Still Having problems with the PROBLEM CHILD-Lean/miss/stumble/backfire!!!!
 

I am still trying to figure out my problems on this fu***ng thing:hothead: :hothead: :hothead: Motor ran FINE first 40 hours or so. I then devoloped a bog/surge when going from a set idle to W.O.T. At idle sometimes its a backfire thru the carb. Also I devolped a distinct miss at cruise above 3300 and below 4500. Under hard acceleration in this range and I would get the bog but no miss till I leveled off at a steady cruise between 3300-4000. At the time of the miss I checked the plugs and noticed that instead of their previous condition they were white as ghosts!!! For the first fourty hours the plug were perfect. when all this started I pulled all the plugs and they all were the same....WHITE AS GHOSTS.....I checked them by running on a w.o.t. in which I would shut the motor off at rpm's (33-5300) and pull them and look. Well here's what I have done and found. 1)New plugs,wires,distibutor (timing verified at idle 8 degrees and at full advance 32degrees this was with old TBolt IV system and new D.U.I.-H.E.I system.)Completley went thru the carb (Edelbrock performer) and found nothing special probally since carb was new. Anyways I went up and tried every spring,jet and rod Edelbrock sold to richen this damn thing up and still NO change at all. I finished the carb up by installing the hi-flow needle and seats....I tried colder plugs and still nothing. I backed off the valves from 3/4 a turn to 1/2 and still nothing. I cheked the fuel pressure and got 4-1/2 lbs...I checked the intake and thought they were o.k. (key word here is thought) I had a "Buddy" torque it up at his garage and found out that his idea of 45ft/lbs was NOT o.k. I sprayed starting fluid around the carb base and no change in idle or rpm....I sprayed the starting fluid around the intake gaskets and WHOLA! the the engine would really drop rpm's every time I sprayed. I put a towel all around the flame arrestor( to make sure the spray wasn't getting in the carb) and still got the same drop. Well I thought(my mistake) o.k. I needed new intake gaskets (probally from the 45 ft.lbs of torque instead of 11 g.m and edelbrock calls for) Well I remove everything to get to the intake and get it off...I find the gaskets(fel-pro) look fine. But the intake (also new a performer vortec) is warped about 1/16-1/8 inch on both sides.....Great news I think yeah Im broke but I just found my problem...Sooooo I fork over the dough for a new intake (performer vortec rpm air-gap) and the recomended gm intake gaskets (the ones reccomended by G.M.,Edelbrock and Car-Craft magazine). I check the new intake with a staight edge and it checks out...I CHECK THE HEADS and they check also....I install everything back up (after fighting rain all week) and TORQUE to GM/Edelbrock specs of 11 ft/lbs. All the while using the correct sequence. Restart the motor and I still have the bog/backfire at idle....Take it to the lake and still NO FU**ING CHANGE!!!! Check the plugs and still white as a ghost. Try the starting fluid thing AND STILL GET THE SAME RPM DROP!!!!!! Well I up the torque to 20lbs and make a run and still no change....I loosen the bolts all up to nothing and retorque to 5lbs....NO CHANGE. Move the torque back up to 12lbs with 15-18 between the problem area with no help.......The leak seems to happen between the front and rear sets of bolts...On the vortec heads the intake uses 8 bolts...2 on each side up front about about 2 inches apart and 2 in the back same way...ALOT of area between the front and rear with out any bolts.....I guess my question is WHAT THE HELL TO DO:hothead: :hothead: :hothead: Ive just lost my vaction to this damn thing and am losing what little hair and patience I have. WHY WOULD THIS THING STILL LEAK if I checked for straightness,used new intake,gaskets and correct torque and sequence. Im temped to put a heavy coat of hi-temp rtv silicone down the length of the intake and try this...At least to find out if my problem lies here or here and somewhere else......THOUGHT ANYONE??????PLEASE PLEASE PLEASE:confused: :confused:

Here is the manifold in question...Note the open area between the front and rear sets on bolt holes...

BH

Wow, youve been busy. I cant help with the problem but Ive been in your shoes enough time to know your fustration. If you can, take a day or two away from it. I usually figure things out when Im doing something completely different. Im sure youll get some feedback hear. Its usually somthing simple thats so hard to find.

