Mazda engine electrical system problem

[Kianbeng]

Hi Guys,

 

Sometime ago I noticed that my car (M323)had a intermitten knocking sound or misfiring sound during idling and can be easily picked up esp when aircon is switched off (idle low).

 

Initially I thought it was my spark plugs (cheapo but honeywell brand) which I just changed. Anyway, last month I changed back to the proper Mazda spark plugs (think it's NGK OEM?) and I can still hear the knocking sound. The sound can be described as follows:

.

 

The interval of each happening is like once every 15-30 secs or so when idling. I know this is usually a electrical problem.

 

I've a regular spare parts shop (Chin Hon) that I've been buying spare parts and repairing at some extremely cheapo workshops over the past 5 years or so. And the cheapo workshop I go to, of course don't have the expensive machine to read the Mazda ECU.

 

Recently I spoke to the shop's boss and he told me that there are a few things that could possibly be faulty and cause this problem to happen. To really diagnose this problem, he said I need to send it to a workshop that has the machine to connect to the ECU to diagnose. He also mentioned that the Cam sensor usually needs to be replaced after 3-4 years due to lifespan?. Anyway he listed 3 potential culprits:

 

1) Air flow sensor ($100+? Out of stock, $200+ at Mazda)

2) Cam sensor ($45) - not sure if spelling correct.

3) Clamp sensor ($80 Out of stock) - not sure if spelling correct but this item is the lower sensor with some cables.

 

He then suggests I go to some workshop ie CityAuto(near my place) and pay them to diagnose. I called Cityauto and he quoted S$40-$60-$80 just for diagnosis. I interprete it as $80 diagnose only, no change. $40-$60 diagnose and change spare parts (additional costs). Basically I'm worried of kenna chopped by these "ABC authorised shops" coz not long ago there was this incident where a M323 owner felt the cost of repair was too high and didn't wanted to proceed after the diagnosis and the workshop demanded alot of money just for the diagnosis. The owner felt the price was way too high for diagnosis and didn't want to pay. So the workshop detained the car. In the end the police was called in to mediate and a lower labour price was paid.

 

My questions to the bros here is

 

1) Anyone with similar problem for their M323?

2) What should I do to possibly cut cost in this repair?

3) Any other workshops that is recommended and can diagnose such electrical problems with the special machine.

4) Or should I just take a gamble and replace the Cam Sensor at $45 since it's cheap and possibly faulty? Labour price for this replacement is insignificant coz it's done in JB.

5) Just let CityAuto do the full repair? I expect the final price to be easily $500 or more as I know many shops just change parts A-Z even though it's not exactly faulty so that they earn on the parts' margin. They will then tell me it's faulty or is not 100% functional.

 

Appreciate any inputs from any one.

Edited December 7, 2006 by Kianbeng

[Yeobh]

Yr mech adv changing of cam and crank sensor - to me he may have diagnose through yrs of experience the engine base timing is out. The other possibility is timing belt may have stretch and the timing may be out by one to two tooth.

[Kianbeng]

Ahh! Crank sensor! ok ok finally make sense of what he's telling me.

 

Actually I didnt clarify enough. It was the spare parts shop boss who told me it might be the 3 faulty thing coz he said these 3 things can make this problem, but cam sensor is the frequently changed item for 3-4yo M323 cars.

 

The mechanic...as he's a cheapo one....he's good for aircon + tyres + routine servicing only. For this problem, he has no idea what was it coz M323 isn't common in JB also.

 

The timing belt was changed 50K ago leh. I used original one leh. Can't be so fast stretch liao bah.

[Yeobh]

Check the base timing with a timing light to make sure the firing timing is right on the spot @ idle speed . The camshaft and crankshaft timing relationship can easily shift just by one tooth during belt replacement (you will get timing problem at high speed) if both the camshaft & crankshaft are not pernamently lock.

The knock can be due too advance in timing - the cause can be due to faulty sensors or timing belt/camshaft/crankshaft timing setting.

 

PS timing light photo

[Genie47]

He has more or less nailed it. Now you know why DOHC is more expensive to maintain. Two cams = double the trouble.

