Still having problems with engine dying

[Anonymous]

I had this problem before I left 4 months ago and now that I'm back I'd really like to figure it out.

The problem is this:
I am driving straight about 10mph and then I push the pedal a little further like to get to 20 mph and the engine dies for a quick second and then comes back alive and I can continue on to 20 mph. Its not dying slowly either, its a real quick death. Almost as if its switching to some other electrical connection or switching to another fuel source then it runs fine. I have noticed some "surging" when I'm at higher speeds, just barely noticeable but It runs "weird". It also does the same thing on left hand turns but not right hand turns, I posted the other stuff on top because its probably easier to figure out. I hope this describes it well.

I've changed the following:
Electrical system - Dizzy, spark plugs, and wires still using Pertronix coil.
Fuel system - Fuel pump, fuel hoses, filter and added a psi gauge to check pressure.

I've been searching for a vacuum leak by spraying some carb cleaner around areas where I think it could be and found nothing. Today I put playdoh all over those areas to try to create a seal and nothing changed.
I've played with my timing over and over again.
The carb is spraying fuel its brand new and worked fine before I rebuilt the engine.

Any ideas?

Side note: the engine runs fine (As far as i can tell) just sitting in the drive way idling or even when I rev it up. Seems like its only under a load on the road.

 

[MustangSix]

Sounds like a weak accelerator pump in your carb. Pull the air cleaner and look into the carb. When you open the throttle you should see a good squirt of gas. Without that squirt, the engine will die when you first crack the throttle.

 

[Anonymous]

it works fine when its sitting idling or even when I pump the accelerator arm in the driveway. I've also checked to make sure the squirt comes when I pump it. Seems like it only happens when I'm driving. I just got back from a long drive the stang too, it still acts funny when I'm driving around 60+ mph, kind of like its getting a little more gas for a sec then back to normal, surging.

 

[Anonymous]

Have you checked the float height on the carb or the float needle etc?
It could be that the float is improperly adjusted or the valve could be sticking.
Doug

 

[jahearne]

You said you replaced the dizzy. What did you replace it with? or in other words, do you still have a pre-68 load-o-matic dizzy?
My Ranchero did the same thing and it turned out to be a bad SCV.

Good luck,

 

[Anonymous]

I had the original one but I replaced it for the 68 one after the problem started. I thought that a new one would fix it, but it didn't. I guess its possible to get a bad part from the store, but what are the odds of the same problem from two parts? how would I be able to check to see if the SCV is bad?

jahearne, what were your symptoms?

 

[wsa111]

If you have the junk pertronix II ignition ignitor in your distributor that could be the problem.

When i had the pertronix II in my distributor, my engine stalled when driving or at idle, & or idled rough like running on 3 cylinders.

I went back to the pertronix I & the engine ran to perfection.

I have sinced swaped to a DS II, or a better option now is the DUI from
FSPP. William

 

[Anonymous]

I do believe that I switched over the Pertronix to the new engine, I haven't tried switching back to points to see if that is causing it or not. That might be what I do tomorrow.

Also I have my vacuum hose that is connected to the distributor also connected to whatever the line is that goes to the transmission. What do you think about that? I'm also going to try just hooking up a straight hose from the distributor to the carb tomorrow. I hope I can get this fixed, it makes me nervous to drive off base and I feel like the engine has so much power that can't come out until I fix it.

 

[Anonymous]

my engine ran much better with the vaccum advance coming form the ported vaccum port in the carb and not mainifold vaccum. also check the timing? but sounds to me like a fuel problem of some kind if the accelerator pump is good and the float level is also correct, maybe a vaccum leak?

what is your feul pressure? you said you installed a guage

 

[Anonymous]

I have the gauge after the fuel filter and its reading about 7 psi. I'm hoping that If I try switching back to points that it will fix it. If it does then I might as well switch to the new DUI distributor, then I will have a reason....YES! If not, then.... hmm back to the drawing board. I've checked and checked for vacuum leaks but I just can't find any. Is it weird that the problem hasn't gotten worse? Its still the same problem today as it was months ago, no better, no worse.

 

[JackFish]

Did you check the vacuum advance unit on the distributor?

 

[Anonymous]

as far as sucking on the end of the hose to see if there is any resistance? not yet. I have taken the hose off and the engine will run crappy until I plug it with my thumb.

 

[jahearne]

You guys have been busy...

My symptoms with the faulty SCV valve was that I could nurse the car along with an easy throttle but as soon as I opened it up or hit a slight incline the car would fall flat on its face. You know, when a load was placed on the engine it would die until you let off on the gas. So, typically it would run fine until 10 to 20 mph and then fall flat. I could nurse it to 30 mph or even 40+ downhill.

Good luck,

 

[Anonymous]

I hooked up the points again instead of the pertronix and the problem still remains. I left the pertronix coil, so I guess that could be next, I still have the old coil. Does anyone think the problem could be with the adjustable rocker arms?

