Hello,
I did a compression test 3.9L V6 Dodge Dakota piston #5 has 25psi that goes to 50 psi with open throttle.
Then I did a leak down test and air goes to piston #3 (110 psi) and #1 (120 psi).
OBDII scan does not show any code. I do not have any misfire.
What is it? Head Gasket?
Should I try Steel seal if is a head gasket?
Please any share of your knowledge would be greatly appreciated.
Antonio
The leak down test is way more accurate than a simple compression test. The whole point of a leak-down test is not so much for the psi reading, but whether there is a "leak down" happening and where the leak is happening. You test each cylinder one at a time by hand cranking the engine until the piston for the cylinder you're testing is at top dead center. When you connect the compressor to the spark plug adapter, you should have a steady reading. While the compressed air is inside the cylinder, LOOK AND HEAR for any leaking air from the intake manifold, coolant reservoir, oil cap, etc. That will give you a good idea on what's causing the leak if you have one (i.e. bubbling air from coolant reservoir may be a bad head gasket).
For the compression test, you simply pull the fuse for the fuel pump and crank the engine WITH the accelerator pedal to the floor to allow as much air into the cylinder. Do this for ALL the cylinders. The psi readings for all the cylinders should be approximately the same. Good compression is around 120-175 psi.
You should all your compression tests with throttle OPEN then compare readings
Razmig & Dion, Ok so I could not wait until the morning.
I went to the garage and did the test with open throttle all cylinders. Also did it wet test with a bit of oil.
Readings are 1-6 Dry test 140, 150, 160, 155, 160, 145
Readings for wet test 160, 160, 160, 160, 165, 150
Should I do the leak test?
@antonio
Ok, so those are pretty good numbers for the compression test. Each cylinder is within a +/- 10% range of each other. I don't think a leak down test is necessary with those numbers, but if you really want to make sure everything is good you can. Was there a reason why you wanted to do a compression test in the first place? Did something worry you?
The reason for doing it is that sometimes the car does not respond to pressing the throttle and seems to lag, and then two thing may happen if you press down the pedal as asking for more gas, it lags and then speeds up quickly or it will sound like backfire on the back muffler and then go, in either case if you feel it is going to happen all you do is to actually turn off the engine, re-start and then it will go fine. I have no code produced from my OBDII scan, nor I can predict when will it happen.
Is it possible for you to share your freeze-frame data from your scantool? And also please provide the year, mileage, and any maintenance you've done on the car. Is your transmission working okay? (Please tag me in your posts with @razmig so I can see them right away)
These are the numbers for the OBD2 iddle, 1500 and 2500 RPM
https://photos.app.goo.gl/XfgBG9DZdYZo4viv6
Ok, this data was very helpful actually and I can see why you're having backfiring problems you say. Your short term and long term fuel trims are okay. Normal fuel trims are within +/- 10% with 0% being perfect. But overall the ECU is subtracting fuel as referenced by the negative fuel trim. But the spark advance for some reason is waaaaay too much especially at 2500 rpm. It should be around 15 degrees. This is causing those backfires and hesitation under acceleration. What octane gas do you use? Have you done any work on the timing belt/chain before? Or the spark plugs? From what I've gathered, there is a problem with your ignition timing. As for the rich fuel trims, try a bottle of Techron fuel system cleaner in the gas tank.
Multiple issues...timing and fuel delivery
- Timing can be off due to worn out timing chain and gears
- Distributor not set in proper position for correct timing
- Distributor gear worn
- Camshaft worn
- Valves not seating properly
- Worn fuel pump...and in-tank filter partially plugged. Debris in fuel tank being sucked up to filter and then falling away when engine is shut off. You can have pressure but not enough volume
That's fine. Can you just take a picture or type up the live data you get at idle? Like the short term and long term trims, etc.
The gas usually 87 .
The timing chain I am not sure, maybe it was done, but if it was it is almost 80K. My brother in law had it before me and he never paid attention and does not know for sure. Spark plugs were changed while back ago about 30K by now. Sure I will put a techron for the gas. Should I consider having the timing chain done. What do you think?
In my honest opinion, I would take it to a trustworthy mechanic to take a look at the ignition timing and see what's causing the super advanced ignition timing. Someone else posted an answer on this discussion listing the possible causes.