Req for info: Non-sequential fuel injection?

OK, the question has to do with the multi-port fuel injection system in my '85 toyota camry. (this is the car that exhibits a peculiar
stall-under-load effect, highly intermittent)
Looking thru the factory manual, it's clear that all four injectors fire at the *same* time. The EFI unit has two output wires, which are tied together. That single line goes two four ballast resistors, and the other end of each ballast resistor goes to an injector. The other end of the injector coil goes to B+, so when the lines on the EFI unit pull low, current flows and the injector fires.
So what has me stumped (and here this is a purely academic exercise) is how does the fuel injection work if the injectors all fire at the same damn time? The manual has a one line blurb that says (paraphrase) 'the EFI computer decides how much fuel is required for the given sensor inputs, and injects one-half of that amount per crankshaft revolution.'
Which makes sense because it is a four cycle motor.
But for my thinking, only one of those injectors is going to fire at the 'right' time, or when the intake valve is just starting to open up. What happens to the other three when the injector fires at some random time - does the cloud of fuel mist just sort of hang out in the intake runner until it's needed?
All comments gratefully accepted.
Jim
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jim rozen wrote:

Exactly. My old Ford ECU book says the charge is "stored" in the intake manifold until the valve opens. Parenthesis are theirs.
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"> Exactly. My old Ford ECU book says the charge is

Exactly. That is probably the definition of non-sequental fuel injection. ASFAIK (which isn't very far) injectors for gasoline in automobile-type engines are not the high pressure types which are used in diesels. In the later, injection pressure has to overcome head pressure. It is my understanding that low pressure injection, metered by a "computer", only serves to better equalize fuel flow over that obtainable under a common manifold.
Bob Swinney

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says...

I guess the intake runners do get pretty hot during opeation. So that could be avoided somewhat. Besides the injectors are *right* there at the valves, right?

There was some hokey explaination that maybe the hydraulic lifters were somehow compensating for the valves not closing all the way, and eventually one would have all the adjustment used up.
The trouble is intermittent and does not correlate with outside temperature, coolant temperature, humidity, or any other observable factor that I can tell.
So far I've checked:
1) gas cap for venting 2) fuel pressure at injector rail (at engine cutoff during the trouble occuring, it was spec at 38 psi) 3) catalytic converter backpressure (never above 5 psi at *full* throttle operation - and when the problem did occur it was below 3 psi)
Next is to instrument with a timing light inside the car to see if maybe spark is going away. And also to monitor injector pulses with a scope after that. Come to think of it, having *all* the injectors fired at the same time implies that this could be a possible failure mode. The EFI unit stops sending out injector pulses or starts sending out short or crippled ones. I had rejectedt that idea with the (incorrect) belief that a bad injector circuit would only affect one cylinder.
Drives me crazy because I cannot see how a mechanical problem would reset drivability, moments after failure under load. So it has to be electrical. But all the electrical fails I can think of would also not allow instant re-start.
Real problem is that the fail is so intermittent it's tough to get it to occur once you instrument something. I think it was gary who said the best way to protect against lightning strikes is to instrument the building to study the effects of lightning strikes. :)
But when it does go bad it really quits, so it makes the car dangerous to drive for my wife. Don't like that so she's got my truck :(
Which leaves me with a bike or four. As long as it doesn't rain....
Jim
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There was a case of a GM car I read about on the IATN mailing list that had an injector intermittently shorting out in a batch fire injection system like your car. Killed the engine and would start again shortly thereafter. The shorted injector was pulling B+,(I'm old, too), down and stopping all injection. Might be worth a try if you've got a meter handy and can catch it in failed mode. Just reread your post and noticed it had ballast resistors. They might be in there to prevent this, and I could be off the mark.
Garrett Fulton
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OK, thanks I will do this. The cap and rotor are new within the year, and the car was doing it's act before it was changed. But I will give it the close eyeball next. Also advance weights, dist. shaft bushings, etc.
The fuel filter actually was the *first* thing I changed. The battery and charging system on this vehicle are fine as far as I know. The battery was also new within the year.
I am trying to avoid shotgunning the problem (aside from being anathema to me) because 1) the car's not worth a great deal of money, and b) almost any major subsystem fix is going to run $500 or so.
Dropping the fuel tank to change the pump, for example, would be about 500 all told. Checking the fuel pressure at failure cutoff and finding it at spec means that would be money completely wasted.
Jim
Jim
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wrote:

I'd leave the ECU for last- they're pretty robust.

Not good enough of a test- try having some one put the car in drive and (very) briefly load the engine (like doing a hole shot). The engine will torque over a fair bit. You might be surprised.

Yep, Toyota makes some nice stuff. Unfortunatly, time takes a toll on vacuum tubing and the Japanese hose is not the best.

Bad O2 sensor won't cause a WOT stall. I'm stll betting on a wire or hose, but on further reflection, I'd look at both sides of the ignition- the pickup coil in the distributor might be ready to fail (it sits near enough to the head to get plenty hot) or part of the secondary circuit is breaking down under load. Can you give us a blow-by-blow of the failure?
-Carl "Back to the thinking chair" "The man who has nothing worth dying for has nothing worth living for"- Martin Luther King, Jr.
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wrote:

Get the car on a lift and rap the exhaust system with a rubber mallet- it's beginning to sound like a piece of muffler or converter has broken free and is blocking the exhaust stream. the clue here is "After the car re-starts it does hang at some small presure like 1/2 psi, even at idle, for about five or ten seconds." Nothing upstream of the exhaust will cause that exact condition.
Some mufflers have spring-loaded valves that pop open at WOT or near WOT.
-Carl "The man who has nothing worth dying for has nothing worth living for"- Martin Luther King, Jr.
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Ah, the old potato in the exhaust pipe syndrome. That could be it.
Gary
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says...

