# low vacumn pontica 400



## trainman115 (Jul 31, 2014)

Hi I am need to this form and I have a problem with my GTO its a 1969 with a 400 A/T my problem is I got one or two cyc that are not firing when the motor is running I can take some of the plug wires off and it does not make a difference I have spark in both plug and wire I have between 150-200 compression in each cyc timing is correct the only thing I see that might be wrong is I have low vacumn I tryied the torch test no difference at all no matter where I go with it I have no clue on where to go from here any idieas will be greatly appreciated Thanks trainman115


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## Roger that (Feb 6, 2010)

If your taking the spark plug wires off when the engine is running and you are not seeing a change in the engine's behavior, I would say you have some very high resistance in your plugs and or wires.


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## trainman115 (Jul 31, 2014)

Thanks for the reply its only in one or two not all of them its a mystery Ed


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## trainman115 (Jul 31, 2014)

what should I do or look for Thanks again Ed


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## ALKYGTO (Mar 29, 2010)

I'd just keep it simple Ed. Have you changed anything recently? Might want to replace those wires or switch them to another cylinder if they won't reach and see if anything changes. Check the distributor cap and rotor and see if anything looks burnt, dirty or just iffy. Another suspect is the condenser if you still have points or the module in a HEI. Weak coil? Check and verify all connections there.

Did you do that compression test before or after the "issue"? Just asking because I've seen a bent valve act exactly how yours is. 


And make sure you only change one thing at a time so you know what fixes it.


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## Rukee (Feb 8, 2007)

Do those 2 cyc have the plug wires crossed??


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## topfuel67 (Dec 23, 2008)

I've had that problem and it was bad lifters.


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## geeteeohguy (Feb 2, 2008)

I've seen engines with OK static compression have dead cylinders running due to flat exhaust lobes on the camshaft. OK--- this is very, very important: Does it do it _just_ at idle, or is it missing/rough at _all_ speeds? Rough at idle only= vacuum leak.
Rough at all speeds, loads, etc. means: ignition or mechanical problems.


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## trainman115 (Jul 31, 2014)

*Gto*

Hi guys thanks for the info I do not have wires crossed thats for sure It seems to run very hot but not showing that on the gauge when you go down the road it seems fine just wont idiel and the sound is not right if you know what I mean I know the intake was changed and a HEI distributor was put in my timing marks are ok I know its the orginal engine to the car by all the matching numbers I guess my next step would be pull the intake off and see whats there I really like to get started restoring my GTO but I like to get her running fine first and boy do I need the parts but anyway this engine is driving me crazy thats for sure Thanks again Ed


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## trainman115 (Jul 31, 2014)

*Gto*

Hi again I just like to add when I shut the car off there is gas vapors looks like smoke coming out of the carb I did try another carb and same difference seems like the gas aint going into cyc its coming out of the top of carb LOL also have to pump the crap out of her to get it to start Thanks again Ed


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## geeteeohguy (Feb 2, 2008)

I will ask again: Does it run rough at idle or at all speeds?


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## trainman115 (Jul 31, 2014)

geeteeohguy said:


> I will ask again: Does it run rough at idle or at all speeds?


Just at idle runs fine when going or giving it gas Ed


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## geeteeohguy (Feb 2, 2008)

Time to look for the vacuum leak. Things to check: hoses, intake runners, carb baseplate. You _did _adjust the carb mixture screws for best idle quality, I hope.


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## trainman115 (Jul 31, 2014)

ya thanks I replaced intake gaskets no leaks anywhere I belive its in the valves I tryied today to adjust them tighten the nut to 20 lbs went to turn the motor by hand went so far and stop seems to me the valve is hitting the piston so I back it up rightaway I took the nut off the rocker and the wsher goes over the stud not sure if its suppose to do that or not my nuts have a shank on them not just a regular nut so I dont know if that the right one or not either the guy who had this before me really messed things up I was hoping the nut was just suppose to go so far and stop and you just torque it to 20 lbs so I have no clue on even what to do next Thanks again for all the help Ed


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