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350matt, Engineer
Category: Mazda
Satisfied Customers: 21600
Experience:  Mechanical Engineer BEng Hons22 years experience
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Have a 1999 Mazda 626 that is going through this issue a

Customer Question

have a 1999 Mazda 626 that is going through this issue a second time now. Our daughter drives 3 hours home from college, has no problems; drives back, which is up into the mountains, then if she goes back to her place, turns off the car for a half hour or so, the car then start to turn over, shudder, and stall, or not turn on at all. She's had it to the shop, and they replaced the vacuum hoses, and the car has been working fine again for a month. She just drove back up today, after having no problems with it, and had the same exact problem after she got there.
JA: Have you checked the battery, particularly the terminal connections? Are they corroded?
Customer: When she brought it to the shop a month ago and they replaced the vacuum hose, they checked everything - including the battery/terminals - and said everything was fine. Unfortunately, as she's now 3 hours away again, I can't look
JA: Are you fixing your 626 yourself? What have you tried so far?
Customer: We have a mechanic at home who has worked on that car quite a bit, and he's stumped as well.
JA: Anything else you want the mechanic to know before I connect you?
Customer: no
Submitted: 7 months ago.
Category: Mazda
Expert:  350matt replied 7 months ago.


I'd say that this is likely to be a poor electrical connection

as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;

Airflow meter

Crank position sensor

Cam position sensor

O2 sensor

Throttle position sensor

unplug each in turn and use some switch / contact cleaner spray on the pins to ensure its all grease / dirt free

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.

Check the resistance of the spark plug leads ( 13-15Kohm / metre) and replace if any doubt or high resistance - Also replace the spark plugs if any of them fail this checklist:

Also its worth checking that the electric pump that feeds the injectors is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V

Expert:  350matt replied 7 months ago.


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