Engine Help on dead cylinder

luisjluis1

Member
Dec 4, 2020
33
4
18
19
Columbia, Mo
I bought a 1990 stang as a project. My intent was to hop the motor up a little and have some fun with a screaming 5.0. Since I was going down and dirty with the project I wanted to convert to carb from EFI and make everything more simple. I bought an intake and carb kit from summit, deleted the CPU, got a new 65,000-volt distributor and a new fuel pump. As I was doing stuff to the body I thought it would be a good idea to tear the motor down and put a motor freshen-up kit in it. It consisted of all new rings and bearings for the crank and gaskets. Everything went on nice and by that time I was ready to drop the motor in and get it started. It fired right up but I struggled with getting it to idle good. I thought it was maybe just the carb needing to be adjusted but I didn't have any luck with that. After finally seeing that the headers on some of the cylinders (1,2,6,8) looked completely new (not getting hot) I knew there was a problem. I took the plug wires off those cylinders while it was running and it made no difference. I put new plugs in it hoping that would fix it but it did not. I then tested compression, it had a good 150psi (10:1) in each cylinder. Then I pulled the vacuum, it had a good steady 16in at 800rpm. After seeing those components were in the clear I thought it could be the distributor. I bought a spark plug resistance tester and that proved a had good solid spark in every cylinder. Then I pulled the valve covers off and reset the lash and made sure the valves were opening and closing as they should. Everything looked fine. I'm very stumped on why some of the cylinders are dead. If anyone could point me in the right direction that would be great. Thanks, Luke.
 
  • Sponsors(?)


HemiRick

I'd be looking at jacking under the house
Jun 28, 2020
764
288
73
58
Memphis TN
All a cyl needs to fire is fuel, compression and spark at the right time.....what's missing?
 
  • Like
Reactions: 1 user

luisjluis1

Member
Dec 4, 2020
33
4
18
19
Columbia, Mo
I've checked compression, spark and it's in time. No real way to check if it's getting enough gas but one would think if some cylinders are getting gas then all should be. Then again it's a brand new carb and intake. Could an intake leak be causing this problem?
 

HemiRick

I'd be looking at jacking under the house
Jun 28, 2020
764
288
73
58
Memphis TN
Yes spray some flammable liquid (carb cleaner, ether) around the intake to head gap and see if anything changes
 
  • Like
Reactions: 1 user

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
20,342
6,908
203
polk county florida
I doubt a carburetor will cause some cylinders to 'fire' and others not, do those plugs look wet?
I don't understand why people think a carb swap from efi is making things easier but that's a conversation for another time.
 
  • Like
Reactions: 2 users

luisjluis1

Member
Dec 4, 2020
33
4
18
19
Columbia, Mo
I doubt a carburetor will cause one side to not 'fire', do the plugs on that side look wet?
I don't understand why people think a carb swap from efi is making things easier but that's a conversation for another time.
The ones that arent firing are more wet than the others. I want to think the problem is an intake leak but it had a steady vacuum. Thanks.
 

luisjluis1

Member
Dec 4, 2020
33
4
18
19
Columbia, Mo
I switched wire from one that was good to the bad one, that did nothing. I bought a cheap distributor with a coil built-in off eBay. I just bought the same plugs it had in it before when it was running. Let me see what they are.
 

luisjluis1

Member
Dec 4, 2020
33
4
18
19
Columbia, Mo
I don't know what distributor you have but I would check wires and cap.
What plugs you running.
This is a picture of a plug on one of the bad cylinders. dark and wet. The plug is a champion 3018. Thanks
 

Attachments

  • 0.jpg
    0.jpg
    45 KB · Views: 21

Monkeybutt2000

Advanced Member
Aug 11, 2019
621
409
73
50
Lafayette,IN
I know you said you checked the plugs with a tester but. I would pull all individually,hook up to their appropriate wire and ensure they are sparking.
 

HemiRick

I'd be looking at jacking under the house
Jun 28, 2020
764
288
73
58
Memphis TN
right with a normal dual plane intake thats how things are fed.....1 bbl feeds 2 cyl on both sides.
 

luisjluis1

Member
Dec 4, 2020
33
4
18
19
Columbia, Mo
right with a normal dual plane intake thats how things are fed.....1 bbl feeds 2 cyl on both sides.
Ive seen both bbls on the primaries working. I know that the secondaries don't work but I was just going to cross that path when I get to it because the car will idol with only primaries working.
 

luisjluis1

Member
Dec 4, 2020
33
4
18
19
Columbia, Mo
I know you said you checked the plugs with a tester but. I would pull all individually,hook up to their appropriate wire and ensure they are sparking.
Its confusing because we tested all the plugs outside the cylinders and they worked just fine. Could the compression be killing the spark if it's not strong enough?