Just a thought if it is an install thing there was a service notice that Mer.changed the pattern of the sequence.On the port side starting at the front and going straight back#8 #4 #2 #6 now starboard side front to back #7 #1 #3 #5. if you draw it out on paper it will come together. Or go to the service bulletins and check it out. :cool:

Yeah, the fuel pressure thing would really be something to check! Had a cam wear off the fuel pump drive lobe on a MK-IV big block once and we about went nuts before we found it. I do hope it's simpler than that however. It gets metal chit in the lower end brgs. when it happens. I feel your pain! --- Jer

I called Edelbrock and they said 4-1/2 pounds was ok.....Especially at the rpm range my problem is happening at. I still want to know what everyone thinks about running the rtv silicone down between the head and manifold....I figure at the very least I can take care of the leakage there and hopefully know that the leak is my problem. If not then it's one less thing to worry about right?

BH

I sure am not an expert but it sounds like you are lean. Do you know someone with a 750 or 800 holley you could borrow for a test. Someone with a setup close to yours and known to be in a good condition. Hopefully if you are lean you have not tuliped a valve or worse. When you stand on the gas and you get a backfire a lean condition can cause this. Timing and other problems can cause also but if plugs are white and you think it is lean well I would think fuel. Have you always ran 4.5lbs fuel pressure. Is the gauge right at the carburetor? Eldelbrock has small fuel bowls and can lead to running lean if fuel delivery is not correct. Good carb just has to have excellent fuel delivery. Sorry not much help just more questions. :( Sorry for your trouble and keep us up to date. Summer is just starting so don't give up.

Paradigm shift-The motor ran GREAT for the first 40 or so hours...Then suddenly I got the miss and lean condition. I Havent' really had someone answer this but WHAT IS HAPPENING when I spray the starting fluid on the intake gasket "alley" between the heads and the gasket? When I do this I get a stumble accompined with a healthy drop in rpm's....What is causing the change in rpm's??? and if it is a leak then woudn't that explain my sudden condition and it's symptoms???? SOMEONE has to be bored enough to sit down and help me trouble shoot this thing out.....PLEASE (God and I really really hate begging:D ) I thing that this is a somewhat common problem with the vortec heads...........

BH

I would agree it sure sounds like you have a vacuum leak. I would think it is odd that ALL the plugs would be white if manifold is just leaking on the ends. I would not recommend the silicone but I guess you could try it as a trouble shooting aid. You would have to make sure everything is very clean or it will not work. Do you use something like permatex #2 around intake ports on your gaskets. If heads or block have been surfaced make sure you get an even crush on gaskets from top to bottom. I have to use the extra thick gaskets on one motor I built or it causes me trouble. Usually around water ports though.

Didn't notice you were on line and I am a slow typist!

Heads and block have not been surfaced....The instructions called for no sealeant on the gaskets as they ar a hard rubber/plastic with a silicone type crush instert around each intake port and water port. The only silicone now on the manifold is on the ends where it is to be used in place of the old cork pieces.....The leak seems to be coming from both sides more towards the center on the sides where there is no bolts... see the pic below. Whould using two gaskets be an option?

Where can I find this service notice at? Should I use this or call Edelbrock? The heads are L31vortec truck heads I bought new from the dealer. What was the reason for the service change? That might tell somethig there.....Thoughts or comments?

Bh

I've built quite a few Vortec engines with the Air Gap intakes. I've never had a leak or any problems. Maybe you have a a flaw in the casting instead of a gasket leak. I had that once in a brand new Dart intake.

Which gasket do you use? Also what about using 2 intake gaskets? Someone reccomended this to me but I thought this would just make it worse? Thoughts?????

