valve spring tool
 

A track motor with a miss fire. I have fuel, fire, compression. Appears to be from the right, maybe #5, but very difficult to isolate it. Would like to pull a valve spring and I am sure there is a tool for that. Anyone with a part number and technic. Very tight in there. Thanks, Bob

P7I and P7E for intake and exhaust, respectively.

Are you thinking that a valve spring is broken?

I am running out of usual suspects. At first a solid miss fire. Switched ignition systems, injectors, checkvalves that sit under the delivery ports on the pump, plugs. Pulled the pump off of my street car and that seemed to clear things up once I made the mixture adjustments. Put the race pump back on it seemed to be better, then degraded again. Have run the injectors into graduated beakers and they seem to be doing what they should. New fuel pump and check valve at the console. What is maddening is that the problem isn't stable. In the process of changing motors and we will see. Thanks, Bob

What makes you thing a misfire is due to a broken spring or two? The engine will run pretty well, at least short of, say, 7,000 RPM, on just one of the two springs - at least for a while. If both are broken, no clearing up, etc.

The tools work pretty well - I just changed this out with the intake tool:
http://forums.pelicanparts.com/uploa...1625189699.JPG
http://forums.pelicanparts.com/uploa...1625189699.JPG

Relative piece of cake, since my engine is mostly out from under the car (didn't need to raise the car the last bit to get it all out to change the flywheel), so just about as easy as if up on an engine stand. Not so much with it in the car.

Last time I did this it was an exhaust at the track - not so easy.

In the past I have shoved thin cord in through the spark plug hole with the piston retracted, then moved the piston up to squeeze the string in a blob up against the valve head. This time I just set to TDC firing and pressurized the cylinder with air (used the hose which screws into the plug threads from my leakdown setup) to hold the valve in place while the spring is being compressed. Both worked, this way a bit quicker.

Pencil magnet and hemostat useful for dealing with the keepers. Rag or paper towel shoved under everything in case a keeper should try to escape.

miss fire
 

Looking for a broken valve spring because I have checked the boxes on all of the other areas that I think would cause this problem. I can't think of any other thing mechanical on this motor that could cause the missfire. I will have motors swapped by the end of the weekend and will see what transpires from that effort. I think the problem will still be there and despite my tests on the MFI pump indicating that it is functioning properly, it will be my main suspect. I don't know how to do further tests on the pump other than by replacing it. I will post when something of substance surfaces. Bob

You don't need to remove the springs to check to see if one or more are broken. As you might expect, even one of the two broken means a lot less spring pressure. You can just press down with something on each one, and see if any move more than the others.

Or make and use this tool:

http://forums.pelicanparts.com/uploa...1625282776.jpg
http://forums.pelicanparts.com/uploa...1625282776.jpg

Some clever guy came up with this (not me) some years back. Put a nut on a nearby valve cover stud, use that to hold the slot. press down. Will quickly tell you the state of the springs. Much more quantitative than pushing with your hand/arm alone on something without any leverage.

Intact springs can be compressed with this, but a lot less than if one is busted.

Thanks Walt, yep, tried that. Threaded a flange nut onto a VC stud, a small curved pry bar, and pressure against the rocker end and they all feel about the same. Thought about welding a socket to the pry bar and using a torque wrench. Engine is out and can see the springs pretty well and with a pick can feel down in the silo and nothing feels loose. Miss fire is right out of the gate and don't know if a broken spring (depends on how broken) will manifest down low. Will figure it out eventually. Bob

Well, my experience with broken springs on my race motors tells me that if just one of the pair is broken, you won't experience anything down low. They just acted like rev limiters up high (as in 8,000 rpm) - My engine wouldn't rev past 7,600, and I finished the race that way. Turns out that would be optimum shift point for that motor anyway. Most of the springs (inners, I think) were broken. The valves would float at higher RPMs, and you could feel the effect on power - just wouldn't rev higher.

I'm pretty sure the pry test will show up any broken spring.

Leaves you with the mystery.

Problems like yours prematurely age a guy. I have a motor where one cylinder won't fire, despite leakdown being fine, has spark, injectors inject, cams open and close valves, other five holes work normally. Despite injectors (swapped or not) firing when tested, starter fluid sprayed into that intake causes it to fire along with the rest. Mixture too lean somehow, but why? Pretty straight forward intake system, no obvious place for air to leak in.

Update! Just finished installing the second motor. Sounded correct in the shop, but track motors are so raw, I don't trust my perception without being able to load it plus my paranoia at this point with chasing this intermittent ghost for several months. Ran it up and down the street in front of my shop and I think it is good. Doesn't quite have the snap that the other one had when it was healthy, but hitting on all 6 and wants to pull. Either the missfire demon became unhinged in the swap, or my missfire is a mechanical issue with the first motor. It had correct compression and leak and as well as I can tell no broken valve springs. Will pull it down, but any thoughts from youse guys as to what mechanically can cause a missfire and it was all through the range. Thanks to all. Bob

Bad plug, bad wire, bad injector? But you've chased those down. Hard to imagine a valve which sticks some (causes misfire), but closes fully when doing a leak down.

valve spring tool
 

Yep, since you don't need a vacuum signal with MFI, I wouldn't think a minor vacuum leak would create a problem. The little check valves beneath the delivery ports on top of the pump will be a problem if one looses its seal. Doesn't hold pressure against the injector, but then you would think the injector would not deliver. Thank you for your input. Bob