bogging/stumble, dying with AC & blower motor on high

2000 with 90,000 miles just started the symptoms in subject line, three episodes so far in last 5 days. SEEMs like fuel starvation and will replace fuel filter first then test fuel pump BUT puzzled as to why symptoms only appear with AC on and blower on high. Could be just coincidence but thought someone would have a suggestion. Coolant temperature does NOT seem abnormally high according to gauge. Engine returns to normal after a shutdown and 30 minute wait.

Thanks

PS When this first occurred a volunteer mechanic (allegedly familiar with Miatas) said it was due to oil level being 2 quartz low. Makes no sense to me. Anyone hear of such.

Reply to
Bob Chappuis
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Bob Chappuis wrote in news:=O4jRYzGiQZEHJ9C= snipped-for-privacy@4ax.com:

Probably not coincidence, the engine might not be increasing the idle speed with the AC on. It's also an additional load, so I suspect that if the idle speed is increasing as it should then something isn't right such as plugs, etc. and it takes an increase in load for it to show up.

Does it return to normal if you don't shutdown but just turn off the AC?

2 quarts low is bad but I don't think it could cause those symptoms.
Reply to
XS11E

I could see how AC on could give you problems if as XS11E mentioned, the idle bump up deal wasn't operating as it's supposed to but 'blower on high' I wouldn't think would have anything to do with it. Once the fan goes from off (with means the AC is actually off) to low speed and on up, that's just different draw on current, not any extra load on the engine. I guess if ignition was a problem additional draw on current could have some negative effect but that would be quite unusual IMHO.

Chris

99BBB
Reply to
Chris D'Agnolo

No, the symptoms continue once they start until the engine is shut off and we wait 20-30 minutes.

Reply to
Bob Chappuis

Based on y'alls replies, I am wondering if combined electrical load of blower on high, both rad fans on with A/C plus added engine load of A/C plus old sparkplugs and wires and the ignition is failing.

I will install new fuel filter, plugs and wires Saturday and hope for the best.

Miata ran all day yesterday (100 miles) w/o problem with the A/C OFF.

Thanks for your ideas.

Reply to
Bob Chappuis

Bob Chappuis wrote in news: snipped-for-privacy@4ax.com:

The AC adds load and makes the engine run a little warmer, that may be a clue.

Reply to
XS11E

If the engine was operated while it was low on oil for substantial time-- I'd check the compression. Low compresssion can cause low power and stumbling under load.

Reply to
Chuck

"Bob Chappuis" Wrote: >

2 quarts low in a Miata means half your oil is missing. In this state, nothing would show on the dipstick, and if you drove around for long would be in the market for another motor. If you really suspect oil is that low, check it before you drive anywhere.
Reply to
Mal Osborne

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