Engine not stay running at idle
 

66 GP - starts fine, smooth, but will not stay running unless keep gas petal down or feather it. As soon as try to idle, stops. Have been thru the fuel system. Gas tank, sending unit restored, tri-powers rebuilt, new fuel lines - pump working fine and gas getting to carbs no problem. played with idle screws, but even when at a too high idle (car roaring) it will die as soon as foot off gas. someone in the past had put a resistor block on firewall that has a wire from starter to coil, then to resistor and back from other resistor plug to negative coil wire then to distributor. My 65 2+2 does not have this so unhooked resistor and it acts the same. would a bad coil affect running after started? Not sure what else to try?

2 thoughts: Carb linkage/idle screw on linkage not adjusted right or maybe Vac. leak? Try disconnecting all Vac. lines & plugging w/ a screw etc. & see what happens.

Have had this happen before, but will have to think longer to remember the cause in my case.

Thanks - tried not any difference, but some of the hoses are very brittle/old - I'll try replacing and see if there might be a crack I can not see. They need it anyway. next weekend project.

I vote vacuum leak 100%. While the engine is revving, it produces enough vacuum to pull fuel/air through the carbs. At idle, the leak is so bad, that it's pulling vacuum through the leak, and not the carbs.

MK

If you block the air horn on all 3 carbs and the car stays running, you have a vacuum leak.

Try disconnecting and blocking the PCV @ the intake.

I hate to say it, but if you have trips, you might have to do a block-off plate on the 2 outboards & run with center only to narrow it down. Block everything off on vacuum side as described above in addition to that & see if it solves Prob. It's part of the joy of 3 carbs! The base gaskets can leak & cause a Prob.

Get it warm and running as slow as it will continue to run. Spray a little choke cleaner at various places where it might have a vacuum leak. Carb bases, intake manifold to head, hoses etc. When you hit the place where it is leaking the engine speed will increase and smooth out momentarily. Even a power brake booster diaphragm that leaks can be a problem.

Still engine stalling issues
 

Thanks much for all of the advice. Has been very helpful and have fixed some of the issues, but still not quite there. I'm sorry to ask for such basic advice, but would be grateful for some more assistance - helps me learn and keep the pontiac going.

I checked for manifold leaks (none), replaced all of the engine vacuum hoses and there were two that were really brittle and had cracks. The engine now idles ok - the vacuumn gauge is at about 16 in. hg when warmed up. The engine runs fine until put into gear, it then slows and stalls. Increased the idle, but did not make much difference and then when turn ignition off - diesels and knocks. Have to turn off in gear or knocks. Put idle back down where vacuum is at 15 in. hg on the vacuum gauge and it turns off ok without knocking, but will not run in gear. So now it is at a point where it will run at idle, but not in gear.

Dont know if makes difference or not, but plugged end leading to the vacuum advance at the distributor to disconnect, car ran the same.

Anything else to check?

Have you checked the ign timing? Do it with advance hooked up and not.

Also if it's an suto car, make sure the vac lin to the trans hasn't come of the modulator causing it to suck air down low.

Mike

I have not checked the timing - quick question, would it be the same degree timing with the advance on and off? It is an automatic and have replaced the hose to the modulator on the transmission (was oily).

No, normally the older cars run Manifold Vacuum which will advance the timing at idle. Unhooked will drop the timing about 12 degrees. I like 32-36 degrees of total advance, mechanical,base and vacuum combined. That'll change depending on Cam, Head flow numbers, ect. Also be sure the mechanical advance isn't stuck. It needs to advance and return freely. Dwell should be set @ 28-32 degrees. If it's off it will affect timing and that in turn will afect the idle.

To Mike's point - take off the Dist cap & see if the weights and springs are free. They get frozen/rusted in case you are not familiar with these.

Also, even if hose is good could be that modulator is toast.

If the modulator hose is oily, I'd say that the modulator is bad. There shouldn't be oil in the hose.

Does it stall when you shift it into gear, or when you step on the brake?

Maybe your brake booster is bad, and you lose vacuum.

Just a thought.

MK

Is this a new startup or a new problem that ran well in the past? If so what have you changed since it ran well?

Every tuneup begins with ignition, 9 of 10 carb problems are actually ignition problems, it took me many years to understand this concept now its a mantra LOL
Once you have verified 30º dwell, 6º initial and no problems with wires, weights etc under the cap, reconnect vac advance and set idle speed to 650 with motor thoroughly warmed up. Who knows it might help.
It may be informative to, with a helper, have a timing light on while slowly reducing throttle speed to the point of faltering. That would highlight any weird ignition short as rpms change.

Sounds easy when Im way over here typing LOL

Steve - Will this produce white Exhuast smoke the majority of the time?

Might help diagnose.

