1998 Mazda 626 Mazda 626 RPM misbehaves + smell

Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Don't worry, we are not finished till we have exhausted our means of solving the problem.

I found a recall for PCM reprogramming and do not know if it is applicable for your model. Maybe you can try calling your local Mazda dealer for some info.


https://www.2carpros.com/forum/automotive_pictures/192750_Recall98Mazda626PCM01_1.jpg



https://www.2carpros.com/forum/automotive_pictures/192750_Recall98Mazda626PCM02_1.jpg



The symptoms described is similar to what you are experiencing.

If it is not caused by the PCM, we should not rule out the possibility of an alternator fault. It could be defects with the design of the alternator and could affect quite a number of them.

I just concluded some diagnostics with a customer who owns a Nissan and he replaced a few alternators all of which gave him similar problem. Finally he agreed that it is a fault with the design and circuit of the alternator. The alternator was making some noise as well.
Was this
answer
helpful?
Yes
No
Thursday, May 28th, 2009 AT 9:36 AM
Tiny
FDQX
  • MEMBER
  • 41 POSTS
By looking at the recall, I don't believe it it applicable to my car, since it has been manufactured in july 1997 (though it is model year 1998) and European version. There were a tag on the PCM that is has been reprogrammed in December 1999. The mazda dealer (importer company) said that the PCM (Ford EEC-V) can not be reprogrammed, but they had the information also on their computer (didn't tell why reprogramming was done). They couldn't explain that.

A year ago, before the car started to burn oil with the old engine, everything worked fine. I could live with the alternator noise, but the other faults not. For example the smell coming inside the car sometimes gives me headache and the fact that it's impossible to change gears smoothly makes driving in the city hellish.

I also yet haven't found a common factor for the reasons when the car works OK. (Driving without electrical load and fast acceleration). After a fast acceleration car can work fine for several days. Couldn't be anything but something clogged?
Was this
answer
helpful?
Yes
No
Thursday, May 28th, 2009 AT 9:54 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
If it is clogging of anything, it would be present most of the time would not disappear after fast acceleration or driving with electrical load.

I would still think it has something to do with the electricals and alternator and would suggest monitoring the charging rate. It would be good if you can install a voltmeter to monitor the alternator charging rate, with and without electrical load.

I will be going through your list and see if I can come up with anything. In the mean time I would post this in the moderators forum to see if anybody has any new input.
Was this
answer
helpful?
Yes
No
Thursday, May 28th, 2009 AT 11:24 AM
Tiny
FDQX
  • MEMBER
  • 41 POSTS
Okay.

I have monitored the voltage while driving with a cigarette lighter battery analyzer, and an voltmeter connected to it. The voltage while driving has been around 14, 4-14, 65V, never seen it drop, even when the RPM goes low. Only slightly for a moment when electrical load is turned on. Only thing which I noticed is that sometimes when I turn ON the headlights or other load, the voltage goes UP about 0, 1 or 0, 2 volts.

The strange thing about the electrical load applied to the car is that I have a 350watt audio system (amp and subwoofer) in the car but that doesn't change the behavior of the car at all like the other things do, no matter how loud I listen music (takes more power than headlights, right?). It has a separate wiring straight from the battery to the amp. The system has been disconnected for months now (the system is physically removed, only the power cable and RCA cable are still in the car but disconnected from both ways and taped with electrical tape), the last three alternators haven't been run with the stereo system connected so the system couldn't be the cause.

That kind of let's me think about the fuse block in the engine bay, but every fuse is OK.

About the fast acceleration thing when it happens: First when I take off (pedal to the metal), the car almost doesn't move, lacks power (maybe misfires?), But then goes off like a rocket after about 50 meters. This has happened three times, everytime before this there was a bad smell coming inside the car, that smell that I haven't had since the clutch replacement.
Was this
answer
helpful?
Yes
No
Thursday, May 28th, 2009 AT 11:47 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
If the bad smell is like rotten eggs, then you need to check the catalytic converter. It could be bad.

The description of the lag in acceleration could be due to :
1. TPS sensing.
2. ECM.
3. Fuel supply inadequate.
4. Misfiring, spark plugs and/or related parts.
Was this
answer
helpful?
Yes
No
Thursday, May 28th, 2009 AT 12:43 PM
Tiny
FDQX
  • MEMBER
  • 41 POSTS
I experienced some things today, that are new.

I got another smell. I don't know which the rotten eggs smell, but it was similar to "fresh" asphalt when road workers repair roads added with fuel. It occurred when I was accelerating very fast, and it took a short while before it stopped.

I also had bad fuel economy day today, the car consumed about 50% more gasoline than usual. I was driving 100km/h on freeway most of the time.
Was this
answer
helpful?
Yes
No
Friday, May 29th, 2009 AT 1:50 PM
Tiny
FDQX
  • MEMBER
  • 41 POSTS
I also noted that there is a hose in the engine bay that goes nowhere and is plugged with a cap. I found out that it's the engine oil cooler water hose.

