302 C4 wont idle in reverse or drive i.e. under load - please help?

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Author Topic: 302 C4 wont idle in reverse or drive i.e. under load - please help?  (Read 711 times)

Offline robdiv

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Hi
I have a 1968 Mustang hardtop with a newly rebuilt 302 Windsor with a new Bosch electronic ignition & new vacuum advance - old 600 Holley.
The car stalls in drive or reverse and seems worse when power steering is also used.
I had the same issue before the rebuild and using the old distributor running petronixs ignition...so nothing has changed still stalls
PVC value works and also vacuum hoses appear good.
Could it be the Holley or something else......any ideas?

Offline pmb0186

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what idle speed?
does anyone remember laughter

Offline GLENN 70

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Re: 302 C4 wont idle in reverse or drive i.e. under load - please help?
« Reply #2 on: November 20, 2020, 01:52:07 PM »
Make sure it has a full 12 volts to the dizzy . Idle speed to as said .

Offline GEOFF289

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What Glenn said.

Original points set up had a resistor in the circuit reducing voltage to the coil to about 9 volts once the engine was running. Early Pertronix distributors were OK with this but newer ones and your Bosch need the full 12 volts.

I had this issue when I put the new engine in a few years ago. The old one had a Pertronix kit in it and I assumed the resistor had been bypassed but the new engine with an MSD in it would start but died if the idle fell below about 1,200 rpm.

I eventually tested my assumption and found only 9 volts at the coil. That's when I learned that early Pertronix kits were OK with the lower voltage. Bypassed the resistor and the problem was solved. 

Offline robdiv

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Re: 302 C4 wont idle in reverse or drive i.e. under load - please help?
« Reply #4 on: November 21, 2020, 01:02:37 AM »
Yes, have a new coil so full 12 volts match to electronic Bosch distributor.
Not sure of actual idle speed as dont have a tacho - but its not slow
Motor is not that old recently rebuilt so in park/neutral revs well etc.
Its only in drive/reverse it "bogs" down and stalls - what are the chances its the torque converter? 

Offline evan

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Re: 302 C4 wont idle in reverse or drive i.e. under load - please help?
« Reply #5 on: November 21, 2020, 09:12:27 AM »
Has the cam been upgraded from stock? Is it possible that it requires a higher stall speed to stop it bogging down under load? Have you tried simply increasing your idle speed (within reason)?

Evan.

Offline scollist

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Yes, have a new coil so full 12 volts match to electronic Bosch distributor.

Don't assume that because you have a '12 volt coil' you will be getting 12 volts to the distributor.

As GEOFF289 said below "I eventually tested my assumption and found only 9 volts at the coil" - you should check that you are getting 12 volts at the coil.

The 'Pink' resistor wire designed into Ford wiring looms is there to ensure that once the car has started, only 9 volts (approx.) is provided to the distributor so that the points don't burn out.  A higher 12 volts is only provided during start cranking.

If you have replaced the distributor with one that requires a constant 12 volts, you must take the pink wire out of sequence. Either by replacing it in the loom, or by using it to power a relay that then provides a direct 12 volt feed from the battery to the coil/distributor.



Offline GEOFF289

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Don't assume that because you have a '12 volt coil' you will be getting 12 volts to the distributor.

As GEOFF289 said below "I eventually tested my assumption and found only 9 volts at the coil" - you should check that you are getting 12 volts at the coil.

The 'Pink' resistor wire designed into Ford wiring looms is there to ensure that once the car has started, only 9 volts (approx.) is provided to the distributor so that the points don't burn out.  A higher 12 volts is only provided during start cranking.

If you have replaced the distributor with one that requires a constant 12 volts, you must take the pink wire out of sequence. Either by replacing it in the loom, or by using it to power a relay that then provides a direct 12 volt feed from the battery to the coil/distributor.

If you test the voltage at the distributor with the ignition on but the engine not running it'll show 12 volts even with the resistor in the circuit. You have to test it with the engine running.

Offline robdiv

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Re: 302 C4 wont idle in reverse or drive i.e. under load - please help?
« Reply #8 on: November 21, 2020, 10:29:23 AM »
Has the cam been upgraded from stock? Is it possible that it requires a higher stall speed to stop it bogging down under load? Have you tried simply increasing your idle speed (within reason)?

Evan.

