no start condition (scope graph)
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New User
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From: Slovakia
no start condition (scope graph)
Hi, I have a 1990 Bronco, 351W, no start condition. Sparks are present when I connect spark plug to wire disconnected from distributor, but not very strong. I have measured ignition with a scope: Maximum voltage at spark plug - 1 kV instead of about 8 kV, on the ign.coil connector (coil discinnected) is AC voltage present but amplitude is under 1 Volt (jumping between 11,5 V and 10,8 V) It looks like there is insufficient ground when TFI is grounding the coil. Where is the problem ? At suppresion resistors? Or?
Voltage graph at coil connector (coil disconnected)
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Voltage graph at coil connector (coil disconnected)
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Fleet Owner
Joined: Oct 2005
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From: Kentucky
I have never had the luxury of using a 'scope to troubleshoot an ignition problem. I would start at the PIP signal then work my way out through the TFI then on to the coil itself.
Some good reading here: SBFTech.com TFI Module/Hall Sensor Testing Procedure
Some good reading here: SBFTech.com TFI Module/Hall Sensor Testing Procedure
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New User
Joined: May 2011
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From: Slovakia
today, scopes are cheap, no reason to avoid them
sparks are present, but not enough energy at discharge to light on pressured air/fuel mixture at compression pressure... Have any idea where to look on ?
sparks are present, but not enough energy at discharge to light on pressured air/fuel mixture at compression pressure... Have any idea where to look on ?
Fleet Owner
Joined: Oct 2005
Posts: 20,780
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From: Kentucky
Verify the PIP signal value then move onto the TFI. The valuee listed in the link above may be a bit more using a 'scope.
Even at 8KV, as you listed before, is probably not enough to fire off the mixture. When visually looking at the spark across the plug gap what color is it? Should be a nice fat blue. Anything less indicates a problem on the secondary side of the ignition coil. There is a reason why the coil is rated at 30-40 KV or better.
Even at 8KV, as you listed before, is probably not enough to fire off the mixture. When visually looking at the spark across the plug gap what color is it? Should be a nice fat blue. Anything less indicates a problem on the secondary side of the ignition coil. There is a reason why the coil is rated at 30-40 KV or better.
Lead Driver
Joined: Aug 2006
Posts: 5,670
Likes: 12
From: Sand Lake, MI
First looks like way more involved then need be, where are you from? I can't read that, is that Russian? (if I'm way off with my guess, sorry about that!) but can tell yea its under 12 but showing a wave form.
Did you test the coil itself? Don't know the exact output of a ford coil off hand but would be more like 20Kv or more, not 8.
High output models are near 50,000volts.
The fact the TFI is grounding the coil, a waveform is created looking at your graph? suggests it is working.
Quick excerpt copy/paste from google,
Using an ohmmeter, check the resistance between the side terminals of the coil. Do this with all of the wires to the coil disconnected.
You should see 0.75 to 0.81 ohm of resistance. Then check the resistance between either side terminal and the center high tension terminal. The reading should be 10,000 to 11,000 ohms. Any significant deviation from these numbers would indicate that the coil could be defective.
Might not be exact for "ford" coil however should be in the ball park.
Did you test the coil itself? Don't know the exact output of a ford coil off hand but would be more like 20Kv or more, not 8.
High output models are near 50,000volts.
The fact the TFI is grounding the coil, a waveform is created looking at your graph? suggests it is working.
Quick excerpt copy/paste from google,
Using an ohmmeter, check the resistance between the side terminals of the coil. Do this with all of the wires to the coil disconnected.
You should see 0.75 to 0.81 ohm of resistance. Then check the resistance between either side terminal and the center high tension terminal. The reading should be 10,000 to 11,000 ohms. Any significant deviation from these numbers would indicate that the coil could be defective.
Might not be exact for "ford" coil however should be in the ball park.
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New User
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From: Slovakia
I have filled some more info, I am from Slovakia, I have one of five FSB in my country.
I have checked all the parts separately - coil resistances (I have two), TFI resistances (I have 3 TFIs here), PIPs (3 pcs), I changed distributor two times (first one reman Cardone, second one is Mallory, all new - PIP and TFI).
That waveform should have bigger amplitude to make higher voltage at secondary side of the coil... Now amplitude is low and it makes only 1,5 kV at the secondary side, thats it. Simply - coil grounding is not sufficient. Question is why ?
I have checked all the parts separately - coil resistances (I have two), TFI resistances (I have 3 TFIs here), PIPs (3 pcs), I changed distributor two times (first one reman Cardone, second one is Mallory, all new - PIP and TFI).
That waveform should have bigger amplitude to make higher voltage at secondary side of the coil... Now amplitude is low and it makes only 1,5 kV at the secondary side, thats it. Simply - coil grounding is not sufficient. Question is why ?
Fleet Owner
Joined: Oct 2005
Posts: 20,780
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From: Kentucky
Before you start condemning the trigger side of the coil, verify what the supply voltage is. Should be whatever the battery voltage is (~12.5- 14.5 VDC).
This should be similar to what you have:
This should be similar to what you have:
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Lead Driver
Joined: Aug 2006
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From: Sand Lake, MI
That and verify all grounds are intact and clean and tight.
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New User
Joined: May 2011
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From: Slovakia
well, again measured the TFI resistances, all of them - within ranges in the table. Supply voltage at the coil is exact battery voltage. Grounding cable in the TFI harness - from TFI connector to coil ground - OK, same are the PCM grounds - no resistance between them and battery ground.
Where to look now?
Where to look now?
Fleet Owner
Joined: Aug 2005
Posts: 23,666
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From: Easton,Ks
Note that the Ignition Ground is inside the distributor and no where else. The Distributor must have a good ground to the engine block. Is the hold down bolt installed for the Distributor?
Also make sure the engine block has a good ground to the battery. The large Neg (-) battery cable must go to the engine block and NOT the frame. If you have it going to the frame and not the engine you will have problems. You may ground the frame but it is not needed for the running of the engine.
Also make sure the engine block has a good ground to the battery. The large Neg (-) battery cable must go to the engine block and NOT the frame. If you have it going to the frame and not the engine you will have problems. You may ground the frame but it is not needed for the running of the engine.
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New User
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From: Slovakia
yes, the distributor has good ground. Engine is grounded perfect via new thick cable from battery negative to a big 3G alternator case. Looks like problem is somewhere else instead of bad grounds...
Posting Guru
Joined: Dec 2009
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From: Calverton
Yes this is very true, block seating area should be shined up...and I had this problem after replacing a distributor...use a multimeter to battery + post and to the distributor housing to check.
Fleet Owner
Joined: Oct 2005
Posts: 20,780
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From: Kentucky
Please define what that means in bold. The ignition circuit on these trucks in not that elaborate. Your low output leads one to believe you have a bad coil, low supply voltage or a grounding issue. Have you manually momentarily grounded the negative side of the coil to see what the output on the secondary looks like? Use a known good ground if you try this. If the secondary value increases then you know it is a grounding/wiring issue. If the value remain the same start looking at the coil, related connections and wiring.
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From: Slovakia
didn't try to scope, for not enough time, just plug the Fluke DVOM and readings were between 3V and about 9V. Tomorrow will post the graph from scope.
When grounding manually the coil, secondary output is a big difference. Also coil has good resistance values, I have two coils, tried both, their resistances are OK
When grounding manually the coil, secondary output is a big difference. Also coil has good resistance values, I have two coils, tried both, their resistances are OK