minor hesitation: need suggestions

cdsmith_2002 · May 7, 2008

I have a hesitation in my '94 Cobra that is only present at full operating temperature. It is fairly repeatable if I apply light throttle in 5th gear @ 40MPH, ~1200RPM. I can get the problem at other parameters too but 5/40/1200 is the most common. I don't have a check engine light on and I don't have any stored codes. The car starts and idles OK, gets normal gas mileage etc. All the tune up stuff is new. I installed a new pump and regulator & filter so I'm thinking the fuel system should be OK. The coil, TFI and distributor are original 179K mile parts.
The MAF & TB have been recent cleaned with the proper specialty chemicals. The problem just started a couple weeks ago at the onset of slightly warmer weather.

new: wires, plugs, cap, rotor, fuel filter, pump, regulator, O2 sensors, MSD Coil
mods: Mac cold air, Mac long tubes, Mac cat-back, 3.73
condition: does not burn oil, gets expected milage @ 20MPG.

What would you guys replace next?

Thanks,
Chad.

LAFENATU · May 7, 2008

Have you looked for any vacuum leaks?

cdsmith_2002 · May 7, 2008

Yes, I did look for vacuum leaks. Visually and the starting fluid technique. I didn't find anything....yet.

2slo95fiveoh · May 9, 2008

you said the coil is factory ford 179K i would replace that, and even if it doesn't fix your problem, it should run
slightly better. as far as your TFI module, you'll know if that's bad, becuase your car wont start/ rough start.
i would replace the coil and go from there.

idro · May 9, 2008

ive read bad things about MSD coils try a stocker?

Addermk2 · May 9, 2008

MSD coils have been known to have many problems... buzzing being one of them.

I'd go with a crane if my current coil went bad

cdsmith_2002 · May 9, 2008

Bummer. I installed the MSD 50 miles ago as a possible solution to my current hesitation problem. Unfortunately no improvement.

I removed the BBK AFPR tonight and put the stock one back on. We'll see what happens on the way to work in the morning. I did another KOEO, Still no codes.

LAFENATU · May 10, 2008

Addermk2 said:
MSD coils have been known to have many problems... buzzing being one of them.

Wow..

Never heard of that. I have had 2 of them and never had a problem..

Guess I have been lucky :dunno:

cdsmith_2002 · May 10, 2008

No solution yet. It's not the FPR, coil or ECT. I'll keep the thread updated with progress for the next guy that fights the same problem.

Steven · May 10, 2008

normally a hesitation is due to running lean, normally. I had an issue with the maf that caused that.

cdsmith_2002 · May 11, 2008

Did you have any codes indicating a lean condition or a MAF problem?

Steven · May 11, 2008

i never scanned it, but it had a back fire through the intake bad, indicating lean. It was my C&L maf and low fuel pressure that caused mine all to hell.

cdsmith_2002 · May 12, 2008

I talked to a local 30 year auto service verteran yesterday. He also recomends replacing the MAF. I guess I'll drive up to Jegs on Monday and pick one up, and some injectors, and some.........

I blocked off the EGR for a test yesterday and it actually seemed to be worse.

cdsmith_2002 · May 13, 2008

I drove up to Jegs and bought a Pro-M MAF, some Accel 36lb injectors, a new distributor and a phenolic spacer and........

So far, the car overall runs worse. The idle is worse and drivability is different, not as good. The 40MPH hesitation is gone though. I drove the car about 12 miles with 2 hot restarts. How long should it take for the computer to learn the new MAF and injectors? I haven't installed the new distributor yet.

2slo95fiveoh · May 13, 2008

why did you decide to step up to a bigger injector with no major mods? 36lbs seems a little large for a motor with no
h/c/i changes. i would try the "fix your surging idle" in the sticky section and that could help your idle/ drivebility issues.
i performed all the steps on my car and it dramatically fixed my idle, and seemed to give my car a little more "pep".
my best advice, not trying to be an a*hole, but start with the little stuff, instead of replacing multiple parts
that may not be defective. :dunno:

Addermk2 · May 14, 2008

common theory is that the largest you should run on a stock motor is a 30# injector. Any bigger than that, and the injector just isnt opening enough for the fuel to atomize properly, and you get a rough idle!

Stangbangin · May 14, 2008

Addermk2 said:
common theory is that the largest you should run on a stock motor is a 30# injector. Any bigger than that, and the injector just isnt opening enough for the fuel to atomize properly, and you get a rough idle!

where did you hear this crap? common sense tells you on a stock motor you run a stock injector. 24 #er's would be too big for him right now. 36#er's are gonna have him running pig rich.

Addermk2 · May 14, 2008

bases solely on the injector timing versus the actual air flow characteristics, going any larger than 30# injectors on a motor thats anything less than mild, will result in a poor idle due to lack of fuel atomization.