Hypothetically Speaking......

06stangtyme

New Member

Feb 4, 2006

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Nashville

Sep 9, 2006

#21

• Sep 9, 2006

• #21

If you have EGR system on the engine look for a crack in the intake around the area of that port...

 

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onefast65

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May 4, 2004

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Sep 9, 2006

#22

• Sep 9, 2006

• #22

No EGR systems and I have already swapped wires 4 and 8 with no change in either cylinder/spark plug after the swap.

 

06stangtyme

New Member

Feb 4, 2006

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Nashville

Sep 9, 2006

#23

• Sep 9, 2006

• #23

a crack between intake port and exhaust port in the head on #4 is possible as well...

 

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onefast65

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May 4, 2004

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Sep 9, 2006

#24

• Sep 9, 2006

• #24

I assume that a crack between the intake and exhaust ports would create low compression. I have 150-160 on all cylinders, including number 4. I have new lifters on order.

 

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310stanger

New Member

Aug 15, 2006

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Sep 9, 2006

#25

• Sep 9, 2006

• #25

my buddy who is a ford senior master certified tech and mustang nut like myself has told me its better to have a valve adjustment on the "slightly" loose side then tight. you need preload, and some valve lash. whenever you adjust your valves make sure u go out of your way to do it correctly its not one of those things you wanna breeze through. theres power in a properly set up valve train. by the problems you are having have you checked pushrod length?

 

JChalfan

Member

Nov 27, 2002

551

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Bellevue, WA

Sep 9, 2006

#26

• Sep 9, 2006

• #26

onefast65 said:

I assume that a crack between the intake and exhaust ports would create low compression. I have 150-160 on all cylinders, including number 4. I have new lifters on order.

Click to expand...

I don't think a crack between the intake and exhaust ports would effect compression, unless the crack extended into the combustion chamber.

The crack theory does seem like a bit of a long shot, but you have already eliminated a lot of the likely causes, so it might be worth looking into.

There is definitely something going on in that #4 cylinder though. Is it possible your intake gasket wasn't sealing well around the #4 intake port, and you were sucking oil from the lifter valley?

You said you swapped injectors already, correct? Is it possible that your wiring for #4 injector is defective somehow? I just noticed you swapped the injector harness plugs, so maybe that's not an issue.

I would double check the plug wire and plug just to be sure.

Have you tried a different distributor cap? I just did some work on my buddy's '68, and the distributor cap looked fine, but it wasn't firing 2 cylinders.

I agree with 310 stanger that it could still be a valve issue. If your intake valve was too tight, it would let combustion gasses back into the intake, making the port black and likely causing a miss too.

You could always adjust that one cylinder with the engine running. I know it's not the preferred method, but it will work.

I know some of the things I said may be a stretch, but I'm just throwing ideas out there. Good luck and let us know how it goes.

Jeff

 

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onefast65

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May 4, 2004

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Sep 9, 2006

#27

• Sep 9, 2006

• #27

Again, all pushrods are the same so if pushrod length was an issue I would expect to see missfiring issues with all cylinders. The photo above shows that only number 4 is the issue. Plus, the shop that helped me design this engine has run similar setups before. My pushrods are 6.70 trick flow and I'm using trickflow track heat heads with 1.6 rockers. Thanks for your suggestions though - any other thoughts. I'm still thinking lifters but it sucks that I have to wait 2 weeks to get a new set of Ford Racing lifters in Calgary here.

 

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onefast65

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May 4, 2004

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Sep 11, 2006

#28

• Sep 11, 2006

• #28

Intake and Head removed

I have now removed the head also and found nothing visibly wrong with the head or valves. Only difference from the other cylinders is that number 4 combustion chamber and the valves are black with soot. I removed the valves and the valves and seats all look good-guess this explains why I still had good compression tests. I'm waiting for new lifters now and hope that that does the trick. If not, I will be completely baffled.

 

JChalfan

Member

Nov 27, 2002

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Bellevue, WA

Sep 11, 2006

#29

• Sep 11, 2006

• #29

bump.

I'm curious to see if the lifters help out.

Jeff

 

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onefast65

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May 4, 2004

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Oct 1, 2006

#30

• Oct 1, 2006

• #30

Lifters did not fix the problem

OK, I finally got the new lifters installed. No change...

I'm about to swap all the injectors from left to right to see what this does but I'm really starting to run out of ideas. The problem really seems to be related to number 4 cylinder - it has a very black spark plug and all the other plugs look like new.

By the way, when I changed the lifters I also pulled the head off and saw no signs of cracks or burned valves. I guess this explains why the compression tested good.

 

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Marlboro_Man

Member

Sep 30, 2005

437

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18

Houston, TX

Oct 1, 2006

#31

• Oct 1, 2006

• #31

After reading through the whole thread and looking at the pic....

My GUESS is that you are getting oil into that cylinder somehow. Is the upper intake port for #4 the same as the port on the head (all black and sooty)??? To much oil getting on the plug, fouling the plug, thus cuasing a miss.?.

Some more stuff to check: Gaskets, Valve seals, Cracked cylinder head, rings.

Compression tests are good but not always the best way to find a problem. Try doing a "Leak down test" if you can, it may be something you need to take the car somewhere and let someone else do. However it MAY help point you in the right direction.


Good luck to you

 

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onefast65

New Member

May 4, 2004

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Oct 1, 2006

#32

• Oct 1, 2006

• #32

I just did a simple leak test - applied compressed air to listen for leaks but did not use a guage to messure leakage. Essentially, at 100 psi there is a very slight leakage of air past the rings. I did number 4 and number 8 and they both sound about the same. I'm assuming that if this was the problem, I would probably hear a difference between cylinders. Is this correct?

 

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onefast65

New Member

May 4, 2004

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Oct 1, 2006

#33

• Oct 1, 2006

• #33

Had a thought

Just had a thought. Today when I moved injectors around, I realized that my fabricated fuel rail retainer puts quit a bit of 'twist' on my Bosch injectors. I am running an Accufab throttle body with a retainer plate between it and the intake manifold. It was not built to very tight specs and thus when I installed the injectors into the rails and then went to push the injectors into the manifold, quite a bit of forcing and twisting is required. If these injectors are plastic throught (not just a plastic outer housing) I could see this causing them to stick intermitently, no?

 

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Marlboro_Man

Member

Sep 30, 2005

437

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18

Houston, TX

Oct 1, 2006

#34

• Oct 1, 2006

• #34

That could be another possibillity, that fuel is flooding out that cylinder.

I dought that you would "hear" a noticeable differance. Get a gauge on there and check at least 3 cylenders (or all of them) to get a more accurate account of whats going on.