Any experienced mechanics here (car repair help)

[berkeley]

I could really use some tips troubleshooting a problem on a Mazda minivan.

I've exhausted all the obvious replacement/testing options for the do-it-yourself person with a Haynes manual.

Please chime in and I'll PM you the details.

Thanks! 

[jock]

Lots of experience with motorcycles, not so much with vans/cars. Can rebuild a 4 cylinder superbike from the ground including engine work/ brakes/electrical loom work.

Let me know the problem and I'll see if it rings any bells.

[disturbia]

I have some experience working on vehicles, but I also have a lot of friends with a LOT of experience. If I can help I will.

[berkeley]

Anyone else . . . still could use some tips . . . 

[lady-t]

I could really use some tips troubleshooting a problem on a Mazda minivan.

I've exhausted all the obvious replacement/testing options for the do-it-yourself person with a Haynes manual.

Please chime in and I'll PM you the details.

Thanks! 

what is it doing or not doing as the case may be?  is it cranking but not starting but still getting fuel?  if so take off the distributor cap and look down at a little flattish piece on the side of the rotor under neath it kind of...if there is a dot on it the electronic part is toast. 

did you rebuild it and now it won't fire?  details please.  you don't have to get ultra detaily just something to go on.

i used to have a used car lot and had to work on lots of "bugs" in vehicles and maybe i can help.

[berkeley]

thanks for the PM's to date

so far in this forum and from some e-mails i have 5 entirely different approaches to pursue. 

i've already dumped so much time and money into this i'm starting to go insane - i've never NOT been able to fix a car with a full saturday's work, and this includes land rovers, which fall apart as you're fixing other things (something always has to be broken on a land rover in principle i think) 

[Six Gun Jim]

Lay it out for me, I turn wrenches for a living. 

[berkeley]

Thanks Jim, sent the details.

[disturbia]

Berkeley,
Can you briefly lay out the 5 different approaches (6 if Jim says something different) and let's see them.

[berkeley]

okay, i'll write up a summary with the suggestions (anonymously) posted.  fyi, a relative who has a lot of wrenching experience has not commented favorably (to be polite) on many of them.  however, that person has also suggested doing some direct-power (with a 12v battery) testing on components, which another mechanic has warned me has the potential to fry one or more expensive sensors, or even the ECU.  i'm getting pretty frustrated with not having a clear endgame in sight.

i did manage to find/download the 1,000 page mazda tech service manual online, so that is going to help A LOT with locating and testing things properly.  the tools are coming out in about an hour, so there will be some feedback after the sun goes down. 

if someone nails the problem/solution, i'll send them a doomer prize from amazon 

[berkeley]

Didn't find/fix the problem on my own.

Had it towed to a mechanic who's got a good rep and has worked on this make/model/year a few times before.

Will reveal the problem(s) when he gets back to me in a day or two, for those who've tried to help out and want to know if they were on target.

Thanks for everyone's help!

[berkeley]

Berkeley, can you briefly lay out the 5 different approaches (6 if Jim says something different) and let's see them.

FINALLY got the car back from the mechanic TODAY.

After verifying the fuel system and computer were up to factory specs, the mechanic went in and replaced the distributor, which has inside of it also the camshaft position sensor.  This did not solve it so he put the old one back on and then targeted the . . . CRANK POSITION SENSOR, as he said this the last piece in the puzzle which could be causing it.  He also said he'd put in a new timing belt while he was in there (you have to go that deep for the crank sensor on this model). 

1. the new crank position sensor finally solved it!

2. when he pulled the old timing belt it had apparently "skipped three teeth" and the thing was in seriously bad shape.  showing it to me, it was missing quarter-inch wide chunks from the edges here and there and the belt was just a pathetic sight.  he said if we hadn't gone in that deep and discovered/replaced it we would have lost the engine. 

So, it's running strong again. 


As far as I can tell the only person who suggested looking at part #1 above was . . . "Zac"

A crank shaft sensor (providing feedback to the ignition system and engine control computer) that malfunctions when it warms up is another possibility.

