More Electrical/Idle Problems

[icejawa]

Hey guys,

I started up my 71 mach today (351C-4V) and it was idling rough, kind of a bumpy up and down idle.. I then decided to randomly press the brakes and the engine would struggle. Same with turning the headlights on. First I thought the brake problem was a vacuum leak but its actually just the brake lights causing the car to struggle when I press down.

A few months back I had installed a redone wiring harness, headlight harness, and fuse block from Midlife which originally made this issue seem to go away.

As of 4/10/2018 I also installed a new engine gauge harness and ignition switch. The car still stalls when I turn the headlights on or use the brake lights.

Thanks in advance

 

[midlife]

Pressing the brakes to make the engine struggle sure sounds like a vacuum leak to me; that and bumpy up and down idle (like surging?) indicates the same.

 

[icejawa]

Pressing the brakes to make the engine struggle sure sounds like a vacuum leak to me; that and bumpy up and down idle (like surging?) indicates the same.

Oh damn, time to spray carb spray all over the usual spots. I am guessing intake manifold leak because I pulled it off once and it had no gaskets.

 

[rvrtrash]

Pressing the brakes to make the engine struggle sure sounds like a vacuum leak to me; that and bumpy up and down idle (like surging?) indicates the same.

Oh damn, time to spray carb spray all over the usual spots. I am guessing intake manifold leak because I pulled it off once and it had no gaskets.

It has a metal "valley pan" that also acts as a gasket for the intake ports, and rubber seals on the ends.

 

[icejawa]

Pressing the brakes to make the engine struggle sure sounds like a vacuum leak to me; that and bumpy up and down idle (like surging?) indicates the same.

Oh damn, time to spray carb spray all over the usual spots. I am guessing intake manifold leak because I pulled it off once and it had no gaskets.

It has a metal "valley pan" that also acts as a gasket for the intake ports, and rubber seals on the ends.

Ah yes. I've also read that the manifold bolts can come loose and cause vacuum leaks. People also claim that a 4 piece gasket set works better than the valley pan gasket. Maybe I should get that setup. I should've probably mentioned I have an edelbrock performer manifold on there right now

 

[rackerm]

If the idle is smooth without pressing the brake pedal and becomes rough when pressing the brake pedal, it could be a bad (leaking)power brake booster diaphragm. I had these symptoms once.

 

[Fabrice]

[ People also claim that a 4 piece gasket set works better than the valley pan gasket]

When you are in Europe and you need a new gasket, this means today at least 2 weeks waiting, and in the past 1 to 2 months waiting.

because of this detail, I've been forced to run without the metal gasket until the new one would arrive. Both on 2V and 4V config.

The only difference is that your carb/intake gets hotter faster, which for short distance trip or during winter improves a bit the fuel mix when air is cold.

Once at operating temp, things changes and the 351, become less responsive to the pedal. I'd say, use the metal gasket.

[ I've also read that the manifold bolts can come loose and cause vacuum leaks.]

I don't want to play the myth buster here, but you got to really do your best to screw up the assembly of your engine to get this kind of situation. Or use the wrong/damaged/corroded/dirty bolts and not torque them in right order/force etc..

In my experience, its pretty much the opposite when done by the book. Even if no bolts would hold the intake, it would not come off without a fight and some kind of lift. Bolts would certainly not come loose either. There has to be something not done right so this can occur. frankly I wouldn't know what.

As you have a vacuum leak, aside making sure you do not assemble anything before contact areas are mirror clean and dry (which can be tedious and hard on your back when engine is in the car), there is one thing I would advise to go outside the book for your install. In my eyes, the cleveland has a small design flaw for the front and rear "s" gaskets, especially if you use after market intakes or have resurfaced your heads. Install these 2 gaskets first on block, with a thin layer of sealant and let dry a few minutes. Then at the 4 corners where block/heads/intake meet, no matter the gaskets quality, always add an extra drop of sealant there and triple check these two gaskets do not move a bit during install. If you do this, I assure you, you'd need to drill your intake to get a leak again

 

[turtle5353]

I never run the turkey pan. Never had an issue. I use the gaskets at the ports and a large bead of silicone on the ends. Ditch the end rubber gaskets.

https://www.summitracing.com/parts/fel-1228/overview/make/ford

 

[Fabrice]

Ditch the end rubber gaskets.

