Will bad Afm cause no spark?
11-09-10, 07:03 PM
#1
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Will bad Afm cause no spark?
I had no spark after taking apart my car, when I pulled the afm I got spark, does this mean my afm is bad? and will replacing it fix my problem?
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11-11-10, 11:05 AM
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yeah s5's will start and run badly without the afm plugged in... s4's wont because of the fuel pump cut switch.
11-11-10, 02:34 PM
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So I just went and started the car, It half assed started then stalled, felt like it was running on one rotor then flooded.
I just put in new leading plugs, spark plug wires, a set of trailing plugs that looked good, injector grommets, cleaned the ecu and coil grounds after the problem started.
what on earth is the deal?
should I swap out the trailing plugs with new ones, or is that just water under the bridge?
I really need to figure this out guys, my car has been sitting on the side of the road for almost two weeks and is at risk of being towed if a neighbor complains
I just put in new leading plugs, spark plug wires, a set of trailing plugs that looked good, injector grommets, cleaned the ecu and coil grounds after the problem started.
what on earth is the deal?
should I swap out the trailing plugs with new ones, or is that just water under the bridge?
I really need to figure this out guys, my car has been sitting on the side of the road for almost two weeks and is at risk of being towed if a neighbor complains
11-11-10, 03:00 PM
#14
had the same problem. airflow meter broke because i was swapping out some intake bullshit, and it died. the ecu would not tell the coils to fire. so i swapped out a good used unit, and the car fired right up. later on i made a thread about it, and it was confirmed by hailers.
11-11-10, 05:53 PM
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had the same problem. airflow meter broke because i was swapping out some intake bullshit, and it died. the ecu would not tell the coils to fire. so i swapped out a good used unit, and the car fired right up. later on i made a thread about it, and it was confirmed by hailers.
My car was running PERFECTLY before I pulled the intake. the problem I found was no spark, pull afm, get spark. I don't know what else it could be! I even swapped the damned ecu, and had the same issue
11-11-10, 05:59 PM
#16
What you might want to do is take the voltage reading on the wire to the Boost/Pressure sensor that is responsible for the Vref and if it reads lower than 5 volts then disconnect the AFM and see if the reading rises to 5 volts. If it does then the AFM is shorting out the Vref and would prevent the AFM and likely as well the ECU also from working.
11-11-10, 11:04 PM
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What you might want to do is take the voltage reading on the wire to the Boost/Pressure sensor that is responsible for the Vref and if it reads lower than 5 volts then disconnect the AFM and see if the reading rises to 5 volts. If it does then the AFM is shorting out the Vref and would prevent the AFM and likely as well the ECU also from working.
thanks for the tip man!
11-11-10, 11:22 PM
#18
Is stands for "voltage reference," which is sent to a handful of engine sensors and supposedly w/o it the ECU will not function properly. If you really wanted to prove this, all that would need to be done is on a working car the Vref pin at the ECU would need to be depinned briefly and see if this affects spark or not.
11-12-10, 12:35 AM
#19
well the reason why mine broke, was because i disconnected it improperly. i undid the two screws (s4) and pulled. yeah. it would crank up, and drive, but the tach needle would jump all over the place.
driving to school, it just died and didnt want to start. checked literally everything, and it all checked out and where in specs. i just happen to catch a glimpse of a thread that has been lost in the great crash of the forum, and low and behold, it was indeed the air flow meter. i yanked it, and teh car fired right up, and died 3 secconds later. boom, problem found.
driving to school, it just died and didnt want to start. checked literally everything, and it all checked out and where in specs. i just happen to catch a glimpse of a thread that has been lost in the great crash of the forum, and low and behold, it was indeed the air flow meter. i yanked it, and teh car fired right up, and died 3 secconds later. boom, problem found.
