is characteristic to a cam timing problem on one bank. Also adding to this is the fact all my running compressions are very high and are much higher then the expected 50% decrease to the cranking comp. I know think Albin is right except why is cylinder 2 so much lower in compression to cyl 4 and 6? Maybe with the timing jumped it could have bent the intake valve which is also evident in my cranking compression test as there is a deep pocket in the exhaust opening area of this capture.
Just to put you all on the right page when I captured my compression readings I marked the cyls wrong, so in my captures Cyl 1 is Cyl4, Cyl 3 is Cly 5, and Cyl 5 is Cyl 6 (So the 3 cyls facing the grill are Cy4,5,6, not 1,3,5 as I first thought)