JohanSA

Vacuum and idling issue

19 posts in this topic

Good day one and all.  Ive bought a 1993 mazda 626 2.0l i4 dohc.  

Ive been struggling to get the car to idle properly and drive without jerking. As soon as i touch the gas the car will stall.  Ive installed a new MAF, coolant temp sensor, distributor and so forth.  Ive done a smoke test to check for vacuum leaks and can only find one.

 Under the throttle body there is two nipples for hoses.  The one goes to the brake booster but the other one has nothing in it.  U will also see that the car does not have a EGR and not all the control valves and gadgets. I guess here in South Africa we dont have the same emmision regulations as other countries. I also could not find a Cat or O2 sensor, only a blankoff where im guessing an O2 sensor could have been.  The car is running very rich.  As soon as it starts u get this overwhelming smell of petrol.  My sparkplugs burns black and at least one dies completely after about 10km. I have to keep on replacing it.  All the videos and data out there shows the same car as i have but they have alot more thing that get vacuum than i do.  

Any help will do.

Thanx in advance

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Might check fuel pressure to make sure it is normal. Connect a fuel pressure gauge to the service port (on end of fuel rail to passenger side of engine) and check for ~35psi at idle, and ~45psi if you remove the vacuum hose from the fuel regulator valve (located at the other, driver's, end of the fuel rail.) If your fuel pressure is too high you could get too much fuel delivery per injector pulse.

The only other thought I have is maybe the engine control computer has not been correctly adjusted to compensate for lack of sensors (O2 and such.)

Does your car have a MAF sensor, and also a TPS sensor?

I know this is probably a dumb question but have you also checked to make sure the air filter isn't clogged?

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Hi. Thnx for reply.  It has a MAF and TPS.  When i bought the car the whole intake system was broken(plastic crap) so i replace it with a short ram intake(cone)  Ill c if i can get hold of a pressure guage to check the fuel pressure.  They r not that easily borrowed or bought in this bloody country.  How will i b able to check or verify if the ECU is programmed correctly.  Just bought a fuel filter today.  Dont know what its gonna help for but R360,00 later it better do something;-) and if it doesnt help atleast i know the filter is new....

Thnx

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Holy crap. Just saw that the previous owner completely disposed of the fuel filter.  This car has nothing. Just straight line from tank to rail, OMW!!!!!! 

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My intake is also making a loud hissing sound. Like a snake holding a microphone:-).  Cant find any vacuum leaks. Any ideas

 

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@JohanSA, try checking your seals around your injectors. I just went through something similar with my car. My profile has the story and how I diagnosed the problem.

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turn out that my timing was way out. Was one tooth off on the distributor.  Now that it is spot on the car idles almost perfect.  Still hearing a little miss on the idle and upon tramping the accelerator the car jerks a bit and makes this very deep sound and doesnt pick up the revs.  Slowly tramping it makes the revs go up better.  Flooring it though is a different matter.  I have to say though that the car is running better now that the timing is sorted out. 

What can cause that jerking and deep swallowing noise.  What can i look at.

Kind regards

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  • Check your primary and secondary coil windings with a multi-meter. It's very easy to check. If either test fails, you could have a weak spark causing a miss under wide open throttle at low RPM. This is exactly what was happening to me. 
  • Also, make sure there are no vacuum leaks.
  • I would still check your fuel pressure, especially if your spark plugs are coming out dark in color.

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Thanx. Never thought of a weak spark. Just checked to make sure i have spark.  Any tips on how to check the different windings;-)

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It is my pleasure. I wish you the best with your repair effort!

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Finally did a full diagnostics of everything sensor related to the car.  Turns out my Throttle Positioning Sensor(TPS) is not working anymore.  Very expensive where I live.  Does anyone know of another car that might use the same type of TPS as the '94 626. Im from South Africa so here that thing costs R2700. Any help will do.

 

Thnx

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If you unplug the sensor, can you get by? Does it make a difference in how it runs? I *think* the ECU will revert to fail-safe operation if it does not detect a TPS... I could be wrong. It could be worth a shot unplugging it though

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