New 351w Fired up Today but 7 and 8 not firing **Solved**

[blade]

I had a cylinder down on my 74, messed with several different things and then decided to pull the valve cover. Turned out I had a damaged push rod and the rocker arm was able to jump off and to the side. Worth checking out if you can't find any other issue.

 

[DirtDonk]

What cam was installed?

Comp Cams 35–512–8 was mentioned earlier.

 

[Ol'Blue]

Thanks all for the suggestions. I did a compression check with my grandfather's 40 year old tester and it seems to work fine

Cyl/psi
1/135
2/155
3/160
4/160
5/150
6/170
7/170
8/170

Im a little concerned with 1 and 5, maybe 2, but motor is not broken in which may cause these variances? I think the good thing is 7 and 8 are good.

To answer some other questions:
Firing order is 1-3-7-2-6-5-4-8 and verified with my comp cams 35-512-8
Carb - I reused my qjet built by carbs unlimited and ran fine when pulled from my 302. I discussed moving the carb to a 351 a couple years ago with them and thought I remember him saying it should work just fine as is on the 351, bust still think that is odd. I have a call into them to discuss, but maybe I have that all wrong and they were referring to the size and not jetting.
I made sure all wires were ran without twists, caps were seated on both ends and they are new Ford Racing wires.
The valvetrain is GT40 heads with Ford Crane Cams 1.7 Roller rockers and I believe comp springs. Heads were freshend up.
I have tried moving the wires around and I could try using the wires off the 302 I pulled out. They worked fine.

Thanks

 

[ssray]

Something I’ve not seen anyone mention is checking the cap. I’m not familiar with your distributor but I’ve had carbon tracking happen in caps. Usually with a lot of hours though and I think more prevalent on engines that run in dirty environments. I think I had a cap that had a crack in it that started arcing one time as well. Maybe with larger gaps the spark may tend to bypass a cylinder under pressure for one that’s not. If you do check for that look closely as it can be hard to spot. Just my FWIW.
Scott

 

[ba123]

Maybe a dumb suggestion, but don't see it mentioned...

You did find TDC the on #1 for sure (pass side front) and then verify the dizzy pointer points to the #1 plug wire and then from there, it rotated COUNTER clockwise 13726548. Not likely to run if you didn't do this right, but thought I'd add.

Not sure it would be a fuel issue with a carb,

Not sure how it would be a valve issue if you have compression, glad you tested that.

There are only 3 things needed for a cylinder to run. Fuel, Compression, Spark. Can't be anything else and you know you have the first two, so spark must be coming at the wrong time.

 

[Broncobowsher]

I lean away from a carb issue. With a dual plane intake #7 and #8 are pulling completely different passages and different sides of the carb. Maybe an intake manifold leak?

The good compression, well that is good news. Not worried about that low number on #1 yet, let the engine break in and see if it comes around.

I would still put the #7 and 8 plug wires on different cylinders and see if the problem follows the wires. It could be a bad wire. New parts are bad a lot of the time these days. And while playing around move the spark plugs as well, put them in #5 and 6. If you can get the issue to follow an external part that moves easy, you can tell what you need. If this was port injected there would also be moving the injectors to different cylinders as well. Moving parts is free, just takes a little time. When you move the problem, what part moved to make that problem move?

 

[Ol'Blue]

Maybe a dumb suggestion, but don't see it mentioned...

You did find TDC the on #1 for sure (pass side front) and then verify the dizzy pointer points to the #1 plug wire and then from there, it rotated COUNTER clockwise 13726548. Not likely to run if you didn't do this right, but thought I'd add.

Not sure it would be a fuel issue with a carb,

Not sure how it would be a valve issue if you have compression, glad you tested that.

There are only 3 things needed for a cylinder to run. Fuel, Compression, Spark. Can't be anything else and you know you have the first two, so spark must be coming at the wrong time.

I verified TDC on #1 a couple of times to make sure and even pulled the valve cover to make sure both valves were closed. Yes counter clockwise. I made that mistake 30 years ago on my firebird thinking it was the same rotation as Chevy. Wont do that again......