Yes it could, but it depends on how bad that it is sucking fluid. I have taken many vacuum hoses off cars with leaky modulator diaphrams that did not smoke.

Not sure what year they started using them but by 68 a lot of cars had an anti-diesling solenoid. It's on the throttle linkage and about the diameter of a half dollar and 1 1/2 inches long with a single wire hookup. The solenoid extends when the key is on and retracts when the key is shut off. The idle adjustment is on the solenoid plunger and you adjust the idle with the key on (of course - cause it's running). Then when the key is turned off the plunger retracts to allow the throttle blades to close completely to shut off any air flow that might cause diesling. If this solenoid doesn't work then you will get some of the symptoms you describe.

Thanks all - sounds like I have a lot of things to check. I'll start with the timing/distributor etc. Will tackle next week - going to check out Norwalk.

Actually car has been running crappy for a while now. Started as problems with running terrible when got hot, then stalling whenever at an idle unless under power. Took to mechanic, got better, but idle was too high and dieseled and rough. They did checked over etc...nothing changed. Then I got the 61 Tempest and neglected the 66 GP by letting it sit too long. It always had tripower issues and sitting made them worse. Ended up with the front carb becoming a drinking fountain and gas leaking into valley pan from several spots - so decided to bite the bullet and took off all 3 carbs and sent to Mike Wasson. He found a lot of issues and clogged areas. Put back together, dropped gas tank, had it redone, had sending unit rebuilt, cleaned out fuel lines, replaced all rubber fuel lines. Ran much better, but then ended up with my first post that started this thread. I made assumption that mechanic checked timing and ingition, but after going to parts house several times this weekend because they gave me wrong parts - I am learning not to take it for granted....

Trying to do more inhouse to save money and have been finding some of the mechanics out there only know how to hook up the diagnostic and do not know how to do anything on these old cars. I've got a great book called AutoRepair for dummys from 1976 and that with the chassis manual and help from you all at the forum seems to be working out pretty good so far. Thank you very much for all your help.

I've got a great book called AutoRepair for dummys from 1976 and that with the chassis manual"

good to have those and check also used book store and Amazon and ebay for a MOTORS Manual that covers 66 they go in 8-10 yr increments of coverage. A greasy dogeared copy will go from 25-40 bucks. Not because they are antique but because they are so darn useful. A lessor but still effective manual is the Chiltons, often for 15$
A CD copy of the original Pontiac factory manual can be had for $35-50. Public Library have manuals you cant check out but can make copies of pages from.

Need assistance - 66 GP stalling when hot
 

Appreciate all of your prior suggestions and there has been improvements. However still having issues. Here is what it is still doing:
It seems to be a little too cold natured - takes it a while to warm up and to stay running.

After driving it awhile - at least 15 minutes, when idling at a light, can hear it start to have a very slight stumble, doesnt feel it like it is missing, but can hear the change in the engine sound. if I put it in neutral, it smooths out and there is no problem when under power. It continues to get worse as drive and if do not shift into neutral, it will stall. (I noticed that the vacumn gauge shows in the yellow around 8, very close to the power orange portion. When in neutral, the vacumn goes to the green around 12-16). After it stalls, when turn key, does not start unless give it more gas. Then it will start....anyway he issue is it is still stalling when it gets hot.

Car is 421 tripower, cam is one level up from stock, power brakes, a/c, fuel system recently redone from tank to tripower, new coil, wires.

Background from early post- items done since then:
-timing is fine
-replaced vacumn lines in engine compartment (were some hard ones)
-replaced brake booster line as it was pinching closed
-had solenoid kickdown installed - cold starting is better than before
- new distributor cap, coil, points
- exhaust looks ok, not white
- replaced some of the vacumn lines under the dash for the heaters. the others seems ok, but could not follow all of them.
- The guy that rebuilt my motor prior found that the tripower manifold had a hairline crack under the center carb and on the side, that would open when hot. Replaced with a spare manifold that was ok.

Shouldn't the vacumn at idle be higher? Shouldnt it be in the green at idle and move to the power when accelerating etc.?? I really thought the cracked manifold was the problem. I think there were a lot of issues and it does run a lot better, but still not quite right.

Any suggestions? :confused:

Is fuel entering the front/rear carbs when it isn't supposed to? If so, disconnect the fuel lines from the front/rear carbs and see if this helps. I had what seems to be the exact same problem with one of my 3x2 cars and it was fuel entering the secondary carbs when it wasn't supposed to enter.

If the car is running properly, you should have 15-18" of vacuum at an idle if you have a somewhat stock motor.

I'm thinking in line with stevep. you can pull the air cleaner(s) off after it has died and look for or stick your finger down the end carbs and see if one is wet.

If you even think the vacuum modulator is leaking on the transmission, change it. Should cost about $10 and about a pint of ATF when you change it. Make sure the old o ring comes out, they like to stay in the case.

