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99 Mazda millenia - severe misfiring

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Sep 18, 2017, 5:55 PM

Post #1 of 3 (481 views)
99 Mazda millenia - severe misfiring Sign In

99 Mazda millenia
210000 miles

The car in question is having severe hesitation right after starting and after long drives and struggles to start sometimes.

The error codes are showing
A crankshaft sensor malfunction
Fuel trim system malfunction
Coolant system malfunction
Misfire cylinder 1
Misfire cylinder 3
Misfire cylinder 5
Multiple misfire

The car has over heated twice due to a leak in a hose which has been fixed. However has recently started losing coolant again with no obvious signs of a leak.

In an attempt to fix the hesitation I performed a tune up. However it got worse and worse after I changed the sparkplugs and wires.I discovered Several of the boots had melted inside the sleeve from when the car over heated. This did not start until 3 days after, upon checking it I discovered the front 3 plugs had worked themselves loose. At which point I pushed the back in and double checked every other wire connection. This helped some of the hestitation, a week later the misfiring grows increasingly worse and the check engine light comes on. Showing the previous stated codes. The wires were once again checked but all were still properly connected.

I am worried the overheating has caused significant electrical damage. But I want other opinions on other possible causes.

(This post was edited by Andrewmwilson90 on Sep 18, 2017, 6:02 PM)

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 19, 2017, 1:45 AM

Post #2 of 3 (411 views)
Re: 99 Mazda millenia - severe misfiring Sign In

Presumably Andrew? Careful with the parts "cannon" on a car that overheated possible up to in flames with 210,000 miles. Never mind codes. Strong bet this engine has totally had it and would be checking it for compression while it still turns/cranks at all.

"melted plug wire boots" OMG - that's way beyond overheating, no coolant or oils can sustain that temp and questionable if alloys everywhere could take that either.

See if this is beyond a fix, compression first,


Ultimate Carjunky / Moderator
Discretesignals profile image

Sep 19, 2017, 5:10 AM

Post #3 of 3 (402 views)
Re: 99 Mazda millenia - severe misfiring Sign In

I agree with Tom. A compression check and possible leak down test is in order.

Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

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