 

[ba123]

yup. you could also test the resistance on the wires. Most wires are rated in resistance per foot and should all be within a close range of that resistance per foot. Not sure what the Ford Racing ones are, but if you have one that is the same length as the 7 and 8, you can compare to each.

 

[TX-ZACH]

This reminds me of a similar experience not long ago for me. If running hot may be timing to far adv especialy with that noise. You should be idling carb down if to far adv. Be sure idle screw is down far enough that orifice to allow air past the butterfly. I forget what the name of it. Mine was running low timing and high idle. Once adjusted right everything fell into place. Tune the timing, then tune the carb.

 

[pcf_mark]

I would also check your wires in firing order and make sure you know which way the distributor is turning. I did this wrong and it ran and idled ok but would pop and hiss when giving it power. Idled fine but I had "weak" cylinders at idle. Then see what is connected to those runners to see if you have leak somewhere. Then swap the wires with another cylinder. See what you learn.

 

[Oldtimer]

Lazer temp on 1-6 all read in the mid 300 degrees but 7 and 8 closer to 200.

What kind of exhaust manifold/headers are you running?
Any chance of a restiction in collector (mislocated gasket, rag, missing wrench) causing lower temp readings?

 

[73azbronco]

Thanks all for the suggestions. I did a compression check with my grandfather's 40 year old tester and it seems to work fine

Cyl/psi
1/135
2/155
3/160
4/160
5/150
6/170
7/170
8/170

Im a little concerned with 1 and 5, maybe 2, but motor is not broken in which may cause these variances? I think the good thing is 7 and 8 are good.

To answer some other questions:
Firing order is 1-3-7-2-6-5-4-8 and verified with my comp cams 35-512-8
Carb - I reused my qjet built by carbs unlimited and ran fine when pulled from my 302. I discussed moving the carb to a 351 a couple years ago with them and thought I remember him saying it should work just fine as is on the 351, bust still think that is odd. I have a call into them to discuss, but maybe I have that all wrong and they were referring to the size and not jetting.
I made sure all wires were ran without twists, caps were seated on both ends and they are new Ford Racing wires.
The valvetrain is GT40 heads with Ford Crane Cams 1.7 Roller rockers and I believe comp springs. Heads were freshend up.
I have tried moving the wires around and I could try using the wires off the 302 I pulled out. They worked fine.

Thanks

OK, little more clarity here. Carb Unlimited guy is outstanding, work is impeccable. But, he does flow each carb based on engine size, so a 302 flowed carb may or may not work on a 351. Idle should work, WOT will most likely be very lean. When you pulled qjet, did you run it dry? Might have gunk in it if it was a length of time between runs. Everytime I shut mine down I turn off the pump, let it die dry. But I store it for weeks between runs.

I would be worried about new to you engine compression being that low. Period. Did you check pushrod length using a pushrod length tester?

Regarding spark, do you have a spark noid tester or does each of the 7 and 8 wires make spark? If they do, you are getting spark.

You pulled plugs, what do they look like?

 

[Ol'Blue]

This may be a topic to look at. Are you sure the timing is correct, the timing marks correct? Have you verified TDC and zero? One tooth off can get you the effect you are seeing.

When I first stabbed the dizzy I checked TDC by finger over #1 checking for compression and seeing both valves closed on #1 with valve cover off. Last night I was double checking and it is hard to tell if on compression stroke or exhaust stroke. Added to that, my new HB has three sets of timing marks for various set ups so its tricky. I ran out of time last night and plan to triple check everything tonight/tomorrow.

https://professional-products.com/p...y-small-block-ford-28-4-oz-in-harmonic-damper

 

[Ol'Blue]

OK, little more clarity here. Carb Unlimited guy is outstanding, work is impeccable. But, he does flow each carb based on engine size, so a 302 flowed carb may or may not work on a 351. Idle should work, WOT will most likely be very lean. When you pulled qjet, did you run it dry? Might have gunk in it if it was a length of time between runs. Everytime I shut mine down I turn off the pump, let it die dry. But I store it for weeks between runs.

