need help. intermittent engine issue in high heat

[HeinousActs]

So I have a 2002 miata se 1.8 vtech 6 speed. Only non stock items are a k&n intake kit, not just the drop in filter, MagnaFlow cat, and cat back system. Very strange issue going on. I'm in Dallas and when driving on the highway, with ac on, in over 100° heat, for over 20 minutes the car will start to studder. Like a fuel pump going out. Or injector failure, vapor locking etc. This never happened in cooler weather, nor does it happen if the ac is off. Only when all of the above conditions are met. Anyone seen or heard of this before?

[Walsted]

Assuming your temp gauge is in the normal range, my next step (were it me) would be to check the electrical connectors on the fuel pump, just because I have had a lot of problems with them in the past. Then I would check battery and alternator connections to make sure the car isn't running short on electrical power with both fans up front, the blower in the car, and all of the usual other things running.

Hope this helps,

[sammm]

How old are the plugs/wires/battery? Where's the temp gauge while this is happening?

[HeinousActs]

Temp gauge is normal, battery, plugs, wires, alternator all less than a year old. I was wondering if it was electrical, but like I said, it's only in the heat of summer that it's happening. I can drive it at midnight with everything else the same, and it never misses a beat.

[HeinousActs]

And if you fun just the blower motor without the ac compressor on, it won't do it.

[Walsted]

Having the A/C on activates the secondary fan, increasing electrical load. When you turn on the A/C, does the water temp gauge indicate a slight cooling?

[POS Racing]

Since it is a full OBDII car you might want to pull some data when it is acting up. May give you a better idea on why it is acting a fool.

[OZMDD]

Temp gauge won't really tell you anything on these, at least not until you are extremely overheated. Throw a scangauge on it to see where the temps actually are. Since you're describing something that could be mechanical, I'd check that the ac compressor is tight to the bracket, and then observe the pulley when the clutch engages to rule-out a wobble of some kind.

After that, I'm inclined to put a multimeter on it and recreate the high temp/ high load condition, then see what is going on with the charging system.

Last, try putting the stock airbox back on. The K&N setup may be creating a heat-soak situation where your ecu is pulling so much timing that the power is down. Are you running 93 octane?

[Walsted]

During the times when my alternator died while I was on the highway, my temperature gauge went from pointing straight up to pointing slightly to the left. I attributed this to battery voltage being lower than alternator voltage.