1994 F250 5.8L

This is driving me and my buddies nuts, #8 will not fire/work it seems.
we have done:
-check firing order, it was fine
-vac gauge, all fine
-comp gauge, checked pass side all 100PSI and #1 on drivers side had 150PSI, gonna test it all again to be sure
-No vac leaks, carb clean didnt do a dang thing
-Ground out all plugs, all ground and shut down except #8 which says the injector isnt firing or the plus dead...
-New cap and rotor
-swapped injectors with good known injector
-swapped wiring for injector
-checked timing-in time
-all new wires and plugs

We did so much im sure im forgetting... but what else would make that one plug not fire??? Im considering leaving the injector off and seeing if it fires outside the cyl, about all we can think of is fuel pressure regulator is bad since its right next to #8, another buddy claims perhaps it is working but the fuel isnt burning up cause of a cam problem or a bad lifter or valve or pushrod?

Im not very good with engines honestly, so forgive my ignorance.

 

if you have compression i would worry about a back lifter or valve, lets start with a bad injector, since you can get to the fuel rail on that side, swap #8 with #7 and see if the dead cylinder changes to #7. if it does than its the injector

 

nah swapped it and it didnt make a difference at all.

Tomorrow gonna mess with it again and ill report back-but all signs are leading to something in the engine not opening a valve or something.

 

Okay, just keep in mind if the regulator was messed up, all cylinders would be getting a surplus amount of fuel

 

Keep the spark plug cable that goes to that cyl separated from the rest and try the engine.

 

Encho, that is an excellent idea to avoid the cylinders 7 - 8 crossfire problem of the 5.0. But he lists his engine as a 5.8L, which has a different firing order, and does not have the 7-8 problem.

 

More testing today leads us to think the following:

1. Compression test on pass side was all 150psi +
2. Compression test drivers side #1: 100, #2 125, #3 150, #4 (number 8 plug and the problem) 100. After putting oil into #8 jumped to 130psi.
3. All valves appear to be working properly.
4. Removed injector and cranked-getting fuel

So that leads us to think either the head is warped, or the rings are bad and the gas is just going by #8. Going to try and see if we can put oil in all cyls on that side and maybe get luck and reseat the rings. If all else fails used motor or its getting sold.

Thankfully I have an old toyota truck I can drive when fixed. It blew a plug out of the head the other day-at least it can be fixed easier.

 

Ok im still stuck on this and its really bothering me and in need of desperate help.

So far several people I know gave me the following advice:
1. timing is off, chain, distributer, etc.
2. headgasket/head is warped on pass side
3. lazy valve on #8 cyl, but that doesnt explain low comp on all drivers side cyls
4. bad rings all on that side
4A. was suggested to add oil to each cyl on that side as gas is washing out those cyls.

I just dont know what to do anymore, I dont have unlimited funds and need to get this truck fixed for winter. It has been suggested I put in a new rebuilt motor from ford (I have a buddy who works the parts counter) but it is like 1800 bucks. other options are to rebuild it or find a motor out of another truck.

I am leaning towards probably needing an engine, but its so very odd that all the rings are bad on that one side?

 

here are my thoughts.
1. the pickup inside the dizzy might be bad. (happened to me)
2. did you change the ignition coil? if not that could also be the culprit.

 

I didnt check/change either of them.

If the coil is bad then why would only #8 have an issue? Every other cyl fires but #8 doesnt seem to be getting spark. Swapping wires and plugs yields nothing. We also ground out each and every plug wire at the distributor and still #8 didnt do a thing-all others shut down and idle changed. The injectors is working, but the plug is lean-white.

Still it doesnt explain the very low comp on the drivers side cyls?

 

okay well the ignition coil might cause random misfires true
but here is where it gets really interesting...
when my pickup inside the dizzy went bad
i only had 1 and 2 misfiring.
not saying that might be your problem but
i mean if you replaced almost everything else...

 

To recap the problem, the engine runs OK except that cylinder #8 is dead, right?

Keep your cylinder numbering consistant as per Ford method or else it gets confusing:
Passenger side front is #1, then 2, 3, 4 to passenger rear.
Driver side front is #5, then 6, 7, 8 to driver rear.

Did you actually take the valve cover off and probe through the spark plug hole for #8 to determine TDC and turn engine with a breaker bar on the crank nut, and watch #8's valves work properly stroke-by-stroke? Besides thinking and stepping through Intake - Compression - Power - Exhaust strokes, you need to note how high the cam lifts the rocker/valve goes down, and compare to a working cylinder, in case of a cam lobe worn off. Of course, when a valve is closed, should spin pushrod with thumb and finger to verify it's straight, though engines usually can run with bent pushrods, unless they bend so much they jump out on one end.

Are you doing the compression testing the right way - Using a screw-in tester, ALL plugs out, throttle linkage blocked wide open (of course, remove block before starting )?

Compression test #8, release the pressure reading, do it again, repeat a bunch of times and see if it is consistant. That can tell you something.
I was recovering a big block once from the dead, did compression tests on all. But one cylinder seemed to jump around. Sometimes fine, then would get only 40 PSI or so. Sometimes heard strange wheezing sound when doing that cylinder. Pulled off valve cover, intake pushrod badly kinked and loose. Pulled it out, probed for lifter, hmmm, no lifter. Pulled intake manifold, bent pushrod had popped out of lifter, hit retaining clip just right, lifter popped all apart and flung it's guts all over. Seems like it should have failed compression test since intake valve closedall the time. But sometimes it passed the test.

 

Thanks for the help torky.

Yes the engine runs fine really except for #8 (yes it is indeed #8 too, back plug on drivers side). We checked for lift by cranking it over, not by hand.

All plugs were out, like I said it keeps coming up the same way:
The drivers side seems to have low compression on #5 (100), #6 (125) #7 (140) #8 (100), when adding oil to #8 it jumped to 120psi after 2 cap fulls of oil from a quart oil bottle.

Engine runs good, BUT it is very hot, the radiator is not good and the waterpump is leaking pretty good. It almost overheated once (boiling water inside the overflow tank and rad took 2-3 gallons of water. I had been wanting to replace all of that-but the misfire was more important.

Im just so utterly confused, I am not a very good engine person and the person helping me knows more about chevy motors than anything else. People have told me the head could be warped, cracked, etc, the headgasket is bad, rings, the injector (it is spraying tho), to the cyls are washing out. The truck sat for about 3 years in a guys wrecking yard waiting for someone like me to buy it. It didnt cost much but I felt it was worth it.

Come next week Im gonna try out the suggestions so far. Thanks everyone!

 

Two more things to check, if you have not already:

Verify that you actually have spark at the end of plug wire #8. Not just at the coil, or at some other plug end, but at #8's plug end. New parts are not a check

A very long shot - Feel around over the top of the upper intake, round the back side near the top (facing the firewall). There is a big core plug in the upper intake casting. Verify that the core plug doesn't have a hole in it or rusted through in a spot. Its at the back end of the plenum, looks like #8 intake runner starts right by there.


A cylinder going up 20 PSI by adding oil does not sound like trashed rings, certainly not bad enough to prevent firing.

 

Usually when you pour oil on a cylinder and the compression jumps, the cause is a worn/broken ring.