Hi Evan,
Its fairly high already, its a rolling cam but mild, I had same issue with stock cam....I can drive for ages in "drive" try to reverse and it just bogs down instantly and cuts out when I engage reverse after park? Only things left to replace or rebuild are holley 600 & torque converter or a vacuum issue?
   

Offline robdiv

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Re: 302 C4 wont idle in reverse or drive i.e. under load - please help?
« Reply #9 on: November 21, 2020, 10:38:09 AM »
What Glenn said.

Original points set up had a resistor in the circuit reducing voltage to the coil to about 9 volts once the engine was running. Early Pertronix distributors were OK with this but newer ones and your Bosch need the full 12 volts.

I had this issue when I put the new engine in a few years ago. The old one had a Pertronix kit in it and I assumed the resistor had been bypassed but the new engine with an MSD in it would start but died if the idle fell below about 1,200 rpm.

I eventually tested my assumption and found only 9 volts at the coil. That's when I learned that early Pertronix kits were OK with the lower voltage. Bypassed the resistor and the problem was solved.

I have changed the distributor and coil to match to Bosch electronic, didn't make any difference to stalling issue from Pertronix set up, motor runs well in park or neutral only cuts out under load even if a fast idle? What is the chances its the transmission or vacuum or holley 600?

Offline robdiv

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Re: 302 C4 wont idle in reverse or drive i.e. under load - please help?
« Reply #10 on: November 21, 2020, 10:43:40 AM »
What Glenn said.

Original points set up had a resistor in the circuit reducing voltage to the coil to about 9 volts once the engine was running. Early Pertronix distributors were OK with this but newer ones and your Bosch need the full 12 volts.

I had this issue when I put the new engine in a few years ago. The old one had a Pertronix kit in it and I assumed the resistor had been bypassed but the new engine with an MSD in it would start but died if the idle fell below about 1,200 rpm.

I eventually tested my assumption and found only 9 volts at the coil. That's when I learned that early Pertronix kits were OK with the lower voltage. Bypassed the resistor and the problem was solved.

Hi mate
How do I test for 12 volts at the coil? and where is the resistor wire located? cheers Rob 

Offline GEOFF289

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If you just connected the original wiring to a new coil the resistor will still be active and the new coil won't like it.

Start the engine - sounds like it will idle OK in Park - put a multimeter on it, positive lead to coil positive, negative lead to a good earth. If it reads 12 volts or more your issue isn't the resistor still being in the circuit. If it reads 9 or so, the resistor is still active.

The pink resistor wire is found at the back of the starter switch. You may have to google how to remove the switch. A few centimetres downstream of the switch there is a kind of bulge in the pink wire which is the resistor. On the engine side of the firewall this pink wire changes colour.

As Shane said, you can either connect a new wire direct to the starter switch, or use the pink wire - whatever colour it is under the bonnet - to trigger a relay that then connects 12 volts direct from the battery.

All of that said, reading the symptoms again I'm starting to think this won't be the issue (but its easy to check and fix so worth doing). As I said, mine wouldn't idle below about 1,200 revs until I sorted this out. It sounds like your's is OK at normal idle in Park but can't handle the 100 or so rpm drop when it goes into gear.

I wonder if its some sort of weird issue with the neutral safety switch?

Anyway, I'm sure you'll get it sorted.

Offline robdiv

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Re: 302 C4 wont idle in reverse or drive i.e. under load - please help?
« Reply #12 on: November 21, 2020, 02:55:35 PM »
If you just connected the original wiring to a new coil the resistor will still be active and the new coil won't like it.

Start the engine - sounds like it will idle OK in Park - put a multimeter on it, positive lead to coil positive, negative lead to a good earth. If it reads 12 volts or more your issue isn't the resistor still being in the circuit. If it reads 9 or so, the resistor is still active.

The pink resistor wire is found at the back of the starter switch. You may have to google how to remove the switch. A few centimetres downstream of the switch there is a kind of bulge in the pink wire which is the resistor. On the engine side of the firewall this pink wire changes colour.

As Shane said, you can either connect a new wire direct to the starter switch, or use the pink wire - whatever colour it is under the bonnet - to trigger a relay that then connects 12 volts direct from the battery.

All of that said, reading the symptoms again I'm starting to think this won't be the issue (but its easy to check and fix so worth doing). As I said, mine wouldn't idle below about 1,200 revs until I sorted this out. It sounds like your's is OK at normal idle in Park but can't handle the 100 or so rpm drop when it goes into gear.