I would vote with this also if you haven't put a new vacuum modulator on the transmission yet try that. From what you are saying it has something to do with the transmission if it idles fine in neutral but the engine dies when you put it in gear. This assuming idle speed is adequate and from what you describe it is. And it sounds like it has to do with something other than the load the transmission puts on it if it happens when things have warmed up but doesn't do it until then as the load stopped and in gear would be the same cold or hot.

"pull the air cleaner(s) off after it has died and look for or stick your finger down the end carbs and see if one is wet.
If you even think the vacuum modulator is leaking on the transmission, change it. Should cost about $10 and about a pint of ATF when you change it. Make sure the old o ring comes out, they like to stay in the case"

Had a "fun" afternoon. Long story short, did not seem to have wet end carbs, actually the center was not all that wet either. Maybe not enough gas from the fuel pump?? What is the fuel pump model number that should be used on 421 Tripower? Changed out the vacumn modulator. The vacumn seemed to bump up a bit, but after it got hot (approx 15 min), when put it in drive with foot on brake and sat there for awhile (like at a long light) - it would start to stumble a bit, noticed a drop from 10-12 HG to 10-8, then it would go back up again to 10-12, after a bit, it did a big stumble under 8 hg and died.

Story of the afternoon - started off good, Had two projects to work on, the suggestions for the GP and flushing the fuel lines on the 2+2 and getting the carbs off to "61-63". Got the 2+2 carbs off and drained so they could be shipped. Next the GP -struggled getting the bolt off the modulator, but finally got it off. Did not have the drain pan positioned just right and the first blast of tranny fluid went on the floor instead. got the modulator off and took to 3 part houses. Autozone not in computer, not in their warehouse, they dont order...Fine...NAPA - not in computer, trouble finding in book, not sure if they have in warehouse. They suggest trying to find one in a junkyard. WHAT??? Guess lots of 66's lying around in yards. Might as well get my air cleaners there too. Finally O'Reilly had some...back to the house, put it back on and test drove the car- looked promising for a while, then after it warmed up...result noted above :( When cleaning up, pulled the drain pan from under the car and somehow managed to get my hair in the tranny fluid - lovely.
Then back to the 2+2, unhooked gas line at the tank, the rubber hose was cemented to the line - took forever to get it loose, then of course the gas runs all down arm and onto shirt. Unhook the gas line at the fuel pump after fighting with hose clamps that are positioned so only a contortionist can reach with a screwdriver/nutdriver. More gas running down the arms. Blew out the line to the tank, ran gas thru the fuel pump to flush it out and got everything back together. Did not notice any crap in the fuel - so the carb crud must be old. Sending the carbs out tomorrow. I now smell much better after cleaning up and don't recommend tranny fluid and gasoline for your hair or skin treatments :)

If anyone has any other ideas for the GP stalling problems, let me know and will try that next weekend...

I'd also check/clean/replace the PCV hose and valve. Also, the pan grommet cracks and gets hard/brittle and leaks lots of air into the engine.

Check out the adjustable kind of modulator for the TH400. I have found those are pretty available. Plus, fun to tinker with. Great with the street/strip kits. Sorry a little late with that, but they were all I could find, so I figured that is what you would end up with.

Last time I fiddled with my trans I realized there was slightly too much fluid in there. I had put a drain plug in, so it will be easy to adjust right? Well, thought I had let it cool down enough, but got the crap scalded out of me and near the usual ATF bath even with the drain plug! So... I feel your pain.

pontiaclady. Next time I make a suggestion like that I'll include part numbers. NAPA should have had a TM15 or maybe an ATP17499. Autozone I want to say is a 1-401 I'll have to look at work tomorrow. Last time I got one for my 65 I think I had to tell them it was a 71 to get the dang thing.

LASJayhawk walks into a Autozone. "Hi, i need a pilot bearing for a 65 Pontiac catalina with a 421 and a 4 speed."

AZ clerk: (looks at computer) "we dont have that"

LAS: "Ok I need a pilot bearing for a 68 Pontiac GTO with a 400 and a 4 speed."

AZ clerk: (looks at computer) "It's $24.95"

LAS: "Amazing since it's the same freaking part."

pontiaclady,

Haven't you ever noticed how car people have the healthiest complexions? It's due to all those years of grease and dirt acting as an exfolient on the skin. That oil and trans fluid is like a sealer, keeping all your moisture in! We all have that youthful glow and we all owe it to working on our cars!

Your satisfaction meter is going to go off the hook when this gets worked out too. Guaranteed to make the frustration all worth it.

I didn't read the whole thread but have you checked the dwell?

Haved you checked the vacuum lines that run to the heater/AC controls under the dash? I had an issue like yours once and it turned out to be a vacuum line under the dash that I accidentally knocked loose while changing some dash lights.