Recently my GT developed a misfire. Code reader said it was the #7 cylinder.

Things I did:
Changed coil pack - no change
Plug wires look brand new and no visible damage
Checked the plugs... horrible condition, some were gapped in excess of .095
Put in new plugs - idled great, seemed like it was fixed, started going down the road, misfire and flashing CEL again.

This time, however, it's 0304, the #4 cylinder.

I've checked for vacuum leaks but couldn't find any, but haven't tried spraying the engine to check for a intake leak.

Anyone have any ideas what could be causing this? could it be fuel related? (such as not getting enough fuel, fuel filter)

Might be prudent to note that it runs OK sometimes, usually at idle, but when you put load on the engine is when it'll start acting up - sometimes worse than others.

Car has 104k miles on it, no blow by, doesn't use oil, anything like that. Compression tests are fine.

Any help would be appreciated.

 

+1 on a possible intake leak, another thing that I've heard is to check the fuel injectors with a mechanics stethoscope. You should hear a rhythmic click every time the injector fires.

 

So far, the problem seems to have largely solved itself the last time I cleared codes and did a KOER test.

The only thing I notice now it sometimes it chugs at low RPMs with load, (almost like a manual that is running too low of RPM), give it some gas to downshift and it's fine. Gas meilage came back in line, too. I'm still surprised it ran before with the plugs in the shape they were, I'm almost convinced they were the original motorcrafts.

 

low RPM like that could be a tiny leak on your intake.

 

Well, it's reared its ugly head again in full fashion. This time however I noticed a small coolant leak at the inlet at the back of the intake, which appears to be filling my #4 plug hole with anti-freeze. I would imagine this can't good.

 

i had that happen to me. youl need to ID the leak to see if you need the new gasket or the whole new intake manifold.

 

Looks like the housing itself is cracked.

 

Still runs like ****, probably just wasted a bunch of money. Also replaced vacuum lines when I replaced the intake

 

I'm having the same issue with cylinder 4 misfire. Same symptoms except that I am getting blow by. Can anyone tell me what normal compression psi is for a 97 gt?

 

Compression test results. Cylinder1 117 cylinder2 125 cylinder3 120 cylinder4 129 cylinder 120 cylinder6 125 cylinder7 125 cylinder8 125. Is there something off with these numbers? Haha