I wonder if its some sort of weird issue with the neutral safety switch?

Anyway, I'm sure you'll get it sorted.

Thanks Geoff...I will give as you said a go, the fact that the motor can idle low or high no problems in Park makes me think torque converter, as all these issues where around with old motor, old distributor, old coil etc. the only things I havent changed are the C4 and the holley....cheers Rob

Offline robdiv

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Re: 302 C4 wont idle in reverse or drive i.e. under load - please help?
« Reply #13 on: November 21, 2020, 06:40:46 PM »
If you just connected the original wiring to a new coil the resistor will still be active and the new coil won't like it.

Start the engine - sounds like it will idle OK in Park - put a multimeter on it, positive lead to coil positive, negative lead to a good earth. If it reads 12 volts or more your issue isn't the resistor still being in the circuit. If it reads 9 or so, the resistor is still active.

The pink resistor wire is found at the back of the starter switch. You may have to google how to remove the switch. A few centimetres downstream of the switch there is a kind of bulge in the pink wire which is the resistor. On the engine side of the firewall this pink wire changes colour.

As Shane said, you can either connect a new wire direct to the starter switch, or use the pink wire - whatever colour it is under the bonnet - to trigger a relay that then connects 12 volts direct from the battery.

All of that said, reading the symptoms again I'm starting to think this won't be the issue (but its easy to check and fix so worth doing). As I said, mine wouldn't idle below about 1,200 revs until I sorted this out. It sounds like your's is OK at normal idle in Park but can't handle the 100 or so rpm drop when it goes into gear.

I wonder if its some sort of weird issue with the neutral safety switch?

Anyway, I'm sure you'll get it sorted.

I checked the voltage it fluctuates but never goes above 9 volts....you guys may be onto something

Offline pmb0186

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Re: 302 C4 wont idle in reverse or drive i.e. under load - please help?
« Reply #14 on: November 21, 2020, 07:51:32 PM »
I expect if the torque converter is locked up when you drop it in drive it will squeal the tyres
If you drop it into drive without brakes with a little revs then come to a stop keeping it running with both feet you will soon workout if it is a locked converter
It will be very hard to get it to stop completely
On other thing what trans is in it?
« Last Edit: November 21, 2020, 08:09:18 PM by pmb0186 »
does anyone remember laughter

Offline GEOFF289

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I checked the voltage it fluctuates but never goes above 9 volts....you guys may be onto something

OK, it does seem that the resistor is still active in the circuit.

Now run a temporary wire direct from the battery to the coil - positive to positive - and see if it'll idle in gear. If this doesn't solve it you have another problem as well but this one is worth addressing permanently anyway.

Offline robdiv

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Re: 302 C4 wont idle in reverse or drive i.e. under load - please help?
« Reply #16 on: November 23, 2020, 07:46:31 AM »
I expect if the torque converter is locked up when you drop it in drive it will squeal the tyres
If you drop it into drive without brakes with a little revs then come to a stop keeping it running with both feet you will soon workout if it is a locked converter
It will be very hard to get it to stop completely
On other thing what trans is in it?

C4 - Its weird because sometimes it will go into reverse with no accelerator work and it will idle but not smooth, but once the motor is warmed up if you put into reverse or drive it just "snuffs" the motor out almost instantly or idles slow, I could increase revs a tad more? could the resistor going to the coil cause this? I will do the straight to battery test first positive coil to battery and see if any different. cheers Rob   

Offline GEOFF289

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If the choke is functioning properly it'll idle faster on the choke of course.

I don't really know anything about converters but I doubt this is the problem. I reckon you'd know all about it if it was locked up.

Offline robdiv

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Re: 302 C4 wont idle in reverse or drive i.e. under load - please help?
« Reply #18 on: November 23, 2020, 11:10:59 PM »
OK, it does seem that the resistor is still active in the circuit.

Now run a temporary wire direct from the battery to the coil - positive to positive - and see if it'll idle in gear. If this doesn't solve it you have another problem as well but this one is worth addressing permanently anyway.

Yep, ran a temporary wire from positive coil to positive battery, seems to idle better, so far it didn't stall, could be the issue.
I will attempt to replace fuse wire (pink) to get constant 12 volts, Blueprint distributors mention a diode in line not sure why?
Thanks for assistance gents.. 

 

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