I would be worried about new to you engine compression being that low. Period. Did you check pushrod length using a pushrod length tester?

Regarding spark, do you have a spark noid tester or does each of the 7 and 8 wires make spark? If they do, you are getting spark.

You pulled plugs, what do they look like?

Agreed, Bruce is great but I think he is on vacation this week as I haven't been able to reach him to discuss. Yes ran it dry.

I didnt check pushrod length with tester as I expected the engine building to take care of that.

I dont have a noid tester but tonight I plan to check each plug for spark.

I would estimate I have about 5-10 minutes of on the motor and the plugs look almost brand new.

So far Im hoping its the carb jetting/settings since I have to way advance it to get it to run better and no building up on the plugs. Also hoping the low cylinder is just due to not broken in yet.

 

[ba123]

When I first stabbed the dizzy I checked TDC by finger over #1 checking for compression and seeing both valves closed on #1 with valve cover off. Last night I was double checking and it is hard to tell if on compression stroke or exhaust stroke. Added to that, my new HB has three sets of timing marks for various set ups so its tricky. I ran out of time last night and plan to triple check everything tonight/tomorrow.

https://professional-products.com/p...y-small-block-ford-28-4-oz-in-harmonic-damper

Yeah, it would obv make a ton of difference if you set it while not in the correct stroke/cycle.

If you have the valve cover off, you should see the intake valve open (closest to front of engine) and then close (this is the compression stroke) and then the exhaust valve open and then close (this is the exhaust stroke). The intake valve opens to allow the fuel into the cylinder and then closes for combustion, and then then exhaust valve opens to let the exhaust out.

To be sure of TDC in the correct stroke, you can get a piston stop/tdc indicator, or there are a number of old school ways (finger, wadded up piece of shop towel, screwdriver in hole...) but since you aren't sure of the marker being accurate, I'd say get a tdc indicator.

 

[Ol'Blue]

So, Last night I went through the process of finding TDC, making sure I had the right timing marks on the HD, checking firing order and a bunch of other stuff. Fired up and still running rough. Grabbed the brake cleaner and started spraying around the carb base and RPMs jumped up (dont get excited). Definitely a leak. Had a couple beers and went to bed. Too late to run it.

This morning replaced the carb gaskets and immediately I could hear a difference. Let it warm up some then went for a drive. Was driving like a champ! (still not time to get excited). Drove for about half a mile and starts running rough again!

Bring it back home thinking for sure it was a carb gasket but this time no change in idle with brake cleaner. Also sprayed all around the intake manifold. So I checked all the vacuum hoses. Except for the hose at the trans, too hot to check yet. I checked timing, loose plug wires and all the other usual stuff and still no change.

Odd because its acting exactly like it did with the vacuum leak.

Im stumped, but that few minutes when it was running well was sweet and now Im pretty sure I can rule out a timing issue and firing order.

 

[Ol'Blue]

Pulled the vacuum line off the trans where it connects under the trans and fuel came out. Im thinking when I replaced the carb gasket I could have tilted the carb and gas ran into the vacuum line?

I cleaned everything up, check the line for leaks and put it back together with no improvement.

 

[DirtDonk]

Are you sure it was fuel? Did it have a reddish tint to it, like it could’ve been transmission fluid? That’s a common failure of a modulator where the inner diaphragm leaks and transmission fluid get sucked into the modulator and the vacuum line.

 

[Ol'Blue]

Are you sure it was fuel? Did it have a reddish tint to it, like it could’ve been transmission fluid? That’s a common failure of a modulator where the inner diaphragm leaks and transmission fluid get sucked into the modulator and the vacuum line.

Yes definitely fuel.

 

[Ol'Blue]

I got ahold of Carburetors Unlimited and Bruce gave me some troubleshooting tips to try. Fingers crossed.