Mechanics

ACCELERATION PROBLEM

1997 Mazda 626

1997 Mazda 626 2.5 litre 145 K miles

Car starts ok, idles somewhat ok, check engine lights erratic display. The only code that comes up is random misfire.

If you are in park brake on idling and accelerate slowly
you can get the engine to rev all the way up to 5k plus
if you step on the throttle as if to take off from a stop or accelerate as if in passing. The engine will choke and nearly, but not quite, die.

If you actually attempt to drive the car these symptoms are magnified. Ie you can not safely drive the car.

In disconnecting the battery and attempting to get and failure codes. Again only random misfire.

The spark plugs and spark plug leads were replaced with no effect.

In contacting a Mazda service department. They are baffled.

Any help appreciated.
Avatar
Bohemian
August 7, 2007.




More info: The condition started when we were 3 hrs into a road trip.

Engine was normal temperature, no other sumptoms, no black smoke
On a hill we notice a serious decrease in powere then the rpm drop off, then down to 20 mph and could go only if we feathered the throttle

When we pulled into a town and came to a stop the idle was a bit rough and about 850 RPM. Pulling off the stop the engine bogged but did not die. Easing the throttle giot us to a parking lot where we attempted to get the engine to rev and the symptoms were as I described in my first post

We towed it home then took it to the shop where the only codes that were pulled up were the random misfire. On resetting the codes ( pulling batt terminals foot on brake for 30 seconds) then startintg up. Same code

Repeating this process we took the car to an Auto Zone where they pulled up the same codes

Back to the dealer. The dealer suggested a capp and wires. No help.

They then suggested a list of items ranging from O2 Sensors to TPS to MAS to catalytic convertor

They were not able to pinpoint he problem and the laundry list looks exopenseive for shooting in the dark

The vehicle did have a distributor replacement 2 years ago. For failure to start. At that time all the ignition oparts wwere replaced

I am not wantting to believe that another distributor has failed. But I would also guess that is possibl; e

Any help in narrowing down the problem would be appreciated

and in hopes that my " donation" of a few days ago might prompt a response.
I am anxiously awaiting getting theis unti back on the road.

Thanks

Tiny
Bohemian
Aug 10, 2007.
This sounds like the timing belt may have slipped a tooth.

Merlin2021
Aug 10, 2007.
How is the spark? Does it doi it mainly when hot or all the time? Has a compression test or leakdown test been done to determine if any of the cylinders are low on compression or valves are leaking/burnt?

Tiny
Jack42
Aug 10, 2007.
Might be possible

Belt was replaced within the last 20K

but possible

I'll check the cam timing

In order for the is belt to " slip a tooth" it would have to slip a tooth in several places as it is a dual overhead cam with idlers etc

I would also imagine that it would then have to equalize the slip and in doing so would get slack somewehere and possibly break

The compression is good all cylinders checked dry and wet and no appreciable " leakdown" we used 2 different compression guages. One, leakdown checker.
All with the same results.

Engine does not get " hot" but the condition exists at all temperatures from cold to normal.

Spark. Hmmm well there is spark to all cylinders but the quality of the spark. Not sure
I am going to get one of the cheapy little plug on spark check gizmos and see what that shows.

I'll check it out

Thanks for the replies

Tiny
Bohemian
Aug 10, 2007.
OK

Worse when engine warmed up to operating temperature

I hooked up a spark checker between the plugs and the lead. The type with a light.

So at idle in Park brake on warmed up

If you give it modest throttle it will rev a bit slowly up to 5500 rpm

if you stomp on it the spark will dim noticeably on all six cylinders

And of course the engine bogs down.
But when it revs to 5500 spark stays strong

there is no classic " misfire" steady but very weak spark shows

When driving the car

if you give it modest thriottle it will bog and sounds like a misfire inside the headers or exhaust.

If you romp the throttle thed this in over drive out of overdrive and in drive 2 all the same

So weak spark because of the coil or weak spark because of a fuel delivery problem?

Any guesses or other tests I should od?

Thanks

Tiny
Bohemian
Aug 26, 2007.
Weak spark is usually the coil itself, fuel delivery wont change the spark, should be bright hot spark all the tme regardless of how much throttle it is being given

Tiny
Jack42
Aug 27, 2007.
If it is the coil
why does the engine NOT misfire when the throttle is romped
and misfires with a modest throttle pressure

usually coils fail under load

Thanks

Tiny
Bohemian
Aug 28, 2007.
Coils dont change quality of spark depending on throttle. Spark should be bright all the time
AD

Tiny
Jack42
Aug 28, 2007.
If the quality of the spark from the coil does not change with throttle position'

'why is it in fact changing with throttle position

when the engine idels strong spark

full throttle strong spark

moderate throttle dimming light

Am I confused

the throttle position or pressure or something is causing the spark to diminish
and throttle is the only thibng that is cuasing it

Tiny
Bohemian
Aug 30, 2007.

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