BH

I guess you probably got us on this one, BUT, I don't really understand the spraying of the start fluid that results in a DROP in RPM. Whenever I had that problem and used that test my RPM's went UP. I don't want to sound as stupid as I am but, Why don't you try a spray gasket adhesive while running and see if it sucks into the problem area stops the prob.?? Good luck! --- Jer

Well then the question then becomes WHY would they drop instead of rise????? I mean it defitnley is a leak that is sucking it in right? As far as the spray gasket wouldn't that get into the intake ports on the heads? That would'nt be good would it? GOD THIS THING IS GETTING MORE CONFUSING AS I GO ALONG......JUST SHOOT ME AND SINK MY BOAT NOW...PUT US BOTH OUT OF OUR MISERY:p :p :p

BH

The space between the two center bolts with the space is only the area where the heat cross over passage is. If it where to be leaking there it would be blowing out.
There are two bolts on either side of the intake ports. They should be sealing that area.
I've alway's used Fel-pro performance gaskets. Use an adhesive around the intake ports(both gasket and head side) and very little silicone around water jackets.
They don't tell you in there directions but I use thread sealer on the bolts. Some of them penetrate water jackets and/or push rod bores.
Other wise, I'd try another carb.

DON'T USE DOUBLE GASKETS!!!
IT WILL LEAK BETWEEN THEM!!!!

There is no 2 center bolts......The intake has 8 bolts 2 in front 2 in the rear on each side........Also NO heat crossover passage on the vortec heads...And you say that even though the carb checks out fine AND that the engine rpm's drop and the engine stumbles when I spray along the intake/head area I should change the carb?? Why would I change the carb If I know I have a leak on the intake?

BH

The pic of the intake, doesn't it have bolt holes between the two front and the two rear ports?
looks like it, but I see the pic of the head and there are no holes???

No it dosn't...I think they are mounting bosses for some sort of accessories or something.

BH

BH

This may sound stupid, but could the motor have jumped time?
One or two teeth off of the chain?
just a thought, the vacum leak does sound screwy.
Greg

I looked at a pic of the GM and it didn't have them.
Woke up this morning wondering why is was thinking carb??
Your right, that doesn't make sence.
It still seems like an intake gasket leak.
The GM shows a water cross over fitting at the center.
The edelbrock does not have this?
Is that a water hole at the center on the head?

Is this the gasket your using?




12529094 Gasket, Intake Manifold "Vortec Design"
This is the production gasket for all Vortec design cylinder heads (four-bolt attachment of manifold to cylinder heads P/N 12529093 and 12558060).

Technical Notes: This gasket requires the use of GM attachment bolt P/N 12550027 because the bolt has a ball design on the end that seats in the head so it will not crush the intake manifold gasket. This kit includes (2) gaskets.

Using the GM bolts?

No I am using A.R.P. bolts that are listed as the correct bolts for the vortec heads...BUT they sure don't have a ball or anything on them...The first manifold was used with a Fel-pro gasket.The gasket was pretty thick and flat. With the new manifold I used the GM gasket 12529094. It is more of a hard plastic with a silicone type ring around the ports.....BUT I did not use the GM Bolts....Wouldn't the ball just prevent an overtorque situation? I am planning of running a bead of Hi-Temp RTV Silicone on the gap today and if the weather holds tommorow I should know If I have an intake leak or not..I figure I will find out if the leak is present and so if it is my problem I have been chasing or just part of it.. IF (BIG IF) it cures the problem (intake or both) then I will look into changing the gaskets again with the GM Bolts....Do you have a picture of those bolts????

BH
(Still on suicide watch and life support:hothead: )

Can't find you a pic, sorry.
Good luck today.

I am not sure how detailed you have checked the fuel supply.According to my manual you need to check both fuel pressure AND volume to be sure that you have adequate fuel supply. the pressure should be 7-9 psi (also at WOT!)and the volume at idle should be "a pint per 20 seconds". If you have a volume problem it will show as fuel starvation at higher speeds, or more precisely as starvation in sustained high torque situations .

Edelbrock told me that 2 lbs was all that was needed for idle and 4lbs at W.O.T. No Granted it sounds like Im low on pressure but if pressure was the problem wouldn't it show up more at W.O.T. The miss I get is at cruise. When at W.O.T. I don't get the miss... Am I "missing:D " something here? Keep the ideas comments coming PLEASE!!!

By the way if you happen to see this "Problem Child" please fix her or put her out of her misery:crazy:

Well, I am thinking more about the surging. That definitely points towards a lack of fuel. If the surging appears when you have the throttle at the end of the travel(irrespective of rpm) such as when accelerating hard, that would point towards the fuel pump not being able to keep up with the fuel demand. In principle the highest demand on the pump per "pumping action" or revolution would be if you are at idle and push the throttle all the way. If you have a volume problem , it would then start surging as soon as the bowl in the carburator is emptied.

