292 not firing on cylinders 5 & 6 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

RThree · 03-28-2019, 12:00 AM

Hey guys I need some help... my stock 292 is running like crap. You can hear it here

https://youtu.be/BLo_5nW8LGE

We tested the exhaust manifold with a heat gun as it warmed up and it seemed that cylinder 5 and 6 are not firing. We then pulled the spark plugs wires for 5 and 6 as it was running and nothing changed confirming that they are not firing.

Cylinders 5 and 6 have 120psi and 135psi of compression respectively which seems good and inline with the others, we have confirmed solid spark on each spark plug from the HEI and the mono jet carb has been rebuildt / readjusted to spec and the other 4 cylinders are firing right along.... so we’re lost HELP!

Any suggestions?

RustyPile · 03-28-2019, 01:31 AM

Check the firing order.. Those two wires could be crossed...

bill3rail · 03-28-2019, 09:18 AM

Quote:

Originally Posted by RustyPile

Check the firing order.. Those two wires could be crossed...

Check valve adjustments. Check valve movement. Could be a hung exhaust valve.

Bill

RThree · 03-28-2019, 12:25 PM

Quote:

Originally Posted by bill3rail

Check valve adjustments. Check valve movement. Could be a hung exhaust valve.

Bill

Ok, so I triple checked the firing order and everything is correct.

I previously took the valve cover off to see if i could find anything obvious but did not do any valve adjustments. This engine ran great but then sat for a couple years. i would assume the valve adjustment wouldn't change but i check that tonight.

-PR

RustyPile · 03-28-2019, 12:40 PM

Quote:

Originally Posted by bill3rail

Check valve adjustments. Check valve movement. Could be a hung exhaust valve.

Bill

OP says 5 & 6 have 120 lb + compression.. Hung valve wouldn't have those compression numbers..

5 & 6 cyl are fed through the same intake port.. Look for vacuum leak on that runner.. Could be intake gasket failure or crack in the runner itself..

RThree · 03-28-2019, 01:01 PM

Quote:

Originally Posted by RustyPile

OP says 5 & 6 have 120 lb + compression.. Hung valve wouldn't have those compression numbers..

5 & 6 cyl are fed through the same intake port.. Look for vacuum leak on that runner.. Could be intake gasket failure or crack in the runner itself..

Thanks for the suggestion!

I had a thought that maybe i left a rag and it got sucked into the intake runner that feeds 5 & 6 when i rebuilt the carb. So I took a scope and feed it down that runner and found no blockage, but i wasn't looking for a crack or seal. Another thing ill take a look into tonight.

Ozark Tim · 03-28-2019, 02:38 PM

You said you have compression and you are certain you have spark so as long as you are getting fuel and its open and not blocked as you said through the intake it should work
A stuck open valve or broken valve spring would show 0 or very little compression (I have seen a broken spring on a 292 before and there was 0 compression)
Double check the plug wires are not switched and that you for sure have spark

bill3rail · 03-28-2019, 03:57 PM

Quote:

Originally Posted by RustyPile

OP says 5 & 6 have 120 lb + compression.. Hung valve wouldn't have those compression numbers..

5 & 6 cyl are fed through the same intake port.. Look for vacuum leak on that runner.. Could be intake gasket failure or crack in the runner itself..

I missed that.

RThree · 03-28-2019, 06:01 PM

Quote:

Originally Posted by Ozark Tim

You said you have compression and you are certain you have spark so as long as you are getting fuel and its open and not blocked as you said through the intake it should work
A stuck open valve or broken valve spring would show 0 or very little compression (I have seen a broken spring on a 292 before and there was 0 compression)
Double check the plug wires are not switched and that you for sure have spark

Yup, I already checked rechecked the firing order is correct and that 5 and 6 wires specifically are correct. ( i was really hoping it was that simple!) I have repeatedly confirmed i have spark for all cylinders. I ran a 14 gauge unfused 12v power source to the HEI, replace all spark plug wires, replaced spark plugs, and replaced the ignition coil in the HEI. I now have a stronger spark that before but still no ignition in cylinder 5 and 6.

i will be looking for a crack or bad gasket in the intake manifold tonight. I really hope its not a crack, yet i really hope i find something so i atleast have an answer.

