Hey guys,

Been checking for threads about the same thing because I know they are out there, but had no luck. So, here goes, I hope someone out there will be able to point me in the right direction.

I got a steal on a 94 929 for$600 and compared to my 88 626, this thing is a Cadillac! I kinda really dig this lil car. Heres the problem...

I went to work on it today, trying to diagnose a poor idle and misfire, and chase down some oil leaks, and I was in there playing with the diagnostic connector in the engine.

Heres where I think I messed it up..The service manual said to check timing, short pins 10 and gnd together, then connect your timing light and blah blah...So, I shorted the connector, and fired it up and started looking for the marks on the pulley. Never found em, but ever since I did that, the car will not idle on its own now. I have to hold my foot down on the gas to open the intake butterflies up enough to allow sufficient air into the engine. This was the last thing I did to it before I lost the ability to idle, and I dont know if I messed something up or not.

The car did have idle problems before, but it at least didnt die like it did. I didnt do anything else to it besides disconnect an o2 sensor to check it and pull codes. It has a 15 code- o2 sensor voltage is out of threshold after 130sec or whatever it says.

I dont know what to check next. I dont know what I did to it. Anybody know offhand whether I did something really bad to the car not knowing it?

 

First I like to congratulate you to your old 929. I expect it will teach you a lot. What you saved in purchase price you may now spent on "tuition". We will try to keep your tuition cost down.
Here you can read up on OBDI codes. Even though that article is based on the Ford Probe you can use it. After all this goes back tot a time when mazda was in the Ford family.
1993-1995 Engine Controller Malfunction Codes

Then I like to refer you to the https://www.mazdaforum.com/forum/maz...%E9g%E9-31136/

If your 929 is normally aspirated you can pretty much apply everything to your car.

Here is a video on diagnosing a misfire:
And here is a list, provided by UseYourNoggin, on potential causes of misfire:
Missfires Can Be Caused By a Million and One Things,

Vac Leaks
Wiring Issues
Spark Plugs(Even Fresh Spark Plugs That Are Crappy Quality.... E3 And Such)
Ignition Coils
Alternators (Search EMI)
MAFS
Injectors
Injector O-Rings
Intake Gaskets
TB Gaskets
PCV Hoses
PCV’s
Malfunctioning EGR
Malfunctioning CAS
O2 Sensors
Aftermarket Intakes
Intake Hoses
Vac Lines
Timing Chains
Timing Chain Tensioner
Broken Cam Gears
Malfunctioning Cam Sensors
Incorrect Crank Gears(The I4 Has Like 40 Different Configurations For Whatever Reason)
Incorrect PCM Flash
Issues Within The PCM
PCM Wiring
Bad Diaphram Within The FPR
Issues Within The Fuel Pump
Dirty Fuel Filter
Dirty Fuel Lines
Pre-Cats/Poor Exhaust Flow

If the above gaskets/seals have not been changed, change them. Clean your MAF sensor, throttle body.
Change your PCV valve and probably that short hose as well.
Inspect the intake accordian tube for cracks. Inspect for vaccuum leaks.
Put in a good Fuel system cleaner: Red Line Synthetic Oil - Gasoline Fuel Additives - SI-1 Complete Fuel System Cleaner
Inspect wires. Re-set ECU after doing above.

 

Thanks Tan! That is really helpful! A good start. Right now I have to try to figure out the no idle situation as that is the biggest determent to driveability. I have found that it will start right up cold, and idle just fine, (for having a blown out exhaust and a miss) but as soon as it is warm, it will still fire immediately, but dies as soon as it receives no throttle input. It doesnt even try to idle.

I dont know if its something I reset in the learned memory (if any such thing exists on this car) and maybe the car is operating to what it thinks should be normal, but fuel trim and whatnot hasnt been learned for the wear and tear? I donno. Just taking a wild guess at that one.

I am not sure if I should start looking at the induction system sensors, or try to test the o2 sensor output first and chase the dtc 15 down. I have limited tools while im not at the shop since I didnt bring anything home with me so Im kinda shooting in the dark here.

Im not a drivability tech so the diag procedure is somewhat new to me. Well see what I come up with I guess! Ill post my findings...

 

94:
I gave you a link for the codes. If you click on "15 " you get some good information.
Possibly the contacts to the hO2 sensors are corroded, just clean them and put them back together. Look at the wires if they are chafed. You can also look for continuity and resistance for the heater circuit.
The computer does not get any information from the HO2 sensors.

 

Ok, Update!!

I tore it down yesterday and replaced the valve cover gaskets, and let me just say, I can see why the guy gave me a deal on the car when I bought it. The shop cost for this job would have been 3/4 of the total resale value of the car. Im sure if I did it everyday, Id be able to do it in a few hours, but this took me and my coworker whos a heavyline tech for GM the better part of a 9 hour block of time.

