Engine stalls and will not idle at low rpm - Pontiac GTO Forum
User Tag List

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 13 (permalink) Old 05-03-2017, 07:00 AM Thread Starter
 
Brian O'Malley's Avatar
 
Join Date: May 2017
Location: Long Island NY
Posts: 5
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Engine stalls and will not idle at low rpm

I have a 68 GTO, 400 motor with TH400 transmission. Car will not idle below 1100, stalls when shifted into drive. I have replaced cap, rotor, wires, pulled carb apart and cleaned it out. Had no fuel filter when I bought it a couple weeks ago so I installed one before I cleaned out he carb. Can't find any vac leaks, adjusted fuel/air mixture. Need help!!
Brian O'Malley is offline  
Sponsored Links
Advertisement
 
post #2 of 13 (permalink) Old 05-03-2017, 10:59 AM
 
pjw1967's Avatar
 
Join Date: Mar 2014
Location: The Woodlands, TX
Posts: 440
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 10 Post(s)
I had a vacuum leak that I couldn't hear. Same symptoms. Friend of mine brought over a Pontiac engine guy. First words out of his mouth were "I don't know what else is wrong but you have a vacuum leak". Turns out the nipple for the PCV line in front of the carb was loose in the manifold. Not much, but enough. JB Weld'd it in and no more leak. A few years later, a little "T" connector that supplied the a/c dashpot worked loose. Milder symptoms. Found it and snugged it up. Good luck.
pjw1967 is offline  
post #3 of 13 (permalink) Old 05-03-2017, 04:02 PM
 
leeps's Avatar
 
Join Date: Apr 2011
Location: CA
Posts: 92
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Garage
IF you have a Pertronix or MSD electronic distributor and a poor performing coil, that would happen. Even if you have factory distributor, your coil could be weakening at lower idle and not supplying enough charge. I had this happen with a Pertronix distributor, swapped the coil (to their Flamethrower coil) and never had another issue.

Torque (tork), n: 1. The tendency of a force to rotate the body to which it is applied. 2. See also: GTO
leeps is offline  
 
post #4 of 13 (permalink) Old 05-04-2017, 05:58 AM Thread Starter
 
Brian O'Malley's Avatar
 
Join Date: May 2017
Location: Long Island NY
Posts: 5
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Not sure what brand distributor but have Accel HEI, If i set idle timing to 12 degrees I only have 5 in of Vac. I have to advance the timing up to 20+ at idle just to get 10-12" of vac. Not sure if the timing is jumped. I will check compression today and see where I stand there. Ran acetylene around the intake and carb and found no apparent leaks, RPM's didnt even jump when I ran acetylene direct into the carb. I will pull valve covers today as well to see if I have and broken valve springs or if anything looks f'ed up in there. I have a 67 tri-power manifold and carbs that I am going to rebuild to see if that helps but I am waiting on rebuild kits to show up. This thing is kicking my ass. If the distributor is set off a tooth, would that cause a low vacuum condition? I only seem to have decent power if I am on the highway, Low end seems to be lagging.
Brian O'Malley is offline  
post #5 of 13 (permalink) Old 05-04-2017, 11:11 AM
 
leeps's Avatar
 
Join Date: Apr 2011
Location: CA
Posts: 92
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Garage
Hi Brian,

Unfortunately, a vacuum expert, I am not. I am dealing with that in my 69 now. From what you have said and assuming over 1000 rpm it runs good, I would suspect the carb. I know you said you took it apart and cleaned it out, but it seems it is not delivering the fuel it needs at idle.

I doubt it is the fuel pump, but you can install a clear filter in line and validate the flow. I still think the coil could be letting you down at idle, BUT from what you said, it dies immediately if the idle is set below 1000 rpm. My experience with my coil was like all electrical, it was not an immediate response. It was intermittent. If you are dialing down the rpm at idle and it quits (and as you said its a dog on low end) it seems like the carb to me.

But I am not an expert, just been around the block. Finally, your "67 tri-power manifold" isn't a 67. I don't think any Pontiac had trips in 67 and I know the GTO did not. That's not important, just so you know


Good luck, keep us posted.

