Miss firing

dvs bullet

New Member

Feb 20, 2004

326

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Ontario, Canada

Apr 3, 2004

#1

• Apr 3, 2004

• #1

How much vacuum is 5.0 supposed to have in the intake manifold? I've got a real stubborn miss that intermittant, and I've checked and replaced all the ignition componants (plugs, wires, cap, rotor etc.) so I think that I have ruled out that. The next thought could be that, I have a vacuum leak or maybe a fouled injector. Any thought or suggestions? thanks in advance

 

dvs bullet

New Member

Feb 20, 2004

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Ontario, Canada

Apr 3, 2004

#2

• Apr 3, 2004

• #2

any one?

 

94_Teal_GT

Founding Member

Aug 14, 2002

405

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Palm Bay, FL

Apr 4, 2004

#3

• Apr 4, 2004

• #3

My 86 5.0L Merc has a vacuum gauge mounted under the hood. Previous owner used it as a tuning tool and decided to leave it there. But anyway, at idle the Merc has a rock steady 21 in.Hg with 242k miles.

Just checked my gauge, it says
0-11 in.Hg is Late Valve Timing or Vac Leak at Intake or Heat Riser
11-15 in.Hg says nothing
15-18 in.Hg is Late Ignition Timing
18-22 in.Hg is 'Normal'

 

dvs bullet

New Member

Feb 20, 2004

326

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Ontario, Canada

Apr 4, 2004

#4

• Apr 4, 2004

• #4

thanks that helps alot

 

dastang2

Active Member

Dec 11, 2003

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46

tx

Apr 4, 2004

#5

• Apr 4, 2004

• #5

also a bad head gasket could do this too. do a cooling system pressure test.

 

dvs bullet

New Member

Feb 20, 2004

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Ontario, Canada

Apr 5, 2004

#6

• Apr 5, 2004

• #6

more info, I just a set of plugs on her and they all came out clean. A friend and I checked around the intake with acetaline, seemed like there was no difference. The vacume is at a steady 17, and the only time that the idle picked up is when when we put the acetaline into the diapham of the egr, it ran awesome. We changed the egr thinking that it was leaking, no luck, the miss was still there.

 

C

cschulzy

New Member

Mar 7, 2003

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Tabuk, Saudi Arabia

Apr 5, 2004

#7

• Apr 5, 2004

• #7

I had a missfire problem on my stock 89 GT 5 speed. I was running splitfire plugs at the time and changed them for stock motorcraft ones, but the problem was still there. As it turned out the old plugs were well worn and I had gapped the new ones to wide. For a cheap fix it might be worth checking your plug gap. My missfire was under load from 1500 rpm up at anything past 3/4 throttle. Hope this helps

Cheers

Chris

 

dvs bullet

New Member

Feb 20, 2004

326

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Ontario, Canada

Apr 7, 2004

#8

• Apr 7, 2004

• #8

cschulzy said:

I had a missfire problem on my stock 89 GT 5 speed. I was running splitfire plugs at the time and changed them for stock motorcraft ones, but the problem was still there. As it turned out the old plugs were well worn and I had gapped the new ones to wide. For a cheap fix it might be worth checking your plug gap. My missfire was under load from 1500 rpm up at anything past 3/4 throttle. Hope this helps

Cheers

Chris

Click to expand...

I'll give that a shot today, thanx

 

dvs bullet

New Member

Feb 20, 2004

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Ontario, Canada

Apr 11, 2004

#9

• Apr 11, 2004

• #9

just an update, again I found a vacuum leak under the plenum of the car (One of the pcv hoses were cracked), this restored the car to 20 inches of vacuum, we then set the timing on it to 12 deg. I also double checked the plug gaps. The car idles smoother but you can still feel a bump in rpm, I also went along with a stethascope to all the injector and all of them were clicking. The plugs that came out before were a light brown colour so there isn't any evidence of a head gasket ( also the engine was rebuilt 10,000km's ago).Any more Ideas? thanks

 

dvs bullet

New Member

Feb 20, 2004

326

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Ontario, Canada

Apr 11, 2004

#10

• Apr 11, 2004

• #10

none?