Need help with this vacuum reading

-
shadango

shadango

Well-Known Member
Joined
Jan 10, 2009
Messages
814
Reaction score
4
Been banging my head against the wall trying to get my 318 running right.....

Have talked about it in other threads.....really low vacuum.....but I thought I might have a cam....major issues with getting it to run....once she is fully hot she wants to die out in idle eventually..........in traffic it happens a lot...to the point where I have ti pull over and sit a few minutes.

In the past I have taken vacuum readings.....but always in park or neutral. Tried it in drive this time and I am afraid of what I see.....

In drive it acts wild, but giving it some gas (while holding the brake) smooths it out for the most part.

If you know what you are doing when it comes to vacuum readings, please take a look at this video and tell me your thoughts

Thanks guys.


http://s349.photobucket.com/albums/q391/shadango_bucket/cuda video/?action=view&current=vacuum01.flv
 
you have to put it in D or Gear not N or P and then tune the carb and timming to get the most vac. without pinging or knock when you adjust the timming
 
Try videoing bringing the idle up slowly instead of stabbing it,also bring idle up in gear.Will be able to see readings then.Might help?
 
i believe you have timing issues or to much cam for the convertor /a big cam with lots of duration will = low vac readings
 
sixpakmopar said:
i believe you have timing issues or to much cam for the convertor /a big cam with lots of duration will = low vac readings
Click to expand...

But wouldn't a wrong convertor cause problems when hot or cold? Would it cause it to die like this?

Keep in mind it also dies while just sitting in park.....let it sit idling and it will just keep getting rougher till it dies.

It doesnt die until its hot.....runs/drives ok to that point....
 
I had a 360 with low compression and a big cam. I had a problem very similar to yours and I was able to solve it. At idle I put a timing light on it and had someone else put the car in gear. What happened to me was that it dropped so much rpm when I put it in gear that the distributor pulled out timing due to the centrifigal advance. My car had a Mopar Performance electronic. What I did to solve my issue was lock out the centrifugal advance and it idled nicely but still had only 5-6 inches of vacuum. The low vacuum was due to a combo of an old 509 purpleshaft and 8 to 1 compression. I bought an MSD billet distributor and played with different advance curves and finally just locked it out. My motor, since it had so much overlap, was able to run on 87 octane without detonation. I hope this helps you out. After seeing your video it really reminded me of my problem from years ago.
 
I just had another thought, could you tell us some more info? Compression, cam, heads, intake, distributor, exhaust, carb, and trans converter.
 
The vacuum reading in N seems o.k,but in D your RPM drops alot.Have you played with your air mixture screws on carb?,with car running and watching vacuum guage?Could your timing be low?I have 2 little holes drilled in my primary flap,to give the carb more air because of my cam.That has helped me when tuning my car.Sounds like a big cam(robbing vacuum)?
 
Thanks.....right now I am running 18* in park. Seems like a lot but I guess maybe not.....I will try the idea of putting it in drive and then adjusting.

But really, it runs fine at first and then slowly begins to degrade in performance...timing is still at 18* right before it dies.....

But will try it next chance.

I have no background on the engine unfortunately...It has a deep sump oil pan, an eddy performer intake manifold and 650 cfm # 1405 eddy carb with electric choke kit.....I was assuming it has a cam because of the idle....it has J heads, and is a '76 block. I was told it has a double roller timing chain......one more reason I assume it has a cam......compression was good across all the cylinders...up around 150-155 as I recall when warmed up.....pretty consistent. I have Doug;s headers on it and magnaflow exhaust kit.

I am half tempted to just say screw it and rip the cam out and start fresh....but that probably means new rods, springs, and who knows what else.....hate to throw out the baby with the bath water, but if the cam is the "problme" I could swap a milder one in.....but if its another internal issue, I wasted time and money. Thats why I am posting teh vacuum readings....hoping someone will see something.

what I need is someone who is experienced to come tale a look! ANyone in the Pittsburgh, PA area? A case of your favorite beverage to whomever can solve this problem! LOL

I have been in touch with the previous owner, a body shop, numerous times....the guy he bought the engine from was supposed to call me and let me know what was in it but seems to not want to......it wouldreally help if he did though. Wish there wasa way to trace an ENGINE to an owner...LOL

When you say "locked it out", do you mean at one particular amount of advance?

