Cruising along at normal city street speeds, nail the throttle and the car pops and stutters and then hooks up and takes off. Mods are pump rewire, 14b, aeromotive regulator, bigger fuel filter and fuel feed line to rail, 3" exh, fmic, upper I/C pipe, 18lbs boost. The car ran perfect in August and has just recently been acting up. I once missed a shift and the revs went crazy. Could a skipped timing belt have caused the problem? I don't have a logger but would love to get it logged if somebody has one for a 2g.

Check the plugs and wires first. After that and if no luck then check the o2 sensor. Maybe your running rich which would cause backfire/stutter.

The plugs and wires are less than a year old. The plugs are a golden brown colour. Since it only acts up under heavy load, how can I check the wires? This may be a silly question but, what am I looking for? There is no misfire or any other problems under normal conditions.

Sometimes it does'nt have to be just under normal conditions. Try swaping with some wires that you know are good and see if that works.
If not then I can suggest the next step is to confirm your timing is set to 5 degree's and that the belt lines up.

Thanks, I'll do that.

Welcome to my world right now Mike ever since my engine swap. Let's keep in touch when we figure out what it is.

Mark, with all that extra fuel and no fuel control, I'd say you are just way too rich. Get an safc or similar.

Back fire is caused by too much fuel getting pushed through the exhaust valves. When it goes though the exhaust system it detonates when there is just enough air to mix with the fuel.
Reason for that is that your running very rich.

Have you upgraded you fuel system without proper fuel control? That's a good cause or a faulty o2 sensor would do the same.

The stutter could very well be too much fuel as well and cannot keep the proper air/fuel mixture you want, thus doing the only thing it can do. Stutter.

Why was the car running so perfect in the summer? I have the stock pump with the aeromotive regulator, upgraded filter with 3/8 line. I was just emailing Noah about it, saying that the car does smell very rich at idle and there is some black soot on the end of the threaded part of the plugs. The electrode is a light brown. The egt's are 1600 f at the end of third gear. Mind you, that's not when it's stuttering. It stutters when it first builds up to 18 to 20lbs. Can the stock fuel pump support that much boost with the upgrades that I have done? I just can't help it. I need the boost! I guess there's too much fuel when boosting but not enough at redline. What do you guys think? What are your egt's at redline? O ya, the o2 sensor is very white.(the front one)

hi guys, i have been having the same problems as well, i am less heavily moddifed though

-stealth TT pump 190 lph rewired
-3 inch turbo back

the car was smoking black on idle since it got cold... does our MAF read air density??? (would it be trying to run more fuel at idle because of the dense air)

anyways, i hacked the maf a little more, turned that screw out all the way, (already had honeycomb removed)

the car doesnt smoke at idle anymore, no more raw fuel smell, i also widened the lower air passage in the MAF, but under heavy load it still gives that momentary hesitation, but i find if you make of the throttle mementarily, then slam it back down, it clears out and pulls strong

Mass
Air
Flow

Sensor.

Yes but mass is volume times density Karmann measures volume airflow, then there's the intake air temp and barometric pressure sensors to get the density part. Personally I don't think these are calibrated properly, or maybe the ecu's calculations are thrown off by our hacked mafs, but it never seems to compensate properly for altitude and ambient temperature.

All this junk should become irrelevant once I get the GM hot wire maf in. That one actualy measures mass air flow directly.

Nathan man come down to the loo sometime and we'll log your car.

I should have elaborated a little. (as usual).

I think he was asking if the airflow sensor in DSMs compensates for changes in temp. (affecting density).

Since our airflow sensors measure mass, yes, they do compensate. Fuel trims help this as well.

That's why it's "easier" to hit fuel cut when it's cold out.

Nope.

Bingo.

Problem fixed! Needed a downpipe gasket so that the second o2 sensor could get the proper readings.

SECOND o2 sensor?? Is this a 2g thing?

Yup, 2Gs have a second O2 sensor.

Mark, I was under the impression that the second O2 sensor was used measure the efficiency of the cat. It doesn't affect the amount of fuel that the ECU provides. I've read that some 2G owners remove the second O2 sensor entirely.

My second O2 was throwing a failure code so I just disabled the diagnostic using DSMLink.

Even though your problem is solved and someone mentioned plug wires, I would like to add that I had the same problem and new plug wires solved it.

My old wires were only about 18 months old but one had a tiny hole in the insulation and was causing an arc between the wire and the cylinder head.

the area around the small hole on the wire was black

That's described here and here .