The parts catalogue tells my car should have the oil cooler, but it is not there. In the parts left from the engine change, there is the another end of the oil cooler hose. The oil cooler seem to have disappeared during the engine change. Can this or the way that hose is plugged affect something?
Was this
answer
helpful?
Yes
No
Friday, May 29th, 2009 AT 4:48 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
With the latest development, did the MIL shows?

The oil cooler hose won't cause any of the symptoms described. Most probably the engine did not come with oil cooler so the hoses were left hanging as it was not transferred from the other engine.

Did you check the oil level, was there any significant changes?

I would like to know the compression readings for each cylinder and if any significant difference, a wet test compression as well.
Was this
answer
helpful?
Yes
No
Saturday, May 30th, 2009 AT 8:55 PM
Tiny
FDQX
  • MEMBER
  • 41 POSTS
My car doesn't have the MIL.

The oil level is OK. The new engine is driven only 45000miles, so I can't believe there's something wrong with the engine itself.
Was this
answer
helpful?
Yes
No
Sunday, May 31st, 2009 AT 5:22 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
You mean the CHECK egine light is not showing or it is not functioning?
Was this
answer
helpful?
Yes
No
Sunday, May 31st, 2009 AT 8:33 AM
Tiny
FDQX
  • MEMBER
  • 41 POSTS
The European version of the car, which I have, doesn't have the Check Engine light at all. AFAIK European 626 has the light from model year 2000 (facelift with the new meter hood), and mine is 1998.

I also checked the OBD codes, but there was none present this time.

I found a cheap used PCM on ebay with the original immobilizer unit, and I think I'll give it a try. The Mazda mechanic said it fits the car since the immobilizer is within.
Was this
answer
helpful?
Yes
No
Sunday, May 31st, 2009 AT 8:55 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Ok, hope it is compatible and works so that we will know if that is the cause of the problem.
Was this
answer
helpful?
Yes
No
Sunday, May 31st, 2009 AT 10:09 AM
Tiny
FDQX
  • MEMBER
  • 41 POSTS
I just remembered one thing: When the engine was changed, mechanic had put too much oil in it (Almost two times too much). It was noticed about two months later, and the extra oil was drained off the engine. Can this have damaged my engine or the exhaust system?
Was this
answer
helpful?
Yes
No
Monday, June 1st, 2009 AT 7:15 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Overfilling of oil would cause performance loss, excessess oil getting to the intake manifold via the PCV due to high blowby gases and could cause excessive carbon buildup. This could cause clogging of the catalytic converters or premature failing due to excessive oil being burnt.

A compression test would tell if the engine is affected.
Was this
answer
helpful?
Yes
No
Monday, June 1st, 2009 AT 9:21 AM
Tiny
FDQX
  • MEMBER
  • 41 POSTS
I ordered the new PCM, should arrive in about a week.
I noticed that the vibration at idle occurs again, it was gone for a few weeks but now the car shakes like a tractor when stopped at idle.
Was this
answer
helpful?
Yes
No
Sunday, June 7th, 2009 AT 8:25 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Is the idling speed same as before the vibrations were noticed?
Was this
answer
helpful?
Yes
No
Sunday, June 7th, 2009 AT 8:53 AM
Tiny
FDQX
  • MEMBER
  • 41 POSTS
Yes. The strength of the vibration varies when electrical load is turned on or off. When the car has worked fine, the vibration has been gone too. It comes somewhere from the passenger side and is stronger in the interior.
Was this
answer
helpful?
Yes
No
Sunday, June 7th, 2009 AT 9:01 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Vibrations getting to the interior are usually caused by bad engine mounts or hoses out of position, etc.

Check if any hose has been misplaced and transferring the vibration from the engine to body.

Sometimes hardened hoses from engine to body can cause it. A/C pressure hose, radiator hoses and power steering hoses are possible culprits.
Was this
answer
helpful?
Yes
No
Sunday, June 7th, 2009 AT 9:22 AM
Tiny
FDQX
  • MEMBER
  • 41 POSTS
Just a thought when waiting for a new PCM:

Just a little time before the engine change, the car had a little accident. Three of the five wheel bolts of the passenger side front wheel came loose (mechanic's failure, forgot to tighten them) resulting the alloy wheel to bend. It had to be replaced.

I just thought, that maybe the ABS/Speed sensor on the wheel could be damaged from that? Can it cause any of my problems? Is this a totally ridiculous thought, or should I look into it?

Just thought of it because the RPM makes a little notch when the car stops, and also the car sometimes works fine for a moment after it has been on the mechanic (probably off the ground?).
Was this
answer
helpful?
Yes
No
Monday, June 8th, 2009 AT 11:54 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
ABS functions are not related to the engine performance and if there are any faults, the indicator lght would show.

Stopping uses the brake booster which requires vacumn from the engine and this can cause minor fluctuation in the idling speed as rake pedal is depressed.

Guess there is nothing worry about.
Was this
answer
helpful?
Yes
No
Monday, June 8th, 2009 AT 12:02 PM

Please login or register to post a reply.

Sponsored links