Sounds to me like the ideal situation to use a vacuum gage. Has this been done?

Also, from my experience, I don't put much credence in what the tech line kids (edelbrock in your case) have to say. I generally teach them things. They are not always the sharpest pencils in the box.

Fuel pressure may not be the problem causing these symptoms, but it is too low and needs to be corrected asap.

my .02

BT :cool:

Blue...What would be the best way to use the vaccum gauge. What should I be looking for on the reading and at what rpm's....

BH

I don't have any reference materials with me for specifics, but you plumb the gage into the intake, and at idle watch how the needle fluctuates. There are specific patterns to look for that will tell you many different things. I think seloc has a section in the merc manual telling what to look for. That, or when you buy a vacuum gage it generally comes with the specific things to looks for.

BT :cool:

One more question on the fuel pressure; is it 4,5 psi all the way up to WOT and full speed? No fluctuations?

That's right mat. If the pressure stays at 4.5 all the way up, pressure is not the problem.

BT :cool:

Well..........................Lets see. I ran a bead of silicone down the intake/head surface yesterday. I took the boat out today and the symptoms actually MIGHT have gotten a tad worse. But the intake leak (or whatever it was) is now gone.I shot the starting fluid down the areas and finally there was no change at all at idle thru-out the rpm range when I shot the fluid down. I put the vacuum gauge on and it was between 14-15. The needle moved pretty rapidly between the two amounts but the amount itself was small. I re-checked the plugs and still WHITE AS A GHOST. I figure the only thing left to change and what several here have suggested is the fuel system....I orderd a Hi-output 6-8lbs & 110gph new fuel pump. So it should be here Wed. So I should have something by Thursday evening......I have a VERY Bad feeling that that it's not the fuel pump but I can't think of ANY thing else to check or replace....

BH:

My take is the reason plugs are showing lean is the leak, air is bypassing the carb thus the lower air/fuel ratio. Leanness can also cause surging. I would try taking silicone & put along where the air is leaking. The longer you run motor lean the shorter the motor will live. Could be you got the motor hot one time & caused the heads to warp. I really could not see this happen but I have seen stranger things.

As for the motor dropping RPM, only reason I can think is you are reducing air volume & idle jetting is on rich side to start out with.

Steady reading between 15-21inches at idle RPM -normal.Extremely low reading but steady at idle RPM-vacuum leak,incorrect timming.Fluctuates between high and low at idle RPM-blown head gasket between two adjacent cyl.Fluctuates 4-5 inches very slowley at idle RPM-spark plug gap to narrow,valves are sticking.Fluctuates rapidly at idle steadies as rpm is increased.-valve guides are worn.Continuously fluctuates between low and normal reading at regular intervals at idle RPM -burned or leaking valve.I don't think you have a vacuum leak :confused: Also I would not spray Starting fluid or W-D 40 on those type of gaskets as it might dammage the rubber. :cool:

Bad-Habit, if you have a fuel supply problem , there could be a number of reasons behind that , eg the fuelpump and fuel pressure valve, the cam lobe that is driving the pump, clogged fuel lines, antisiphon valve in the tank, the fuel filter or that the system is sucking air somewhere before the pump. You may have done this already but I would carefully observe the pressure at the carburator all the way from idle to WOT and under hard acceleration ,to see if there are any fluctuations in order to get a clue of what is actually not working.

Bad Habit
I would try the orange high temp silicone, it will handle the temperature and maybe temporarily segregate the problem. Test it after you let the stuff dry, the same way you tested it to get the rpms to drop, if they do not drop and idle stays the same, then do anothe plug read.
Post what you find.
Good Luck
Brian

If the fuel pressure dropped as the engine rpm increased I was going to say check the anti syphon valve, tank screen or fuel tank venting. Could be the fuel pump pressure control valve as well. Let's hope that is it!!

Good luck,

BT :cool:

Here's something else, that hasn't been brought up. Have you checked your water pressure at WOT? If all plugs are white, like new. You can be getting some water in the cylinders. Just a thought.