Flat cam??
Thread Starter
4th Gear Member
Joined: Mar 2007
Posts: 1,747
From: Portland, OR
RE: Flat cam??
ORIGINAL: Scott H.
If it back fires that's not likelyto bea flat cam issue.
Back fire through the carb is mostcommonly ignition (primary usually, but really bad plug wires or carbon tracking can cause it on the secondary side as well), back fire through the exhaust is most likely carburetor (fuel puddling in the intake, failed power valve, float issue, etc).Sporadic engine miss is more likely related to a leancondition orignition issue.
So far from what you've said, flat cam is way down the list of what I'd be looking for.
But you still haven'tdished out all the details.And when trouble shooting the best way is to start with a complete list of symptoms. From that you find theengine subsystem(s) that can cause your symptoms. Then you test that/those subsystems using some simple gauges and tools.
Shouldn't take more than 30 minutes to nail the problem once the car is warmed up and the hood is open.
Start with a fully warmed up car.
Dissable the coil and crank the engine. If it cranks smooth and steady, the problem is not mechanical (see above).
if it cranks rough or unsteady, fire up the car and (using spark plug boot pullers) remove each plug wire one at a time, find the cylinder that does not make a change in rpm. Pull that valve cover, and look at the valves. Are they both there? Springs good? all the heights even? disable the coil and crank the engine over, do both valves open and close like the rest?
Yes? Cam timing or piston-rod-block issue. Run compression test on that cylinder. Cam timing will be low (probably somewhere in the 60 psi range) but steady compression. Piston rod or block problem will show on plug and be close to zero compression.
No? cam flat-lifter sunk-pushrod bentproblem. spin pushrod in fingers, does it wobble (if so it's bent), Take your mom's best silver serving spoon and place the spoon portion between the rocker and pushrod, push down on the spoon (if it goes down and will slowly return, it's not the lifter). BTW: you could use any cheap spoon, but this will help you move out of the house and become independent sooner
so if the first two tests are passed, then yeah, you may just be a redneck... uh, excuse me, I meant to say, you may just have a flat cam.
I have a sneaking suspicion that your problem is cheap and easy to fix. Least that's what I'm hoping for!
So let us know how you do.
Good luck
If it back fires that's not likelyto bea flat cam issue.
Back fire through the carb is mostcommonly ignition (primary usually, but really bad plug wires or carbon tracking can cause it on the secondary side as well), back fire through the exhaust is most likely carburetor (fuel puddling in the intake, failed power valve, float issue, etc).Sporadic engine miss is more likely related to a leancondition orignition issue.
So far from what you've said, flat cam is way down the list of what I'd be looking for.
But you still haven'tdished out all the details.And when trouble shooting the best way is to start with a complete list of symptoms. From that you find theengine subsystem(s) that can cause your symptoms. Then you test that/those subsystems using some simple gauges and tools.
Shouldn't take more than 30 minutes to nail the problem once the car is warmed up and the hood is open.
Start with a fully warmed up car.
Dissable the coil and crank the engine. If it cranks smooth and steady, the problem is not mechanical (see above).
if it cranks rough or unsteady, fire up the car and (using spark plug boot pullers) remove each plug wire one at a time, find the cylinder that does not make a change in rpm. Pull that valve cover, and look at the valves. Are they both there? Springs good? all the heights even? disable the coil and crank the engine over, do both valves open and close like the rest?
Yes? Cam timing or piston-rod-block issue. Run compression test on that cylinder. Cam timing will be low (probably somewhere in the 60 psi range) but steady compression. Piston rod or block problem will show on plug and be close to zero compression.
No? cam flat-lifter sunk-pushrod bentproblem. spin pushrod in fingers, does it wobble (if so it's bent), Take your mom's best silver serving spoon and place the spoon portion between the rocker and pushrod, push down on the spoon (if it goes down and will slowly return, it's not the lifter). BTW: you could use any cheap spoon, but this will help you move out of the house and become independent sooner
so if the first two tests are passed, then yeah, you may just be a redneck... uh, excuse me, I meant to say, you may just have a flat cam. I have a sneaking suspicion that your problem is cheap and easy to fix. Least that's what I'm hoping for!
So let us know how you do.
Good luck
But here goes:Idles rough, backfires when you let off the gas and coast to stop (put it in neutral and it does not backfire). Once it is warmed up, it will start to backfire while it is parked andin neutral. Mash the gas and it hesitates. Disconnect the vacuum hose to the rear of the manifold and the idle smoothes out and the rpms pick up a little.
