resurrected_jimmy
1/2 ton status
bad cat would cause poor conditions across all cylinders or across one bank if its dual cats, it wouldn't be isolated to 1 cylinder
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
Help diagnose engine problem...
- Thread starter Keitha
- Start date
Compression check will verify if your problem is internal related or external tune up related type stuff.
What do you look for on a compression check?
You want the readings as even as possible more than anything. Ideally no more than about a 10% difference between the low and high readings.
So is 0psi on the #3 cylender a bad thing?
#1 = 190psi
#3 = 0psi
#5 = 190pdi
#7 = 190psi
Any thoughts? No oil on the spark plug.
#1 = 190psi
#3 = 0psi
#5 = 190pdi
#7 = 190psi
Any thoughts? No oil on the spark plug.
Can almost guarantee a burnt exhaust valve/seat as the culprit of zero compression.
My engine builder just lent me his leak-down tester. It read 100% leakage (no surprise w/ 0psi) but I could hear the hissing from the tail-pipe.
Is there any way to verify w/o pulling the head off?
What causes a burnt valve/seat?
What is actually a burnt valve? It is one of those things I always hear mentioned, but never experianced.
thanks,
Is there any way to verify w/o pulling the head off?
What causes a burnt valve/seat?
What is actually a burnt valve? It is one of those things I always hear mentioned, but never experianced.
thanks,
Hearing the hiss from the exhaust just verified you have a burnt exhaust valve/seat. Basically a portion of the valve burns away from extreme heat. The heat can be caused by a sharp edge on the valve which never has time to cool off so it starts to burn away a portion of the valve, with many miles the valves will eventually bury into the seat making the valve no longer seal correctly and now you constantly have hot combustion always passing the valve/seat creating an even faster wear rate.
Actually, hissing from the tailpipe is good. Hang on, keep reading before you think I've lost my mind.
Hissing from the PCV valve would be much worse than the tailpipe.
That would mean a hole in a piston.
I'm going to go WAY out on a limb here and say its not a burnt valve. As I remember from the start of this thread, it happened fairly suddenly.
Valves usually don't go out that suddenly unless they fall into the cylinder, and you would have noticed that I suspect.
Before I got to deep involved, I would pull the valve cover on that side and see if something has happened to your valve train.
If you are lucky, something has jammed in the rocker arms and is holding that valve open.
BTW, I once saw a piece of carbon do that.
We pulled the valve cover and everything was good, but the valve was stuck open.
We pried it down a little farther and tapped it. Whatever it was, I'm guessing carbon, fell out into the cylinder and got crunched when we carefully turned the engine over with a cheater bar.
Since it was my friend's mom's car, and it all started when he tried to blow out the carbon that months of really slow driving had built up, we felt it was a chunk of carbon.
Car ran fine for years after that.
Hissing from the PCV valve would be much worse than the tailpipe.
That would mean a hole in a piston.
I'm going to go WAY out on a limb here and say its not a burnt valve. As I remember from the start of this thread, it happened fairly suddenly.
Valves usually don't go out that suddenly unless they fall into the cylinder, and you would have noticed that I suspect.
Before I got to deep involved, I would pull the valve cover on that side and see if something has happened to your valve train.
If you are lucky, something has jammed in the rocker arms and is holding that valve open.
BTW, I once saw a piece of carbon do that.
We pulled the valve cover and everything was good, but the valve was stuck open.
We pried it down a little farther and tapped it. Whatever it was, I'm guessing carbon, fell out into the cylinder and got crunched when we carefully turned the engine over with a cheater bar.
Since it was my friend's mom's car, and it all started when he tried to blow out the carbon that months of really slow driving had built up, we felt it was a chunk of carbon.
Car ran fine for years after that.
You are correct in that it did happen all of a suden. I have already pulled the valve covers and the rockers are moving fine. No hiss from the pvc or oil fill.
I just went out and hooked 60psi right from my compressor and I could feel a breeze from the tail pipe.
The motor and heads only have about 2,000 miles on it since full rebuild . Engine never overheated at all. I don't think it has seen 190 degrees. It has had a ticking that I wrote off as a header leak (I even noticed a bit of discoloration on a couple sparkplugs facing the flange.
