Vintage Mustang Forums banner

Issues beyond my level of expertise

1235 Views 37 Replies 14 Participants Last post by  dylan81
I've got an A-code 289 that was taken from a 67 mustang that I rebuilt and installed recently. The engine had clearly been redone before as it was already .30 overbore and had forged .30 over pistons to match. The cylinder bores were in great shape (no excessive taper or wear) and I just cleaned the bores with a 120 grit ball hone. The cam bearings were replaced at my local machine shop and my main bearings were installed and measured for oil clearance. I'm using the factory ford heads that are ported and polished with pinned rocker studs. I'm using a comp XE 262H with the 351w firing order and Trick Flow TFS-16942-16 valve springs. The ignition resistor wire has been bypassed for my 12v ready-to-run electronic distributor. Finally, it's topped off with a Weiand Street Warrior intake and 600cfm Edelbrock AVS2 carburetor.

I have run the flat-tappet cam break-in process with no perceived issues. The valvetrain has no clatter and the rockers kept their adjustment. The oil pressure was a steady 60-65psi at break-in rpms and also had no overheating issues. I've since run it in park and attempted to work on my timing and carb adjustments. The motor sounds great and revs very responsively and clean. However, I did have one rocker arm snap after cam break-in and it has since been replaced.

I'm having some issues finalizing my tune. I cannot get the car to idle below 1100 rpm while sitting in park and the engine stalls under load. The engine will sometimes die when turning the wheel and using the power steering pump in park. When shifted into gear (C4 auto), I have the give it a lot of throttle to keep the engine from stalling. Additionally, the engine will stall when braking to a stop. While driving the car feels like it has no power at all. Something definitely isn't right.

I've tried retiming the engine, making more adjustments to the carb, plugging all of the vacuum ports and spraying carb cleaner around the intake and carb base gasket. Checked my fuel pressure and spark plug gaps. I've run a leak-down test across all my cylinders and they averaged around 5% leakage. I'm not sure where to go from here. Any advice would be appreciated!
1 - 20 of 38 Posts

· Registered
Joined
·
29 Posts
Discussion Starter · #2 · (Edited)
I forgot to mention I've also took off the timing cover, intake manifold, and removed my rocker arms and pushrods to inspect for damage and couldn't find anything. On paper, the motor sounds healthy but something is wrong. I've changed out the oil several times already and there hasn't been any excessive metal flake or chunks.
 

· Registered
Joined
·
45,104 Posts
Every fresh diagnosis should begin with two tests...

1. Warm engine cranking compression test. Coil wire removed from distributor and grounded. Throttle blocked wide open. Battery fully charged. Record each cylinder's results after 1st "pulse" and after 6-7 "pulses".

2. Engine manifold vacuum check, at idle. Include not only the gauge reading but the activity of the needle (slow waver, "flicking", steady, etc.).

My initial thoughts, based on your description of the work done and the symptoms are, in order of possibility....

a. Valve pre-load too tight.
b. Significant vacuum leak.
c. Improper valve timing.
 

· Registered
Joined
·
29 Posts
Discussion Starter · #5 ·
I have a vacuum gauge on it, and it was quickly fluctuating between 16-19 inhg, but that was with the broken rocker arm. I haven't tested since. I believe I had my preload too tight to begin with, but I'm not entirely sure how. I got to zero lash on all valves, and added 3/4 turn for my preload.
 

· Registered
Joined
·
29 Posts
Discussion Starter · #6 ·
Every fresh diagnosis should begin with two tests...

1. Warm engine cranking compression test. Coil wire removed from distributor and grounded. Throttle blocked wide open. Battery fully charged. Record each cylinder's results after 1st "pulse" and after 6-7 "pulses".

2. Engine manifold vacuum check, at idle. Include not only the gauge reading but the activity of the needle (slow waver, "flicking", steady, etc.).

My initial thoughts, based on your description of the work done and the symptoms are, in order of possibility....

a. Valve pre-load too tight.
b. Significant vacuum leak.
c. Improper valve timing.
There is something going on with the valvetrain for sure, I've never seen a rocker arm snap like that before. I'm pretty sure there is no vacuum leaks as I have searched and searched for one. The car doesn't have power brakes or anything too complicated with vacuum, and I have plugged all there ports are sprayed around the intake manifold and carb base gasket.
 

· Registered
Joined
·
45,104 Posts
There is something going on with the valvetrain for sure, I've never seen a rocker arm snap like that before. I'm pretty sure there is no vacuum leaks as I have searched and searched for one. The car doesn't have power brakes or anything too complicated with vacuum, and I have plugged all there ports are sprayed around the intake manifold and carb base gasket.
I had a 454 short block replaced a long, long time ago (in a galaxy far, far away, btw) which proceeded to break TWO rockers within 100 miles of the assembly. Ended up replacing all of them. Sometimes s^%t just happens.....
 

· Registered
Joined
·
434 Posts
Silly probably, new carb right? Is your choke on/misadjusted? I did an intake, HEI & 4 barrel swap on my cousin's 360 FE F250. And it fired up at the first hit of the key and it was a'racing and for the life of my I didn't think of checking the choke for a couple minutes. I had already sprayed starter fluid looking for an intake leak, set the timing light on it, tried choking it out at the carb, and it was the GD choke 😄
 

· Registered
Joined
·
29 Posts
Discussion Starter · #10 ·
Are the secondary throttle blades closed at idle? I'm not sure how/if those are adjustable for any contribution at idle, but if you're sucking air in through that circuit, it creates a vacuum leak.
I've checked to see if the air valves have enough vacuum pressure to overcome the springs and they are pinned to the bottom at idle. I haven't messed with the secondary blades at all.
Silly probably, new carb right? Is your choke on/misadjusted? I did an intake, HEI & 4 barrel swap on my cousin's 360 FE F250. And it fired up at the first hit of the key and it was a'racing and for the life of my I didn't think of checking the choke for a couple minutes. I had already sprayed starter fluid looking for an intake leak, set the timing light on it, tried choking it out at the carb, and it was the GD choke 😄
The carb is brand new yes. I've tried both with the electric choke hooked up and not wired in. It didn't seem to make a difference once the engine is at operating temps.
 

· Registered
Joined
·
63 Posts
I'd do another vacuum test even if it is just to start ruling some possibilities out. Have you looked at your transmission modulator? Make sure the lines are free and connected. Cheap replacement if it's old.

I typically opt to spray soapy water when checking for vacuum leaks around the base of the carb. Personally, my engine will surge and idle wonky as the carb catches the carb cleaner mist.
 

· Registered
Joined
·
29 Posts
Discussion Starter · #15 ·
I'd do another vacuum test even if it is just to start ruling some possibilities out. Have you looked at your transmission modulator? Make sure the lines are free and connected. Cheap replacement if it's old.

I typically opt to spray soapy water when checking for vacuum leaks around the base of the carb. Personally, my engine will surge and idle wonky as the carb catches the carb cleaner mist.
I have looked at that, I ended up replacing that line and it didn't seem to help much.
 
1 - 20 of 38 Posts
Top