D1 compression test numbers
- Thread starter LRDONE
- Start date
I got 145-155 cold on my D1 4.0 Not much better warm but she is at 145k and tired.
150-160 is considered normal.. 10% +/- across cylinders is the bigger goal/desire.
190psi seems Very high for these engines, but that is normal for a honda engine.
I'm guessing you have LOTS of oil in that cylinder?? Or some Water inside it??
150-160 is considered normal.. 10% +/- across cylinders is the bigger goal/desire.
190psi seems Very high for these engines, but that is normal for a honda engine.
I'm guessing you have LOTS of oil in that cylinder?? Or some Water inside it??
I've got nothing in the cylinders. The thing has sat for 2 weeks. I unplugged the fuel pump and cranked it for a few seconds about an hour before I did the test. My procedure was 10 compression strokes on each cylinder with the throttle wide open. I'll post my numbers at the bottom of this message. I've always chased a rough idle with this motor and I've tested a lot of things and nothing is obvious. I'm getting ready to take it on a trip and I'm just doing a good round of maintenance on it, I was curious about how healthy the motor was.
8. -190psi 7. -175psi
6. -185psi 5. -165psi
4. -175psi 3. -175psi
2. -190psi 1. -190psi
14% difference from high to low which concerned me. I thought the numbers might be a little high for being stone cold.
*I should also point out that the motor has 81,000 miles on it.
8. -190psi 7. -175psi
6. -185psi 5. -165psi
4. -175psi 3. -175psi
2. -190psi 1. -190psi
14% difference from high to low which concerned me. I thought the numbers might be a little high for being stone cold.
*I should also point out that the motor has 81,000 miles on it.
Well from those numbers you got yourself a Golden Nugget! I wouldn't be concerned with those numbers. As for rough idle, Plugs and WIRES!! I got the STI wires that are 8mm and ohm'ed out my old and new set. Ended up finding 2 bad old wires and even 1 bad NEW wire. STI sent me a replacement asap for it. Apparently these GEMs motors eat wires like gas 
Thanks! So I actually have the sti 8mm wires on it, brand new ignition coils and champion copper plugs. I was looking at the spark plugs when I pulled them. I have 3 plugs on one side that seems to be just a tiny bit more rich than the rest. That happens to be the same three injector plugs I repaired when I first got the thing home. I just used a standard butt connector with shrink tube. Maybe the ecm is picky about that or I have resistance issue somewhere else on those circuits. Reason for repairing was the rubber on the wires were cracking. So I’m gonna do some looking into that too.Well from those numbers you got yourself a Golden Nugget! I wouldn't be concerned with those numbers. As for rough idle, Plugs and WIRES!! I got the STI wires that are 8mm and ohm'ed out my old and new set. Ended up finding 2 bad old wires and even 1 bad NEW wire. STI sent me a replacement asap for it. Apparently these GEMs motors eat wires like gas
You could have a lot worse numbers than that and have absolutely no idle issues. This is my 230k mile bottom end with heads I put on almost a decade ago that have about 50k on them as I was "resurrecting" it from having sat behind my barn for 5+ years and it idles perfect. It absolutely did not when I started it but that was all down to plug wires (cheap 7mm ones that had a couple of ends no longer snap onto the plugs properly).
I'm sure 8mm wires will do something for some of these old boat anchors, but it's certainly not going to be noticeable.
I'm sure 8mm wires will do something for some of these old boat anchors, but it's certainly not going to be noticeable.
15w-40 most of the time however before I owned it, who knows. I did use a cheap Meijer oil one time because I didn't know any better but I think the damage was already done before that. From now on I'm only going to use oil with zinc engineered into them, no additives.
There was a good article once that explained why gas engines shouldn’t use diesel oil due to the excessive detergents. I’ve used Rotella 15/40 a bunch too. I’m about one oil change from 200k and just recently changed to 20/50 with zinc for the warmer months. Who the heck knows.
After all of this, that’s the conclusion I’m coming to as well. The excessive detergents actually wash away the zinc. We use a lot of penngrade or formally known as Brad penn 20/50 in the old 911s at work. I thought about switching to that but it’s real thick oil. Driven makes a really nice zinc formulated 10w-30 and 10w-40.
Yeah I decided on penn grade 20/50. I only drive it in the summer time here in michigan.