11-12-10, 02:18 AM
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well the reason why mine broke, was because i disconnected it improperly. i undid the two screws (s4) and pulled. yeah. it would crank up, and drive, but the tach needle would jump all over the place.
driving to school, it just died and didnt want to start. checked literally everything, and it all checked out and where in specs. i just happen to catch a glimpse of a thread that has been lost in the great crash of the forum, and low and behold, it was indeed the air flow meter. i yanked it, and teh car fired right up, and died 3 secconds later. boom, problem found.
driving to school, it just died and didnt want to start. checked literally everything, and it all checked out and where in specs. i just happen to catch a glimpse of a thread that has been lost in the great crash of the forum, and low and behold, it was indeed the air flow meter. i yanked it, and teh car fired right up, and died 3 secconds later. boom, problem found.
Also what was it doing when it didn't want to start? because I have gotten my car to start twice (out of like 1 million tries), albeit they were short wonky starts that ended in flooding.
Thanks alot everyone for putting time into this thread!
11-12-10, 03:44 AM
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Without the afm, the car should idle almost normal, because that is a basic setting and throttlebody adjustment.
but It will die as soon as you hit the throttle, because there is no fuel being injected to compensate the air going in
but It will die as soon as you hit the throttle, because there is no fuel being injected to compensate the air going in
11-12-10, 12:03 PM
#23
A Vref short is a good idea, but from the sound of it the car will start up briefly, then just die. Or is that with the AFM unplugged? If there was actually no spark, you would not have ignition. How do you know you have no spark? Have you put a timing light on the plug wires during cranking, or pulled a plug/wire & cranked the engine?
Will the engine start and idle at all with the AFM attached, but unplugged? It should idle very rough, but as furb mentioned, it'll die if you open the throttle.
You can also check Vref voltage at ECU pin 2A. The FSM spec is 4.5 - 5.5v. You can do this with the key to 'ON' or the engine running. I would try it with and without the AFM plugged in.
Here's a page out of the training manual describing what the AFM does:
Will the engine start and idle at all with the AFM attached, but unplugged? It should idle very rough, but as furb mentioned, it'll die if you open the throttle.
You can also check Vref voltage at ECU pin 2A. The FSM spec is 4.5 - 5.5v. You can do this with the key to 'ON' or the engine running. I would try it with and without the AFM plugged in.
Here's a page out of the training manual describing what the AFM does:
11-12-10, 12:43 PM
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A Vref short is a good idea, but from the sound of it the car will start up briefly, then just die. Or is that with the AFM unplugged? If there was actually no spark, you would not have ignition. How do you know you have no spark? Have you put a timing light on the plug wires during cranking, or pulled a plug/wire & cranked the engine?
Will the engine start and idle at all with the AFM attached, but unplugged? It should idle very rough, but as furb mentioned, it'll die if you open the throttle.
You can also check Vref voltage at ECU pin 2A. The FSM spec is 4.5 - 5.5v. You can do this with the key to 'ON' or the engine running. I would try it with and without the AFM plugged in.
Will the engine start and idle at all with the AFM attached, but unplugged? It should idle very rough, but as furb mentioned, it'll die if you open the throttle.
You can also check Vref voltage at ECU pin 2A. The FSM spec is 4.5 - 5.5v. You can do this with the key to 'ON' or the engine running. I would try it with and without the AFM plugged in.
I checked spark by pulling a plug/ wire and setting it on the block, then having a buddy crank the car looked at the end of the spark plug, with the AFM attached I didn't have anything, When I unplugged it A nice blue spark jumped the gap on the plug.
I am going to go see if the car will start without the AFM right now, will post results!
11-12-10, 03:43 PM
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ok Tried starting it without the afm...nothing, fired a couple times but no start, then it flooded.
De-flooded and tried again, did this 4 times an no start.
I am completely confused at this point
If my trailing plugs were junk would that cause my car not to start? they looked fine so I re-used them along with a new set of leading plugs
De-flooded and tried again, did this 4 times an no start.
I am completely confused at this point
If my trailing plugs were junk would that cause my car not to start? they looked fine so I re-used them along with a new set of leading plugs