7.3 miss

[idination]

Ive got a problem guys and any help you could give me would be greatly appreciated. Ive got a 90 f250 with a 7.3 that has a miss on the number 1 cylinder. So far ive replaced injectors, all fuel return parts, a valve spring and both lifters. when i pull the glow plug and put air to the cylinder you can hear it hiss out of the tail pipe. if i loosen the rockers for that cylinder it goes away. Any ideas?

also while it is running if i crack the line loose on the number 1 injector you can hear it run a little worse.

 

[towtruckdave]

Ive got a problem guys and any help you could give me would be greatly appreciated. Ive got a 90 f250 with a 7.3 that has a miss on the number 1 cylinder. So far ive replaced injectors, all fuel return parts, a valve spring and both lifters. when i pull the glow plug and put air to the cylinder you can hear it hiss out of the tail pipe. if i loosen the rockers for that cylinder it goes away. Any ideas?

also while it is running if i crack the line loose on the number 1 injector you can hear it run a little worse.

First things first, Are you sure you are on the low part of the cam lobe?

 

[idination]

while i had the valve cover as out of the way as i could get it i had friend bar the engine over until i saw the intake valve close.

 

[hesutton]

while i had the valve cover as out of the way as i could get it i had friend bar the engine over until i saw the intake valve close.

What about the exhaust valve? If it is loosing compression out the exhaust then the exhaust valve wasn't closed when you where testing the cylinder. Is there and slop in the valve guides?

Heath

 

[idination]

No play in the valve guide. Since this engine has hydraulic lifters is there a chance that i have an oil gallery thats plugged or restricted thats causing the lifter to expand too much?

 

[idination]

I have yet to pull the heads off of this engine im trying to avoid major disassembly until im done with college and back on my feet.

 

[hesutton]

Do you have a compression tester? If so, that would help you be certain what cylinder or cylinders are giving you problems. Still, you need to find out why the exhaust valve wasn't closed when you pressurized that cylinder.

Heath

 

[idination]

i have a compression tester but it wont measure pressures that high. i know for a fact its the number one. if i bar the engine over with the valve cover off and compare the height of all the rockers i can see that the valve isn't closed entirely. If i pull the gear cover off of the front of the engine will i be able to access the oil galleries for the lifters or am i going to have to take the entire engine apart to do that?

 

[GenLightening]

If the lifter extends too far it won't work for very long as it will leak the pressure out and possibly come apart. If you replaced the lifters and the problem is still there then they weren't it. Is it "woofing" out the exhaust when running?

 

[idination]

yes but you hear a ticking sound out of the tail pipe at the same time.

 

[towtruckdave]

It sounds like it is time to pull the heads off.

Then take them to an engine shop that knows diesels and ask for a budget valve job. Most shops charge a couple hundred bucks.

Ask them to try not to surface the head, there is minimal room to surface the head. It likely will not require surfacing.

 

[idination]

Sounds like that's as good a place as any to start.

 

[OLDBULL8]

i have a compression tester but it wont measure pressures that high. i know for a fact its the number one. if i bar the engine over with the valve cover off and compare the height of all the rockers i can see that the valve isn't closed entirely. If i pull the gear cover off of the front of the engine will i be able to access the oil galleries for the lifters or am i going to have to take the entire engine apart to do that?

Compression tester: Gage should register 400+ psi. You will only get about 350+ on that engine.

Oil gallery is virtually impossible to plug up.

Before pulling the head make sure you actually have too. What your saying about the valve not closing doesnt make sense, unless someone has put a valve in there with a longer stem, or if that push rod is longer than the rest of them. Remove the rockers on that cyl. and compare push rods, exh. to the intake should be the same length. Then blow air in that cyl., if it still blows thru then you have a bad valve or seat.

Below is the oil system and cylinder rotation.

The engine rotates in a clockwise direction as seen from the front of the truck, and for every 1/4 turn of the engine(crank) each next piston will arrive at TDC. So, When the line on the vibration damper is at the 2 oclock position, cylinders 2 and 5 will be at TDC. When the mark is at the 5 oclock position, cylinders 7 and 6 will be at TDC, 8 oclock has cylinders 3 and 8 at TDC, and back to 11oclock, 1 and 4 will be at TDC.

Cylinder numbers are assigned 1,3,5,7 on the left (passenger USA) bank from front of truck to back, and 2,4,6,8 on the driver's side (USA), front to back. Firing order is 1,2,7,3,4,5,6,8.

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[OLDBULL8]

So far ive replaced injectors, all fuel return parts, a valve spring and both lifters. when i pull the glow plug and put air to the cylinder you can hear it hiss out of the tail pipe. if i loosen the rockers for that cylinder it goes away. Any ideas?

Did you do that on #1 cyl., meaning the spring and lifters? There is your problem.