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Intermittent miss

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Pistollero56
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Intermittent miss

Post #1 by Pistollero56 » Wed Oct 02, 2019 12:07 am

I have a 1976 Ford F100. I replaced the 300 in it with a 1990 300 and the 5 speed that was attached to it. I deleted egr, used the 1976 intake and ex.aust manifolds. Put a new yf carb on it for now. I changed the distributor to an hei which was on my old 300. The engine has 160lbs of compression on all cylinders. Timed to 10° btdc. New spark plugs and wires and has 18- 20 lbs of vacuum. It has a little mis every once in a while. It would hardly run and backfire out exaust, and sputter when under any load. I have timed and re timed, replaced the intake gaskets just in case. The last time I timed I forgot the hook the vacuum advance hose back up. It ran pretty smooth buy it still had the little miss every now and then. I have a video that shows the miss. I plugged the va hose back up and started to backfire again. So for one I guess the diaphragm on distributor is bad. But cannot find the miss to save my soul. If tikkng ought is hooked up it runs smooth then every once in a while it bounces retarded 20°. Thanks for any help. I have no problem donating to this site but some members have posted that they are unsure the money gets to the forum. Thanks for any help again and if money is going through ill donate. Thanks

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THE FRENCHTOWN FLYER
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Re: Intermittent miss

Post #2 by THE FRENCHTOWN FLYER » Wed Oct 02, 2019 8:53 am

When you swapped distributors did you put on new wires and cap? Maybe you're getting crossfire / misfire there.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

Pistollero56
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Re: Intermittent miss

Post #3 by Pistollero56 » Wed Oct 02, 2019 3:32 pm

No I did not, and it's very possible it got cracked. Thanks sometimes I overlook the small stuff . I will check when I get home today.

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MechRick
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Re: Intermittent miss

Post #4 by MechRick » Wed Oct 02, 2019 7:13 pm

Pistollero56 wrote:I plugged the va hose back up and started to backfire again.


Check the wires to the pickup inside the distributor. They move when the vacuum advance articulates, maybe one of them is broken inside of the insulation.

Backfires are almost always ignition-related, it takes a seriously screwed-up carb to cause a backfire.
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
EFI head w/mild port work, 3 angle valve job
1996 long block, stock pistons, ARP rod bolts
Stock cam, aluminum cam gear
Hedman header, full mandrel bent duals, crossover, super turbos
http://fordsix.com/forum/viewtopic.php?f=2&t=73244
Bronco II with a 2.3L swap http://fordsix.com/forum/viewtopic.php?f=13&t=72863
1988 F250 2x4, 460 ZF 5 speed.

sdiesel
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Re: Intermittent miss

Post #5 by sdiesel » Thu Oct 03, 2019 10:09 am

nobody on this forum has ever crosswired an engine.....and spent hours in double checking everything...except for wires, then a buddy comes along, and presto,I look like the fool I am, the mask slips.
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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THE FRENCHTOWN FLYER
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Re: Intermittent miss

Post #6 by THE FRENCHTOWN FLYER » Thu Oct 03, 2019 10:22 am

sdiesel wrote:nobody on this forum has ever crosswired an engine.....and spent hours in double checking everything...except for wires, then a buddy comes along, and presto,I look like the fool I am, the mask slips.

That reminds me of the time I posted on Inliners site I was planning on attending an Inliners race. When somebody pointed out that first prize in the race was a Chevy six cylinder engine I replied, FINE. I'll take off a plug wire and race for SECOND place." wink wink
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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68Flareside240
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Re: Intermittent miss

Post #7 by 68Flareside240 » Thu Oct 03, 2019 11:12 am

THE FRENCHTOWN FLYER wrote:That reminds me of the time I posted on Inliners site I was planning on attending an Inliners race. When somebody pointed out that first prize in the race was a Chevy six cylinder engine I replied, FINE. I'll take off a plug wire and race for SECOND place." wink wink


That's great :lol:

Reminds me of the time my dad and granddad were working on his 31 Model A. They had been trying for 30 minutes to get it to run after a oil change and tune up. I was about 7 at the time, and came outside after a nap to them scratching their heads. I asked if they had turned the gas on under the dash. They just looked at each other and laughed, cut it on and fired it up. Air, fuel, spark. Always.