-PR

**slomotion** · 03-28-2019, 06:36 PM

Are the lifters good? Sitting for a long time they may have bled down.

**Steeveedee** · 03-28-2019, 07:05 PM

Spray some WD-40 or something like it at the intake runner where it meets the head and see if the idle changes. That will pinpoint a leak if there is one there. Spray up from the bottom, as well. I've seen where they leak at the bottom and spritzing on top may not do the trick.

RThree · 03-28-2019, 11:13 PM

Quote:

Originally Posted by Steeveedee

Spray some WD-40 or something like it at the intake runner where it meets the head and see if the idle changes. That will pinpoint a leak if there is one there. Spray up from the bottom, as well. I've seen where they leak at the bottom and spritzing on top may not do the trick.

Alright ran this test tonight and got some results! I sprayed some carb cleaner at the top and bottom of the intake runner to cylinder 5 & 6 and it definitely effected the idle speed (more so when spraying at the bottom) So I’ll get another intake/exhaust manifold gasket installed and see if that’s the main issue. Fingers crossed!

Thank you so much guys for the support! I’ll keep you posted.

-PR

**Steeveedee** · 03-29-2019, 10:48 AM

Quote:

Originally Posted by RThree

Alright ran this test tonight and got some results! I sprayed some carb cleaner at the top and bottom of the intake runner to cylinder 5 & 6 and it definitely effected the idle speed (more so when spraying at the bottom) So I’ll get another intake/exhaust manifold gasket installed and see if that’s the main issue. Fingers crossed!

Thank you so much guys for the support! I’ll keep you posted.

-PR

RThree · 04-01-2019, 04:47 PM

Well I spent Saturday replacing the intake and exhaust manifold gasket and that solved the issue! Were now firing on all cylinders and running so much better. Thank you guys for the help!

Here is how it sounds now: https://youtu.be/Pocn6DxMCxk

-PR

weq92f · 04-01-2019, 06:23 PM

That sounds good! Nice truck.

-klb

**Ol Blue K20** · 04-01-2019, 06:43 PM

Sounds pretty good, I'm glad it's solved

**NewBayColony** · 04-01-2019, 09:53 PM

Love the 292!

03-28-2019, 12:00 AM	#1
RThree Registered User Join Date: Jun 2014 Location: Santa Rosa, CA Posts: 124	292 not firing on cylinders 5 & 6 Hey guys I need some help... my stock 292 is running like crap. You can hear it here https://youtu.be/BLo_5nW8LGE We tested the exhaust manifold with a heat gun as it warmed up and it seemed that cylinder 5 and 6 are not firing. We then pulled the spark plugs wires for 5 and 6 as it was running and nothing changed confirming that they are not firing. Cylinders 5 and 6 have 120psi and 135psi of compression respectively which seems good and inline with the others, we have confirmed solid spark on each spark plug from the HEI and the mono jet carb has been rebuildt / readjusted to spec and the other 4 cylinders are firing right along.... so we’re lost HELP! Any suggestions? __________________ - 1972 K20 Longhorn, 4wd conversion. "TAWNKAA" Project. 292ci Inline 6 / '93 NV4500 / 32 spline 205 TC / Dana 60s front & back / rear Detroit Locker / 4.10 Gears / 35" BFG MT KM2 / 4" Tuff Country lift. "TAWNKAA"Build Thread http://67-72chevytrucks.com/vboard/s....php?p=6823933 - 1970 C10 Lonbed, 292ci Inline 6, 3 on the tree, stock.

