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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Reply to
jim rozen
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Exactly. My old Ford ECU book says the charge is "stored" in the intake manifold until the valve opens. Parenthesis are theirs.
Reply to
Jim Stewart
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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Reply to
jim rozen
B+ ? Damn, you're an old fart (: Next time say Vbat and you'll look all technical and modern.
I'm going to go out on a limb here. If it were my car and my money, I'd change the coil. I've seen a failing coil do this sort of thing.
Reply to
Jim Stewart
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
Reply to
gfulton
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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Reply to
jim rozen
What's that smell??
OK, then I will check for spark with the timing light as the next OBD setup. Thanks.
Jim
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Reply to
jim rozen
Certainly true - but then why does the car restart so reliably every time, after failure? I would think if the coil were punching thru, it would run rough after that. Also that the problem would be much worse during rain or high humidity conditions. It's not.
Still, it's an easy thing to check. Thanks for your suggestions.
Jim
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Reply to
jim rozen
So that could be avoided somewhat. Besides the injectors are *right* there at the valves, right?
Good design wouldn't depend on heat to vaporize the fuel. Yes, the injectors are aimed at the back of the valves.
As for your real problem, I haven't a clue. It does sound electrical/fuel management but I wouldn't swear to it. I think your ideas for trying to spot it with o-scopes etc. are your best hope.
Pete
Reply to
PLAlbrecht
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.
Reply to
Carl Byrns
I'd bet more on the air flow meter, MAP sensor, or associated connectors or wiring. Those devices are easy to test with just a volt-ohm meter, but if they're OK I'd look at fuel pressure and delivery.
Carbon on the valves can cause hesitation (they absorb fuel and hold it) but I've never heard of stalling. A bottle of Chevron Techron can dissolve almost all the carbon and will also clean the injectors. Don't get the injectors cleaned by a garage because the solvent is so strong that it eats solonoid coil insulation and so is prohibited by some car makers.
Reply to
do_not_spam_me
"> 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
Reply to
Bob Swinney
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.
Reply to
Carl Byrns
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
Reply to
Gary Coffman
Punch thru isn't as fatal to parts of the electrical secondary circuit as it would be to a solid state circuit. As soon as the condition demanding higher voltage is gone, the symptoms usually disappear too.
Chamber pressure is lower during starting, and light loads while driving on the flat. So a marginal ignition system won't show any problems under those conditions. But under heavy load (WOT when engine RPMs are pulled down below the torque peak), it'll begin to show problems.
Gary
Reply to
Gary Coffman
OK, but in my past experience, once an ignition coil has been punched through like that, it never is right ever again. What steers me away from this conclusion is that the car can and does perform flawlessly under WOT condtions, 95% of the time.
I would expect to find a problem like that show up more in wet or damp weather. This does not *seem* to correlate at all here.
Given the number of callouts on it, I am going to move 'ignition HT' up on the list a bit though.
Thanks - Jim
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Reply to
jim rozen
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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Reply to
jim rozen
Ah, the old potato in the exhaust pipe syndrome. That could be it.
Gary
Reply to
Gary Coffman
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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Reply to
jim rozen
Jim, are you saying that the fuel pressure is always 38 psi?
38 at idle? 38 at WOT?
Reply to
Neil Nelson

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