I have my vac advance disconnected and the port plugged.

So you dont think its a bad head gasket? That wild fluctuation made me think that.....
 
pettybludart said:
The vacuum reading in N seems o.k,but in D your RPM drops alot.Have you played with your air mixture screws on carb?,with car running and watching vacuum guage?Could your timing be low?I have 2 little holes drilled in my primary flap,to give the carb more air because of my cam.That has helped me when tuning my car.Sounds like a big cam(robbing vacuum)?
Click to expand...

I had tried drilling 1/16" holes in my primaries on the 750 cfm carb that was on it and no joy there. But have not tried it on THIS smaller carb.......afraid of doing anything that I cant easily put back......cant get new plates, according to edelbrock....liability issues...
 
Not knowing the cam really sucks!It does sound a bit lumpy.Maybe just install a new cam?This way you,ll know what you have and will be much easier to tune.My 2 cents.Good Luck!
 
put a little more timing in. it ajust carb air bleed screws.geter ideling around 8or9 hunderd rpms and i think youl be good to go
 
godfatherofchry said:
put a little more timing in. it ajust carb air bleed screws.geter ideling around 8or9 hunderd rpms and i think youl be good to go
Click to expand...
I'm beginning to wonder if the timing chain wasn't installed straight up.
Car sounds good from here. Usually a fluctuation vacuum reading has a lot to do with valve seal at the seat.

George
 
Well, I agree that a fluctuation in vacuum is normal with the amount of lope it has. When I speak of locking out the distributor, I mean that you lock the centrifugal advance weights from moving by mechanically lock them to the shaft. On my car the timing would hang in there and when it started to run real rough and loose rpm you could see the timing drop by 5 degrees or more. Aside from the obvious, a vacuum leak will also make it behave this way and it would be worse when the car is warm and could also make it hard to start. Im just throwing out some ideas from my experience. Alot of things can be ruled out with a little effort and a little money. Stick with it and you will figure it out and you will learn alot along the way.
 
skybolt said:
Check out this article. Hope it helps.

http://www.underhoodservice.com/Art...ressures_of_intake_manifold_vacuum_tests.aspx
Click to expand...

Good article, thanks.

The last paragraph was interesting....

"Although I could lift the valve cover only a few inches due to interference from the air conditioner compressor, I discovered that the #5 exhaust valve guide was completely worn out, which allowed exhaust gases to pass through the guide and overheat the valve spring. The over-heated, carbon-covered spring had weakened to the point of barely closing the exhaust valve. Although the spring would close the valve well enough to a cranking compression test, the weak spring allowed exhaust gas to be drawn into the cylinder on the intake stroke, which diluted the air/fuel mixture and caused the intermittent rough idle condition."

I guess he just looked at the spring/seal to see the issue? I may pull my covers again and look again......but I swear all the springs looked brand new....

Also, not sure why , if I had a problem like bad spring, it would run great for a while then at some point when hot crap out.....seems like a bad spring would make it run bad all the time......?????
 
I just took a ohms reading on my coil.........while cold it is reading about 10,800 ohms or so from one terminal to the center. When its hot, it is reading around 13,600 to 13,800......

The coil is an Accel super stock coil....according to their website it should read

Priomary 1.2 OHMS
Secondary- 8.9 K OHMS.

Cold, mine is reading
Primary 1.5 to 1.6 ohms
Secondary - 10,900 ohms

Hot, mine is reading
Primary - in the 2.0 range as I recall, didint write that down.
Secondary - 13,600 or so, as high as 16,000 at one point

Wonder if that is enough of a jump to be causing my issues? Maybe the spark is weakening when it gots hot and there isnt a strong enough spark to keep her running?