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woodbutcher
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Re: Intermittent miss

Post #8 by woodbutcher » Thu Oct 03, 2019 12:12 pm

:rolflmao: Yep.If ya ain`t got suck,squeeze,bang,blow ya ain`t going nowhere.
Good luck.Have fun.Be safe.
Leo
"People never lie so much as after a hunt,during a war,or before an election".
Otto von Bismarck

guhfluh
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Re: Intermittent miss

Post #9 by guhfluh » Thu Oct 03, 2019 2:59 pm

Just a note here that may at least help it run better. The distributor you purchased probably does not have the correct ignition curve for a 1990 EFI headed 300. If you used the 1990 head on the engine when you swapped it into your truck, it probably needs a lot less advance curve under cruise and load above idle than you're original 1976 carb head engine and a generic HEI distributor curve will give.
1967 F-250 Crew Cab 2wd, 300 6cyl, T-170/RTS/TOD 4-speed overdrive
240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

jzjames
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Re: Intermittent miss

Post #10 by jzjames » Thu Oct 03, 2019 3:10 pm

woodbutcher wrote: Yep.If ya ain`t got suck,squeeze,bang,blow ya ain`t going nowhere.

:lol: :lol: :lol:
I’m gonna be using this. :lol:

Pistollero56
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Re: Intermittent miss

Post #11 by Pistollero56 » Thu Oct 10, 2019 3:55 pm

guhfluh wrote:Just a note here that may at least help it run better. The distributor you purchased probably does not have the correct ignition curve for a 1990 EFI headed 300. If you used the 1990 head on the engine when you swapped it into your truck, it probably needs a lot less advance curve under cruise and load above idle than you're original 1976 carb head engine and a generic HEI distributor curve will give.


I have an aftermarket Hei distributor , I have tries to set the vacuum advance curve not quite sure I have it right. Can you run the 1990 head with the 1976 intake ? I was told i needed to swap heads and cams on the 1990 motor to work with the carburator intake. I took part distributor and tested everything and even replaced the cap and rotor. Still has miss and when I'm going h down the road it drives fine unless i accelerate to fast if I ease it up I can drive great up to 80 mph. If I try to pass or get on it it stumbles and backfires on 4th and 5th gear. Thanks again for any help.

pmuller9
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Re: Intermittent miss

Post #12 by pmuller9 » Thu Oct 10, 2019 4:11 pm

The 1990 engine uses different timing than the 1976 engine.
The 76 engine uses a total timing (Vacuum advance disconnected) around 36 degrees BTDC
The total timing on the 90 engine is closer to 30 degrees BTDC because of the fast burn combustion chambers.
The mechanical advance on the HEI distributor needs to be shortened.

There is no problem putting the 76 intake manifold and carb on the 90 engine.

You also need to check the distributor phasing.
Turn the crankshaft to 20 degrees BTDC and see how close the rotor is pointing to the distributor cap contact for #1 plug wire.

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MechRick
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Re: Intermittent miss

Post #13 by MechRick » Thu Oct 10, 2019 4:31 pm

Pistollero56 wrote: I have tries to set the vacuum advance curve not quite sure I have it right.


Pistollero56 wrote:If I try to pass or get on it it stumbles and backfires on 4th and 5th gear


Does it 'stumble and backfire' with the vacuum advance unplugged? I'm going to echo my post above, simply because I've seen this sooo many times since the first HEI distributors appeared in the 70's. Very common. I like to stretch the pickup leads to test them. Copper won't stretch, but broken copper allows the insulation to stretch like a rubber band.

Pistollero56 wrote:Can you run the 1990 head with the 1976 intake ?


Yes, you can.

