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Intake backfire on acceleration! Please help

27439 Views 7 Replies 4 Participants Last post by  LevGT
Hi guys!

Recently, my GT started bucking (backfire in the air filter) on low rpm's during acceleration, mostly when engine is cool. This also occurs when I shift gear from 1st to 2nd even when engine is wormed up.

Computer codes indicate that the EGR vale is bad. "EGR not opening...".

I have seen posts in which people say that the EGR valve can be safely removed or disabled at all and it will not affect engine performance, but at the same time I read official instructions that this valve helps cool combustion process and it is important for proper fuel/air mixture. I'm little bit confused and decided to buy a new one but I need your comments to be sure this is what I need. Last thing is, could it be a MAF sensor somehow related?

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Here's what was posted in another thread about backfiring out the intake:

Backfiring out the intake is either a valve stuck open or a lean mixture or spark plug wire(s) connected to the wrong cylinder(s). Check compression on all cylinders and then look for vacuum hoses loose, cracked, or misconnected. Check the line for the vapor recirculation system – it is easy to knock loose and not see it when you connect the air pump plumbing. If the vacuum line for the EGR valve and the air pump are cross connected, some very strange things can happen. Check the mass air flow electrical connection and see that it is tight, the same goes for the fuel injection wiring harness connectors up on top of the manifold near the firewall.

Sticking valves: If a intake valve is bent, has a bad spring or is misadjusted, the engine will sometimes backfire through the intake. Use a vacuum gauge connected to any convenient spot on the intake manifold. Run the engine at 1000 RPM & look for 18-21 inches of vacuum with a steady needle. A problem intake valve will make the vacuum gauge needle sweep 5-10 inches.

Lean fuel mixture breaks out into several sub categories:
A.). Vacuum leaks
B.) Air entering the intake without passing through the MAF on Mass Air cars (89-95 models).
C.) Failure of the MAF, BAP/MAP (Baro or Manifold Air Pressure, same sensor, different name), ACT (air charge temp), or ECT (engine coolant temp). These should set a code in the computer.
D.) O2 sensor problems: one or both O2 sensors with low output or bad O2 sensor heater ground. This should set codes 41/91. The O2 sensor heater ground is an Orange wire in the engine mounted fuel injector harness. Ground it to the back of the head or intake manifold.
E.) Leaking exhaust gases from EGR valve at WOT or EGR opening when it should not be open.
F.) Poor fuel delivery due to bad fuel pump, clogged filter or bad fuel pump wiring. Look for low pressure or fluctuating pressure. Standard injector pressure is 39 PSI at idle, with the vacuum line disconnected from the regulator and capped.
G.) Clogged fuel injectors.- see the cylinder balance test below
H.) Fuel injector wiring problems causing injector not to deliver rated flow (dirty or stuck shut injectors).
I.) Computer problems: (computer problems are not common like sensor problems)
J.). ROM has bad data in fuel or timing table. This should also set a code in the computer.
K.) Failure of one or more of the computer's driver transistors for the fuel injectors. No code set on this one. Use a noid test light to test the injector wiring & injector drivers,
L.) MAF calibration off or mismatched to injectors.
M.) ACT or ECT bad. Sometimes the sensors will be off calibration, but not bad enough to set a code. If they falsely read too high a temp, the engine will back off fuel delivery.
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completely lost (
Just went through this with my 88 GT it was the fuel pump. It would back fire thru the intake when gave it gas but could feel it take off when i let off. Had fuel pressure tested and was only 21psi. Put new pump in and runs great.
no, I have checked the pump, it's ok, it was my first thought when this problem began. Anyway, thanks for you suggestion. I think its EGR valve, but not sure, some people say its MAF sensor or water temp sensor, not sure anyway, so I'm stuck in my mind.
We have checked ignition system and discovered spark illumination around ignition coil on high rpm's. What does it means? Do I need to change coil or spark plugs, or both of them or even wires? Could this cause a backfire through intake?
My 2010 gt does this too. I thought it was just a ford thing
Does exactly what? Same backfires as mine does or just spark lights?
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