Missing under load @ low RPM's

Just got back from vacation for a week and the car gave me no problems. It sat for 2 days after that and when I drove it it seems to have a miss under load and sometimes at idle @ low RPM's. The plugs, COP's, and fuel filter have all been changed recently. The car is a 2000 Mustang GT. It driving me nuts.

Is the Check Engine Light (CEL) on?
Are there any Diagnostic Trouble Codes (DTC)?
Was the car setting outside when you were on vac?
Could weather, or water be a factor?

No check engine light. I took the car on vacation and had no issues. When I got back on Friday it sat for the weekend. When I fired it up on Monday it had the miss. It was dry all weekend so it shouldn't be water.

Try to get your car to throw a code by driving safe & hard.
If no codes, lets do some tests.
MAF
Fuel pressure
Catalytic converter back pressure test

No check engine light. I took the car on vacation and had no issues. When I got back on Friday it sat for the weekend. When I fired it up on Monday it had the miss. It was dry all weekend so it shouldn't be water.

I've tried to get it to throw a code and it just doesn't want to cooperate.i do have a predator tuner that can data log. It will show all the PIDS like fuel pressure and stuff. I just don't really know what I'm looking at when I use it.

I still have not been able to get a code from it. I don't know how it code miss like this and the computer not see a fault.
As far as the test...what should I look for. I do not have converters on the car. There are MIL elimonaters to on the rear O2's.


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1) Try to have a local muffler shop do a back pressure test on your catalytic converters for free.
or Google ''Youtube Auto DIY Catalytic converter test''.

If DIY, use a compression tester in place of the upstream H20 sensor instead of drilling hole.

Would that do anything for me if I don't have converters? I was also told people have been having problems with GMS street fighter coils that I put on my car. Don't know if anyone else has had a problem with them.


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Are you using simulators upstream?

No, the down stream O2's have a jumper between them and the connector. The upstreams are working normally. At least they should be.


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Tests:
Catalytic converters - None
MAF - Did you try cleaning Air filter + MAF sensor?
Fuel pressure Test - ?
Smoke Test - ?

I've cleaned the MAF in the past but I'm sure it could use it again. The air filter is one of those k&n types but I'm not sure how it was cared for before I got the car. The fuel pressure I can look at with my tuner...just not sure what it is supposed to be anyway and I haven't seen any smoke.


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We can't rule out a bad or dirty MAF sensor.
Fuel pressure Test - ?
Smoke Test - ?

I'll try to clean that MAF when I get a chance. My fuel pressure seems to stay around 40psi. I don't know what it does when I'm driving, I'll have to check when I get out of work. The car seems to take off fine as long as the revs stay above 2K. I only really see the problem when I am trying to accelerate moderate to hard in a high enough gear that it keeps my revs under the 2K mark. The farther below 2K, the worse it is and then seems to clear up.


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I wonder if this car has 2-fuel pumps, the other would be for 2krpms + ,it takes alot a fuel pressure to flow through an injector.

Caution - There's probably a Rev limit of 2K rpms in P or N pos.

No ,it has one fuel pump @ WOT a 20psi boost signal is added to the Delta fuel pressure.
50% of OEM replacement fuel pumps are bad!

40psi - 60psi should be good.

Air Mass Meter, or Massive air flow (MAF) sensor.
$72-$168 @ www.partsgeek.com (http://www.partsgeek.com) + Free shipping
You might consider buying a new one @ local salvage yard. MAF = $20

I would have no problem in replacing the MAF, because of age + mileage.
If the other is good, you could always keep it as a spare.

I found a video for a Smoke test, Google ''Youtube auto diy scotty cigar''

That's a good little trick. I'll have to try a few of these things out as soon as I have the time. Today though I haven't felt a miss at all and I haven't done anything to it. I think this is going to be one of those intermittent things that will drive me nuts for a long time. Thanks for the help.


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