Super Pissed at the Z71 - Cylinders 7 & 5 not firing

Ricky B

Ricky B

Wiiide Open
Joined
Mar 20, 2005
Location
LKN - Tha Dirty Mo (Mooresville, NC)
Idk, I'm sooo tired of continually trying to keep this damn thing running and it breaking somewhere else as soon as I Fix it . . . whatever Z71's are still that Hotness, and I'd rather push a Chevy than drive a ford, etc, etc . . .

but anyway, its running like crap, loss of power, misfires on hard throttle

Cylinder 7 is not firing, cylinder 5 is barely firing

replaced plugs, wires, cap, rotor button, ignition module with no results

You can remove power to cylinder number 7 while the truck is idiling and it makes no difference, you can also drive around with cylinder number 7 unplugged with no difference compared to if it were plugged.

Cylinder 5 while idling if unplugged makes no difference, while driving with it unplugged it makes kind of a difference in power but not much as in comparison to the rest of the cylinders if unplugged.

So from what I know it seems to me like the only other possible things to try is replace the dizzy itself in case it has a fracture somewhere.

Or to run a compression test on cylinders 5 and 7 to see if I have sticking valves or something causing a loss of compression. Only reason I havn't done so yet is because of my aftermarket shorty headers are in the way and are a PITA to remove/reinstall because the exhaust doesn't line up.

any tips before I drive her off a cliff :shaking:

but seriously I guess my only other options are to try a new dizzy or run the compression test on the cylinders in question . . . .

Thanks
 
Dizzy won't cause 5-7 miss, without causing other issues.

THe dizzy CAP could though, are you using AZ crap or AC parts ? Had MANY of issues solved by using GM parts, Dizzy cap being the biggest issue, lotta power flying around in that plastic, VERY easy for it to internally cross fire.

Also, you ABSOLUTLEY SURE your plug wires are in the right position ? VERY easy to do with the flat cap.

Do a compression test, you may find a bent valve or a blown headgasket, both NOT uncommon, especially on some thing that it throttled hard.
 
Im gonna sound like an echo, but the cylinders are side by side sequential in the firing order.

Id make sure I was using a GOOD new Dizzy Cap and had my plug wires in the right spot, then Id suggest blown head gasket...
 
Yea it's TBI,

I'll go check again but pretty sure I didnt cross the wires or anything.

I left out how it started which I think Is kinda throwing ya'll off a bit, the problem didnt just start when I replaced the dizzy cap, etc.

The truck has been running fine for a while then last friday when we were heading down I40 from Raleigh to the BDB event is when it origionally started, and I didn't really notice it till we stopped for gas near winston-salem that it was running bad.

I have a problem with exhaust header bolts and spark plugs backing themselfs out of the block. The number 7 had done so and obliterated itself so I assumed that was the problem, replaced that sparkplug but it didnt make any difference.

I replaced all the ignition stuff yesterday in an attempt to find the culprit with no success.

SO the problem started before i started unplugging any wires while I was towing the Jeep down running like 3400 rpm at 70mph or so down I40.

If it was the headgasket would it not have either water in the oil or oil in the water? Because there's no water in the oil and pretty sure theres no oil in the water . . . .
 
not necisarily could be burning it out of the exhuast and cat is eating up the white smoke. do a compresion test and report back that will eliminate mechanical problems.
 
Had a little bit of time on my hands so I messed with it a little more, did as much as I could w/o pulling the exhaust.

Checked the wire order everything is correct, allthough I was wrong its cylinders 6 and 7 that are bad, not #5

Pulled the valve covers all rockers seem to be moving freely.

Checked compression on a couple of the good cylinders just for the heck of it got bout 70 to 80 psi from each (cylinders 1,3,2,4) can't get to the back four cylinders w/o pulling the headers.

Under hard acceleration that causes it to pop/misfire it causes it to pop out of the throttle body some.



Have had suggestions from a couple people that timing may be off???

Also that the cam may be worn out and/or the dizzy shaft cracked.



I guess I'm just trying to check everything possible before I pull the headers cause trying to get the exhaust to line back up is gonna be a frikin chore and a half. Might try to check timing on teusday I'll have some free time teus afternoon.
 
Cperry said:
not necisarily could be burning it out of the exhuast and cat is eating up the white smoke. do a compresion test and report back that will eliminate mechanical problems.
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Im right here in my line of thinking.

Pulling the Jeep at Istate speeds could have contributed.
But, now t 6,7 so they are opposite banks....

I *have* seen a cam gear wear and cause a dizzy to jump off tooth at the cam, once. But Id think its damn unlikely.

Then again the spitting back through the tb does suggest off time.

Really need more complete diagnostic work.

But if it is 6&7 not 5&7 Id stop chasing head gasket as that wouldn't be it. Could still check CR to eliminate some strange cam wear/lobe issue.
 
SkyHiK5 said:
Im right here in my line of thinking.
Pulling the Jeep at Istate speeds could have contributed.
But, now t 6,7 so they are opposite banks....
I *have* seen a cam gear wear and cause a dizzy to jump off tooth at the cam, once. But Id think its damn unlikely.
Then again the spitting back through the tb does suggest off time.
Really need more complete diagnostic work.
But if it is 6&7 not 5&7 Id stop chasing head gasket as that wouldn't be it. Could still check CR to eliminate some strange cam wear/lobe issue.
Click to expand...

