I recently aquired a 1976 Buick Electra 225 Limited with the GM 455 cubic inch V-8 with a 4bbl rochester quadrajet carburetor that I rebuilt. ( I dont have the model number but I can retrieve it) Here is my problem:
I replaced ALL vacuum lines and have them all routed correctly. I also had to replace BOTH thermal vacuum switches that mount on the intake and are coolant temp. sensitive. My problem is that I have a light stumble on acceleration with a load on the engine and I also can notice this in a slight rough running or hesitation sound if I just lightly hold the engine at maybe 2000-2500 rpm with no load. It is more pronounced with a load on it though and makes it easier to identify.
I have narrow the problem down to an "excessive EGR flow" problem. If I disconnect the EGR vacuum supply line from the vacuum tree, the problem is GONE, yet when I drive it I get lifter noise which I am assuming is due to none of the exhaust gases being let into the combustion chamber to cool the process so, therefore, I am getting a light "pre-detination" if you will. I have tested all of the vacuum ports as per the service manual and been through the testing of "ENGINE STUMBLE ON LIGHT ACCELERATION" and all vacuum tests look ok. When a vacuum gauge is applied to the line connecting from the vacuum tree to the EGR valve at IDLE, no vacuum is present, yet when you tack the throttle you get vacuum. If you accelerate slowly the vacuum does not exist till you get to maybe 1500-2K rpm.
The EGR valve is new, all lines are new and the ported vacuum trees are new. EFE (exhaust manifold valve) for aid in warm up and all other butterflys and such are working in the breather cover, etc. I have checked the timing and it is fine too. I see NO adjustment for the mixture on this rochester quadrajet other than the primary barrels IDLE adjustment. I have tweaked those too and to no avail. So, the only thing I have not been able to do is to richen the carb's mixture so that when I accelerate, I am not trying to burn as un-volatile mixture of gas and air.
Does any-one have any ideas as to what could be causing this? There seems to be NO vacuum delay valve in the line from the vacuum tree to the EGR valve either. I am assuming this is done at the ported tree itself because when cold, no matter how much gas you give it, there is no vacuum from the EGR port on the tree to the EGR valve until it warms a little. So basically I can drive it with the stumble which robs low end power, or I can disconnect EGR and deal with lifter noise and I don't want that. Please let me know any ideas, I am pulling my hair out! Merry Christmas everyone, I am enjoying it in the garage tuning my engine, LOL....... 8-)
From your very detailed description I'd say you're on track with your
diagnosis. I'll do this from memory because I don't see '76 Electras
1. Yes, you are hearing detonation when you crack the throttle, not a good thing.
2. I can't think of a Quadrajet that doesn't have mixture screws. During the early smog years most of them had plastic caps or tin plugs that had to be removed to make adjustments but they should be there. In addition some early smog Q-jets had backward mixture screws, clockwise rich, counterclockwise lean.
3. My guess is your problem isn't to much EGR flow but too much too soon. You're probably getting a vacuum signal to the valve earlier than you think. Your new EGR valve is a more or less universal part. To match it to your engine it should have come with a baggie of calibrated orfices (they look like a bunch of tiny washers) that restrict EGR flow. To determine which one you need there should be a chart that matches orfice number to the EGR OE number.
Hope this helps, that car looks too nice to run like crap.
Thanks for the reply on CHRISTMAS!! :-) Yes I certainly agree with you regarding the problem being that the flow is too soon rather than too much. I should have thought about that before I posted it, rather that is what I am thinking. I should not have a flow at the start of acceleration, rather it should be probably in the higher more steady throttle acceleration.
As far as the carburetor, I am going out to the shop now and reading about the carburetor. One thing I did right when I bought this was to also buy all the service manuals on E-bay for her. I am sure you are right and I bet those damn adjustments are hidden under some cover for the mixture and that is why I have not seen them. I know that the primary (front) barrels are idle screw controlled for mixture and I have toyed with those and set them. Also, I dont remember any orifice washers for restrictioni but I have all the packages that my parts came in, so I will look at this tonight too. OUT TO THE SHOP I GO, HO HO HO....lol.....thanks again, will be back to you on this soon. The car drives like new, it is amazing.....tight as it gets. I get many looks in it. You can just feel this stumble when first taking off. It robs a little low end on it but if you mash it a little more, it is less pronounced. Do you think richening the mixture might help too??? :-)
Richening the mixture might crutch the stumble but it won't fix the problem. Something I failed to mention in the last post was the fact that early smog engines like that weren't known for their perfect drivability so... it might be as good as it's going to get right now.
Ok, I have checked everything.....I don't have any restriction washers for
the egr vacuum line or anything like that. I never got any. I can't help
but wonder though if I can't get some valve that would go in the egr vacuum
line that would retard the vacuum going to the valve, sorta like a delay
valve. Do you know of anything like that? I am not sure how it would know
when to open and allow vacuum to pass, but in my opinion it is just
slightly too early right now. It seems that this should not be the way it
is, seems like it should be right and run smoothly all the time.
Is there a way to circumnavigate the EGR valve and at the same time not get the lifter noise from the pre-ignition?
One more question.....I have been thinking of taking off the cat converter on this and running a straight pipe and then y'ing it off to duals OR doing the H-pipe thing with true duals and no Cat with a set of one or two flowmasters. Is this smart? If I remove the cat is that taking away too much backpressure or will I really notice a gain in HP? I've read many thoughts on this and YOU'RE GOOD, so I want yours! :-) I have taken out the muffler as of now and put in a single pipe and it still has the cat. It is not THAT loud but you know it is a V-8. Naturally, I am not excited about having the converter on there, so let me know what you think please. Thank you.
Hmmm, okay let's try another crutch. I know you have a timing light so,
with the EGR hooked up, advance the timing in two degree increments until
the stumble goes away or you start to experience detonation. Make sure you
readjust the idle speed after bumping the timing. This will do two things
or you. The additional advance will give better throttle response and it
will raise the idle speed, forcing you to close the throttle plates more at
idle thereby delaying the onset of vacuum to the EGR.
Although technically illegal, losing the cat will no doubt help the overall performance of your car. Keep in mind if you have any kind of vehicle inspection in your area you might not pass. Being an early generation converter which was fairly restictive when new, and the fact that it's almost 30 years old and probably has some additional restriction, you really have nothing to lose except weight and excess backpressure. You'll see the most gain by going with the true dual system. Don't cheap out and use a glass pack or standard style muffler. Spend the extra few (very) dollars and get decent turbo mufflers.
Ok, I am going to play with it today and see what I can do.......I will let yiou know! :-)
Yeah, hahah, sorry to get you all hot and bothered. :twisted:
Ok this is what I have done. I went to a pet store and bought an adjustable air vavle for a fish tank that you can tune so that the incoming vacuum or pressure can be adjusted to lessen the outgoing supply. Pretty cool huh? So I have that on there cutting down the vacuum a bit and then what I did is to advance the timing about 3 degrees to take out the lifter noise from pre-ignition. Right now, it is running perfectly. I had to tune the valve with a vacuum gauge and apply vacuum then adjust the adjustment screw to tweak it to the right place. Then I simply repostioned the distributor and off we went. No lifter noise and I have cut the allowance of egr exhaust gases back into the intake a fair amount. What do you think, seems to work??!! Now I am gonna play with the exhaust! :-)
You're going to play with it today... That might be more information than I wanted. :twisted:
Are you related to Rube Goldberg by chance. I say if it works and you're
happy, congratulations. Nothing like a little good old American ingenuity.
Mr. Reuben Lucius Goldberg