[Kianbeng]

Hmm..the timing belt was changed about 50K ago and this "electrical" problem only seems to arise 10K ago.

 

On high rev, the problem seems to go away. ie, when aircon is running, usually the idle rpm is higher and I can't hear this knocking. But when everything's switched off, I'll be able to hear it. So shouldn't be a timing belt problem? since I assume timing belt problems will be even more audible when RPM goes up?

 

So diagnosis of such problems is not Mazda specific? I mean I don't have to go to a Mazda workshop? Just go to any workshops that specialises in engine problems? Seems like it's a generic tool?

[Kianbeng]

Is it really a DOHC thing? I thought it's because nowadays all cars got so many computers, sensors thingy. Last time, all the adjustments were manual. But of course that explains why the old cars last time so lousy FC. Now with high tech, it's more optimal combustion..?

[Mzrmazda3]

Bro, i dunno if City Auto has this diagnosetic tools or not cos as far as i'm concern, they only do normal servicing & repair and anything to do with ECU/Electronics thingy gonna go back to Mazda Motor for verification

 

Well, maybe i'm wrong

[Genie47]

Now you know why if you are a real cheapo and like easier maintenance because you DIY will like carburetted cars.

 

I wouldn't say old cars FC lousy. Their FC can be very good but the reason all these sensors and stuff are in cars today is not just FC. It is emissions.

[Route88]

Mainly if to self diagnose is not easy. It happened to my car,eratic idling during cold,car died in the middle of the road.

Auto tranny somemore

Go to mechanic wanna me....sensor fault la,ecu need to change bla bla BS.

I self diagnose,turn out to be dirty Throttle body.Buy a carburator cleaner,dig it deep deep.Voila solved

 

For ur case,what fuel grade u fill ?

[Route88]

He has more or less nailed it. Now you know why DOHC is more expensive to maintain. Two cams = double the trouble.

 

 

Thats why i dont like DOHC and timing belt

[Genie47]

What to do? Pushrod cars are mostly going to the museums or rather non-existent in Singapore!

 

Anyway, SOHC also got timing belt.

[Route88]

Nah,i skip timing belt, i go for timing chain.

[Kianbeng]

I think they have. Chin Hon boss said they do.

[Kianbeng]

Actually last time my older car's carburettor also failed before. Sometimes if can service it back, very cheap. But if need to replace, wow $1.4K sia! Best price liao after calling all the spare parts shop in sg, jb and batam. Really! (ok lah, I didn't call batam)

 

The first generation of EFI engines also don't have so much sensors bah?

[Kianbeng]

You see, thats the problem. If you don't know the mechanic well, many a times they knife you deep deep coz you are not a regular anyway. Maybe it's a 1 off business.

 

Last time workshops are really good in business coz everytime they do a insurance repair, they strike 4D. Now maybe harder. But still their standard of living has already risen. If can't take from left pocket, then must take from right pocket.

 

Last time I also buy a aerosol carburettor cleaner and use it regularly. After each use, it's really like a servicing lor. Can feel the difference.

 

Oh in sg, I'm using Ron95. In Msia it's Ron97. So on avg, I think it's Ron96 based on the frequency I go into msia and also the 3/4 rule. Sometimes I pump 1/2 tank worth of Shell's V-Power back.

[Pisces69]

Wow. What car carb cost $1.4K

[Genie47]

Carburetor now costs 300 bucks to get brand new. Actually any carburetor can fit any caburetted car engine. Just need one that is jet for the displacement.

 

The Starlet guys survive on a fodder of Proton SU carburetors. 1.3L ones slap on the Iswara's and the 1.5L ones slap on the Saga's.

 

SUs got a nice throaty roar. Very maintenance free.

 

I still have my Weber 32/36DGAV progressive carburetor. 32mm for economy and will open the 36mm when you need the power so a combined orifice size of 32+36mm! Bad thing about it is there is a lag when the 36 opens up. Like kenna turbo lag.

 

Last time EFI like carburetted car, Not many sensors. Everytime need to check tuning with gas analyzer. Don't have on board diagnostics.