Most of the Chevy HEI distributors have about 32-34 degrees of total mechanical advance, which is very close to what the EFI head needs. Other GM makes (Olds, Buick, etc...) will use different advance curves dependent mostly on combustion chamber shape. Check total timing by unplugging the vacuum advance, rev the engine to 3500 RPM and note the amount of advance above base timing with a timing light.

For instance, base timing 10 degrees, 44 degrees at 3500 RPM with the vacuum advance not connected, 44-10 = 34 degrees of mechanical advance.

You can also take note of when full advance comes on, and change springs to move that point up or down. Springs in the HEI are easy. Ford hides theirs below the advance plate, HEI is on top.

What plug gaps are you running?
Last edited by MechRick on Thu Oct 10, 2019 7:12 pm, edited 1 time in total.
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
EFI head w/mild port work, 3 angle valve job
1996 long block, stock pistons, ARP rod bolts
Stock cam, aluminum cam gear
Hedman header, full mandrel bent duals, crossover, super turbos
http://fordsix.com/forum/viewtopic.php?f=2&t=73244
Bronco II with a 2.3L swap http://fordsix.com/forum/viewtopic.php?f=13&t=72863
1988 F250 2x4, 460 ZF 5 speed.

guhfluh
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Re: Intermittent miss

Post #14 by guhfluh » Thu Oct 10, 2019 4:52 pm

MechRick wrote:
Pistollero56 wrote: I have tries to set the vacuum advance curve not quite sure I have it right.


Pistollero56 wrote:If I try to pass or get on it it stumbles and backfires on 4th and 5th gear


Does it 'stumble and backfire' with the vacuum advance unplugged? I'm going to echo my post above, simply because I've seen this sooo many times since the first HEI distributors appeared in the 70's. Very common. I like to stretch the pickup leads. Copper won't stretch, but broken copper allows the insulation to stretch like a rubber band.

Pistollero56 wrote:Can you run the 1990 head with the 1976 intake ?


Yes, you can.

Most of the Chevy HEI distributors have about 32-34 degrees of total mechanical advance, which is very close to what the EFI head needs. Other GM makes (Olds, Buick, etc...) will use different advance curves dependent mostly on combustion chamber shape. Check total timing by unplugging the vacuum advance, rev the engine to 3500 RPM and note the amount of advance above base timing with a timing light.

For instance, base timing 10 degrees, 44 degrees at 3500 RPM with the vacuum advance not connected, 44-10 = 34 degrees of mechanical advance.

You can also take note of when full advance comes on, and change springs to move that point up or down. Springs in the HEI are easy. Ford hides theirs below the advance plate, HEI is on top.

What plug gaps are you running?
I would disagree that the EFI 300 needs 44* total advance under WOT at any RPM, or 34* mechanical advance.

Total under WOT maybe 30* or less and mechanical around 20* or less.
1967 F-250 Crew Cab 2wd, 300 6cyl, T-170/RTS/TOD 4-speed overdrive
240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

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THE FRENCHTOWN FLYER
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Re: Intermittent miss

Post #15 by THE FRENCHTOWN FLYER » Thu Oct 10, 2019 7:05 pm

guhfluh wrote:...Total under WOT maybe 30* or less and mechanical around 20* or less.

X2
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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MechRick
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Re: Intermittent miss

Post #16 by MechRick » Thu Oct 10, 2019 7:11 pm

guhfluh wrote:I would disagree that the EFI 300 needs 44* total advance under WOT at any RPM, or 34* mechanical advance.
Total under WOT maybe 30* or less and mechanical around 20* or less.


Is this something you were able to reference, or observe? The one time I tried to map an EFI 4.9L timing map with a scan tool (ignition advance is an available PID), I was seeing 32 degrees at WOT (base plus 22 degrees). Very erratic, but that's probably because I forgot to unplug the knock sensor while taking my readings. I wasn't recommending 44 degrees on the 4.9L. That was just an example. It would be more like base timing 10 degrees, 34 degrees at 3500 RPM, for total mechanical advance of 24 degrees. I can confuse myself sometimes.