Thanks for everyone's interest in helping me out - It's appreciated!

Here's the complete list of suggestions:

____________________________________
(person 1)

discussed this with hubby ( he da guru around here)  he thinks the catalytic converter is plugged or mostly plugged.  he says take it loose and see if it runs better. --- careful not to burn anything. ---( brother burned a truck to the ground once by accidentally drilling a hole thru one once)    did you use ethanol?  it can clog up catalytic converters.  let me know if it works.

this is a no cost test.  no parts involved.  just to see if it works. hubby is great with motors btw.  the back pressure is killing the motor from the catalytic converter .  that's what hubby says.


____________________________________
(person 2)

have you checked the O2 sensor/s on the exhaust. If they are clogged or fucked they can send wrong signals to the computer and kill the fuel. I am servicing my car at a mates house tomorrow. Will run this by him and see what he reckons.

just to clarify what I said, the O2 sensors monitor your exhaust to help determine how rich or lean the fuel mixture is. If they are faulty (reading your exhaust is rich) they could send signals to the computer to  lean out your fuel to the point the car stalls. This mate I was talking about had exactly that problem when he replaced his headers with a set of extractors and the O2 sensors were moved further down the exhaust. They had to be moved back to their original positions. Anyways, will let you know later tonight if I find any more info.


____________________________________
(person 3)

I scanned the attached out of one of my GM service manuals and it might be helpful.  The problem sounds like its heat related.  My guess is the problem is related to the fuel injection or ignition systems.  One distinct possibility is there is a problem with the pressure regulator for the fuel injection system causing pressure to drop after it warms up.  I have a fuel pressure gauge if you want to use it.  (it fits GM, but don't know about mazda)  A crank shaft sensor (providing feedback to the ignition system and engine control computer) that malfunctions when it warms up is another possibility.  A blocked exhaust system is unlikely, but could also produce similar symptoms.

Another possibility is a bad ignition module.

Also, the crankshaft or cam position sensor usually needs to be working to have the ignition system operate (and the engine run).  In electronic ignition systems, it's used to synchronize the firing of the spark plugs.


____________________________________
(person 4)

First glance at your problem makes me think automatic choke or choke sensor is faulty, running extremely rich at cold startup then bogging and dying as engine approaches optimum operating temperature but the air fuel mix remains far too rich.

That's just the first thought that occurred to me. I'll have a think about other possible causes.


____________________________________
(person 5)

Ok, I had a chance to talk with my mate. He has had a similar problem on his motorbike. He said that it is either the spark or the manifold vacuum pressure, but almost definitely the spark. There is something probably in the distributor that as the engine heats up, the heat is increasing resistance somewhere and killing the spark. This explains why it takes about 5 mins to start playing up, why it happens straight away when you try it again, and why it goes back to 5 mins after you leave it awhile. You need to be able to find a way to measure voltage at the spark plug continously from when the engine is started and until the problem occurs to see if that is it. Then backtrack from there until you have found the problem.


____________________________________
(person 6)

Okay so feed it fuel. Get a spray bottle when it starts to rough idle and give it tiny little spritzes of fuel directly into the throttle plate, hold it open just a hair while you do it. If that changes nothing or makes it worse then start pulling plug wires and see if you have a single or all cylinders miss condition. Pull each one and note if it changes anything at all, use a boot puller so you don't get hit. If that changes nothing or nothing can be noted see if you have a part throttle air sensor that supplements the mass airflow, I don't know Mazda well enough to say. Then check your  vacuum and crankcase vents, vacuum issues such as collapsed lines effect idle. Also check the TPS and see if your throttle position is accurate by ohms, they DO NOT always throw codes. Best I can think of for now but let me know, it sounds to me like an electrical problem. Temperature sensitive is usually related to a coil or a wire. You might also put some Seafoam brand fuel treatment in it. Seafoam actually works, unlike 99% of the other shit.


____________________________________
(person 7)

[was always thinking it was a fuel problem, somewhere]

[Six Gun Jim]

Hey cool, at least it got fixed.