The plus? Everything on the car was well taken care of. Sure there were rock solid vacuum lines here and there, but not one bolt was stripped or any other backyard stuff going on in the engine. It was all factory. The valve cover retainer nuts were all hand tight, so that was a contributing factor in the spark plug oil leakage.

We cleaned the v/c gasket mating surface on the heads, slapped the new gaskets in and replaced the valve cover gaskets. The passenger side was cake walk compared to the left side. Whole lotta more vacuum lines and switches and other junk over there. Oreillys gave me the wrong lower intake gasket so the old one had to go back on, (nobody stocks 929 parts apparently), and on with the intake.

The car fired right up, smooth as a glass. After the car went through its learn modes and we adjusted the idle, and tied up a small coolant leak spraying on the heads, the car ran like a champ. The MIL came on on the drive home, but I havent checked the code yet. Not too worried about it. Im assuming I crossed some vacuum lines here or there.

But the miss fire is gone, the idle is level and smooth and the car drives a whole heck of a lot better.

I also cleaned the throttle body out while the intake was off, so that probably helped a bit.

I dont know if you guys like pictures like my Nova forum guys do, but I took some just in case anybody needs to see what the thing looks like torn down, for reference or whatever. Let me know and I can post em up.

Ill check that code probably tomorrow or later today. Thank you Tanprotege for the info! Im still learning Mazdas and it would have taken me a while to figure out what you graciously placed at my fingertips. I appreciate that!!

Nate

 

Congrats to a job well done!



Are you kidding? We are gluttons for pictures! The more the merrier.

 

Good deal! Ill post them up after work today if I can. Also there will be exclusive sneak peek at my modified exhaust!!! I cut out the blown out pre muffler and put a straight pipe inline just yesterday, then waxed her. I forget shes running sometimes because Im used to hearing the thing from around the corner!

Thanks again Tanprotege!

By the way, do I have to use photobucket or an equivalent to post pictures?

 

READ: https://www.mazdaforum.com/forum/new...-photos-30911/
AND: https://www.mazdaforum.com/forum/new...cs-post-30904/

 

Ill mess with this more later, but was unable to upload all the pictures I wanted to, and at that, havent gotten them posted to this thread yet. I did make an album, and you can take a gander at my little 3.0's dohc valve train, or look at the exhaust fix. I warn you, my exahust work is ugly having done it myself on a budget, with over the counter auto parts supplies, but the repair seals, and the car is fixed, so Im not too worried about it.

A note about the exahust, I had to use the black exahust wrap for those of you who may be curious. The white kevlar mesh sheet that you soak in the solution and then wrap the damaged pipe sucks, and its messy. The black stuff seemed to to the trick after wrapping that repair with aluminum and clamps. Ghetto, yes, and as a mechanic I should be ashamed of myself, but as I said, it works, so it works for me for now. Pictures of that are not shown because I didnt get a chance to take them. This is the first (failed) repair I have pictures of.

UPDATE ON CAR DRIVABILITY:
I dont remember where I left off, but to date, the following parts have been replaced since I bought the car a month ago:
Valve cover gaskets
Plugs and wires
Fuel filter
premuffler with a straight pipe

--Then the engine ran well enough to diag the MIL light. The car was giving me a 15 code initially before the repairs; LEFT SIDE O2 SENSOR: SENSOR OUTPUT LESS THAN .55V 130SEC AFTER EXCEEDS 1500RPM.

After the repairs above where made, the car threw a 15 AND 17 code. 17:LEFT SIDE FEED BACK SYSTEM: SENSOR OUTPUT CONTIUES UNCHANGED 50SEC AFTER ENGINE EXCEEDS 1500RPM. With both codes pointing to the left side o2 sensor, and being as there is only one sensor upstream, and none downstream of the cat converters, I decided to just replace the left o2 sensor with a new Bosch from the parts store.

The car does now throw any more codes, and the light hasnt come on since the o2 sensor was replaced. I am going to put some miles on the car today and see. Then, if all goes well, Ill reset the ecm, drive it some more so the computers can learn whatever they want to learn, and then get her smogged so I can finally get that tow truck repellent, AKA the little yellow sticker that tells law enforcement personnel that you have paid your registration

Tanprotege, thanks again for your help! You saved me a lot of headache and time working on this! Useurnoggin thanks for the photo upload help. Since every forum seems to be different I cant even figure out how to figure things out anymore!!

Car really runs like a champ for how bad she was when I picked her up. Definitely not a $600 car now!! Next up is the power windows to be fixed. Not one stinking window in that damn car works right, the rear not at all.

Ill just keep adding to this thread as I go along, since I at least know how to find it every time!