Req for info: Non-sequential fuel injection?

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.

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.

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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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

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

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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That's not a safe assumption. It is easy to get high pressure in a flow restricted system.

Gary

Well, that one has tripped up quite a few good mechanics. My fuel pressure gauge has a push-button tap (bleeder) for burping the air out, if I burp a stream of fuel and the engine stumbles or stalls, I know the pump is weak. Seen plenty that had spec pressure but fell down when bled this way. The known good ones handle the fuel being bled with no problem.

My experience is that Asian imports are very sensative to aftermarket ignition parts. I've had Nissans that wouldn't run a week on an aftermarket ignition rotor, dynamic scope testing revealed the spark shunting to ground (distributor shaft) under snap throttle (load). just a thought...

Ah, maybe stuck advance weights...

I had a Toyota come in a few years back where some ham fisted hood lifter had busted a pretty good sized hole in the side of the distributor cap (car was by me for unrelated service) the thing ran fine, no complaints about wet weather performance, which I found astounding. Distributor cap replacement was highly recommended anyway.

There are but a handful of things that react load sensative on an engine, fuel delivery, air measurement, secondary ignition, timing.

Good luck, I'm sure you'll find it.

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.

That's the crazy thing. When the car's running, it responds to throttle snap just *fine*. But somehow, during wot operation, something _happens_ and motor dies, gradually. And this problem is intermittent. Something's going on and it's definitely a bugger to find. Problem is the car's not worth a big investment - so that rules out handing it over to a shop and saying 'fix it' because they would run through the value of teh vehicle, in charges, in no time at all.

I doubt there's a serious mechanical problem, it's gotta be something dumb. Easily fixed. And I can't let it go, because now it's got me 'interested' in finding the bug. Ahh....

Jim

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Don't understand. That's like saying, you can get high voltage at a low impedance point.

If the current (flow rate) is not forthcoming, the voltage (pressure) at the test point will drop, the moment the impedance (flow restriction) to ground is reduced - ie, all the injectors are firing.

Should I be retracing my steps?

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

No, it is like saying you can get high voltage at a high impedance point. If there is a flow restriction, it doesn't take much flow to give a high pressure reading. But because of the flow restriction, you've got a problem supplying transient flow demand when the injector opens.

The injectors only open for a small fraction of a second. Your pressure gauge probably can't respond fast enough to show you what's actually happening in that short period. But that's the period when all the action is going on.

The 1 pint every 15 seconds spec certainly doesn't represent

*sustained* fuel demand. That much flow is only needed to handle *transient* demand while the injector is open. Your pressure gauge reading is only showing you *average* pressure. If flow is restricted, you may actually have near zero pressure while the injector is open.

Well, it is pretty obvious you've overlooked *something*, or you'd already have it fixed. The service manuals call for both a pressure and a flow test for a reason.

Gary

Actually somebody just did this morning, and it's a good idea. His comment was to simply monitor the voltage on the existing sensor. A nice idea.

Don't think I didn't think of that - but the factory manual seems to imply this car has no knock sensor.

Thanks for the help, with all the assistance I'm sure I'll get to the bottom of this...

Jim

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Does the throttle have a WOT switch? Some electronic injection systems have this switch IIRC to switch into an open loop mode for maximum (though limited) acceleration.

I have to admit I've forgotten what kind of car you're working on.

Cheers,

Kelley

Ok Jim,

Please dont think I am crazy(I may be), but hook up an oil pressure guage to monitor actual pressure during your engine failure. I had a vehicle with your symtoms that the pressure relief valve would stick and float the lifters causing a gradual power loss then a shut down. The car would then have a longer crank time while the lifters bled down.

Check for moisture > OK, the question has to do with the multi-port fuel injection system