Backfires through intake, please help.
11/10/12, 07:54 AM
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Backfires through intake, please help.
Hi guys,
My 94 GT has backfires through intake on low rpm's under load (mostly when engine is cold). After inspection of an ignition system, we have discovered spark illuminations around ignition coil on high rpm's. Does it mean that the coil is bad and it may cause backfires on low rpm's? Could also bad spark plugs produce this problem? Factory sparks are Motorcraft with .55 and I have installed Bosch with 0.44.
Before ignition system check, we've also checked computer codes and it says EGR valve is bad, but most people say that this can't create backfires in the intake manifold but instead, it can create backfires in the exhaust system on deceleration.
So I really need your help on this, I need to decide what components I need to buy, well, here's list:
Ignition coil
Spark plugs (factory ones, with 0.55 gap)
Spark plug wires
MAF sensor
Water temp sensor
EGR valve
Thanks to all
My 94 GT has backfires through intake on low rpm's under load (mostly when engine is cold). After inspection of an ignition system, we have discovered spark illuminations around ignition coil on high rpm's. Does it mean that the coil is bad and it may cause backfires on low rpm's? Could also bad spark plugs produce this problem? Factory sparks are Motorcraft with .55 and I have installed Bosch with 0.44.
Before ignition system check, we've also checked computer codes and it says EGR valve is bad, but most people say that this can't create backfires in the intake manifold but instead, it can create backfires in the exhaust system on deceleration.
So I really need your help on this, I need to decide what components I need to buy, well, here's list:
Ignition coil
Spark plugs (factory ones, with 0.55 gap)
Spark plug wires
MAF sensor
Water temp sensor
EGR valve
Thanks to all
11/10/12, 09:56 AM
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Wires are as much old as the car itself I think, more than 10 years or so. It's a very loud backfire in the air filter. It's almost impossible to drive when engine is cold. It produces backfires so many times, I have to first warm it up good to drive relatively well.
11/10/12, 01:44 PM
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I'm not getting how a bad wire or coil would cause a backfire through the intake/air filter. Would the coil be random firing while an intake valve is open? Is that what happens when coils are going bad or do they just fail? Even if a plug wire is fautly, how does that ignite air/fuel in the intake? 
I would be thinking more along the lines of a stuck valve - possibly even a cam timing issue - that is allowing the plug to fire while an intake valve is still open.
And why did you gap the Bosch plugs closer? Has it run ok with the Bosch before this started happening?
I would be thinking more along the lines of a stuck valve - possibly even a cam timing issue - that is allowing the plug to fire while an intake valve is still open.
And why did you gap the Bosch plugs closer? Has it run ok with the Bosch before this started happening?
Last edited by cdynaco; 11/10/12 at 01:48 PM.
11/10/12, 02:02 PM
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ok, how you associate this with engine temperature? If it is a timing issue, why the car works better when it's warmed up? That why I don't think that it's a timing. I have replaced spark plugs just because they were just too old. I didn't gave much attention to gap that time, it was just .44 bosh sparks which I bought at rockauto. Car was working normally, then this happened.
11/10/12, 02:12 PM
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I still don't understand how a failing coil or bad wire would allow detonation while an intake valve is open.
The only other think I could think of if that's it, is the wire is arcing to the intake and the air/fuel in the intake itself is igniting - not from firing through an open cylinder.
But is that possible? Is that intake metal?
11/10/12, 02:26 PM
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no, engine sound is good. just a little bit rough when idle. Maybe not detonation but misdetonation?? Fact is that the coil is nicely illuminating in dark like a weld. Distributor is brand new motorcraft.
11/10/12, 02:29 PM
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11/10/12, 02:33 PM
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You didn't mix the plug wires up did you when you put the cap on? I did that some years ago and it would backfire through the carb. Run rough at idle but at a higher rpm it would smooth out some. I thought 'no way - I know I put those wires on correct'. After an hour or so of nothing else working, I went and checked them again and
ermm.... I'll double check it.