I am guessing that I will probably need to pull the head.
thanks,
I just went out and hooked 60psi right from my compressor and I could feel a breeze from the tail pipe.
The motor and heads only have about 2,000 miles on it since full rebuild . Engine never overheated at all. I don't think it has seen 190 degrees. It has had a ticking that I wrote off as a header leak (I even noticed a bit of discoloration on a couple sparkplugs facing the flange.
I am guessing that I will probably need to pull the head.
thanks,
Ok, now you tell us it's a fresh engine rebuild. Talk to whoever built the engine and find out if they installed hardened exhaust seats (if they did one may have fell out). Also, a valve can definately go bad in just a minutes notice but it was already starting to go bad and just happened to fail. This happened to my engine last year, was running good when i parked it, then the next time i started it it ran fine for about 5 minutes then had a miss and had burned the exhaust valve in the #7 cylinder.
I will check on the hardened exhaust valves.
I just checked the compression on the pasenger side and have the following:
#2 = 120psi
#4 = 190psi
#6 = 190psi
#8 = 185psi
Could the #2 be going bad as well?
For what it is worth I have ProTopline heads. They are about 5 years old. I know that the builder replaced the seats when he did the work, just don't know if they are hardened.
Thanks much for all the advise.
I just checked the compression on the pasenger side and have the following:
#2 = 120psi
#4 = 190psi
#6 = 190psi
#8 = 185psi
Could the #2 be going bad as well?
For what it is worth I have ProTopline heads. They are about 5 years old. I know that the builder replaced the seats when he did the work, just don't know if they are hardened.
Thanks much for all the advise.
With the readings you are getting there is something wrong with the #2 cylinder as well, that is a 37% difference between the high and low reading. The seats don't matter if they are hardened or not just the fact that seats have been installed and could have either fallen out or aren't hardened seats and have prematurely gotten "buried"
Then when you get your heads straightened out I would record some data and make sure your engine is running correctly with the Holley TBI, 383 and TBI chip. Have you ever run a wide band O2 sensor during WOT runs to make sure your not running lean?
I have been datalogging and the engine was showing fairly rich with BLM's in the low 100 range. I was cruizing at about 75mph when the motor craped on me and from previous runs I think I had BLM's in the 115 range.
Ironic thing is that the Inovative Wide Band O2 that I ordered showed up the same day this happened.
Ironic thing is that the Inovative Wide Band O2 that I ordered showed up the same day this happened.
Yep, if its fresh heads, I'm betting you dropped a valve seat. It could have been loose for a while and that was the clicking you heard.
Look at the valves for that cylinder and compare the end of the exhaust valve with the exhaust valve of the one next to it.
Bump it around until it is closed. I'm betting it will be higher than the good one. With the seat gone, the valve can ride a lot higher into the head.
In fact, it might go past the range of the lifter and be loose.
If you have dropped one, number two might be ready to fall out.
J.
Look at the valves for that cylinder and compare the end of the exhaust valve with the exhaust valve of the one next to it.
Bump it around until it is closed. I'm betting it will be higher than the good one. With the seat gone, the valve can ride a lot higher into the head.
In fact, it might go past the range of the lifter and be loose.
If you have dropped one, number two might be ready to fall out.
J.
OK, the heads are comming off! I will post a picture of what I find.
This is a pain in the ass!
This is a pain in the ass!
Sad pictures:
The Valve does not appear to be burnt but there is a gap on one side of the seat. I do not see any obstruction that is keeping the valve open. Could this be a bent valve? What could cause this?
Does the carbon build-up on the heads/valves look like it is running very rich?
I hope it does not rain much because I will be on the motorcycle until this is fixed.
thanks,
Keith
The Valve does not appear to be burnt but there is a gap on one side of the seat. I do not see any obstruction that is keeping the valve open. Could this be a bent valve? What could cause this?
Does the carbon build-up on the heads/valves look like it is running very rich?
I hope it does not rain much because I will be on the motorcycle until this is fixed.
thanks,
Keith
The valves are very sooty which means too rich. That exhaust valve is either bent or galled on the stem and not closing properly. If the stem is galled it is caused from either insuffiecent valve stem to guide clearance or the engine got hot enough for the valve to seize in the guide.
If the side not shown is touching I would say it's bent... could also be a valve seat out of place...