03-28-2019, 01:31 AM	#2
RustyPile Registered User Join Date: Dec 2017 Location: Elkhart, Texas Posts: 1,865	Re: 292 not firing on cylinders 5 & 6 Check the firing order.. Those two wires could be crossed...

03-28-2019, 02:38 PM	#7
Ozark Tim Registered User Join Date: Aug 2004 Location: Oakville, MO Posts: 1,018	Re: 292 not firing on cylinders 5 & 6 You said you have compression and you are certain you have spark so as long as you are getting fuel and its open and not blocked as you said through the intake it should work A stuck open valve or broken valve spring would show 0 or very little compression (I have seen a broken spring on a 292 before and there was 0 compression) Double check the plug wires are not switched and that you for sure have spark

03-28-2019, 06:36 PM	#10
slomotion Old Duffer Join Date: Mar 2003 Location: Maine Posts: 1,822	Re: 292 not firing on cylinders 5 & 6 Are the lifters good? Sitting for a long time they may have bled down. __________________ '68 Short C20 Flatbed Dually w/ 292 4bbl, Langdon cast headers, and WC T5 trans. '81 G10 Shorty Van "Good judgement comes from experience, and a lot of that comes from bad judgement." Will Rogers "Under promise, then over achieve."

03-28-2019, 07:05 PM	#11
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,785	Re: 292 not firing on cylinders 5 & 6 Spray some WD-40 or something like it at the intake runner where it meets the head and see if the idle changes. That will pinpoint a leak if there is one there. Spray up from the bottom, as well. I've seen where they leak at the bottom and spritzing on top may not do the trick. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

04-01-2019, 04:47 PM	#14
RThree Registered User Join Date: Jun 2014 Location: Santa Rosa, CA Posts: 124	Re: 292 not firing on cylinders 5 & 6 Well I spent Saturday replacing the intake and exhaust manifold gasket and that solved the issue! Were now firing on all cylinders and running so much better. Thank you guys for the help! Here is how it sounds now: https://youtu.be/Pocn6DxMCxk -PR __________________ - 1972 K20 Longhorn, 4wd conversion. "TAWNKAA" Project. 292ci Inline 6 / '93 NV4500 / 32 spline 205 TC / Dana 60s front & back / rear Detroit Locker / 4.10 Gears / 35" BFG MT KM2 / 4" Tuff Country lift. "TAWNKAA"Build Thread http://67-72chevytrucks.com/vboard/s....php?p=6823933 - 1970 C10 Lonbed, 292ci Inline 6, 3 on the tree, stock.

04-01-2019, 06:23 PM	#15
weq92f Registered User Join Date: Oct 2016 Location: Dallas Texas Posts: 3,267	Re: 292 not firing on cylinders 5 & 6 That sounds good! Nice truck. -klb __________________ 67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold

04-01-2019, 06:43 PM	#16
Ol Blue K20 Proprietor of Dale's Corner Join Date: Nov 2012 Location: Vacaville , CA Posts: 16,271	Re: 292 not firing on cylinders 5 & 6 Sounds pretty good, I'm glad it's solved __________________ "Some Days Chickens And Some Days Feathers" Dale XNGH ECV Sam Brannan 1004 R.I.P. 67ChevyRedneck R.I.P. Grumpy Old Man R.I.P. FleetsidePaul

04-01-2019, 09:53 PM	#17
NewBayColony Senior Member Join Date: Mar 2017 Location: Northbridge,MA Posts: 496	Re: 292 not firing on cylinders 5 & 6 Love the 292! __________________ 72 C20 292 3OTT 77 GMC 2500 4x4 Longstepper 350 4sp 50 3100 ex Airforce/Town of Mendon fire truck 72 GMC 1500 2wd short stepside 250 4sp 78 GMC 2500 4x Longstepper 292 4sp 54 6400 Chevy 5 window 4 sp 2sp vac rear end Shell oil truck/dump truck (Norman)



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