# 2 Low compression
 

HI, I have a 2000 F-250 Powerstroke, No Mods. Truck has a miss and lots of white/blue smoke coming at start up, seems to clear up a little after warm up. After repairing a couple of fuel leaks, changing oil, filter and fuel filter, truck still smokes and has a miss. I used a SOLIS scan tool and performed a cylinder contribution test, #2 and #8 show an unbalanced fault. I performed a compression test: #1-360, #2-110, #3-370, #4-400, #5-380, #6-380, #7-360, and #8-400, all checks were done with 6 cranks. I feel that these readings are fine with the exception of #2. My question is, is there a way to determine what is causing the low pressure in #2: piston, rings, valves, head, or gasket?? Note: while performing the compression test, the pressure went to 110 within the the first two cranks and never moved after that. I also swapped #2 and #4 injectors, just because i thought i might get out easy, no luck, still the same readings. Thanking you in advance.

Jeff

how many miles are on the engine?

has it ever used any coolant? you probably know if its burning coolant through a bad head gasket youll see lots of white, sweet smelling smoke.

and you say the compression in #2 dropped from whatever it was to 110 after a few cranks. will it hold it after you stop cranking?

i think the only way you can check if its a valve, pull off your intake manifold Y-pipe and put your hand over it while cranking, if its an intake valve youll feel it push back. for exhaust while running you should maybe hear a loud (louder than the rest) pop or ping in the exhaust. (listening from the outside)

also if your scanner indicates a fault in cylinder 2 and 8, swapping your injectors to different holes will not elimanate the problem, you'll only see it transfer holes. but having bad compression in a cylinder will throw the test off. a cylinder contribution test looks at fuel trim, injector response time, rpm, and a bunch of other junk in terms of power output per cylinder. a major loss of compression in that one cylinder will SIGNIFICANTLY drop the power output of that one cylinder, and throw an injector fault for that cylinder, even though the injector may be fine. cylinder 8 could be another story though.

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either way besides your injectors, its something mechanical. out she comes and off with her heads! :pca1:

truck has 220,000 miles on it. Does not seem to using or burning coolant. I apoligize about what i said about #2, it only goes to 110, no higher. After you stop cranking it, it does hold pressure. Thanks for the info, I really appreciate it.

It is probably rings but you could get a leak down tester and confirm whether it is rings or valves. Valves would be the easier problem to solve because you wouldn't have to pull the engine out.

he said the cylinder holds pressure after cranking, rings are good, he just did a leak down test.

have you ever over revved the engine? mods?

Cylinder hold pressure after cranking?????? Not sure we are diagnosing this correctly. When using a compression tester the guage holds the cylinder pressure in the guage do to a schrader valve in the tester. Now if you are talking about doing a cylinder leak down test thats a different story. You can listen for where the air is leaking with the air pressure is on the cylunder. I have seen several that have been run with a bad injector too long and scored the cylinder. So I hope that is not what has happening to yours. Low compression on one cylinder would get me to do a cylinder leak down test so I could listen for where the compression is going. Hopefully it is a valve like some one above has already said... Hopw this helps

that could also be a possibility ^^ hopefully not.

but im still thinking its a valve. i say this because what could be happening is when your piston is coming up on compression, you could have an intake or exhaust valve thats not seating correctly, or at the right time due to being bent, burned, or the seat's ruined. but it will eventually seat and hold compression (not enough), too little too late.

First off, thanks to all of you for the very useful info. I tried a leak down test, and still could not pinpoint it, so i pulled the head. Sure enough #2 cylinder is scored. So I am going to replace the engine with a used one with 123,000 miles on it. Hopefully it's a good engine. Again, thank you all for the info.

is the engine still in the truck?

good call^^ :c: