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Old 22-04-2017, 09:00 AM   #1
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Join Date: Apr 2017
Location: Southern Highlands
Car: Mazda astina
Posts: 2
SP20 cranks but does not fire

Hi all

I have a cranking but no start for a Mazda (2002 2 litre, double overhead cam BJ SP 20).

Vehicle blew a head gasket back in December. The head gasket was changed, head was machined, new water pump, hoses, timing belt etc

In short, it has spark, fuel and timing is right.

On timing, crank is on 0 or at the top, the intake and exhaust marks face each other and the cam lobes face outwards from the engine centre on No 1 therefore I assume it is on the compression stroke.

Currently, the only remaining clue left is that when I crank the motor, there is no movement on the RPM tacho which in theory indicates that the crankcase sensor cannot see the motor turning?

I did a resistance test on the crankcase sensor and the result was 525 which is within the range of 200-500. I also tested the camshaft sensor and it had a resistance of 1.1 when set on 200. However, my reading indicates that it should be 2.2 rather than 1.1 but I'm not sure.

I recently purchased a reader and when I plugged it in and cranked it, the reader indicated that the rpm was 225. So perhaps there is nothing wrong with the sensors?

Earlier on in this saga, there was some backfire and fuel vapour leakage when it cranked. Did some homework and then focussed on valve clearances and leakage in inlet manifold/ fuel injectors?

I replaced the fuel injector O rings and insulators and the backfire ceased.

I then thought the problem could have been a camshaft clearance issue associated with the shims which fell out when I turned the head upside down prior to having it machined. I spent another month trying to get them back into their correct order and clearance even ordering some new ones.

Inlet shim clearances now range from .180 to .229
Exhaust shim clearances now range from .229 to .250

So, in theory, okay

I then purchased a leakage tool to check to see if there was possible issues with valves such as bent or non sitting valves. The results were all good.

So, I would love to hear if anyone has some advice to provide on this four month mystery.

Many thanks
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Old 22-04-2017, 12:29 PM   #2
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Join Date: Apr 2017
Location: Southern Highlands
Car: Mazda astina
Posts: 2
Just conducted a wet compression test. All cyclinders have less than 25psi. Timing?
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Old 25-04-2017, 05:03 PM   #3
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The cam locating pins should be pointing up when all timing marks are aligned, If they are in the other slot on the cam belt pulleys it won't start.
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