Whats CR?

I mean after checking the timing is my next step pretty much the compression tests?

I have a buddy with a spare Dizzy, I guess I could try putting his in and see if its my dizzy thats the problem?
 
jrraw23 said:
Checked compression on a couple of the good cylinders just for the heck of it got bout 70 to 80 psi from each (cylinders 1,3,2,4)
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I'd damn sure make sure the compression gauge you have is working properly, 70-80 psi on 4 holes is not good. shouldn't be lower than 125min, prefferably 150 or better.

I hope your gauge is wrong.

Hard pull, at highway speeds, ( you never said how fast you were going) and then you state your header bolts come loose, tells me you may have valve issues.
been nice and cool recnetly, sucking cool air into the hot exhaust port repeatedly over a long period of time can certainly effect the valves ( causing them to crack and burn).
any chance you over revved the engine on a downshift at anypoint ? that would float the valves causing parts to meet, benting the valves, and cause the issues you have.

I've seen both happen a few times.
 
I may have been doing the compression test thing wrong I just screwed it in and let the engine run at idle and see what it built up to

Go about 65 to 75 max on the interstate usually runs at like 3000 to 3500 rpm at those speeds

The header bolts have always been coming loose, but at the time they were actually all tight and the exhaust was all good and sealed up (still is) but yea the header bolts and spark plugs like backing themselfs out over time.

Don't think I overreved I tow in 3rd gear so there's never really any downshifting.
 
ok sorry if im a retard here, but dont you do the compression test with the engine off and just spinning it over?
 
dear lord RICKY BOBBY you have invented a new compression test, Now i would venture to say the way you did it would not really change the numbers that much if not increase them. but i would not know form expierence. Pull your header on one side at least check the compresion on the one side. remove all the plugs ground your coil wire to the body so you don't have sparks fying everywhere. screw guage in one hole at a time, just turn vehicle over for about 8 seconds or until guage stops moving up. watch the guage it should jump fast to 50 and then build 70 90 120 150 done. then we know if its mechanical. if timing is off compresion will be off, if valves are bent, burnt whatever compresion will tell us. we can move on from there.
 
That's right (or at least how I do it)...pull all the plugs, unplug the dizzy, open the throttle, and crank it over.

Stole this off the web, 'splains the process and a couple of pitfalls pretty well:

An engine compression check will quickly tell you whether pistons, rings or bore, are badly worn or damaged. It'll tell you if the inlet and exhaust valves are burned or failing to seat properly. It can even tell you if the cylinder head gasket has failed.

It is very simple to carry out too. All you need is a willing assistant, a purpose-made and fairly cheaply available compression tester, a suitable socket spanner and wrench to remove the spark plugs, a small trigger-type can of engine oil and a pen and paper.

Begin by warming the motor to its normal operating temperature. Remove all the spark plugs, disable the ignition system by disconnecting the coil connection, then attach the compression tester to each plug hole in turn, while an assistant cranks the engine on the starter and you note the readings.

Simple, but there are important points to consider. First you'll have to zero the gauge after you've carried out each test and written down the result. Secondly, make sure the gauge, if it's of the cheaper push-in rather than screw-in variety, seats properly against the cylinder head to avoid falsely pessimistic reading.

And finally you must make sure that not only does the engine turn over at or near its normal cranking speed for long enough for the reading on the gauge to stabilise, but that your assistant keeps the throttle wide open throughout. The high manifold depression created by a closed throttle would provide a falsely low reading.
Click to expand...

shamelessly stolen from http://www.volvoadventures.com/howtodocompressiontest.html

...because it was the first thing that came up under Google.
 
It's Ricky Science, Rocket Science is too advanced at this time........
 
you don't need to warm it up as you are going to have to pull headers and plugs i myself am not a fan of burning my skin. it won't change the numbers much and we are looking for major problems not worn rings
 
Cperry said:
dear Little Baby Jesus RICKY BOBBY you have invented a new compression test, Now i would venture to say the way you did it would not really change the numbers that much if not increase them. but i would not know form expierence. Pull your header on one side at least check the compresion on the one side. remove all the plugs ground your coil wire to the body so you don't have sparks fying everywhere. screw guage in one hole at a time, just turn vehicle over for about 8 seconds or until guage stops moving up. watch the guage it should jump fast to 50 and then build 70 90 120 150 done. then we know if its mechanical. if timing is off compresion will be off, if valves are bent, burnt whatever compresion will tell us. we can move on from there.
Click to expand...
Fixed it for ya'

So Ricky, you're saying you can't change the spark plugs on the back cylinders without removing the headers?
 
rattlecanpaint said:
Fixed it for ya'
So Ricky, you're saying you can't change the spark plugs on the back cylinders without removing the headers?
Click to expand...

I can but barely, i cant use a wratchet i have to use a wrench on the end of the spark plug socket

I can get the fitting for the compression tester to screw in just cant get the line to screw into it not enough room.

your cam is wiped out
Click to expand...

I know I tryed to call you after i found that it was popping outta the tbi some, but we'll see i guess prob gonna try to pull the pass side header tommorow to get to # 7 at least
 
I would say it is your cam also pull the valve covers and the dizzy wire and have someone watch as you turn it over if its your cam you will see the rockers for that valve not moving
 
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