Things I have already replaced:
5 month oldedelbrock carb and fuel filter at the same time, MSD 8.5 wires, MSD dizzy, new plugs, and new coil. Took it to a exhaust shop and had it tested for exhaust leak, didnt find one. Took the carb apart and checked the float level, they are good
The car holds steady vacuum at 18. I set the a/f mixture with the vacuum gauge, set the timing at 10*, and the idle at 850.
6th Gear Member
Joined: Oct 2006
Posts: 6,417
From: Cork, Ireland
RE: Flat cam??
listen to Scott, I'm on par with what he says.
a flat cam will cause the valves not opening up, or not opening up fully.
that means that you have none or very few fuel mixture pulled into your cylinder (no power).
if it's the lobe for the exhaust valve the engine will struggle exhausting the burned gasses.
again no power as it has problems pulling fresh mixture in. and in extreme cases the piston will push the exhaust gasses all the wat up to the car.
That will cause all sorts of things, but I still can't see the misfiring.
I'd check as well for carb and ignition first.
And earlier on is a good response with checking on the rockers that push the valves. when the engine is running (or you turn over by hand) you shuld every single one of them moving up and down.
Running the engine in idle with no valcecovers can be very messy though :-) (oil all over the shop). i usually used cardboards on the sides of the heads to catch the spurts ...
kalli
a flat cam will cause the valves not opening up, or not opening up fully.
that means that you have none or very few fuel mixture pulled into your cylinder (no power).
if it's the lobe for the exhaust valve the engine will struggle exhausting the burned gasses.
again no power as it has problems pulling fresh mixture in. and in extreme cases the piston will push the exhaust gasses all the wat up to the car.
That will cause all sorts of things, but I still can't see the misfiring.
I'd check as well for carb and ignition first.
And earlier on is a good response with checking on the rockers that push the valves. when the engine is running (or you turn over by hand) you shuld every single one of them moving up and down.
Running the engine in idle with no valcecovers can be very messy though :-) (oil all over the shop). i usually used cardboards on the sides of the heads to catch the spurts ...
kalli
Thread Starter
4th Gear Member
Joined: Mar 2007
Posts: 1,747
From: Portland, OR
RE: Flat cam??
The motor is pretty mild. Not sure what cam is in it, but if it is not stock, its pretty close. The highest I have set the timing was at 12* and it didnt ping. So I will bump it up a bit more like you said and see what happens. I just filled the tank about a week ago and I always run 91 octane (highest I can find here). I dont have any smog equipment on the car. If I cant figure out what the problem is, I guess it isnt that big of a deal. Sometime in February I am pulling the engine anyway to store the car for 15 months. Gotta deploy. When I get back I wanna try to rebuild it. It will be my first rebuild.
I really appreciate all the help. I am gonna try to check some of the stuff you mentioned in your first post tomorrow. Just gotta convince the Mrs. to watch the little one and give me some garage time
I really appreciate all the help. I am gonna try to check some of the stuff you mentioned in your first post tomorrow. Just gotta convince the Mrs. to watch the little one and give me some garage time
6th Gear Member
Joined: Oct 2006
Posts: 6,417
From: Cork, Ireland
RE: Flat cam??
what do you guys actually mean with "steady vacuum at 18".
are you measuring manifold vacuum ? if yes, at idle ? if yes, how much should that be ?
I believe I can't measure manifold vacuum in my car, as I only have ported vacuum and no servo brakes. all ports are locked (closed) ....
kalli
are you measuring manifold vacuum ? if yes, at idle ? if yes, how much should that be ?
I believe I can't measure manifold vacuum in my car, as I only have ported vacuum and no servo brakes. all ports are locked (closed) ....
kalli
Thread Starter
4th Gear Member
Joined: Mar 2007
Posts: 1,747
From: Portland, OR
RE: Flat cam??
I bought the rebuild book about 2 months ago (been planning it for awhile). I have already read it cover to cover, but it will go with me to the "beach". Got nothing better to do over there.
Kalli,
Yeah, manifold vacuum. Usually between at idle, 15-22 is considered good. I have a vacuum line that I use on the rear of the manifold.
Kalli,
Yeah, manifold vacuum. Usually between at idle, 15-22 is considered good. I have a vacuum line that I use on the rear of the manifold.