Bad Spark issue
Thread Starter
Drifting
Joined: Jan 2003
Posts: 1,894
Likes: 3
From: Reading PA.
Bad Spark issue
Ok guy's here's the deal I replaced the plugs the wires are fairly new so I replaced the Ign. module and just yesterday replaced my Hypertech coil,cap and rotor. I used one of those spark checkers that has the clear tube in it so you can see it flash when it sparks. Well I connected it between the plug and the wire and it has a bad spark (not steady) so I take the plug wire out of the equasion and hook the spark checker between the dist. cap and the plug wire and it also has bad spark from there also. What else could it be causing this. My car is a 90 auto with about 42k on the speedometer. Pipe
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
It could be a lot of things. Look at the rotor right under the center of the rotor. There is a hemispherical depression under the center of the metal arm and if you have an open plug wire, the spark jumps through this depression and makes a carbon track . Look at the inside of the cap with good light, you might find carbon tracks. No matter how new your plug wires are, pull each one, one at a time and measure their resistance, they should be about 5000 ohms per foot. Look at your wire looms and replace any that are missing or broken. Plug wire looms keep plug wires from touching metal and all plug wires have microscopic pinholes in them and if touching metal, spark through these pinholes. I once had a miss on 2 day old plug wires, one became open circuit. New wires are not necessarily automatically good.
Thread Starter
Drifting
Joined: Jan 2003
Posts: 1,894
Likes: 3
From: Reading PA.
Thanks Jfb for the reply. The cap and rotor and coil are brand new. When I tested with the spark checker it was bad spark allready coming from the dist. before it even got to the plug wires. Could it be a bad dist. or is it a bad ECM? Everything in the dist. is just about new. Pipe
Instructor
Joined: Jul 2007
Posts: 174
Likes: 0
From: Toronto Ontario
Check your ground harnesses for corrosion. Also what's your battery voltage like? While vette is running you should have at least 14.5 volts. Also check voltage at v+ terminal at distributor. Use dielectric grease on ignition wire boot terminals ( both at the cap and spark ends). Also spray break parts cleaner inside cap to get rid of any carbon tracks.
Thread Starter
Drifting
Joined: Jan 2003
Posts: 1,894
Likes: 3
From: Reading PA.
Trackman44 you mean check the ground coming from the battery to the engine block? and the terminals right behind the battery? How can I check the volts at the dist? I'm going to test the volts at the battery and also when it's running i'll let ya know whats up. Pipe
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
When you start looking for the problem, NEVER assume because you have new parts that the new parts are ok. Open circuit plug wires will not allow your spark checker to flash. You need to measure the resistance of each plug wire. Brake cleaner sprayed inside the cap will not fix carbon tracks. Carbon tracks are forever! A test voltmeter will allow you to see if the 12v power to your distributor is constant or not and you cannot have a spark when there is no 12v present. Check for intermittent 12v on the distributor.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
I have an 87, so if the 90 is like my 87, then you will find on the left side of the distributor a large pink wire which is the 12v that powers the circuits inside the distributor. There is also a pickup coil that supplies reference pulses to the ECM and is a purple/wh wire. If you have an oscilloscope you can watch these pulses and determine that they are continuous. The ECM uses these pulses to tell the spark module to generate a spark, no reference pulse, no spark, intermittent reference pulses, intermittent spark.
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Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
You may want to check the pick-up coil as well since you got the thing open......pictures with procedures:
http://www.autozone.com/az/cds/en_us...es.htm#hd1-1-1
Race Director
Joined: Jan 2006
Posts: 10,039
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From: CA
Or does it show a weak spark.If the car runs ok,maybe it's a bad tester.
Instructor
Joined: Jul 2007
Posts: 174
Likes: 0
From: Toronto Ontario
Is the vette running ok? ( idles fine, no erratic idle, doesn't bog or hesitate when accelerating?) If so why are you concerned about spark? If you didn't have spark, the engine wouldn't run. Also battery voltage is about right for your vette (12.6v not running, 14.5v running). If you have missfires or hesitations, let us know.
Instructor
Joined: Jul 2007
Posts: 174
Likes: 0
From: Toronto Ontario
Ok now we are getting somewhere. Did you ohm your injectors? ( should be around 16 ohms each). Maybe some injectors are bad and thats the reason for missfires. Also check fuel pressure. You probably have a fuel delivery problem rather than a spark problem.
Thread Starter
Drifting
Joined: Jan 2003
Posts: 1,894
Likes: 3
From: Reading PA.
Trackman44 you replied to my post a few weeks back when I had problems with the car not starting and it turned out to be the coolant temp. sensor. Back then I replaced the injectors with new FMS #24 LB. injectors. My old #22lb.ers might still be good yet. Anyway the temp. sensor is new the ign. module, coil, cap and rotor are new. Before I put the new injectors in the fuel pressure was at 42lbs. when I put the new injectors in I backed off some on the pressure regulator but didn't really check it after the new injectors were installed. THANK YOU FOR ALL THE HELP Pipe
Instructor
Joined: Jul 2007
Posts: 174
Likes: 0
From: Toronto Ontario
Last edited by trackman44; Sep 2, 2007 at 05:34 PM.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Your symptoms match exactly, missing spark. Measure your plug wires and also, at night, turn off your underhood lights and look for sparks along each plug wire.
Also, measuring d.c. ohms on injector coils is almost worthless, but it will find gross problems. An ohmeter will not find an injector coil that has a turn to turn short (common coil failure), but an impedance bridge that measures coil inductance and coil Q will easily find a turn to turn short. A turn to turn short will make an injector not work well (very sluggish pintle movement). I found a bad injector on my 87 with my impedance bridge. D.C. resistance was perfect, but its inductance and Q were 1/2 the value of the other injectors.
Also, measuring d.c. ohms on injector coils is almost worthless, but it will find gross problems. An ohmeter will not find an injector coil that has a turn to turn short (common coil failure), but an impedance bridge that measures coil inductance and coil Q will easily find a turn to turn short. A turn to turn short will make an injector not work well (very sluggish pintle movement). I found a bad injector on my 87 with my impedance bridge. D.C. resistance was perfect, but its inductance and Q were 1/2 the value of the other injectors.
Last edited by jfb; Sep 2, 2007 at 11:29 PM.
Thread Starter
Drifting
Joined: Jan 2003
Posts: 1,894
Likes: 3
From: Reading PA.
Ok guy's here's the latest find. I removed the wire connector at the dist. that said bat. and put a voltmeter lead in it and grounded the other. It showed 12 volts coming to the dist. with the key on. Next I removed the cap and unhooked the connector from the pickup coil to the ign. module. The Haynes manual said the wires should ohm between 500 and 1500 ohm's steady. My test 823 ohms steady so I guess it can't be the pickup coil can it? Ithought about putting the old injectors #22s back in and see if there's any difference. Maybe I should try new plug wires. And maybe my spark checker isn't any good. When I jump on it hard it pops and don't accelerate smooth. YOU GUY'S ARE A GREAT HELP THANKS AGAIN. Pipe