Backfires Through Intake, Please Help.

Lev · Nov 10, 2012

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

revhead347 · Nov 10, 2012

I'd say either a bad coil or bad wires. Not sure that's your problem with the backfiring though.

Kurt

Lev · Nov 10, 2012

thanks, I'll get both of them

toyman · Nov 12, 2012

You should never see any spark illumination. That will be a sign that the wires are damaged and need replacing. Backfiring into the intake is usually a timing issue. Check the HB to ensure that it's okay. Look for rubber protruding from the center hub on the engine side or any wobble/movement in the HB. With a bad HB you cannot assume the timing you read is correct and is most likely off. I'm sure you meant to sat the gap is o.o54. That is the factory spec and should be used.

Lev · Nov 13, 2012

thanks

well, I've ordered spark plugs with factory gap, wireset, coil and water temp sensor. All Motorcraft. Waiting for delivery. When I get them, I'll also check vacuum leaks around EGR, maybe I'll disable it. What's HB? Harmonic Balancer?

VibrantRedGT · Nov 13, 2012

I've backfired through the intake when my distributor was off. It was so loud it blew my trophies off a shelf behind the car. My neighbor ran over to see I didn't blow myself up. The was first start up with the 347 stroker. Found TDC and readjusted the distributor and it fired right up.

Lev · Nov 13, 2012

The fact is when I accelerate slowly it never backfires even if rpm is way at full. It does when I need relatively more power at low rpm's. It's not as loud as you saying but it's enough to be worried. My dizzy is at right position.

toyman · Nov 13, 2012

Lev said:
thanks

well, I've ordered spark plugs with factory gap, wireset, coil and water temp sensor. All Motorcraft. Waiting for delivery. When I get them, I'll also check vacuum leaks around EGR, maybe I'll disable it. What's HB? Harmonic Balancer?

HB=Harmonic Balancer. There isn't really such a thing as plugs with a 'factory gap' as the plugs may have multiple applications with different gap requirements. So, check the gap. What specifically are you referring to as the 'water temp sensor'? The ECU gets it's signal from the ECT (Engine Coolant Temperature) sensor and the dash gauge from the temperature sender. Different devices and in different locations. The ECT is in the housing above the T-stat and the sender is in the lower intake behind the distributor.

Lev · Nov 14, 2012

Yes, I think it's good, replaced recently. Well, I read spark plug requirements under hood, it was ASF-42C with 0.54 gap. I realized that I've installed wrong plugs, because they are with 0.44. So IMHO, I will get new plugs with 0.54-0.55 gaps, because they are exactly the same model I saw in requirements. I meant coolant temp sensor, I just used to say water temp sensor, I think it's slightly sending inaccurate information to PCM, especially when water is cold.

toyman · Nov 14, 2012

For accuracy the gap is 0.054 - 0.055 not o.54 - o.55 (those are bigger than 1/2 inch). There is nothing in your first post to indicate a bad ECT sensor. Visible arcing will cause all kinds of operating issues. I would suggest you deal with issues one at a time and check for trouble codes before replacing parts that may be fine.

Lev · Nov 15, 2012

thanks

Backfires Through Intake, Please Help.

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