That's one way to fix the "flaw"

 

[icejawa]

I was unable to find a vacuum leak near the intake, so I am guessing either brake vacuum leak, or could it be the alternator? When I turn the headlights on the same thing happens as pressing the brakes does. The ALT gauge surges in a pattern. (assuming it works properly with the new wiring harness)

 

[Fabrice]

If you set a volt meter at positive coil, after engine runs, does it drop when you switch lights on? It should be > 12

if yes, I'd disconnect the ignition wire from positive coil and test with a wire directly from batt+ to see if the drop still occurs.

Also check that your engine is grounded.

 

[icejawa]

I'll have to post a video after I try that in just a sec thanks for the advice

 

[icejawa]

I attached a test lead wire from the battery to the + terminal on the coil. The car started on the first crank and ran smoother. When I screwed with the head lights it didn't stall. When I took it off and screwed with the lights it would stall out again. It looks like we narrowed the problem down but I still am not sure what needs to be done.

 

[midlife]

You're probably losing voltage from the battery to the ignition switch and back out to the coil. Has your wiring been butchered in the past? Any signs of damage anywhere? Are your connections tight and solid?

Disconnect your wire to the coil, and put the key in RUN. Measure the voltage at that 90* slip-on connector as well as battery voltage, and post that here. If you have a good difference, disconnect the engine gauge feed harness and probe the red/green wire female bullet lead at the harness from the headlight side. Is it the same as what it was at the disconnected coil or better?

 

[icejawa]

You're probably losing voltage from the battery to the ignition switch and back out to the coil.  Has your wiring been butchered in the past?  Any signs of damage anywhere?  Are your connections tight and solid?  

Disconnect your wire to the coil, and put the key in RUN.  Measure the voltage at that 90* slip-on connector as well as battery voltage, and post that here.  If you have a good difference, disconnect the engine gauge feed harness and probe the red/green wire female bullet lead at the harness from the headlight side.  Is it the same as what it was at the disconnected coil or better?

I had my headlight and under dash harnesses refurbished by you if I recall correctly so they should be good. The wires to the ignition coil look good too but I didn't do those myself. I did the voltage test in the slip on connector and I got about 8.1 Volts. I forgot to get the battery reading and I will have to check the rest tomorrow since its getting late. I wish I had a mini-pocket-midlife that could diagnose electrical problems.

LOL and I think my valve covers are on the wrong sides, oh my god the guy who sold it to me grrrr. The oil filler cap is under the passenger side brace

 

[midlife]

Are you using your original engine gauge feed harness? I've found that these do not hold up well over the years. 8.1V at the coil while the engine is not running is not good at all, and that's the source of your problems. Make the measurements at the connector (now disconnected) of the engine gauge feed harness and see what you get.

My bet is on a bad engine gauge feed harness.

 

[icejawa]

Are you using your original engine gauge feed harness?  I've found that these do not hold up well over the years.  8.1V at the coil while the engine is not running is not good at all, and that's the source of your problems.  Make the measurements at the connector (now disconnected) of the engine gauge feed harness and see what you get.

My bet is on a bad engine gauge feed harness.

There is a repro engine feed harness in there right now which I think is from CJPony Parts. My guess might be that this harness is for a 302 v8 because there is also one for a 351C on the CJP site which costs more. The voltage reading at the plug that the harness goes into reads roughly 11.8 DCV.

 

[midlife]

There ya go! Somewhere between the plug from the harness and the coil, it is losing a lot of voltage. Even repro harnesses may not be as good as you think. You can measure the resistance between the coil lead and the male pin on the gauge feed plug to see if it anomalous (greater than ~ 1 ohm).

 

[Don C]

The ignition switch is a likely source of the problem. The internal contacts get corroded and dirty over time, and the springs get weak and rusty.