OT: an ignition problem.

[Gib Bogle]

OT, but there are a few petrol-heads here who might have useful suggestions.

I have an old but good 91 Toyota Camry wagon, not worth much to sell but worth a lot me as a useful workhorse. It has an intermittent problem that I haven't seen for many months, and the fact that it's resurfaced makes me think it might be temperature-related (it's mid-summer here, although only about 20-23 deg.C).

The typical symptom is that I drive somewhere, park, come back to the car an hour or so later, and it will not start. (On a couple of occasions the engine has stopped when I was driving at a low speed, e.g. coming up to a traffic light.) The battery is good, the engine turns over, but no spark (I've checked this using a timing light with a pickup on the spark plug wires.) In almost all cases it will start after 10-30 minutes, and run as if nothing had happened. On one occasion it didn't start even the next day, and I had it towed to a mechanic. He couldn't find anything wrong (not surprising since it was working by the time he got it), but replaced the distributor on the off-chance. Of course it made no difference.

I've been over every obvious part of the ignition circuit, but everything tests out as OK. The error code (in light flashes) is 43, which according to the manual is:

Starter signal. No STA signal to ECU when vehicle stopped and engine running over 800 rpm.

1. Main relay circuit
2. IG switch circuit (starter)
3. IG switch
4. ECU

I'm beginning to suspect a faulty relay. The manual has the circuit diagrams, but it isn't obvious which part is the "Main relay circuit". I presume it includes the section labelled "Power source and starting circuit", but possibly also includes the EFI main relay, and maybe some other stuff. The circuit isn't really that complicated, but it's often unclear to me where the physical components and connectors are on the car.

I just had a look at the fuse/relay box next to the battery, after running the engine for a few minutes. Some of the relays have plastic cases, some metal. In attempting to pull the relays out, I discovered that a couple of the metal-case ones are very hot - too hot to hold. These are labelled Fan no.1 and EFI main. Is it normal for these relays to get very hot?

Any tips?

Thanks Gib

[thirty-six]

Some ignition coils can suffer an internal breakdown if they get too hot. You could try blasting the coil with a refrigerant spray to check for this specific problem. It may also be that you are simply asking for too big a spark, check to see that your plug gaps are in range (and not getting oiled up) and that your resistive HT leads are not broken. Changing to non-resistive plugs and leads also lessens the ignition coil loading.

[Ericp]

Last time I had this problem, the fuel tank air intake was blocked. This can be a small hole in the filler cap.

As you drive fuel is pumped from the tank and a small vacuum starts to build up in the tank.

At reasonable speed the vacuum is not sufficient to restrict fuel flow but at lower speed it is.

Also when you park the car the vacuum can be sufficient to drain a lot of fuel from the carb and make starting difficult. Diesels can be more of a problem.

[Dave Liquorice]

Relays shouldn't normally get hot at least not "ouch that's too hot" hot. But cars are weird things...

As you have an error code that implicates the "Main relay circuit", how much is new one? Worth a punt if it's only a fe dollars surely.

[harryagain]

[harryagain]

You sure it's not a fuel vapour lock problem or some other over heat problem?

[Dave Plowman (News)]

I dunno this setup, but where is the actual coil driver? That is the most likely thing to fail - and like all electronics can be intermittent.

[Davey]

Sounds like the vapour lock problem we had on a Singer Chamois (Hillman Imp) many years ago. Identical symptoms.

[Doctor Drivel]

It is obviously ign not a vapour lock.

[Weatherlawyer]

I would ignore any advice from people who think that a blocked air vent will initiate sparking problems.

Apart from that I don't have a clue. Replace what you can when you can if you can find old parts in a scrap yard.

Your battery contacts are clean? No salt or corrosion on them?

But that isn't usually self clearing or only partly inclined not to work. Is it?

Hot contacts usually mean a poor circuit somewhere along the line.

I presume the condenser isn't shot as that would give you a misfire. You say it runs OK when it is working. How "OK" is that?

What do the caps of the HT leads look like? It might be worth replacing them.

[Mark]

if it was mine i would first be looking at wiring connector issues to the relay board and ECU due to age of car.

-

[thirty-six]

Another thought is that your radiator fan has stalled and drawing excessive current so dropping the ignition supply, or the engine management is simply shutting the engine down due to the overheat. Check that your fan is actually kicking in as the engine gets hot, give it a twirl to get it going. Check the current it's drawing with the maufacturers specificatiom.

[Baz]

Are you sure you don't have a spark? (I've checked this using a timing light with a pickup on the spark plug wires.) Using a Timing light is not the best way to check. Baz

[Dave Plowman (News)]

Indeed. I have a posh one which allows you to check the advance via a control on it. It won't work at all with EDIS wasted spark. My older basic one does, though.

[Gib Bogle]

I think you win the prize. A number of responders talked about issues other than the spark, while the error messages made it clear that the STA line is not high when it should be, causing the ECU to fail to initiate the spark.

I got my Chilean mechanic/jack-of-all-trades to take a look. He called it a "fantasma" (phantom) and phoned his Chilean auto-electrician pal, who according to him "likes fantasmas". He came to my house immediately. He checked out the connections to the ECU, and found they were all OK. He then fiddled with the wires going to the IG switch, and zeroed in on a nearby board with relays and fuses. After establishing that opening one multi-circuit connector killed the spark, he then noticed some corrosion on one of the contacts of the connector. He cleaned this, and is confident that this has fixed the problem. According to this guy, most electrical problems with Japanese cars are fixed by taking apart, cleaning, and remaking connectors.

[thirty-six]

So was this corrosion in the pasenger compartment and not the engine bay?

[Mark]

yes i have a 91 Toyota Hilux in Ireland the only thing that has ever caused problems, apart from rust, is the wiring connections.

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[Dave Plowman (News)]

It has a distributor, but the spark controlled by the ECU?

[snip]

It's a good place to start with most.

[Gib Bogle]

Yes.

[Gib Bogle]

Yes. The circuit diagram shows that the ECU controls the igniter, which drives the ignition coil and also has connections to the distributor. Clearly the ECU sets spark advance.