When running a Megasquirt on my '96 pickup it seemed to like ~32-34 degrees.
1994 F150, 4.9L/ZF 5 speed, C-Vic police driveshaft
EFI head w/mild port work, 3 angle valve job
1996 long block, stock pistons, ARP rod bolts
Stock cam, aluminum cam gear
Hedman header, full mandrel bent duals, crossover, super turbos
http://fordsix.com/forum/viewtopic.php?f=2&t=73244
Bronco II with a 2.3L swap http://fordsix.com/forum/viewtopic.php?f=13&t=72863
1988 F250 2x4, 460 ZF 5 speed.

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xctasy
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Re: Intermittent miss

Post #17 by xctasy » Fri Oct 11, 2019 3:07 am

MechRick wrote:
guhfluh wrote:I would disagree that the EFI 300 needs 44* total advance under WOT at any RPM, or 34* mechanical advance.
Total under WOT maybe 30* or less and mechanical around 20* or less.


Is this something you were able to reference, or observe? The one time I tried to map an EFI 4.9L timing map with a scan tool (ignition advance is an available PID), I was seeing 32 degrees at WOT (base plus 22 degrees). Very erratic, but that's probably because I forgot to unplug the knock sensor while taking my readings. I wasn't recommending 44 degrees on the 4.9L. That was just an example. It would be more like base timing 10 degrees, 34 degrees at 3500 RPM, for total mechanical advance of 24 degrees. I can confuse myself sometimes.

When running a Megasquirt on my '96 pickup it seemed to like ~32-34 degrees.



Same as the 1996-2005 205 hp Explorer/ and whatever 2004-2010 Mustang and 00 tees Ranger 4.0 SOHC Cologne V6, even though its EDIS.

Same matters...the the advance steps back if knock is present. I've not seen more than 36.5 degrees total.

Programmed TFi is so much fun, none of this recurving. You can even fit a TFi Hall pickup and remote TFi in the old Duraspark II box if you'd like to.


Now, an note on the "dynamic retard" from the pink wire to the DSII. Duraspark does indeed have a function to pause the base timing crank 5 degrees when actioned by voltage to another wire.


Fords Duraspark has a Magnetic VR (Variable Reluctance) spark control, with a micro pause delay in the Duraspark box. There are two OEM (scratch that, maybee more than two OEM wiring types...) the types of wiring due to Fords response to emission requirements and White Box suppliers. Pre 1979, and post 1979 actually, but no one who's selling cares much about the details.

Often, they are wired wrong if replaced, and you can have a, um, " Cadillac Deville" of a time trying to fix it.

The quality of replacement VR Electronic ignition triggers and Duraspark II caps, as well as the more complicated TFi Hall Effect Electronic ignition triggers and caps has felled many 100% reliable cars on the next spring start up. Even the spark plug terminals are in the wrong spot on some.

Generally, if its stockville Duraspark II, it'll always work fine until it starts miss firing, and then stops dead. Replacement of the VR sensor is easy, but wiring it up, and doing it right, with the "reluctor stars" wired and indexed right is a pest.


White box wiring replacements are spat outta the sausage machine, and I've had so much grief with replacement sensors that are designed to make a stable square wave or a self generating "plip/blip" that electronics trigger from.

Wire codes are what the maker decides, and when you replace them, the wires are often wrong, and the square wave mircopause goes in the wrong direction, with base level timing bend out of shape.


For HEI's, the problems are the actual curve isn't a patch on any of the stock 240/300 curves. Solution is is to make sure the parts are good quality, because cross fire and other problems happen with this unit. GM stuff has some solutions to cross fire, and some extra problems. Even silicon wire diameter increases cause problems that don't happen with a stock DSII plug set.

I have an old Sun Scope. Tracing misfire used to be simple with a scope and a rolling road, rather than throwing parts at a "maybee this is the problems" scenario.
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