Doubt it, because when the problem occurs, the pressure in front of the cat converter as never been seen to be above about three psi.
And I've seen pressures there up to about five psi, during normal WOT operation, for brief periods. And no malfunction.
The key presenting symptom *during* the fail is that the pressure in front of the converter oscillates with about 3 psi p-p amplitude, very rapidly. The bourdon tube gage cannot really follow that but I can see and hear it buzzing. This is in contrast to normal operation where the gage is pretty much steady.
The exhaust system is new btw, as of a month ago, from the converter back to the tailpipe.
Jim
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wrote:

OK, in that case, your exhaust measurements are leading us down the garden path.
Wait a minute... Is there a WOT throttle switch or throttle position pot on this guy? Probably a pot- check the resistance through out the range of travel (move the throttle slowwwwly) and see if you hit a flat spot. There may be an adjustment for closed and/or WOT. If this pot is sending the wrong info to the ECU, it might be misinterpreting the data as a being at idle condition and adjusting the fuel flow accordingly.
-Carl "The man who has nothing worth dying for has nothing worth living for"- Martin Luther King, Jr.
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I just fixed a similar problem with my Jeep Commanche, except it would buck a bit as it lost power. The problem was solved by new plugs and wires. The issue is that chamber pressure rises under load, requiring a higher secondary voltage to fire the mixture.
But a *smooth* loss of power is confusing. Even if the problem were a clogged fuel filter (or other restriction in the fuel system), limiting the amount of fuel to the engine, I'd expect lean misfiring as it loaded down to engine shutdown.

Ok, that sounds like a lean misfire symptom, even though you aren't feeling any bucking.
I'd be looking for a restriction somewhere in the fuel delivery system which is preventing enough fuel from reaching the injectors during high flow volume situations. I'd also take a second look at the ignition secondary circuit to make sure that plugs or wires, or the coil, isn't breaking down under the voltage rise needed to fire under heavy engine load.
Gary
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says...

Yep. Real smooth. When driving under ordinary conditions (not WOT testing, I know where *all* the big hills around here are...) the first presenting symptom one notices is, 'hey, my foot's on the floor!'

If it is, it's happening between the injector rail and the the injectors themselves. I've had the pressure gage that measures the rail pressure zip-tied to my side view mirror, and was steady at 38 psi (spec for that system) during flame-out. The pump, lines, venting, filters, up to that point are defined as 'good' in my mind, until somebody informs me of some way the injectors can plug intermittently from junk in the rail. All of them, at once. And then unplug just as fast.
If it's a fuel problem then it has to be the injector pulses going away, I think, and I am going to check that soon.

Agree. If this is happening, though, why does it fail only 5% or so of the time during WOT running?
Jim
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<<snip>>

Jim, are you saying that the fuel pressure is always 38 psi?
38 at idle? 38 at WOT?
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wrote:

That would be a normal reading- fuel injection depends on a constant fuel pressure.
-Carl "The man who has nothing worth dying for has nothing worth living for"- Martin Luther King, Jr.
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wrote:

You'd think so, but the highest pressure is achieved at start up, before vacuum can control the regulator. Even at WOT, there's enough vacuum present to control fuel pressure. The processor cannot measure or modify fuel pressure- all it can do is change the injector pulse width. Beyond a certain point, the pulse frequency becomes too high for the solenoids in the nozzles- they 'buzz' and fail to control flow. In order to prevent this, the ECU fires the nozzles half as often, and holds them open twice as long.
Clever, those Japanese.
-Carl "The man who has nothing worth dying for has nothing worth living for"- Martin Luther King, Jr.
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Good, rules out a stuck regulator which isn't all that uncommon.

Correct. Everything WRT the intake system and injectors has to be considered on the basis of absolute pressure where a perfect (or near) vacuum is zero psi and increases along with an increase in barometer. IOWs, even at 18"hg intake vacuum, there is still an absolute pressure in the intake manifold. Absolute pressure equals baro minus vacuum.

My pleasure.

Yup, I just grabbed some numbers for example.

Could the snorkle tube be collapsing?

Lean can be checked very easily. Back probe your DVOM set to DC volts into the oxygen sensor connector, ground lead to battery negative, drive it at WOT until the engine falls flat, if it's getting enough fuel your oxygen sensor voltage will be near 1 volt, 900mv or there abouts is acceptable, if it's below 600mv at WOT, it's leaning out. Nice simple easy test using the vehicles own resources to verify fuel supply.
O2 volts low = lean O2 volts high = rich

Absolutely.
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says...

And it does. The vacuum controlled fuel pressure regulator is working properly - the pressure is about 32 to 34 at idle, the number I quoted is spec for WOT operation: 38 psi.
Jim
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says...

No, the vacuum regulator is working. 38 at WOT, it is more like 32 or 34 at idle. Agrees with the shop manual's specs.
Jim
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says...

I've seen this called out, but it seems that if the fuel pump were unable to deliver the fuel volume, the pressure would drop. Ohms law and all. So I've omitted the beaker test for now.

Not yet.

Also yet to be done. However this is a long shot as far as the HT leads and plugs, as the car did have those replaced a year ago, and the problem was invariant over the changeover.
I am planning on giving the distributor a real close eyeball as well, it is indeed the kind with the coil integral under the cap. Also cent. advance, vacuum advance (has both) and leads to trigger sensor.
My experience with HT lead problems is they always get worse in the rain. This one does not seem to do that, only an observation. And I do drive the car a lot during the rain, as it's my alternative to motorcycling.
Thanks for the suggestions.
Jim
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