 

[Anonymous]

I'd check where you have the dist. vac advance hooked up. Sounds like it is hooked up to manifold vacuum. If you have a vac gauge hook it up and you're probably pulling about 16-20 inches vac on that line at idle (the line you mentioned that both the tranny and your dist. are hooked up to), in turn this causes your timing to be way advanced at idle and causes problems during acceleration because the vac advance that is normally used for about the first 15 degrees (that varies with the distributor advance module) of advance during acceleration is already maxed out. That would mess up your timing and cause problems. Not so noticeable at idle but during acceleration when spark advance is critical, you could have problems. Not sure which distributor you are using, but if it is off a 68 it probably has mech. advance as well as vac. advance. Try hooking the vac advance to the ported connection. Set the timing with the vac advance hose disconnected. At idle the ported connection has very little vacuum, but as you accelerate the vacuum increases which increases your vac. advance. At some point during acceleration the vac. advance maxes out and the mechanical advance takes over till rpm's get high enough to max the mechanical advance out. If you're really energetic you can plot the timing curve....

 

[Anonymous]

Wow, it is better now. Not completely gone it will still bog down a little but it doesn't sound like its going to die. I probably still have some more to mess with the timing. I set it idle (with hose disconnected) to about 14. I'm glad I mentioned the tranny and dizzy hooked up together because this thing was killing me. Any recommendations on what the timing should be set at? Any thing below 12 and it runs like crap around 14 and it will idle okay.

THANKS!!!! I LOVE this forum!

 

[Anonymous]

it should be able to idle with less advance that unless I am much mistaken(i have mine at 14 too). I would play around with the idle mixture? power valve? those are the other things that I would think to check

 

[Anonymous]

Assuming the mark on the harmonic balancer is correct, and valves are properly adusted (n/a for hydraulic lifters) the engine should be able to idle and run perfectly at factory timing recommendation. If not already done, check/set the gap on your spark plugs. Then warm the car up to operating temp and check the idle rpm's. If you have a choke installed, verify it is not engaged (shouldn't be since car is at operating temp). Adjust the idle screw on the carb so that engine is at factory idle recommendation. The idea here is to set everything involved with the spark side of the engine and then adjust the carb. But to do that you have to set your idle rpm's. Once you have the plugs gapped, and the idle rpm's at the right level, then set the timing to factory recommendation. Don't forget to disconnect the vac. advance hose when setting the timing! After the timing is set, re-check the idle rpms and reset if necessary. After that is done, check the dwell angle (gap) of your points. If you do have the Pertronix installed then you dont have to worry about doing that. However, if you do have points installed, then do it. They sell cheap meters to do this, usually the meters have a tach in them too. Very handy when working in the engine compartment. After all that is done, go back and re-check your timing and rpm's to verify they are proper before ajusting the carb.
On the carb, check/adjust the float level. If you have a vacuum gauge hook it up to the manifold vac connection (the one the tranny is hooked up to) and using the vacuum gauge, adjust the carb mixture screw inwards until the engine starts missing or until you see vacuum being lost on the gauge. When that happens then start turning the mixture screw out until the the engine smooths back out and maximum vacuum is obtained. At some point it may seem like vacuum isn't changing anymore as you turn the screw out, if that happens then you went too far, so screw it back in until you find that "sweet spot" where vac. is maximum and screwing it out doesn't really change it anymore. Once you find that sweet spot, turn the screw out 1/2 to 1 turn. This will set your carb very close to optimum. Hopefullly you have a vac gauge because they are the excellent and cheap diagnostic tools for these old engines.
As a note, the needle on the vac. gauge should not be jumping around a lot while you look at it (and aren't ajusting anything). It should be pretty steady, varying maybe 1/2" or less at any one time. If the needle is jumping up and down when no adjustments are being made, there is a different problem (valve adjustment or something else).

Now that the timing is set and the carb is set, check the idle rpm's again and reset if necessary. At this point your engine is set to a baseline and from here you can slowly increase the timing to get optimum power. If factory setting is 12 degrees, it should run nice at 14 degrees for everyday driving, but when you start pushing the advance up too much (and leaving it there) it can cause engine problems. Don't forget to recheck/set your idle rpm's after changes in timing. Good luck!

 

[Anonymous]

I'm going to follow your steps. I appreciate all your help. I had to go to 5 different stores today to find a vacuum guage! I didn't think I was ever going to find one that wasn't part of a brake bleed kit but I did for about $15.

 

[Anonymous]

Okay, I tried what you said. I adjusted the rpm to 550 and set timing to 12BTDC with vacuum hose disconnected and plugged. Then I adjusted the Fuel mixture screws inwards but I didn't really notice it start dropping in pressure. Only one of them even made the engine bog down. I backed that one out but was only able to get about 16 on the vacuum guage the other one didn't really do anything so I put it at about the same distance as the other one. Then I hooked everything back up and set the rpms again to 550 and bumped the timing up to 14 and drove it. It is better now then before. Only problem it seems to be having now is when I make the left hand turn it will stall or cut out. If I come to a stop sign and then turn left its fine, its only during the rolling left hand turns that the engine will die but then catch itself like its lost all vacuum. Any Ideas?