Torque (tork), n: 1. The tendency of a force to rotate the body to which it is applied. 2. See also: GTO
leeps is offline  
post #6 of 13 (permalink) Old 05-04-2017, 12:37 PM Thread Starter
 
Brian O'Malley's Avatar
 
Join Date: May 2017
Location: Long Island NY
Posts: 5
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Correct, the tri-power is a 66
Brian O'Malley is offline  
post #7 of 13 (permalink) Old 05-04-2017, 06:23 PM
 
Lemans guy's Avatar
 
Join Date: Oct 2014
Location: Nashville, Tennessee
Posts: 737
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 70 Post(s)
Brian. a low vacumn reading is consistent with a vacumn leak at intake...

somewhere,...likely spots are where you checked, around intake gasket,..at base of carb, vacumn hoses to blend doors through firewall to brake booster and to PCV. ///

you can just clamp those off for a few minutes as a test....and see if there is any changes...if so remove one by one and zero in....

just make sure that you remove them so you have brakes and crankcase ventilation.

also your throttle valve may be open too much allowing too much air right there,....mixture may be off..

the best way to find a vac leak is with a smoke machine and most garages have them....they will show up very small leaks.

as for distributor being off a tooth, can easily happen and distributor gera can e put on wrong as well and that knocks it off a tooth....

have you had the dist out? or the Gear off? if so it may bear rechecking...

Also is your wiring to distributor correctly powered. Here is why, on that car it was points, a white cloth covered "Ballast" wire that runs at firewall to Dizzy is the coil is the "run " wire, but the "Ballast" aspect means it drops the voltage from 12 to 9 or even 8.5......so the points don't burn...

The HEI's take the full 12 volts and coils operate between 8 to 18 give or take a volt.....if you did not correct that, or PO did not it will make the car quit or run bad....just a place to make sure, ...

If you have a garage nearby you can have it smoke tested might be a good idea, chasing vac leaks is very frustrating....

hang in there you will get it perseverance pays off!
Lemans guy is offline  
post #8 of 13 (permalink) Old 05-05-2017, 05:10 PM
 
leeps's Avatar
 
Join Date: Apr 2011
Location: CA
Posts: 92
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Garage
Brian, meet my 'vacuum guy' from another thread!

Torque (tork), n: 1. The tendency of a force to rotate the body to which it is applied. 2. See also: GTO
leeps is offline  
post #9 of 13 (permalink) Old 05-07-2017, 07:43 PM Thread Starter
 
Brian O'Malley's Avatar
 
Join Date: May 2017
Location: Long Island NY
Posts: 5
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Ok, got into it today. Removed distributor and reset, I thought maybe it jumped time but seems like it was OK. Ran compression test and had 120psig
on all cylinders except 5 which was 112. Pressure tested the #5 cylinder and was passing air through the carb with valves closed, opened the valve covers and found all the rocker bolts made up all the way, adjusted the rocker bolts and it held air much better, didn't feel anything passing through the carb anymore, loosened up the all the rocker bolts until they started knocking, then tightened it up a half turn each. Next thing it was like whack-a-mole and had to keep adjusting all rockers until they were once again tightened up all the way. I am going to order new lifters and remove the intake and valley. Hopefully the cam is in good shape still. In my head I'm thinking with the rocker bolts tightened up all the way, the springs were tightened up too much causing the valves to not close properly which in turn is only giving me 12' of vacuum with the timing advanced to over 20 degrees BTDC just to keep idle. Any feedback will be greatefully appreciated as I am a plumber, not a mechanic.
Brian O'Malley is offline  
post #10 of 13 (permalink) Old 05-08-2017, 03:05 PM
 
Lemans guy's Avatar
 
Join Date: Oct 2014
Location: Nashville, Tennessee
Posts: 737
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 70 Post(s)
I think you may be right on it as your plumbing diagnostic skills have to be good as well! just instead of water you have air, and I agree thst if valves were not totally shut poor vac at the intake is a result.

you will get a very smooth idle on these cars at 20 BTDC, but that should be with 10 base and 10 from the vac can....

so if you test and your smoothest idle is at 20 degrees at base with vac disconnected you are on the right track, don't leave it there as your centrifigal and base should total 36......34 to 38 ok...

but you dial in the timing after you get that vac right and the idle running.

super car!.....and great plumbers are smarter than the rest of us! lots of knowledge and technique in there....
Lemans guy is offline  
Sponsored Links
Advertisement
 
Reply

  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO General Discussion

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Pontiac GTO Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Low rpm's Alex McCoy Service, Maintenance and Technical Discussion 3 12-07-2015 03:22 PM
1970 GTO: Why are RPM so high when speed is low? TheBestVMan 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring 22 02-29-2012 01:06 PM
loose oil pressure at low rpm?? skapegoat 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring 10 10-31-2011 06:28 PM
Engine Stalls When Gas is on 1/4 or less LSX Service, Maintenance and Technical Discussion 6 10-02-2011 09:23 PM
HP Production Low in 3.5k+ RPM davidbutzin Service, Maintenance and Technical Discussion 6 09-09-2010 06:58 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome