help! power loss when accelerating

[BOOMERBIRD]

'Im racking my brain. I have complete power loss when accelerating in my 58 bird with a 352FE. It was running fine and then bam, i went to give it gas and it bogged out on me but was just fine at idle. Its acting like the points went bad or the timing went way off but it idles just fine. I've looked at the electrical and fuel with out any hits. I'm flat dead in the water. I changed the points, coil, condenser, set timing, patched exhaust leaks and everything else seems ok. Carb appears to be getting enough fuel as well and the filter is clean. what could this be?

I'm sure this has happen to someone else here. Any help is greatly appreciated.

Boomer

[simplyconnected]

If you're getting spark, it's most likely starved for gas. (Check your flow). I've had rust in my tank that clogged off my in-tank gas screen after a few blocks or a few miles.

If your flow is good, you may need a new coil or resistor. (Swap w/another engine.)

[Joe Johnston]

Power valve in carb working? Vacuum advance working?

(diaphragm may have torn/ruptured in either)

[tbird430]

I'd agree with the above recommendation, lift your trunk mat up & remove the sender access door. carefully remove the lock ring & sending unit.

Get a flashlight an shine it down into your tank & see what the pick-up tube "sock/filter" looks like.

Report back to us....

-Jon in TX.

[BOOMERBIRD]

i replaced the power valve, new distributor and vaccum advance, new points, cap/rotor, condenser, new coil and wires, checked the filters in the tank and they looked clear, pulled the card apart to check out the floats and all is normal. i do believe after re-checking everything again i've found that when i remove cylinder number 4 plug wire from the cap there was no change in idle but had good spark. i replaced the plugs and wires too and once again went through pulling every plug wire and they all effected the idle except for #4. when i had this loss in power the other day i was driving at 25 mph with out stomping on it at all. i'm going to do a compression check on it but at this point i would thing i'm DOA? I'm fearing that i'm going to have to go ahead and do a rebuild or replace it with some sort of 390FE crate. any ideas or am i done at this point with searching for any other issues???

[Astrowing]

The accelerator pump is another item to check. Make sure you are getting a good squirt into both front barrels. I've had the venturis get clogged. When you say you have a good idle, are you talking in neutral or drive? The load in drive will really show fuel problems as poor idle quality.

[simplyconnected]

You're not done. We know so little about your engine it isn't funny. How many miles are on this engine? Certainly, a compression check will tell us a lot more. So will a vacuum check because that will indicate any valve leaks.

I haven't heard any results from doing fuel flow checks, or Jon's suggestion of looking into the tank. If junk accumulates in the tank, it has nowhere to go.

A worn timing chain that jumps a tooth will let the engine idle, but run really bad.

Pull your rocker covers off and watch the rocker arms. Are they all going up and down, all the way? A non-functioning valve will cause #4 plug to 'not make a difference'. To check timing, turn your crank until #6 rocker arms are inbetween exhaust and intake, just when they are dead level (use a flat stick). At this point your timing marks should read, TDC AND your rotor should be pointed directly at #1 spark plug tower.
If you are off one tooth, the rotor will be between towers when the points open. If this is the case, pull the distributor off and turn it. Don't worry if the distributor doesn't drop all the way down at first. Leave it engaged and hand turn the crank. Within 1/3-turn either way, the oil pump shaft will align and the distributor will drop into place.

I assume you have all the spark plug wires on the correct plugs. (It's a weak suggestion, but still valid.) Hope this helps and we are eagerly awaiting your test results. - Dave

[kevin_tbird]

if you are pulling $4 plug wire at the cap then you could still have a bad plug wire or spark plug. I would remove spark plug #4 and see if I have spark from the plug to the block.

A compression check is absolutely the next step.

Kevin

[BOOMERBIRD]

im a little confused about how to check number 6 cylinder. to check #6 are you saying that the pistons in #5 and #7 should be all the way to the top? i have the rotor pointed at #1 cylinder right now and the piston is all the way down. I thought the piston should be right there at the spark plug hole when i was td, with the rotor pointed at #1 cylinder. am i wrong about that? before i pull the distributor i want to make sure i understand what you mean about#6 rocker arms are inbetween exhaust and intake, just when they are dead level.

[BOOMERBIRD]

Dave,

The bird has 72k original miles on the 352. the car sat for 20 yrs until a yr and a half ago. I got it running and have put 20k on it my self with out any trouble at all until now. she has run great since and the car was purchased new by my grandmother in 58. the car was taken care of pretty good up until it was parked and ive been replacing things as ive been going along. the fuel lines and filter in the tank look great, spark plugs look good at the plug too, I need to get my hands on a compress tester to check the compression. I really feel that its timing or there is something wrong with #4 cylinder. I would like to think the timing chain jumped a tooth but i need to understand the #6 rocker arm check and tdc test you talk about. i really thought that the piston was suppose to be all the way to the top of the cylinder when the rotor was pointed at #1 cylinder and that meant that i was tdc.

Thanks Boomer

[scumdog]

i really thought that the piston was suppose to be all the way to the top of the cylinder when the rotor was pointed at #1 cylinder and that meant that i was tdc.

Thanks Boomer

To make it easy:

Take a piece of newspaper about 8" X 6" , screw it into a tight was about the diameter of a spark-plug thread and screw it loosely into the No1 spark-plug hole.
'Bump' the motor over with the key until the paper 'plug' pops out.

That should be pretty close to TDC, you'll soon know by looking at you timing mark if you've gone too far/not far enough..

[simplyconnected]

Chad, your thinking is correct, but think it all the way through. Look at the firing order:
1-5-4-2-
6-3-7-8
(I put the firing order on two lines to demonstrate the following: )
When #1 piston is on top, so is #6 piston.
When #5 is on top, so is #3, etc.

If you randomly put your timing marks on TDC, the distributor rotor may either be pointing at #1 OR #6 spark plug towers because this is a 4-stroke engine.

So, while #1 is firing on its Power Stroke, #6 is on its Exhaust Stroke. We can use this mechanical action to our advantage in discovering the true timing of the cam and crank.

Again, we know that after the Exhaust Stroke comes the Intake Stroke. On some 'hot cam' engines they overlap a little (for scavenging), but that doesn't matter. Exactly between Exhaust and Intake, when the #6 rocker arms are dead level, #6 piston is at TDC. So is #1, but #1 is firing and the rotor is pointed directly at the #1 spark plug tower.

If the timing chain jumped a tooth and you put #6 rocker arms level, your damper pulley won't point at TDC any more. It will probably be off about 15 degrees (and the rotor will be pointed nearly at #1 spark plug tower).

So, pull the driver's side rocker cover off, and watch the second set of rocker arms. There will be a long pause in the action, then the exhaust rocker arm will move. Just as it stops moving, the intake rocker arm will start. At this point, when they are dead level (use a stick), go over to the timing marks and see where they are on the crank. If the marks are off of TDC, they are not to factory settings.

Old timing chains stretch about two degrees or slightly more before they start 'jumping time'. This slop does two things, it advances the crank timing giving terrible low-end torque, and it puts a lag in the gas pedal (like at a light). That is why new engines are so much more responsive. Timing chain slop also makes spark timing irratic, and you can feel the engine surge.

Hope this helps. - Dave

[simplyconnected]

This information isn't covered in any of the manuals because it deals in the principles of how the crankshaft, valve train, and ignition timing are related. And, most of it is common sense. Need a Degree Wheel? Download one for free.

In every case, the first task is to generally get the crank and cam in time, then mount the distributor. That makes perfect sense because these three components are geared together.

Most mechanics trust keyways and timing marks and assemble according to the book. When I build my engines, I spend a little extra effort finding true crank TDC. Then I check it to the cam's timing which costs nothing extra.

I retard the crank (or advance the cam 4-degrees) for street engines. This does two things, it moves the torque curve slightly toward low-end rpm's for better street performance, and it 'anticipates' chain stretch.

All measurements reference #1 cylinder and the relationship to #6 valves, since both pistons are @ TDC at the same time. These same rules apply to ALL engines regardless of brand. The end result is an amazing engine that is in perfect crank/valve/ignition time.

Harley-Davidson was one of the first engines to take advantage of firing both cylinders at the same time, which really meant there is no need for a dizzy cap, just a crankshaft sensor and a coil. While one cylinder is on its power stroke the other is on its exhaust stroke; no conflict. Ford Romeo engines (4.6L) did the same using fewer moving parts and saving tons of money.