93 Corona stumbles then eventually stops

[slow_cripple2]

Long story short.
Originally it took 30km before faltering occasionally then clearing, and she's all good.
After first two break downs with tows, two visits to the mechanic ($445) with assurances at each visit that the problem has been remedied.
The damn thing began stumbling again on Sunday after 7kms travel. We managed to reach our destination without coming to a complete stop ; a distance of 12km.
Looking back, this 7kms seems to be the common distance when the problem first shows, then gets worse till a full stop and no starting.
Anyhow, on our return 3 hours later it started up and ran fine until, sure enough at about 7kms it begins to stumble etc. We made it home.
Now here is the interesting bit. Sitting in the driveway we ran it up the rev scale and held it there until it began to miss(?) and run rough. I smelled something that seemed familiar so into my chair and to the exhaust end.
Sure smells like burnt fibreglass (?). I got my wife to drop the revs and I felt the pressure at the pipe- not too strong I thought. So she brought it up to higher revs and I couldn't detect any appreciable increase in flow but it was bloody hot and that strange stink.
Shut down the car and went inside.
The next morning it started fine with good exhaust pressure that increased with revs as you would expect. So we went for a test drive. This time we decided to drive 6 km and then return so that when it crapt out we would be able to get home. Sure enough, 10km later...................

I have had the exhaust system checked and it is all good (no cat either)

Items replaced by mechanic: fuel filter, distributor cap, rotor, electronic coil, plugs.

I called him and he said it had indicated a code 31 but he wasn't convinced that was the problem.(????)

Vacuum line to the MAP sensor appear /feel pliable and no sign of splitting. I disconnected the plug and closed up the female contacts then re-attached the connector; now nice and tight. It came off easier than when I attached it so could have been loose. Strange, the sensor(?) from the airfilter housing was disconnected)I wonder when that happened as it was in position when I fitted a good intake hose ( the other was completely split)
Its off to the local electrician for a plug-in today. Fingers crossed he gets a result and its not another exercise in cash for no remedy

Can anyone shed light on this problem? I am tired of throwing funds at it with no result.

[BZG Wagon]

Whats code 31? And what do you mean by 'stumbling'?

I presume it takes 7 - 10km for the car to get warm?

Looking at everything you've replaced I'd guess an oxygen sensor, air flow sensor or cam position sensor.

To an extent; when the car's cold the engine is programmed to run a certain way regardless of what the sensors read. Then once it hits normal operating tempreture one of your sensors is feeding the wrong information to the ECU, and the car isn't coping.

[slow_cripple2]

Whats code 31? And what do you mean by 'stumbling'?
I presume it takes 7 - 10km for the car to get warm?
Looking at everything you've replaced I'd guess an oxygen sensor, air flow sensor or cam position sensor.
. Then once it hits normal operating tempreture one of your sensors is feeding the wrong information to the ECU, and the car isn't coping.

Stumbling; its like a temporary ignition/fuel loss, then it recovers for a short distance, getting worse until a complete shut down if you persist in continuing to drive.

from what I can find, a code 31 is MAP sensor related/\

" To an extent; when the car's cold the engine is programmed to run a certain way regardless of what the sensors read " Thanks, I wasn't aware of that.

[Crucible]

How did they check the exhaust?

The smell out the back would be something id be trying to rectify first. May have a collapsed muffler. The only real way would be to cut the front pipe off manifold, roadtest and see if there is a differance.

The symptoms certainly sound like a restricted exhaust.

If it is getting too much backpressure it will upset vacuum at intake which will of course upset map signal. A vacuum gauge check will also show any probs.

[slow_cripple2]

How did they check the exhaust?

If it is getting too much backpressure it will upset vacuum at intake which will of course upset map signal. A vacuum gauge check will also show any probs.

Pete has been at the game for decades. I just spoke with him and to be absolutely sure would require cutting the muffler open. He looked for evidence of heating in the manifold/heatshield region and saw nothing that would raise his suspicions re blocked muffler/s.
If it is not resolved with the anaysis today I'll hook up the vacuum gauge and take it for a run and observe. Should I just T into the MAP sensor unit line or is there a better source?

[edwagon]

Have personally seen blocked exhausts do a similar thing many times - most recently on an accord which was as strong as an ox for the first 3-4km and would then gradually but very certainly weaken over then next km until it was running like a dog - eventually ran out of options and threw another muffler on it and it was like a whole new car

Unbolt the rear muffler and go for a drive, ignore the noise and see how it performs

[sergei]

collapsed muffler is easily (5min) diagnosed: disconnect at the headers (2 bolts).
It could be fuel pump (similar symptoms).

[edwagon]

collapsed muffler is easily (5min) diagnosed: disconnect at the headers (2 bolts).
It could be fuel pump (similar symptoms).

Absolutely - just re-read and saw that you haven't mentioned this - have seen a couple of Coronas with weak pumps recently too

[Crucible]

Should I just T into the MAP sensor unit line or is there a better source?

You can do or anywhere after throttle body.

[slow_cripple2]

Well let's hope so

I collected the car from the auto electrical shop on Friday arvo.
My wife had dropped it off that morning and as luck would have it, the car was missing when she arived.
2 1/2 hours labour later the car is all good.

It turns out that the loom had been chaffed through enough to cause an intermittent short. The location was beneath the front fuse-box.
I was informed that a similar problem can arise where the loom passes between the rear of the cylinder head and the throttle body



30kms later and no sign of the problem recurring--fingers crossed.

A big thanks for all your assistance.

[allencr]

I hope you've been able to get those assholes that threw parts at it "with assurances" to acknowledge that they owe you something.
Replacing parts that couldn't possible cause a problem with out having very obvious to see defects, except for the coil, is just plain incompetence.

[slow_cripple2]

I hope you've been able to get those assholes that threw parts at it "with assurances" to acknowledge that they owe you something.
Replacing parts that couldn't possible cause a problem with out having very obvious to see defects, except for the coil, is just plain incompetence.

I'm not bitter allen; frustration was the emotion and inconvenience was the real price. We're too reliant on the car but that comes with the territory.
Yes, I am going to pay a visit to the original mechanic and spell out what the cure was. Firstly to increase his knowledge which may benefit other customers; secondly about the excess time to arrive at a solution to the problem.
Having said that in the 6 years we have owned this vehicle this is the first fuel filter, distributor cap and rotor, plugs and a new coil. So I expect that those items are long overdue for replacement except maybe the coil; but that had cracks and who knows how long it would have lasted.
Rationalising it, the maintenance costs over the last 6 years including this recent drama has been in the order of $3 per week. before this recent event it was $1+/ week. That's a good average don't you agree?
My main gripe is the time involved before a resolution and the breakdowns/tows. Fortunately the towage costs were covered under our AA contract.

[allencr]

You're a better person then I am.
The out of the ordinary Toyota reliability does lull me into false sense of perpetual motion that gets offended when anything actually needs fixing.
The loom should show signs of whether the contact point has been there since new or is something recent. Every manufacturers wiring looms can get chaffed, but most problems are really caused by mechanics & panel beaters leaving off clips & not taking any care when doing work nearby IMO. Just a little tug or twist away from an edge can make it last the life of the car or it'll wear through in a month.
Good luck.