The manual for my car shows cold readings for the stock coil and the cold readings I have are in the same ballpark.....they dont list hot readings.....
 
I would relay the info on your coil to Accel and see what they say about it. Hopefully its something that simple. I assume you have ruled out any vacuum leaks and you have already done a compression check so the engine must be in pretty good shape. I don't know of a real accurate way of getting #1 at tdc to check you camshaft installation without tearing it down. Someone on here might know an old indian trick for that one. The outer ring on harmonic balancers have been known to slip causing the timing marks to be inaccurate. Got any real sharp engine guys around there? Good luck!
 
Look high & low for vacumn leaks. All it takes is a loose carb,intake manifold or bad line. All carbs, especially eddy's when they get warm seem to hate todays gas. If your car sits days/weeks between startups that can create probs. also without a additive in the tank. I was constantly having stalling probs. with my valiant until I added a phenolic spacer & started using a fuel cocktail. Your coil could also be getting to hot. Is it mounted upright & if you still have a ballist resister set-up most after market coils need the resister they come with, usually like a .85 ohm instead of the factory 1 ohm. Just some thoughts. Good luck.

Oldschoolcuda
 
I replaced the coil today with a Duralast gold from autozone....readings were lower when cold than the accell I have so I crossed my fingers......

Let the car run in my driveway for 40 minutes to warm it up.....then went for a long ride with the son....about 25-30 miles, keeping close to home, some red lights but not many....but pulled over on purpose several times and just sat idling in drive.....not one stall or fart. Went to a buddy's house to commiserate a bit and show off the car...stopped for about an hour... and then headed about 5-7 miles or so home. No problems. I didnt hammer on her at all...just mellow cruising.....

Now, I dont know if the coil did it, if the weather has something to do with it, or if the next time I go out it will die.

Guess we will see.

What fuel cocktail/additives do you use? I was wondering about the ethanol in the gas and such.....with all the underhood heat, the carb could be boiling the ethanol laced gas....even with the phenolic spacer I have there like you.....

I am hoping that was it.....but not really expecting it will be....the new (oem style) coil measures 12k ohms in the secondary circuit versus 13,500 up to 16k on the accel when hot.....I dunno if thats enough to make the spark weak enough to want to die or not?

Or maybe my fish is just waiting to sneak up on me and die again just when I am not expecting it...LOL

I dont think that any vacuum leaks I may or may not have really come into play now.... at least not as far as the car dying goes.....if i have a vacuum leak somewhere it would cause crappy running all the time not intermittantly, wouldnt it?

I dunno....my head hurts. LOL :angry7:

I DID successfully change one set of window whiskers and fix the door lock......maybe it was just a good day...LOL :toothy10:

Tell ya what, I so appreciate this forum and the cuda-challenger.com forum.....you folks are so helpful.

Sometimes just being able to commiserate a bit helps.8)
 
If it has a PCV valve, try plugging it. Maybe it's not staying closed when the vacuum drops as it's put in gear.
 
Well, "not really" i guess would be the right answer...LOL

The car isnt dying out like it was....replaced the coil (again) and found a loose connection at the ballast and so far, after a couple weeks of car cruises, no issues....

The idle is still rough etc, but it runs real good when you gas it........revs up high and pulls hard....

So all I can figure is that I have a cam as has been suggested and that the idle is the way it is because of that.

I still have an oscillating vibration that I cant figure out quite yet....dont think that is related to the vac readings though.

I have decided to drive it for a bit and see what pans out.

A guy I met at a car cruise who seems to have a lot of experience building these things took a quick listen to my engine and felt the vibration I was talking about and he seems to think that I should just drive it until it either gets worse or I hear other noises etc.....not sure that is the best approach really but given my choices I guess it makes some sense.

The whacky vac readings at idle? Dunno. It runs too good mid range to the top to be a mechanical issue, I think.....:angry7:
 
You must log in or register to reply here.
-

Back
Top